Some notes for anyone who might be watching this video and repairing their own PM-50: The power transistors used in this amp (2SC3280, 2SA1380) are obsolete, and commonly faked. Unfortunately most of the Toshiba power transistors sold are fakes unless you get them from a reliable source like Digikey. Onsemi NJW0281G/NJW0302G work well in this amplifier. When you replace the output transistors in a power amplifier, you should re-adjust the idle bias current through them. Ideally you should start by turning the bias pots (R719 and R720) to maximum resistance, so that there is no bias current. Then connect a voltmeter in millivolts mode across the two outer terminals of the emitter resistors R743/R744. Adjust the trimpot until 14mV appears across the emitter resistors - you will need to adjust it further as the amplifier warms up. (edit: OK - Jan does do that.. but ideally you should reduce the idle current to zero BEFORE you power on for the first time :) A nice trick to prevent things going bang, is to get an 60W incandescent (old filament type, no LED/CFL/energy saving) bulb, and wire it in SERIES with the Live connection of the mains input. If the amplifier is operating correctly you should get a brief flash followed by a dull glow. If the bulb lights brightly, there is a problem. The service manual is available on Hifi Engine: www.hifiengine.com/manual_library/marantz/pm-50.shtml
One of the main issues with the driver chip is heat. Often the chip does not fail but the solder connections become cracked and open circuit which upsets the bias to the output transistors turning them hard on which blows them up. As you noticed the replacement driver does not get as hot as the old one did so extra heat sinking is probably not required. Thank goodness the use of these hybrid drivers were short lived.
+Michael Beeny Yes, that's most probably what happened here. These STKs are really a pita. Even in my very short 'career' of repairing audio gear, I saw many of them fail. Especially when used as power amp stages in lower specced amps. I'll keep an eye on the temperature. Thanks for the advice (to both of you)!
Jan. Great video! Following your instructions I managed to fix my PM-55. Replaced the STK with exactly the same STK as you used. (all markings numbers the same on EBay imported from Germany to UK). None of the power amp transistors needed replacement mind you. The old broken STK delivered an incorrect high voltage to the left channel power amp only - right channel tested to spec. I guess the incorrect high voltage on the left channel was detected by the protection chip and prevented the speaker relay from operating. I did have one disaster ..managed to short-out the small power supply board during testing of the old STK (probes slipped!) which blew the 1 ohm fused resistors on the power board. Replacement 1 ohm 1/4 watt resistors continued to slowly blow (I got through 12 of them!). So I completely recapped the small power board but the 1 ohm resistors continued to blow. Apparently the power rating for 240v supply UK 1 ohm resistors SHOULD be 1/2 watt not 1/4 watt as per service manual. The lower 1/4 watt spec is maybe for 110v USA only. I got around the problem by adding 3x 1 ohm 1/4 watt fused resistors in parallel replacing the blowing single 1/4 watt resistors. Now all is stable and well. The PM-55 is a lovely sounding amp well worth saving! BTW I also bought the same ZD-915 desoldering station as yours - works great! Do you know if it is possible to buy a soldering iron to plug into the ZD 915? Would be useful to use it as a multipurpose solder/desolder station rather than just for desoldering. Many thanks for this video. Regards Peter.
Hi Peter. Good to hear you were able to fix your amp. These are very nice sounding machines indeed. The STKs are flawed but it was an inexpensive way to get great sound which is always a good idea, I guess. Had a similar problem like yours with a Technics amp I was fixing a while back where the service manual was also for the US version and I had some components that didn't match. I realized it before I soldered it up though luckily. ;) I'm not aware of a soldering iron that you can plug directly into the ZD-915. Should be possible to hack something together though. The circuitry probably is quite simple and there are a couple of similar soldering stations around. Maybe I'll look into that some time. Thanks for your kind words and for letting me know about your successful repair! More audio repairs coming up in a bit.
Wow, not many fans of this amp, but I chose it over the Technics, Kenwood, Yamaha and other £250ish offerings at the time because of its clean sound. Since I am commenting here, you may have guessed that after plenty of years of reliable service it's developed a fault and I hope some helpful electronics wizard might point me in the direction of what component is likely to be failing and giving me the fault I'm experiencing. I would love to get my PM-50 back up and running because I still love the clean sound not afforded by my Sony AV amp that is currently the center of my system. The problem: Sound levels are fine through both speakers, but I get occasional LOUD pops through the left channel. These pops are loud no matter what volume the master volume is set at and don't happen regularly but can be frequently or sporadic from time to time. I didn't expect it would do my speakers a deal of good, so it got retired, but I miss it and would like to have a bash at sorting it out if anyone can help. Thanks for the video Jan Beta and thanks in advance for any help anyone can offer.
+TheDefpom The new STK already runs a lot cooler than the old one would. Upgrading the heatsink would still be a good idea, I suppose. I have some old video gear to salvage stuff from at the moment, maybe I'll find something fitting the STK in there.
This worked on a Marantz PM52. Purchased STK from a German suppler on Ebay. A bit tricky aligning the pins for the stk with the heat sink attached but got there in the end. I perhaps over did the heatsink compound! Really easy to cleanly remove the old stk using solder braid. Bias setting on PM55 is 8mv compared to PM50 which is 14mv as in video. DC on speaker terminals was around 20mv which is ok. Saved this from the dump as someone was going to bin it. I did not need to replace anything else.
Fallen into a rabbit hole; watched a recent audio fix video from your Patreon and now found myself addicted to your older audio repair videos too. Really enjoy them, they're a welcome change of pace and direction from my day job!
Thanks Rob! I actually planned on doing a channel with audio repair focus in the first place but then got distracted and started getting into the old computers... :)
Interesting video.. I've got exactly the same fault on my PM50, except the left channel works perfectly and the right channel is dead and only crackles.. I've tested all 10 transistors mounted on both heatsinks and no shorts are apparent. Each sides value match. In regards to the STK I've discovered that it's no longer sending +1.7v from pin 10 in to Q702. I've ordered a replacement. Once query, however, you metered a short on the Right-hand 2SC3280, and you removed it.. But you also removed the left hand 2SC3280 albeit that you'd tested it and it appeared okay.. You called it cactus??. Very good video thank you..
I am going to try this on a Marantz PM52. It has the same original STK so I will replace with the one shown on the video from a German supplier. Got the amp for free so going to give it a go otherwise it would have been thrown away! Any thoughts would be appreciated.
Did this amplifier work properly after STK replacement ? Any distortion and similar sound problems ? Did this new STK3082III wchich you soldered to this amplifier was original or replacement ? I ask you about it because I have too two amplifiers based on STK chips - my amplifiers are Marantz SR620 and Marantz SR620L. These two my amplifiers are based on STK2250 as power amp and STK3042II as voltage amp. I bought in stock two STK2250 and two STK3042IIA for these my amplifiers and I'm afraid will these STK chips wchich I bought be working properly in the future when I will have to solder them to my amplifiers if my current STK chips worked now in my amplifiers will damage in the future. I hear on net that STK replacements like cause problems like sound distortion or burning when we listen music at more power. I hear on net for example that STK3042III like cause such problems if somebody will solder this to amplifier in wchich before originally worked STK3042II - that's why I bought STK3042IIA chips instead STK3042III chips. Did I right ? Does it true with these problems if mean about replacement STK3042III instead STK3042II ? In one of my these amplifiers, concretely in Marantz SR620 is soldered STK3042 - no original STK3042II or popular now STK3042III and this amplifier work properly for me. So STK3042 can solder to amplifier in wchich originally worked STK3042II, yes ? And vice versa ? Does STK3042II can solder to amplifier in wchich originally worked STK3042 ? What is difference between STK3042II and STK3042IIA wchich I bought, do you know ? No application notes in PDF or even other formats for STK3042IIA on net - I was looking this and nothing. Maybe you have application note for STK3042IIA ? I have application notes in PDF format for STK3042, STK3042II and STK3042III, but I don't have application notes for STK3042A and/or STK3042IIA.
Excellent video Jan thank you. I have a PM52se that looks the same internally as the PM50. The problem with mine is there is no relay click. It sometimes clicks but after some warm up time but then I get loud pops and click sounds that could damage the speakers so I am presuming there is DC coming through. Does anyone have any suggestions what it could be please?
If the relay doesn’t click, there’s most likely something inherently wrong with the power amp circuit. If there’s too much DC, the relay won’t engage for protecting the speakers. So I would suggest looking at the main amp transistors at first, maybe one or more of them are shorted. Might be something in an earlier stage but I suspect the power amp section from your fault description!
Normally, when we see modules, we drop the unit quick for scrap, and advice against any repair, as it in most cases will not be reliable over time. However, when the customer insist we can do a much better (sound) and reliable job with LM3886 or eq. amplifier boards. Therefore, taken this time to repair with compatible original parts, the whole board should have been replaced with LM3886 boards, a much, much better alternative in the same time!
Hello! I have another question. I noticed you checked if the transistors were fine by checking for continuity between each pin. So, none of the pins should have continuity between them? Thank you!
You can basically measure a transistor as if it was two diodes. It should be open in some directions and short in others (depending on which kind of transistor). If you measure continuity in all polarities between the pins, the transistor is definitely shot.
Hej Jan I have a PM-50 where the right channel is blown I guess. Very subtle scrachy sound to no sound is coming out. I bought new output transistors 2SC3280 and 2SA1301. I see you check you check yours in circuit, how do you check them? I found one is NPN and the other is PNP but when I check them in circuit it doesn’t make sense. I guess the right channel is on the right side of the board when you see it from the top? Thank you
I just check if the transistors are dead shorted. That usually also works in circuit. If they have other issues you have to use a proper tester or the diode testing mode of a multimeter out of circuit. As for the scratchy sounds: did you check all the inputs? The channel switcher is notorious for not making good contact. Also, the protection relay sometimes doesn‘t make good contact, too. Try carefully hitting it with the backside of a screwdriver or something while powered on to see if that changes the sound/brings it back for a short time. Also try cleaning the pots and switches with contact cleaner. I found that the output transistors are usually either completely dead or completely functional. If you have any output at all it‘s pretty likely to be something else. Mostly contact issues somewhere in the chain. Hope that helps!
Jan Beta Thank you for fast reply. I’ve tested all the inputs and it’s the same for both right speaker outputs 1 and 2, no sound but scratchy peaks of kickdrum and snare comes through. I tested the transistor I think is the right channel of them circuitboard and there is connection in all the 5 steps I tested for. So I think it’s shorted. When I test the PNP transistors 2SA1301 the are both showing around the same value but the look shorted also. It doesn’t make sense to me because I hear no problem with the left channel. I have new transistors of both type and I will try put the in the right side of the board. Right speakers are controlled by the right side of the amp seen from the front top right? Thanks again
Jan Beta Update I took out the 2SC3280 of the right side and it tested out perfect, nothing seems to be wrong with it. I tested the complementary 2SA1301 of the right side and it was also fine. Then I checked the left side and they both failed when I hook the postitive meter lead to the COLLECTOR (C) and the negative meter lead to the EMITTER (E) - and swap - they didn’t OL Then I put back the transistor I took out and the right side failed the testing again. Only in circuit they read wrong. I using these 5 steps to test them: vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-07 How do you check them in circuit? This is how it sounds: th-cam.com/video/4HvJVOhuU8E/w-d-xo.html I’m sorry I have all these questions, I hope I don’t bother you
Hallo Jan! Ich bin als Webentwickler nicht nur Leser von Golem, sondern auch Besitzer eines Marantz PM-50 ... 🙂 Ich habe Probleme mit instabilen Ton/Kanälen, vermutlich liegt es am Source Select-Schalter. Nutzt Du Deinen PM-50 noch? Statt einen neuen Verstärker zu kaufen, möchte ich lieber in den vorhandenen Investieren. In Berlin lebend, suche ich nach einer Starthilfe für eine Reparatur. Ich würde es gerne selber machen, würde aber bei Null anfangen. An wen ich mich alternativ wenden kann, weiß ich leider nicht. Ich kann da nur auf die allgemeinen Angebote im Internet zurückgreifen. Hast Du einen Tipp ... Oder bietest Du vielleicht selber Instandsetzung von Verstärkern an? Vielen Dank! 👍
Hi! Sorry, ich lese das erst jetzt. Ich kann leider selbst keine Auftragsarbeiten durchführen, weil mir einfach die formelle Ausbildung und die entsprechende Versicherung fehlt. Dein PM-50 lässt sich vermutlich aber mit etwas Kontaktspray wieder zum Laufen bringen. Ich benutze da immer Teslanol T6 Oszillin. Das Zeug ist nicht korrosiv (andere Kontaktsprays zerstören gerne mal empfindliche Potentiometer und Schalter). Wahrscheinlich braucht dein Amp eine gründliche Reinigung aller Schalter und Potis. Das habe ich in den meisten meiner Hifi-Reparatur Videos gezeigt. Der Eingangswahlschalter beim PM50 ist so ein längliches Dings auf der Platine, mit dem Schalter an der Front nur mechanisch verbunden. Wenn du das Teil mit Kontaktspray flutest, es ein paar mal hin und her bewegst und dann nochmal einsprühst, sollte das erstmal wieder korrekt funktionieren. Die Dinger "richtig" sauberzumachen ist leider extrem schwierig (müsstest du auslöten und komplett zerlegen). Das "Fluten" mit Kontaktspray funktioniert aber erfahrungsgemäß zumindest für eine (lange) Weile. Ich hoffe, das hilft ein bisschen!
hello Jan.....i have a Marantz PM55 whith almost same configuration as PM 50 ..but my amp have diferent simphtom, whem i power on the amp the relay clic normaly and after 3 or 5 second the relay click into protection mode
If the protection clicks after a couple of seconds again, probably something changes with heat (output transistors, capacitors?) and draws too much current or shorts the outputs. Difficult to tell from a distance. Maybe you can check if any components get unusually hot quickly after powering it on.
@@JanBeta none of the components get hot during this short process and after ,,,,also i check the tranzistors and the current ,,,,,everithing seems fine, no heat or hight voltage.Single part who get hot its the STK ,the preamp ,but i dont thing that its the cause ....cuz are no connection betwen preamp and relay......maybe im wrong i dont know
Hi Jan, I'm new to hifi-technics, especially repairing them. I have a marantz pm-50 but the sound output on one of my speakers is down by 90 %. Do you have idea what might be causing this and how I can fix it? Kind regards
Most of the times I found one channel cutting out or being more quiet is a contact problem. Check the speaker relay (you can try tapping it with the handle of a screwdriver while the unit is running to see if the sound changes) and check if the volume, balance etc pots are working and clean. It might be a transistor issue or a cold joint on one of the transistors, too, but in my experience it mostly is one of the problems I mentioned first. Hope that helps!
I've got a kit of 2 cheap stubby short screwdrivers, a slot head and a Philips #2, i think i got them elsewhere but saw them at EuroShop for 1€ recently, same shitty quality, but good enough for something you almost never need. Also i got a bit screwdriver with ratcheting and tilting mechanism at... ehr what was it, Hagebaumarkt? not too long ago, i wouldn't normally use it, but it can be helpful when space is at a premium or you need a lot of force.
Yeah, the Marantz has a very flat frequency response with less bass than other amps of the era. I like it a lot because I'm used to studio work where flat frequency amps/monitors are commonly used.
what kind of desoldering toll your using ?and i ave a cheap 200$ pyle 2000watts amp...what can i do to beef up the capacitors transistor ? and what is the outcome of that ?
It's a ZD 915 desoldering station. I'd still recommend it. I understand you want to change transistors and capacitors for beefier ones in your amp? That's never easy. You would have to choose the parts very thoroughly to have them play together nicely. It's not a trivial task and you would have to change a lot of the other circuitry as well if you want to get more power out of it.
So far I didn’t encounter a fake one (at least I think so). They are probably not too trivial to spot. For IC, you can often tell by the print quality on the case and such. Maybe that works for the STKs, too. You would need a real one to compare though.
@@JanBeta Got it! Thank you so much. I have a distortion issue with a PM-65AV and that distortion is only introduced by some signals which is really weird. I'm not an expert, so I'm going in blind trying things one by one. And without a scope, it becomes rather hard.
Hello I have the same amp in which the speaker 1 does not work but on the other hand the speaker 2 works very well. could you tell me what this failure comes from thanks in advance
hi my friend currently has a marantz pm50 amplifier it is broken main power can you help me the circuit diagram because the ball burned out all the stats then thank you
Check the large transistors. There might be a short somewhere. I also repaired a receiver recently that had one of the pre amp transistors in the wrong way around which caused similar issues. Maybe check the preamp section, too.
I'm not familiar with that particular model. It's quite a bit different from the PM 50 I think. I assume you could use any usual power lead that has a reasonable diameter and attach it to the transformer. If you don't know how to do it, let someone look at it who knows their way around electronics as this involves high voltages that may kill the amp or in the worst case even kill you. You can get service manuals and such for it from hifiengine.com.
I bought the replacement from a reputable supplier who sells NOS stuff. I bought some parts from them and they were all good (or at least equally as bad as the original part in this case...). I agree that the STKs are usually crap. I saw quite a few of them fail in my short-lived career fixing this stuff.
@@JanBeta Could you tell where you found NOS STK modules? When I analyse the circuit, the input voltage VCC is +-46,4V while the stk3062 module has a recommended operating condition rated at +-41V. No wonder this blows if it is pushed at its limits. The stk3082 is rated at 47V (recommended, max 65v) so your replacement would make more sense. I guess economics pushed that decision to use inferior parts.
Some notes for anyone who might be watching this video and repairing their own PM-50:
The power transistors used in this amp (2SC3280, 2SA1380) are obsolete, and commonly faked. Unfortunately most of the Toshiba power transistors sold are fakes unless you get them from a reliable source like Digikey. Onsemi NJW0281G/NJW0302G work well in this amplifier.
When you replace the output transistors in a power amplifier, you should re-adjust the idle bias current through them. Ideally you should start by turning the bias pots (R719 and R720) to maximum resistance, so that there is no bias current. Then connect a voltmeter in millivolts mode across the two outer terminals of the emitter resistors R743/R744. Adjust the trimpot until 14mV appears across the emitter resistors - you will need to adjust it further as the amplifier warms up. (edit: OK - Jan does do that.. but ideally you should reduce the idle current to zero BEFORE you power on for the first time :)
A nice trick to prevent things going bang, is to get an 60W incandescent (old filament type, no LED/CFL/energy saving) bulb, and wire it in SERIES with the Live connection of the mains input. If the amplifier is operating correctly you should get a brief flash followed by a dull glow. If the bulb lights brightly, there is a problem.
The service manual is available on Hifi Engine: www.hifiengine.com/manual_library/marantz/pm-50.shtml
Thanks for the additional tips! I'm going to pin your comment so people can refer to it.
No problem :)
Peter Mulholland Man knows his shit.
I was just to write the same about fake Toshiba transistor and the idle current
You may also Chek the caps near the STK ic. They usely get faulty
Bloody excellent video! I'm doing this to my Marantz amp right now. Always the same faults with these things.
I am Japanese. It was very helpful. I'm looking forward to your next video.
You made a great how-to! My Marantz PM-50 spawned with your support! It was easy to change the STK to make him running again. THANKS!
Hey, that's great news! Glad the video was helpful. May the Marantz live a long happy life! :D
One of the main issues with the driver chip is heat. Often the chip does not fail but the solder connections become cracked and open circuit which upsets the bias to the output transistors turning them hard on which blows them up. As you noticed the replacement driver does not get as hot as the old one did so extra heat sinking is probably not required. Thank goodness the use of these hybrid drivers were short lived.
+Michael Beeny Yes, that's most probably what happened here. These STKs are really a pita. Even in my very short 'career' of repairing audio gear, I saw many of them fail. Especially when used as power amp stages in lower specced amps. I'll keep an eye on the temperature. Thanks for the advice (to both of you)!
Jan. Great video! Following your instructions I managed to fix my PM-55. Replaced the STK with exactly the same STK as you used. (all markings numbers the same on EBay imported from Germany to UK). None of the power amp transistors needed replacement mind you. The old broken STK delivered an incorrect high voltage to the left channel power amp only - right channel tested to spec. I guess the incorrect high voltage on the left channel was detected by the protection chip and prevented the speaker relay from operating.
I did have one disaster ..managed to short-out the small power supply board during testing of the old STK (probes slipped!) which blew the 1 ohm fused resistors on the power board. Replacement 1 ohm 1/4 watt resistors continued to slowly blow (I got through 12 of them!). So I completely recapped the small power board but the 1 ohm resistors continued to blow. Apparently the power rating for 240v supply UK 1 ohm resistors SHOULD be 1/2 watt not 1/4 watt as per service manual. The lower 1/4 watt spec is maybe for 110v USA only. I got around the problem by adding 3x 1 ohm 1/4 watt fused resistors in parallel replacing the blowing single 1/4 watt resistors. Now all is stable and well.
The PM-55 is a lovely sounding amp well worth saving!
BTW I also bought the same ZD-915 desoldering station as yours - works great! Do you know if it is possible to buy a soldering iron to plug into the ZD 915? Would be useful to use it as a multipurpose solder/desolder station rather than just for desoldering.
Many thanks for this video. Regards Peter.
Hi Peter. Good to hear you were able to fix your amp. These are very nice sounding machines indeed. The STKs are flawed but it was an inexpensive way to get great sound which is always a good idea, I guess. Had a similar problem like yours with a Technics amp I was fixing a while back where the service manual was also for the US version and I had some components that didn't match. I realized it before I soldered it up though luckily. ;)
I'm not aware of a soldering iron that you can plug directly into the ZD-915. Should be possible to hack something together though. The circuitry probably is quite simple and there are a couple of similar soldering stations around. Maybe I'll look into that some time.
Thanks for your kind words and for letting me know about your successful repair! More audio repairs coming up in a bit.
Wow, not many fans of this amp, but I chose it over the Technics, Kenwood, Yamaha and other £250ish offerings at the time because of its clean sound.
Since I am commenting here, you may have guessed that after plenty of years of reliable service it's developed a fault and I hope some helpful electronics wizard might point me in the direction of what component is likely to be failing and giving me the fault I'm experiencing. I would love to get my PM-50 back up and running because I still love the clean sound not afforded by my Sony AV amp that is currently the center of my system.
The problem: Sound levels are fine through both speakers, but I get occasional LOUD pops through the left channel. These pops are loud no matter what volume the master volume is set at and don't happen regularly but can be frequently or sporadic from time to time. I didn't expect it would do my speakers a deal of good, so it got retired, but I miss it and would like to have a bash at sorting it out if anyone can help.
Thanks for the video Jan Beta and thanks in advance for any help anyone can offer.
I recommend that you upgrade the heat sink on the stk if it runs hot, no reason why you cannot strap on some more to keep it cooler.
+TheDefpom The new STK already runs a lot cooler than the old one would. Upgrading the heatsink would still be a good idea, I suppose. I have some old video gear to salvage stuff from at the moment, maybe I'll find something fitting the STK in there.
Agree with that!
This worked on a Marantz PM52. Purchased STK from a German suppler on Ebay. A bit tricky aligning the pins for the stk with the heat sink attached but got there in the end. I perhaps over did the heatsink compound! Really easy to cleanly remove the old stk using solder braid. Bias setting on PM55 is 8mv compared to PM50 which is 14mv as in video. DC on speaker terminals was around 20mv which is ok. Saved this from the dump as someone was going to bin it.
I did not need to replace anything else.
Nice work! I guess the same STK is useable in a number of Marantz amps.
Fallen into a rabbit hole; watched a recent audio fix video from your Patreon and now found myself addicted to your older audio repair videos too. Really enjoy them, they're a welcome change of pace and direction from my day job!
Thanks Rob! I actually planned on doing a channel with audio repair focus in the first place but then got distracted and started getting into the old computers... :)
Interesting video.. I've got exactly the same fault on my PM50, except the left channel works perfectly and the right channel is dead and only crackles.. I've tested all 10 transistors mounted on both heatsinks and no shorts are apparent. Each sides value match. In regards to the STK I've discovered that it's no longer sending +1.7v from pin 10 in to Q702. I've ordered a replacement.
Once query, however, you metered a short on the Right-hand 2SC3280, and you removed it.. But you also removed the left hand 2SC3280 albeit that you'd tested it and it appeared okay.. You called it cactus??.
Very good video thank you..
Hi,
Thank you for the information. I replaced the STK and working good, it cost only 2$.
Glad to hear it worked for you! Enjoy the great amp. :)
I am in Vietnam very much looking forward to receiving your reply soon I am having a hard time repairing the marantzpm50 amplifier sincerely thank you
Nice and instructive.. Ich danke dir 👍
great work
Thanks! :)
I am going to try this on a Marantz PM52. It has the same original STK so I will replace with the one shown on the video from a German supplier. Got the amp for free so going to give it a go otherwise it would have been thrown away! Any thoughts would be appreciated.
Did this amplifier work properly after STK replacement ? Any distortion and similar sound problems ? Did this new STK3082III wchich you soldered to this amplifier was original or replacement ? I ask you about it because I have too two amplifiers based on STK chips - my amplifiers are Marantz SR620 and Marantz SR620L. These two my amplifiers are based on STK2250 as power amp and STK3042II as voltage amp. I bought in stock two STK2250 and two STK3042IIA for these my amplifiers and I'm afraid will these STK chips wchich I bought be working properly in the future when I will have to solder them to my amplifiers if my current STK chips worked now in my amplifiers will damage in the future. I hear on net that STK replacements like cause problems like sound distortion or burning when we listen music at more power. I hear on net for example that STK3042III like cause such problems if somebody will solder this to amplifier in wchich before originally worked STK3042II - that's why I bought STK3042IIA chips instead STK3042III chips. Did I right ? Does it true with these problems if mean about replacement STK3042III instead STK3042II ? In one of my these amplifiers, concretely in Marantz SR620 is soldered STK3042 - no original STK3042II or popular now STK3042III and this amplifier work properly for me. So STK3042 can solder to amplifier in wchich originally worked STK3042II, yes ? And vice versa ? Does STK3042II can solder to amplifier in wchich originally worked STK3042 ? What is difference between STK3042II and STK3042IIA wchich I bought, do you know ? No application notes in PDF or even other formats for STK3042IIA on net - I was looking this and nothing. Maybe you have application note for STK3042IIA ? I have application notes in PDF format for STK3042, STK3042II and STK3042III, but I don't have application notes for STK3042A and/or STK3042IIA.
Hi Can you please tell me the equivalent transistors of B1254 (2SA1263), D1894 (2SC3180). its really hard to find to me..
And back a road again. Nice video!
+saarike Thanks. Happy to have the Marantz working again. :)
Excellent video Jan thank you. I have a PM52se that looks the same internally as the PM50. The problem with mine is there is no relay click. It sometimes clicks but after some warm up time but then I get loud pops and click sounds that could damage the speakers so I am presuming there is DC coming through. Does anyone have any suggestions what it could be please?
If the relay doesn’t click, there’s most likely something inherently wrong with the power amp circuit. If there’s too much DC, the relay won’t engage for protecting the speakers. So I would suggest looking at the main amp transistors at first, maybe one or more of them are shorted. Might be something in an earlier stage but I suspect the power amp section from your fault description!
Hi can you give me an idea as to where to get a reliable STK chip?
I would like to know that too and I am in the UK.
Normally, when we see modules, we drop the unit quick for scrap, and advice against any repair, as it in most cases will not be reliable over time. However, when the customer insist we can do a much better (sound) and reliable job with LM3886 or eq. amplifier boards.
Therefore, taken this time to repair with compatible original parts, the whole board should
have been replaced with LM3886 boards, a much, much better alternative in the same time!
this kind of old amplifiers works on higher voltages than LM3886 supports...so what did you do in that case?
Does Marantz use Transistors or Moffett in PM 6007. I am planning to buy pm 6007
Yes i live near Bradford , west yorkshire
Hi
Thanks for the useful video
Regards
Thanks! You are welcome! Hope it helps. :)
Hello! I have another question. I noticed you checked if the transistors were fine by checking for continuity between each pin. So, none of the pins should have continuity between them? Thank you!
You can basically measure a transistor as if it was two diodes. It should be open in some directions and short in others (depending on which kind of transistor). If you measure continuity in all polarities between the pins, the transistor is definitely shot.
@@JanBeta Alright, thank you! You've been of great help!
Толково ! Золотые руки !
Hej Jan
I have a PM-50 where the right channel is blown I guess. Very subtle scrachy sound to no sound is coming out. I bought new output transistors 2SC3280 and 2SA1301. I see you check you check yours in circuit, how do you check them? I found one is NPN and the other is PNP but when I check them in circuit it doesn’t make sense.
I guess the right channel is on the right side of the board when you see it from the top?
Thank you
I just check if the transistors are dead shorted. That usually also works in circuit. If they have other issues you have to use a proper tester or the diode testing mode of a multimeter out of circuit.
As for the scratchy sounds: did you check all the inputs? The channel switcher is notorious for not making good contact. Also, the protection relay sometimes doesn‘t make good contact, too. Try carefully hitting it with the backside of a screwdriver or something while powered on to see if that changes the sound/brings it back for a short time. Also try cleaning the pots and switches with contact cleaner.
I found that the output transistors are usually either completely dead or completely functional. If you have any output at all it‘s pretty likely to be something else. Mostly contact issues somewhere in the chain. Hope that helps!
Jan Beta
Thank you for fast reply.
I’ve tested all the inputs and it’s the same for both right speaker outputs 1 and 2, no sound but scratchy peaks of kickdrum and snare comes through.
I tested the transistor I think is the right channel of them circuitboard and there is connection in all the 5 steps I tested for. So I think it’s shorted.
When I test the PNP transistors 2SA1301 the are both showing around the same value but the look shorted also. It doesn’t make sense to me because I hear no problem with the left channel.
I have new transistors of both type and I will try put the in the right side of the board. Right speakers are controlled by the right side of the amp seen from the front top right?
Thanks again
Jan Beta
Update
I took out the 2SC3280 of the right side and it tested out perfect, nothing seems to be wrong with it.
I tested the complementary 2SA1301 of the right side and it was also fine.
Then I checked the left side and they both failed when I hook the postitive meter lead to the COLLECTOR (C) and the negative meter lead to the EMITTER (E) - and swap - they didn’t OL
Then I put back the transistor I took out and the right side failed the testing again. Only in circuit they read wrong.
I using these 5 steps to test them:
vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-07
How do you check them in circuit?
This is how it sounds: th-cam.com/video/4HvJVOhuU8E/w-d-xo.html
I’m sorry I have all these questions, I hope I don’t bother you
Hallo Jan!
Ich bin als Webentwickler nicht nur Leser von Golem, sondern auch Besitzer eines Marantz PM-50 ... 🙂
Ich habe Probleme mit instabilen Ton/Kanälen, vermutlich liegt es am Source Select-Schalter.
Nutzt Du Deinen PM-50 noch?
Statt einen neuen Verstärker zu kaufen, möchte ich lieber in den vorhandenen Investieren.
In Berlin lebend, suche ich nach einer Starthilfe für eine Reparatur.
Ich würde es gerne selber machen, würde aber bei Null anfangen.
An wen ich mich alternativ wenden kann, weiß ich leider nicht.
Ich kann da nur auf die allgemeinen Angebote im Internet zurückgreifen.
Hast Du einen Tipp ...
Oder bietest Du vielleicht selber Instandsetzung von Verstärkern an?
Vielen Dank! 👍
Hi! Sorry, ich lese das erst jetzt. Ich kann leider selbst keine Auftragsarbeiten durchführen, weil mir einfach die formelle Ausbildung und die entsprechende Versicherung fehlt.
Dein PM-50 lässt sich vermutlich aber mit etwas Kontaktspray wieder zum Laufen bringen. Ich benutze da immer Teslanol T6 Oszillin. Das Zeug ist nicht korrosiv (andere Kontaktsprays zerstören gerne mal empfindliche Potentiometer und Schalter). Wahrscheinlich braucht dein Amp eine gründliche Reinigung aller Schalter und Potis. Das habe ich in den meisten meiner Hifi-Reparatur Videos gezeigt. Der Eingangswahlschalter beim PM50 ist so ein längliches Dings auf der Platine, mit dem Schalter an der Front nur mechanisch verbunden. Wenn du das Teil mit Kontaktspray flutest, es ein paar mal hin und her bewegst und dann nochmal einsprühst, sollte das erstmal wieder korrekt funktionieren. Die Dinger "richtig" sauberzumachen ist leider extrem schwierig (müsstest du auslöten und komplett zerlegen). Das "Fluten" mit Kontaktspray funktioniert aber erfahrungsgemäß zumindest für eine (lange) Weile.
Ich hoffe, das hilft ein bisschen!
hello Jan.....i have a Marantz PM55 whith almost same configuration as PM 50 ..but my amp have diferent simphtom, whem i power on the amp the relay clic normaly and after 3 or 5 second the relay click into protection mode
If the protection clicks after a couple of seconds again, probably something changes with heat (output transistors, capacitors?) and draws too much current or shorts the outputs. Difficult to tell from a distance. Maybe you can check if any components get unusually hot quickly after powering it on.
@@JanBeta none of the components get hot during this short process and after ,,,,also i check the tranzistors and the current ,,,,,everithing seems fine, no heat or hight voltage.Single part who get hot its the STK ,the preamp ,but i dont thing that its the cause ....cuz are no connection betwen preamp and relay......maybe im wrong i dont know
Hi Jan,
I'm new to hifi-technics, especially repairing them.
I have a marantz pm-50 but the sound output on one of my speakers is down by 90 %. Do you have idea what might be causing this and how I can fix it? Kind regards
Most of the times I found one channel cutting out or being more quiet is a contact problem. Check the speaker relay (you can try tapping it with the handle of a screwdriver while the unit is running to see if the sound changes) and check if the volume, balance etc pots are working and clean. It might be a transistor issue or a cold joint on one of the transistors, too, but in my experience it mostly is one of the problems I mentioned first. Hope that helps!
I've got a kit of 2 cheap stubby short screwdrivers, a slot head and a Philips #2, i think i got them elsewhere but saw them at EuroShop for 1€ recently, same shitty quality, but good enough for something you almost never need. Also i got a bit screwdriver with ratcheting and tilting mechanism at... ehr what was it, Hagebaumarkt? not too long ago, i wouldn't normally use it, but it can be helpful when space is at a premium or you need a lot of force.
Those STK chips were made by Matsushita for Technics. They sound pretty clean , but no bass and they blow like crazy.
Yeah, the Marantz has a very flat frequency response with less bass than other amps of the era. I like it a lot because I'm used to studio work where flat frequency amps/monitors are commonly used.
what kind of desoldering toll your using ?and i ave a cheap 200$ pyle 2000watts amp...what can i do to beef up the capacitors transistor ? and what is the outcome of that ?
It's a ZD 915 desoldering station. I'd still recommend it. I understand you want to change transistors and capacitors for beefier ones in your amp? That's never easy. You would have to choose the parts very thoroughly to have them play together nicely. It's not a trivial task and you would have to change a lot of the other circuitry as well if you want to get more power out of it.
thanks you ,I appreciate your time and great vid
Thanks a ton for the video! I read a lot of the comments here and people keep talking about fake STKs. How can you spot them?
So far I didn’t encounter a fake one (at least I think so). They are probably not too trivial to spot. For IC, you can often tell by the print quality on the case and such. Maybe that works for the STKs, too. You would need a real one to compare though.
@@JanBeta Got it! Thank you so much. I have a distortion issue with a PM-65AV and that distortion is only introduced by some signals which is really weird. I'm not an expert, so I'm going in blind trying things one by one. And without a scope, it becomes rather hard.
good expl.
Thanks!
Hello
I have the same amp in which the speaker 1 does not work but on the other hand the speaker 2 works very well. could you tell me what this failure comes from thanks in advance
Relais group1 speakers cleaning internally or replace the relais. grtz, Luc
hi my friend currently has a marantz pm50 amplifier it is broken main power can you help me the circuit diagram because the ball burned out all the stats then thank you
I am in Vietnam very much looking forward to receiving your reply soon I am having a hard time repairing the marantzpm50 amplifier sincerely thank you
Hi. In my amp stopped working and the resistor (RGB33/0.18 Ohm KX2/NOBLE U54) is heating up and starts smoking.
Check the large transistors. There might be a short somewhere. I also repaired a receiver recently that had one of the pre amp transistors in the wrong way around which caused similar issues. Maybe check the preamp section, too.
Great.. thanks..you are right.. replaced.. working fine now thanks again :-)
Hi my mate gave me a PM-54 but he had no power lead or anything what do I need for it?
I'm not familiar with that particular model. It's quite a bit different from the PM 50 I think. I assume you could use any usual power lead that has a reasonable diameter and attach it to the transformer. If you don't know how to do it, let someone look at it who knows their way around electronics as this involves high voltages that may kill the amp or in the worst case even kill you. You can get service manuals and such for it from hifiengine.com.
Hi , How much to recap a Pioneer A300r please.
I don’t do any paid repair work, I’m sorry.
Always use a dim bulb tester!
PLEASE NEEDED DIAGRAM MARANTZ PM 243 OR PM 143
STK modules are disasters waiting to happen. I hate them. So called "new" ones are even more unreliable, usually counterfeit junk.
I bought the replacement from a reputable supplier who sells NOS stuff. I bought some parts from them and they were all good (or at least equally as bad as the original part in this case...). I agree that the STKs are usually crap. I saw quite a few of them fail in my short-lived career fixing this stuff.
@@JanBeta Could you tell where you found NOS STK modules? When I analyse the circuit, the input voltage VCC is +-46,4V while the stk3062 module has a recommended operating condition rated at +-41V. No wonder this blows if it is pushed at its limits. The stk3082 is rated at 47V (recommended, max 65v) so your replacement would make more sense. I guess economics pushed that decision to use inferior parts.
Never be stingy and always coat evenly when it comes to thermal compound.
PLEASE I AM NEED DIAGRAM MARANTZ PM 243 OR PM 143
your voice sounds like the dyson vacume cleaner guy
Stk3062v replace 3062 11
never use other component then advertize by manufacture. Its all calculated and those components can take high temperature..
🙋👍❤️
PLEASE DIAGRAM MARANTZ PM 243 OR PM 143
D1508 Transistor eqlent
Those stk modules are a pile of absolute peice of crap they have no proper thermal or overload procection, and just randomly fail.
PLEASE NEEDED DIAGRAM MARANTZ PM 243 OR PM 143
PLEASE I AM NEED DIAGRAM MARANTZ PM 243 OR PM 143