These are my favorite style vids. You passed on a lot of interesting info in this one. Love to see more of these. Even a few tutorial vids would be cool for some of the noobs.
i am "youngster" but the old luxman gear is Great stuff! got some luxman cassette decks i love. and i love ur videos. keep em coming. this is priceless to for thoose who love vintage stuff.becouse of u and some other youtubers made me manage to repair several cassette decks for own use. very nice of u Dave. greetings from across the globe.
Luxman = beautiful sound. I got my first Lux in 1987; an LV105U. I absolutely loved this amp, and finally after 34 years I had to replace it due to parts being unavailable as you stated. I have been listening to my new L-505uxii for about 4 months now and have started a whole new love affair. I still have my 105u, not willing to relegate it to the recycler. I enjoyed the video, thanks.
Yes they do have beautiful sound. That's why in 1984 I spent about two grand on my new lv103. My friends thought i was crazy but the type of music i listen to the instruments just popped with that amp. The only amp that I have that sounds better is a full tube amp.
Could those lamps not be replaced with appropriate coloured LEDs with limiting resistors? I would fit the LEDs in line with the leads and use to heat shrink tubing to make a neat job.
They cant or at least they shouldnt in this case since they are crucial to the right function of the ciricuitry. In this and some other Luxman models they should be replaced with 24V 50mA bulbs since their turn-off time is utilized by the ciricuit to discharge a capacitor. If i understood it right those Luxmans dont have a relai to prevent the speakers from making a "pop" noise when turning on.They use a fancy ciricuitry for this job and i think part of it is the light bulb. If the Light Bulb fails, it causes the d112 diode and the green Resistor next to it to overheat (which is why the PCB is burned under the diode of nearly every survivor of those Amps). The heat also stresses the Capacitor next to it so its a good idea to replace all of those components and to solder the new diode higher (the way the green Resistor is soldered in) to prevent further damage of the PCB
@@kaiaphasful Yikes. That's clever, but also not a particularly great design to make a consumable component part of proper operation. If this were mine, I think I would re-design that circuit to use a power resistor in parallel to an LED light. That way you get your nearly-infinite lifespan and proper discharge capability.
@@nickwallette6201 I agree on the part that light bulbs are destined to fail (but so are capacitors) and leds have a longer lifespan at least on paper. You could use a resistor together with an led to achieve the right readings, however there was an explanation that slips my mind on why you shouldnt do that either (i think bcs an led works like a diode or so?!) . Since i own amps with all working light bulbs which are over 50 years old (i own at least 15 from the 60s, 70s and 80s i dont think that they were nearly as badly designed as every cell phone with a glued-in battery. From all my amps the finest piece i have and the one i love the most is my Luxman l190 cos its the one i can clearly say i hear a difference (tube amps excluded) . It has a very detailed, fine sound. The white noise on full volume is the lowest compared to all my other amps, when i turn the knobs and press the Buttons i dont hear any scratching. On the inside all caps are ELNA most of them blue caps, it has ALPS Buttons and is designed service friendly. If you can get your hands on a luxman for a fair price dont miss it
@@kaiaphasful I was thinking of having a resistor _parallel_ to the LED, so it acts like the filament of a bulb. The LED itself would have its own current-dropping resistor (since the circuit's operating current is designed around that 50mA bulb, and that's way too much for an LED) and so should be fairly negligible alongside the larger resistance. Even if the diode effect is troublesome, the parallel resistor wouldn't be polarized. I haven't looked at the full schematic, but it seems like it should work. ;-) Never heard a Luxman myself. It did look nicely built. Still a phenolic board, which I'm not crazy about, but otherwise quite stylish, serviceable, and designed to last. I hope to cross paths with one some day.
I like when you don’t just fix the unit, but also teach us about those diodes, for example. I have some electronic knowledge, but not as much as my dad.
@@catsbyondrepair hahahahaha. Good one. You need to get our more and listen to a few. Each brand and design sounds a little different. Every brand adds a little color to sound.
With a blown lamp and no Zener wouldn't the voltage across the 35v rated capacitor be a little too high? Also if the cap was allowed to charge to 42v then this would be discharged through the pilot lamp when the lamp is activated. Of course if all bulbs ok and the switch is not a break before make then this would not occur. LEDs would be my way to go.
For even more fun, grab a 12 VAC wall-wart, a 1kilohm 1% resistor, and a scope with X/Y mode, some test leads, and a diode (or zener) to test. Wire one end of the diode under test to the wall-wart, the other end to the 1k resistor, and the other end of the resistor to the other end of the wall-wart secondary. Hook the X-inputs of the scope across the DUT, and the Y-inputs across the resistor (to measure the current in mA.) Plug in the wall-wart, and turn on the scope and set it to X/Y mode with DC coupling on both channels. You should now see the characteristic curve of the diode. If the knee-voltage of the zener is less than the peak inverse voltage (or, about 16.9 volts), then you should see that in the 3rd quadrant (lower-left.) You can also test capacitors and inductors with it, too.
20:55 One shop I worked in had a set of lead bending pliers to put those 'U" shape bends in the leads at just the right place and make it nice. Wish I had a set of those now.
When you measured the voltage across a blown bulb it was 40v which showed that the zener had failed and, since the cap across it was rated at 35v, I would have changed that too in case its life had been reduced.
I have a Luxman L-430 and I replaced the panel lights and the light over the volume control with warm white 5mm LEDs and the one for Phono with a green one. The look great and will never burn out.
Nice to see (or hear) the Cats doing ok and comming in to learn some skills! Love the story of the busted tube. Reminds me of when my old boss refused to replace a significant benefit i had. It cost him in 6 months the price of a small house. NEVER steal from your employees. They WILL bite back.
My dad got a L-230 new 1986. A year later an incandescent light gave in and the voltage regulator, consisted of a zener diod, burned. I removed both the current restriction resistor and the diod and changed it out for a 7805. Instead of the incandescent light I mounted LED’s. The amplifier still work some 36 years later. Regards PeO
My first thought was why not use LEDs for the indicator lights but then you pointed out the Zener diodes to limit the supply voltage and prolong the bulb life. Did you consider LEDs? Is there a reason you decided against LEDs? Just curious. I love your videos, you get right into the issues without a lot of extraneous commentary. Very informative.
I have the same Luxman 230 with the same problem - bulbs not working. I just replaced the Xenor diode with a 28v 5 amp. - still no lamps working. The diode was showing burn marks underneath just like yours. I believe I placed it properly. Any other suggestions for this newbie? Thanks for the great video. Edit: Guess what? I got them to work. I had indeed reversed the Xenor diode. Also, for what it’s worth, if the polarity on the LED bulbs are reversed, they will not light up and gives the illusion they are burnt out. Went to what’s left of Radio Shack and bought unmarked bulbs and hoping they aren’t being tested too heavily as I’m guessing they are 12v on a 28v circuit. Time will tell.
It always makes me wonder why they use underated zener diodes. I always replace them with higher rated ones. Regarding the dry joints, i find it's best to remove the old dried out solder, and replace wih fresh solder. These amps will last a long time with some tlc.
The thing with solder. When you heat it, the new solder and flux will mix with the old and form a new alloy. No need to remove the old.The process of melting it will drive out the oxygen that has bonded with the tin and lead over the years.
@@12voltvids Not in my experience, re-heating old solder with new will create a new metal with unknown reliability on components that run hot. It only takes a short time to remove the old solder and use new solder that will last a few years. This is what i was taught as an apprentice Hi-Fi tech many tears ago, and having been lazy in the past, only for the same joint to be the reason for the failure of a repair.
Thank you for using incandescent bulbs as a replacement. I don´t like LED replacements at all, they just look "not right" if the initial design of an indicator light was meant to have an incandescent bulb.
@@12voltvids You can solve this somewhat by sanding the lens of the LED. It diffracts into more of an omni light. Not exactly the same, but it might be enough.
How about using a curve tracer to check a zener? Or a small lamp in series with the zener to limit the current? That would give a visual of current draw as the lamp starts to glow. I do believe my curve tracer is limited to something like 12 volts however. I need to check the 43v zener in the power supply of my Heathkit IG-28 signal generator. Output is not stable, has amplitude modulated output around 2 Hz. Been eluding me as to the root cause. Simple device, just over thinking it and had to shelve it for awhile.
I have purchase the L205 a weeks ago. The pilot lamp is burnt but the D112 diode is fine. What im doing is i just change the light bulb without measure the voltage. It looks fine but suddenly the D112 turn burnt out but the pilot lamp is still working. That cause the output sound become slower also. What should i do next sir?
My dads Yamaha amplifier receiver used a 28 volt bulb the green cover fell to pieces but it looks better in warm white .My kenwood kr 3010 from 1979 uses 8 volt bulbs .
I just finished serviced a GE Musiphonic tube radio that had an oddball dial light it was a 1828, 37.5 volt @ 50ma. They ran it off the AC line thru a dropping resistor because there was no rectifier tube to tap a low voltage lamp as it used a selenium rectifier, the closest I had was a 1820 28v @ 100ma it lit about normal but ran the resistor a bit warmer I also had a 120MB 120v @ 25ma that lit about the same as the 1820 but ran the resistor cool so I used the 120 mb, the nice thing was I didn't have to modify the lamp circuit due to the different current ratings of the bulbs all worked about normally with the original dropping resistor so if the 120mb pops and someone sticks in a 1828 either will work ok. The 120mb's I had looked just like a standard shaped panel lamp such as a #47 it did not have the longer glass with the flat top.
Ac driven bulbs will last longer than DC driven ones, as they don’t suffer metal migration in the filament due the current flowing in one direction all the time. Low voltage bulbs like 5V ones last longer still as the filaments are thicker. On aircraft panels 28V bulbs make it easier to place as they are all in parallel and a single bulb failure is not much of an issue. But series/ parallel strings of 5V bulbs will last longer. But the placement of the blubs is more of a problem as you can’t have a string going out making a part of the panel unreadable. More to bulb selection than you would think
I have an old Luxman R 114 receiver and also an R 113. They are the best sounding amps I have ever owned, and I've owned more than a few over the years.
i did that with a cover on a Panasonic vcr about 12 yrs ago when putting on the cover it hit something and shorted it out. i can't really remember what i was trying to fix on it maybe something with the tuner. i only paid $5 for the vcr from the thrift store so not a big loss.
It was a very common design used in a lot of equipment from many manufacturers of that era. Under normal circumstances, it did the job well enough, and had a very low production cost.
I'm a bit disturbed by changing the color sleeve orientation around. I have one of these amps and the color scheme is exactly the way it was, now you have changed it around. My unit has never been serviced nor was there a need for it. Green for Phono, Yellow for AUX and clear for the Tuner (Color orientation for quick glance recognition). Changing that around would certainly upset me without asking. It doesn't surprise me that diode broke apart after you heated it so much. The bulbs are actually 24v bulbs, it even says that on the schematic right next to L2 24v, this is why you are getting just under 24v after replacing the diode. Thanks for the video and the attention to detail, now I will be more cautious who I take my equipment to for repair.
The diode was broken before he touched it. The open circuit voltage was over 40v which shows the zener wasn't doing it's job of voltage regulation to 22v
Actually they are 28 volt bulbs. I looked up the number. The zener had already failed. That is why I had 0 volts the first time I tested it. Then it went completely open, hence the 40 volts on the open circuit. I changed the color scheme around just to get under your skin.
Lamp sleeves weren't a real common item even back when and then to find 1 that fits your size and shape of lamp. Think ones for something like a 47 lamp were sort of easy to get.
A few things: 1. Those transistors do blow due to a cr@p protection-circuit ... you can replace (upgrade) the power transistors for a matched pair, 2SA1694 and 2SC4467 by SANKEN ... they are actually better than the Toshy (Toshiba) originals. 2. D112 (22V/3W) ... The original design is a bit "iffy", the zener should ideally be 5W (hence the burnout), plus it needs a heatsink applied to it, only if the original (24v) bulbs are used. The Zener's 22volt supply is there for a reason ... it increases the longevity of the bulbs even @24v (as per Schematic), or 28v ... without it you'll be back to square one in a short time ... 3. Bulb to LED replacement ... D112 can be removed and R153 (300ohms) can be replaced by 1.5k to 5.6K 2W resistor, depending on LED type. Other MODs for this amp include: RIAA caps upgrade, PSU upgrade, Power-amp input caps, loudness, muting circuit, etc. It's a nice 80's amp.
I have an old Sanyo Plus series 55 Am/FM Stereo Receiver, don't know if you've ever worked on one. Everything works expect the audio, I have no audio for the speakers as well as the headphone jack.
This'll take some good old-fashioned methodical troubleshooting. Get the service manual from HFE and observe what the unit does. If there is no relay click at startup, find out why. The unit might be in protection, so check DC offset at the output of both power amplifiers. If within +/-100 mV each, proceed to look at relay driver and relay power supply. If one channel is out of spec, proceed to check the STK0050 output hybrid, the feedback resistors (the 2x 47k in particular) and the 2SA798G input pair, a type that quite commonly fails if memory serves. Look up 2SA798 replacement options if need be, a pair of KSA992FB epoxied together (for thermal coupling) seems to be one of the better solutions. Appsarently this model is also commonly suffering from a worn-out power switch with arcing issues. The tuner in this thing has some neat tricks up its sleeve btw. There is RF AGC so that even the relatively modest 3-gang frontend should do quite well even in strong-signal environments, selectivity with its 3 IF filters (with no limiters in between) should be good, and a PLL circuit with sampling mixer is used to lock the local oscillator to 100 kHz increments (modulo-f PLL), with a varicap diode providing limited frequency pulling of the LO like in a conventional AFC circuit. This is not a feature I would have expected in a midrange receiver, I am mostly associating it with fancy tuners from a few years prior (Pioneer TX-9800, Mitsubishi DA-F20). Looks like it inherited the whole quartz lock board from the T35 tuner, while sporting a more typical cost-reduced frontend and IF strip. Cool.
Nice testing the zeners, I also do this with unmarked ones. Well, I think you will be seeing this amp again when lamps burn out. Then that poor half-watt zener will dissipate more than 2 watts (easy to calculate from voltages and series resistor value)..
I recently restored a jvc a-x7 amplifier. It uses 6.3v bulbs for its panel. Found they were all wired in series. So if one bulb didn’t work. None worked. Think the bulbs were acting as a fuseable resistor within itself. Possibly to keep things simple and low voltage
I would leave some space for all the diodes and resistors, also I would separate the caps from radiators or at least use some aluminium foil to soak the heat
The zener and that cap across it could both be removed. The only reason that there would be a problem is when the circuit is switched to an open lamp, without the zener the cap would charge to full supply and discharge that thru a good bulb. If the cap and zener are gone the whole problem is solved.
Instead of bulbs I guess LEDs could be used with a suitable resistor to limit current to about 5mA or thereofs (6.8k to 10k, 0.5W). That way the zener would not be required.
Back when I was doing Radio and TV work, I broke a 19 inch Sony picture tube. Knowing Sony only has brand new tubes, we had to purchase a new one. Moreover, the customer was a wealthy guy and that hurt even more !
It is a shunt and is always passing current. When the bulb blows they pass even more. The reason the initial bulb was out was because that zener was shorted. Then it went totally open.
@@12voltvids Seems like a bad design. Shouldn’t each bulb have its own zener diode? Could you place a tiny heat sink on the diode to help keep it from overheating?
@@sunspot42 the zener should under normal circumstances only discipates a few miliwatts as the lamp burns up the bulk of it. It's only because the lamp blew that it overheated. The reason it is there is to limit the voltage to the lamp to 23 volts and the bulbs are rated 28. This extends their life
@@12voltvids I got that. It just seems like if a bulb burns out on that circuit the diode suddenly has to dissipate more heat. That’s why I was thinking it might be better if there were one diode for each lamp. Then it wouldn’t have to cope with 2 or even 3 burned out lamps.
@@v12alpineAgree with you. I meant where ever required in general .I have seen places where the B+ supply is dropped by just a single resistor to supply the LED. I design power amplifiers as a hobby .None of the panel LEDs use unregulated power. Advantage is, their brightness never change due to mains fluctuation .Even the cooling fans use regulated power.
You know what happens next, right? Yep, after said nitwit let’s the magic smoke out of some customer’s expensive gear, the loud bang scares any nearby employees, who then proceed to do something equally idiotic, such as dropping a hot soldering iron in their lap (or on the floor), or the accidentally touch exposed mains voltage, etc… Then you have a shop full of cussing employees, and an angry boss.
These are my favorite style vids. You passed on a lot of interesting info in this one. Love to see more of these. Even a few tutorial vids would be cool for some of the noobs.
i am "youngster" but the old luxman gear is Great stuff! got some luxman cassette decks i love. and i love ur videos. keep em coming. this is priceless to for thoose who love vintage stuff.becouse of u and some other youtubers made me manage to repair several cassette decks for own use. very nice of u Dave. greetings from across the globe.
Luxman = beautiful sound. I got my first Lux in 1987; an LV105U. I absolutely loved this amp, and finally after 34 years I had to replace it due to parts being unavailable as you stated. I have been listening to my new L-505uxii for about 4 months now and have started a whole new love affair. I still have my 105u, not willing to relegate it to the recycler. I enjoyed the video, thanks.
Yes they do have beautiful sound. That's why in 1984 I spent about two grand on my new lv103. My friends thought i was crazy but the type of music i listen to the instruments just popped with that amp. The only amp that I have that sounds better is a full tube amp.
Another great fix as always, thanks Dave. I also enjoy the stories that you tell as well, keep it up.
Great educational content...and entertaining as well! Thanks, Dave!
Could those lamps not be replaced with appropriate coloured LEDs with limiting resistors? I would fit the LEDs in line with the leads and use to heat shrink tubing to make a neat job.
They cant or at least they shouldnt in this case since they are crucial to the right function of the ciricuitry. In this and some other Luxman models they should be replaced with 24V 50mA bulbs since their turn-off time is utilized by the ciricuit to discharge a capacitor. If i understood it right those Luxmans dont have a relai to prevent the speakers from making a "pop" noise when turning on.They use a fancy ciricuitry for this job and i think part of it is the light bulb. If the Light Bulb fails, it causes the d112 diode and the green Resistor next to it to overheat (which is why the PCB is burned under the diode of nearly every survivor of those Amps). The heat also stresses the Capacitor next to it so its a good idea to replace all of those components and to solder the new diode higher (the way the green Resistor is soldered in) to prevent further damage of the PCB
@@kaiaphasful Yikes. That's clever, but also not a particularly great design to make a consumable component part of proper operation. If this were mine, I think I would re-design that circuit to use a power resistor in parallel to an LED light. That way you get your nearly-infinite lifespan and proper discharge capability.
@@nickwallette6201 I agree on the part that light bulbs are destined to fail (but so are capacitors) and leds have a longer lifespan at least on paper. You could use a resistor together with an led to achieve the right readings, however there was an explanation that slips my mind on why you shouldnt do that either (i think bcs an led works like a diode or so?!) . Since i own amps with all working light bulbs which are over 50 years old (i own at least 15 from the 60s, 70s and 80s i dont think that they were nearly as badly designed as every cell phone with a glued-in battery. From all my amps the finest piece i have and the one i love the most is my Luxman l190 cos its the one i can clearly say i hear a difference (tube amps excluded) . It has a very detailed, fine sound. The white noise on full volume is the lowest compared to all my other amps, when i turn the knobs and press the Buttons i dont hear any scratching. On the inside all caps are ELNA most of them blue caps, it has ALPS Buttons and is designed service friendly. If you can get your hands on a luxman for a fair price dont miss it
@@kaiaphasful I was thinking of having a resistor _parallel_ to the LED, so it acts like the filament of a bulb. The LED itself would have its own current-dropping resistor (since the circuit's operating current is designed around that 50mA bulb, and that's way too much for an LED) and so should be fairly negligible alongside the larger resistance. Even if the diode effect is troublesome, the parallel resistor wouldn't be polarized. I haven't looked at the full schematic, but it seems like it should work. ;-)
Never heard a Luxman myself. It did look nicely built. Still a phenolic board, which I'm not crazy about, but otherwise quite stylish, serviceable, and designed to last. I hope to cross paths with one some day.
I really quite like that Luxman, lovely warm sound.
Same prob with zener so thé lampe were broken....
You hit knee voltage of Zener, seen that on a Tektronix spectrum analyzer when in school,2000 -2003 . Man I am getting old, Good video.
Gonna remember next time I do a bulb like that to get the center first to
have it as a holder. Great time saver there... Genius! 🍻 Cheers! -AC
I like when you don’t just fix the unit, but also teach us about those diodes, for example. I have some electronic knowledge, but not as much as my dad.
I love those amps, they sound amazing.
They do sound amazing.
Lol all class a/b amps sound the same
@@catsbyondrepair hahahahaha. Good one. You need to get our more and listen to a few. Each brand and design sounds a little different. Every brand adds a little color to sound.
I`d ask 12volt to show off the face of the equipments he fixes. They have a face and deserve some notoriety! Keep the good job.
that amp is beautiful with its rounded bold selectors. is it possible and advisable replacing bulbs with led lights?
With a blown lamp and no Zener wouldn't the voltage across the 35v rated capacitor be a little too high? Also if the cap was allowed to charge to 42v then this would be discharged through the pilot lamp when the lamp is activated. Of course if all bulbs ok and the switch is not a break before make then this would not occur. LEDs would be my way to go.
Awesome video, thanks !
Nice job Dave. Thanks for sharing.
For even more fun, grab a 12 VAC wall-wart, a 1kilohm 1% resistor, and a scope with X/Y mode, some test leads, and a diode (or zener) to test. Wire one end of the diode under test to the wall-wart, the other end to the 1k resistor, and the other end of the resistor to the other end of the wall-wart secondary. Hook the X-inputs of the scope across the DUT, and the Y-inputs across the resistor (to measure the current in mA.) Plug in the wall-wart, and turn on the scope and set it to X/Y mode with DC coupling on both channels. You should now see the characteristic curve of the diode. If the knee-voltage of the zener is less than the peak inverse voltage (or, about 16.9 volts), then you should see that in the 3rd quadrant (lower-left.) You can also test capacitors and inductors with it, too.
20:55 One shop I worked in had a set of lead bending pliers to put those 'U" shape bends in the leads at just the right place and make it nice. Wish I had a set of those now.
When you measured the voltage across a blown bulb it was 40v which showed that the zener had failed and, since the cap across it was rated at 35v, I would have changed that too in case its life had been reduced.
When I see caps, it's like looking at a mine field of little bombs waiting to malfunction.
A wise man once said the reliability of any electronic device is inversely proportional to the number of electrolytic capacitors it contains.
Yep bosses, "Do as i say, Not as i do"
They get angry when you remind them of the rules they ignore.
Just remember not all bosses are assholes, some of them are dicks.
Lol
I have a Luxman L-430 and I replaced the panel lights and the light over the volume control with warm white 5mm LEDs and the one for Phono with a green one. The look great and will never burn out.
Nice to see (or hear) the Cats doing ok and comming in to learn some skills!
Love the story of the busted tube. Reminds me of when my old boss refused to replace a significant benefit i had. It cost him in 6 months the price of a small house. NEVER steal from your employees. They WILL bite back.
My dad got a L-230 new 1986. A year later an incandescent light gave in and the voltage regulator, consisted of a zener diod, burned.
I removed both the current restriction resistor and the diod and changed it out for a 7805.
Instead of the incandescent light I mounted LED’s.
The amplifier still work some 36 years later.
Regards PeO
My first thought was why not use LEDs for the indicator lights but then you pointed out the Zener diodes to limit the supply voltage and prolong the bulb life. Did you consider LEDs? Is there a reason you decided against LEDs? Just curious. I love your videos, you get right into the issues without a lot of extraneous commentary. Very informative.
I have the same Luxman 230 with the same problem - bulbs not working. I just replaced the Xenor diode with a 28v 5 amp. - still no lamps working. The diode was showing burn marks underneath just like yours.
I believe I placed it properly. Any other suggestions for this newbie? Thanks for the great video.
Edit: Guess what? I got them to work. I had indeed reversed the Xenor diode. Also, for what it’s worth, if the polarity on the LED bulbs are reversed, they will not light up and gives the illusion they are burnt out.
Went to what’s left of Radio Shack and bought unmarked bulbs and hoping they aren’t being tested too heavily as I’m guessing they are 12v on a 28v circuit. Time will tell.
It always makes me wonder why they use underated zener diodes.
I always replace them with higher rated ones.
Regarding the dry joints, i find it's best to remove the old dried out
solder, and replace wih fresh solder.
These amps will last a long time with some tlc.
The thing with solder. When you heat it, the new solder and flux will mix with the old and form a new alloy. No need to remove the old.The process of melting it will drive out the oxygen that has bonded with the tin and lead over the years.
@@12voltvids Not in my experience, re-heating old solder with new will create a new metal with unknown reliability on components that run hot.
It only takes a short time to remove the old solder and use new solder that will last a few years.
This is what i was taught as an apprentice
Hi-Fi tech many tears ago, and having been lazy in the past, only for the same joint to be the reason for the failure of a repair.
Thank you for using incandescent bulbs as a replacement. I don´t like LED replacements at all, they just look "not right" if the initial design of an indicator light was meant to have an incandescent bulb.
It is a very nice sounding amp!
The L-230 is a great amp. I just had mine serviced - output caps all replaced, bulbs replaced and lots of joints resoldered. Phono is green on mine.
I would like to see you work on some of those D-Theater Machines
Well i can only work on what i have access to. I only do this part time.
Good video, educational as usual. Would you ever work on an Ampex Consumer deck? I can’t find anyone willing or experienced?
LED don't give nice even light like incandescent bulbs.
@@12voltvids You can solve this somewhat by sanding the lens of the LED. It diffracts into more of an omni light. Not exactly the same, but it might be enough.
You could but additional resistor in series to brightest lamp to dim it on same level with others.
How about using a curve tracer to check a zener? Or a small lamp in series with the zener to limit the current? That would give a visual of current draw as the lamp starts to glow. I do believe my curve tracer is limited to something like 12 volts however. I need to check the 43v zener in the power supply of my Heathkit IG-28 signal generator. Output is not stable, has amplitude modulated output around 2 Hz. Been eluding me as to the root cause. Simple device, just over thinking it and had to shelve it for awhile.
The lamp is in series until it burns out. It lasted for 40 years.
Thanks Dave for the zener diode testing tips. JwgK
the zener diodes need heat sinks or replaced by highter voltage and raised above the boad. they tend to overheat.
I have purchase the L205 a weeks ago. The pilot lamp is burnt but the D112 diode is fine. What im doing is i just change the light bulb without measure the voltage. It looks fine but suddenly the D112 turn burnt out but the pilot lamp is still working. That cause the output sound become slower also. What should i do next sir?
Nice Job As Usual Dave Regards mike
My dads Yamaha amplifier receiver used a 28 volt bulb the green cover fell to pieces but it looks better in warm white .My kenwood kr 3010 from 1979 uses 8 volt bulbs .
why was the resistor in mid air ,
Because it went high⚡
This might be off topic. Where do I find schematic diagrams for things like car headunit?
Couldn't tell you as I don't and never have had anything to do with car audio.
I just finished serviced a GE Musiphonic tube radio that had an oddball dial light it was a 1828, 37.5 volt @ 50ma. They ran it off the AC line thru a dropping resistor because there was no rectifier tube to tap a low voltage lamp as it used a selenium rectifier, the closest I had was a 1820 28v @ 100ma it lit about normal but ran the resistor a bit warmer I also had a 120MB 120v @ 25ma that lit about the same as the 1820 but ran the resistor cool so I used the 120 mb, the nice thing was I didn't have to modify the lamp circuit due to the different current ratings of the bulbs all worked about normally with the original dropping resistor so if the 120mb pops and someone sticks in a 1828 either will work ok. The 120mb's I had looked just like a standard shaped panel lamp such as a #47 it did not have the longer glass with the flat top.
How good is this unit? Are there some gems, models that are good and don't cos a ton?
They are good units. Most of the gear from this era is very good.
Ac driven bulbs will last longer than DC driven ones, as they don’t suffer metal migration in the filament due the current flowing in one direction all the time. Low voltage bulbs like 5V ones last longer still as the filaments are thicker.
On aircraft panels 28V bulbs make it easier to place as they are all in parallel and a single bulb failure is not much of an issue. But series/ parallel strings of 5V bulbs will last longer. But the placement of the blubs is more of a problem as you can’t have a string going out making a part of the panel unreadable.
More to bulb selection than you would think
I have an old Luxman R 114 receiver and also an R 113. They are the best sounding amps I have ever owned, and I've owned more than a few over the years.
The Luxxman R117 was a great receiver from 1987
i did that with a cover on a Panasonic vcr about 12 yrs ago when putting on the cover it hit something and shorted it out. i can't really remember what i was trying to fix on it maybe something with the tuner. i only paid $5 for the vcr from the thrift store so not a big loss.
I think this a bad design as the tiny zenner diode has to handle a lot of current .
It was a very common design used in a lot of equipment from many manufacturers of that era.
Under normal circumstances, it did the job well enough, and had a very low production cost.
@Douglas Blake You are right . But the engineers who designed the amp did not take that into account .
I'm a bit disturbed by changing the color sleeve orientation around. I have one of these amps and the color scheme is exactly the way it was, now you have changed it around. My unit has never been serviced nor was there a need for it. Green for Phono, Yellow for AUX and clear for the Tuner (Color orientation for quick glance recognition). Changing that around would certainly upset me without asking. It doesn't surprise me that diode broke apart after you heated it so much. The bulbs are actually 24v bulbs, it even says that on the schematic right next to L2 24v, this is why you are getting just under 24v after replacing the diode. Thanks for the video and the attention to detail, now I will be more cautious who I take my equipment to for repair.
The diode was broken before he touched it. The open circuit voltage was over 40v which shows the zener wasn't doing it's job of voltage regulation to 22v
Actually they are 28 volt bulbs. I looked up the number. The zener had already failed. That is why I had 0 volts the first time I tested it. Then it went completely open, hence the 40 volts on the open circuit. I changed the color scheme around just to get under your skin.
Lamp sleeves weren't a real common item even back when and then to find 1 that fits your size and shape of lamp. Think ones for something like a 47 lamp were sort of easy to get.
A few things:
1. Those transistors do blow due to a cr@p protection-circuit ... you can replace (upgrade) the power transistors for a matched pair, 2SA1694 and 2SC4467 by SANKEN ... they are actually better than the Toshy (Toshiba) originals.
2. D112 (22V/3W) ... The original design is a bit "iffy", the zener should ideally be 5W (hence the burnout), plus it needs a heatsink applied to it, only if the original (24v) bulbs are used.
The Zener's 22volt supply is there for a reason ... it increases the longevity of the bulbs even @24v (as per Schematic), or 28v ... without it you'll be back to square one in a short time ...
3. Bulb to LED replacement ... D112 can be removed and R153 (300ohms) can be replaced by 1.5k to 5.6K 2W resistor, depending on LED type.
Other MODs for this amp include: RIAA caps upgrade, PSU upgrade, Power-amp input caps, loudness, muting circuit, etc.
It's a nice 80's amp.
I have an old Sanyo Plus series 55 Am/FM Stereo Receiver, don't know if you've ever worked on one. Everything works expect the audio, I have no audio for the speakers as well as the headphone jack.
This'll take some good old-fashioned methodical troubleshooting. Get the service manual from HFE and observe what the unit does.
If there is no relay click at startup, find out why. The unit might be in protection, so check DC offset at the output of both power amplifiers. If within +/-100 mV each, proceed to look at relay driver and relay power supply. If one channel is out of spec, proceed to check the STK0050 output hybrid, the feedback resistors (the 2x 47k in particular) and the 2SA798G input pair, a type that quite commonly fails if memory serves. Look up 2SA798 replacement options if need be, a pair of KSA992FB epoxied together (for thermal coupling) seems to be one of the better solutions.
Appsarently this model is also commonly suffering from a worn-out power switch with arcing issues.
The tuner in this thing has some neat tricks up its sleeve btw. There is RF AGC so that even the relatively modest 3-gang frontend should do quite well even in strong-signal environments, selectivity with its 3 IF filters (with no limiters in between) should be good, and a PLL circuit with sampling mixer is used to lock the local oscillator to 100 kHz increments (modulo-f PLL), with a varicap diode providing limited frequency pulling of the LO like in a conventional AFC circuit. This is not a feature I would have expected in a midrange receiver, I am mostly associating it with fancy tuners from a few years prior (Pioneer TX-9800, Mitsubishi DA-F20). Looks like it inherited the whole quartz lock board from the T35 tuner, while sporting a more typical cost-reduced frontend and IF strip. Cool.
@@PileOfEmptyTapes Thanks for the reply.
Nice testing the zeners, I also do this with unmarked ones. Well, I think you will be seeing this amp again when lamps burn out. Then that poor half-watt zener will dissipate more than 2 watts (easy to calculate from voltages and series resistor value)..
The original was a 1/8 watt.
@@12voltvids Wow, 16 times the power into the original with open lamp
You could be just the man I'm looking for. My sansui AU 717 needs attention. I'm here in London though
I recently restored a jvc a-x7 amplifier. It uses 6.3v bulbs for its panel. Found they were all wired in series. So if one bulb didn’t work. None worked. Think the bulbs were acting as a fuseable resistor within itself. Possibly to keep things simple and low voltage
Thanks for sharing..
I would leave some space for all the diodes and resistors, also I would separate the caps from radiators or at least use some aluminium foil to soak the heat
The zener and that cap across it could both be removed. The only reason that there would be a problem is when the circuit is switched to an open lamp, without the zener the cap would charge to full supply and discharge that thru a good bulb. If the cap and zener are gone the whole problem is solved.
Instead of bulbs I guess LEDs could be used with a suitable resistor to limit current to about 5mA or thereofs (6.8k to 10k, 0.5W). That way the zener would not be required.
Back when I was doing Radio and TV work, I broke a 19 inch Sony picture tube. Knowing Sony only has brand new tubes, we had to purchase a new one. Moreover, the customer was a wealthy guy and that hurt even more !
The local rebuilder used to do sony tubes out this way.
I wonder why the diodes go out on them like that on these models, worked on the same model with the exact same symptom
It is a shunt and is always passing current. When the bulb blows they pass even more. The reason the initial bulb was out was because that zener was shorted. Then it went totally open.
@@12voltvids Seems like a bad design. Shouldn’t each bulb have its own zener diode? Could you place a tiny heat sink on the diode to help keep it from overheating?
@@sunspot42 the zener should under normal circumstances only discipates a few miliwatts as the lamp burns up the bulk of it. It's only because the lamp blew that it overheated. The reason it is there is to limit the voltage to the lamp to 23 volts and the bulbs are rated 28. This extends their life
@@12voltvids I got that. It just seems like if a bulb burns out on that circuit the diode suddenly has to dissipate more heat. That’s why I was thinking it might be better if there were one diode for each lamp. Then it wouldn’t have to cope with 2 or even 3 burned out lamps.
@@sunspot42 there is only 1 lamp running at a time.
excellent, thank you
1:51 lamp condoms... hahahahahahahahahahaha
That looks around 81 to 84 design.
Why not put LED's in and forget about the fail-prone zener and bulbs? Did the customer want is 100% original?
I did put LEDs on some amps and decks using appropriate resistors and regulator they work fine.
@@manusudha4269 For this unit I don't think you need a regulator, just the proper resistor in line should do the trick.
@@v12alpineAgree with you. I meant where ever required in general .I have seen places where the B+ supply is dropped by just a single resistor to supply the LED.
I design power amplifiers as a hobby .None of the panel LEDs use unregulated power. Advantage is, their brightness never change due to mains fluctuation .Even the cooling fans use regulated power.
@@manusudha4269 Gotcha, makes sense in this case.
Very cool
Nice amp
You know what happens next, right? Yep, after said nitwit let’s the magic smoke out of some customer’s expensive gear, the loud bang scares any nearby employees, who then proceed to do something equally idiotic, such as dropping a hot soldering iron in their lap (or on the floor), or the accidentally touch exposed mains voltage, etc… Then you have a shop full of cussing employees, and an angry boss.
👍🇵🇱🇵🇱👍👍😎😊😀😁
I'm no Einstein but why not put a transistor with the zener and have a series regulator??? Enjoy your videos...
That would add cost, and another point of failure. The zsners only job really is to protect the lamps from power surges.
meow! 😹😹😹
ZEEner
In Canada and pretty much the rest of the English speaking world Z is pronounced "zed" not "zee".