Sanyo DCA 401 amplifier repairs [2/2] - New Output Transistors
ฝัง
- เผยแพร่เมื่อ 14 ต.ค. 2024
- Replacing all Output Transistors with newer types and making sure the amplifier still runs stable. But then the whole project turns out to be a fail...
Part 1: • Sanyo DCA 401 amplifie...
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![Sanyo DCA 401 amplifier repairs [1/2] - Diagnosis](/img/n.gif)
I have had the same noise problem with my philips 22rh720. It turned out to be a faulty 3300uf filtercapacitor. The sound that is present is rather similar to the sound i heard at the time. Sometimes it will be completely gone and sometimes it is very noticable. Good luck!
And, by the way, you're, by far, the best English speaking German chap I've ever heard. Congrats! No offence intended to my many German friends ;)
Thank you :)
That's life with Sanyo. The slogan they used in the 1970's - 80's advertising.
Hi thank you for the very valuable video I have just a question about the output bjts replacement
Why these low power parts ? i would have use some powerful 125W bjts in to220 package
More powerful bjts have a wider safe operation area And they should be more reliable in the end
Their price is very low
Pity it did not work out, i really like the look of it 👍
The case will be used for a future project, so the look of it is not lost :)
I've had noises like this, and found that on (or underneath) the circuit board there were poorly soldered contacts which effectively produced micro-arcing.
The solder joints all look fine. I am quite sure it's semiconductor noise.
Well done Sir, my best compliments! I have learned many interesting things. Super Like.
Thank you :)
It's about time.
Many thanks.
I found a rotel RCD-855 with original remote in immaculate condition.
Is this a good cd circa 1988-1990
Would you please stop commenting about when I upload videos? Videos are uploaded when they are ready.
Hi, Jonas.
I'm posting here because, first of all, I couldn't find a "send message" button in your profile section, so I don't think I could reach you any other way and, secondly, because this is your latest video, so I guess the chances that you see this are better this way. My apologies to the other viewers out there: my (rather long) post is not about this video. Sorry, guys.
I'm really glad I found your channel, as you are so good at what you're doing. I hope to be able to learn a lot from you ;)
Let's get down to my problem real quick. I found a mint Akai VCR on ebay, the VS-A1100. It has all the bells and whistles - Hi-Fi, Dolby NR, etc It came in its original box and it even had the protective foils still in place on the LCD display and remote. Besides, it was dirt cheap.
But, as I got it from the UK (and I live in Romania), the sound standard is different. The result? I get no sound from any of my pre-recorded tapes. Second issue: the picture exhibits some slight "jaggies", especially visible on less-than-perfectly recorded footage. Furthermore, the still frames are pretty noisy, which is annoying (I didn't expect that issue, since the unit is pretty new - in VHS terms , like 1994 - and it has 4 video heads).
First question: can the audio filters (or whatever they're called) be replaced, in order to play back and record sound properly? Second question: what about the picture quality issues (jaggies and bad stills)? Could there be any electronic component to be blamed? Ageing capacitors or something? Maybe dirty heads (I don't think so...)?
I'd be happy to keep this unit, as it seems to be a really low-mileage VCR, with great features.
Could you help me out with some suggestions, please?
Thank you!
I am not an expert on VCRs by any means, so I can only give basic advice such as cleaning the heads to try and reduce the video noise. Have you tried adjusting the tracking? I unfortunately have no idea how to redesign or readjust the audio circuitry. Sorry, this reply is probably not what you were hoping for...
Thank you!
Is the noise from the same channel that had the rounded edges to the square wave? Could be transistors but capacitors in the audio path going leakey can make the same noise, Would also explain the uneven volume level and the rounded edges to the square wave. Too nice to part out i think :)
The noise was present on both channels. The amplifier has now been parted out.
Always enjoy your videos.
Hi and will start by thanking you for all the great videos ! I was hoping if you could tell me if you have ever covered verifying that earlier stages/transistors are OK when you have failed output transistors. If not would it be possible for you to cover this subject use bare bones equipment (like me ) and what to look out for as to save yourself another run to the electronics shop .Thanks again
Ron (Fremantle downunder)
Hi, Jonas.
If you wanna a small vintagel yet powerful amp, go to the Cyrus Two you dismissed.
Once fixed it's light years better in all aspects than this poor Sanyo.
Greetings.
Not a bad old amp, i like the good old sanyo, they made good stuff before they really cheaped out
Thank you doctor for last answer. I have a new question. I have a Cyrus one integrated amplifier an old one from 1985. I was listening to music through one of sources in this case phonograph records and I was using a phono pre amp through the tuner inputs. After the music was finished I heard a hum coming from the speakers. I thought it was the phono pre amp because when I moved the phono pre amp around the hum seem to fade in and out. So I turned off the phono pre amp and turned it back on. Now all the sources on the Cyrus one don’t work. No sound at all.
I think I found the problem. There are two fuses in the amp that are used to protect the power amp section. One of them blew. The hum was coming from a condition know as “ground loop”. “An audio problem called a ground loop is a common cause of hum problems. Slight differences in the AC voltage levels between two pieces of equipment creates an audio hum . Ground loops in home stereos typically occur when turntables or other sources are plugged into different electrical outlets than the amplifier”. I did have the turntable and phono pre amp plugged into different outlets other than what the integrated amp was plugged into. But my question is why would this cause the fuse to blow?
Oh we were so close too. But one dies so another or more may live again. All wins to me. Enjoyed the video.
This thing works, wow! Hey, I thought you will have some fire works in the process :) You can have also noise from preamp section or cold solder, preamp might cause the rounding of square wave or some caps are bad. For 1970s it's a miracle it works. I do like the chassis, so you could use it to build a real amp if there's enough space inside for big trafo and real heatsink, or good D-class modules.
Is this Marantz CD player you have? Looks like the '63' model. It's Onkyo - no, nothing against older Onkyo pieces, actually some Integra pieces are really good. Nice scope Dr. - my old college when it closed the electronics department some 15years ago, they basically scraped or sold for cheap older equipment - I just wanted good 150MHz analog scope and function generator 😭
Yeah, I also have bunch of parts mostly from older 5.1 receivers, since people now buy equipment with HDMI (no better amp section), should do something with it, but I don't like the trafos - quality isn't near as good as what you get in Hi-end, heat being main issue.
The noise can in no way be influenced by any of the controls, that's why I think it's not the preamplifier. Also, the preamp only uses one dual opamp, and the freeze spray had no effect on it. The solder joints all look fine. The rounded off square wave is another problem, then there is the louder right channel, and yes, there may also be bad capacitors. Also, the preamp instead of having a proper regulated power supply it's fed by the power amp supply through a voltage divider. This lack of voltage stabilization causes a constant hum in the background. Many problems that I would want to fix, but the amplifier is just not worth this much work. I was going to use it in my studio since it's not worth selling even in working condition, but I have since found a much better Kenwood amplifier that should hopefully work fine but has some cosmetical issues so also that one is not worth selling. So the Sanyo amp is both broken and useless.
@@DrCassette
Yes too many things to go wrong, and quality of the design the way you described it, isn't worth the effort. Nice chassis though. The 45xx op-amps aren't the greatest sounding, 5532 are a bit better, but they are rather old comparing to new designs. Kenwood, better than Sanyo. I used to have OK amp, high current from Sima circa 1990, but it got cocked when I was away, v. similar to Prof Leach design. Now using older Denon AVR, sounds - it will pass, better than Sony.
Doctor, this question is somewhat unrelated but do I need to remove the old solder before repairing broken solder joints or can I just solder over the old solder? Thanks
Generally you can just add new solder to the existing solder. But if there is then too much solder, use the soldering iron to take off some solder.
Sorry for the loss, at least it’s basically functional aside from the noise. I can relate spending time on something that didn’t quite work out. I recently learned a painfull lesson with floppy ribbon cable’s, it’s those darn twists. I had bought a rather expensive 5 1/4” floppy drive on ebay only to discover that my cable had the twist in the wrong place. I sent it back to the seller but I am now in stage to try to get my money back through paypal. The seller has become awfully quite after he received it back (apperantly refunding is so hard). Oh the horror😓😰.
No need to be sorry, I think just the case of the amplifier is going to be much more useful than the amplifier as a whole :)
It's just frustrating that I've wasted three days working on this. Oh well, at least I got two videos out of it, and learned about testing stability on audio amplifiers in the process.
Shame i quite like the look of that amp
The case will be used for a future project, so the look will not be lost.
Enjoying your videos DrCassette!
Just some thoughts if I may ....
(a) I assume these output transistors are operating in Class-B mode?
(b) Rounded square wave = slightly excessive damping?
I'm just thinking out allowed here (as we say), is there slightly too much transistor junction capacitance, and can this be slightly offset in some way? Are these transistors slightly biased in their Class-B mods? The amount of bias may affect the junction capacitances. Just a thought.
A square wave at about 500Hz has many 1/3, 1/5, 1/7, 1/9 1/11 etc harmonics, the waves look pretty good, although some evidence of noise/oscillations on the waves themselves.
Ooooppps ...... later you mention Class A-B operation. Ignore my comment! ;o)
Interesting video sir!
Class A/B I think. Class B is not used in transistor audio amps because it sounds crappy
@@westelaudio943 Yep, probably due to non-linearity and crossover distortion? Just me thinking about it now - they would have to be partially biased, makes sense! :o))
@@JamesE707 Yes, an unbiased (class B) output stage forces the transistors to operate outside of their linear region which causes a lot of crossover distortion. Class B in solid state technology is like class C only used in RF amplifiers or other amplifiers dealing with simple waveforms where accuracy is not needed or the original sine wave can be recovered by a low pass filter.
The junction capacity on the old and new transistors is almost the same. The bias was set too high, maybe the square wave would look different now that I have it adjusted properly. I am not going to repeat the test. But these are some good thoughts.
I stumbled upon your video because i have a faulty Sanyo DCA 200 amp. One channel is dead so I wanted to look up what can be done. I am no expert in electronics so this advanced diagnostics is beyond me, although I can get an oscilloscope and a signal generator and try some of your recipes. I have soaked the switches in Kontakt Chemie 60 but no effect. Left channel produces loud noise and cracking even when not under load, and no matter where the volume pot is at. What could be wrong? Other channel works normally.
But your comments assured me it is a shitty amp. I got it for 25€. It is not even a full-width component. It will make a good practice to try to fix it.
Replace all fuses, otherwise you may need an ESR reader and voltmeter to check caps and transistors
I think the noise comes from bad resistor/s ... anyway the noise can be easily tracered by non-contact high gain audio probe ... you can make one from tape head preamplifier and an LED + audio amplifier at output stage ... Also i doubt that this lightbulb at primary winding will save transistors at all on secondary side of linear transformer because there always will be output voltage ... for SMPS PSU it can 100% and even protect from short.
I am working on building a proper signal tracer. I have etched the circuit board but haven't gotten any further yet. The lightbulb certainly isn't perfect, but it is better than nothing.
@@DrCassette on second watch of the video i realized that blue signal is deformed by electrolithic capacitor leakedge (not phisical but electrical current leakedge) wich also can cause lowered signal. With aging, dielectric becomes conductive. You passed the hard work on that signal tracer, the soldering is the sweet part when making PCB's (at least for me). For the noise i am pretty sure it is resistor because they crack and cause sparkling on the spot where carbon does not make proper contact i had this problem many times
Love the videos good job mate.
Thank you :)
I had a feeling that you would do that lol
Looked like a good amp to me?
No, this was not a good amp at all. And with so many bad electronic components, it really wasn't worth any more effort.
Sad...
I am happy, because I can use the case for a new project!
@@DrCassette That's the spirit!!! :-D
I read that Sanyo also produced under the Otto brand but as far as I can see it's not related to the Otto Versandhaus. See: www.hifi-studio.de/hersteller/sanyo-otto-hifi/
I think I have heard of Sanyo's OTTO brand before, at the time it was a common strategy of manufacturers known for budget oriented equipment to create a separate brand for their high end products. Sharp created the Optonica brand, Toshiba created the Aurex brand. Also, some manufacturers sold their products under different names on their domestic Japanese market. Hitachi for example sold their equipment in Japan under the Lo-D brand.
@@DrCassette Yes, and it's still happening. Like Tascam is selling professional equipment, TEAC consumer equipment and Esoteric is the very very expensive High End brand (€40.000+ amplifiers). And it's all the same company.
very interesting, rare amp
But unfortunately not a very good amplifier...
@@DrCassette Im sure its not
sorry for your loss.
I am happy, because I can use the case for a new project!
Could it be that the other channel'\s transistors are bad to?
I replaced the output transistors on both channels...
upgrade the small signal transistors
That is too much work. It's not like I could just stuff in any other transistor you know...
aww man thats too bad i liked that little amp i checked it out on hifi engine 22watts /per ch like other comment said check the preamp stage driver stage transistors dont part it out yet cold or lose solder point maybe .
The noise can in no way be influenced by any of the controls, that's why I think it's not the preamplifier. Also, the preamp only uses one dual opamp, and the freeze spray had no effect on it. The solder joints all look fine.