Sansui 210 Output Transistor Replacement - Step by Step
- Thread starter americannigh
- Start date
kevzep
Its all about the Music
We have to stop meeting like this....
americannigh
Active Member
Glad I can contribute here. I'm usually sapping advice from other people so thought this would be a good opportunity to contribute something to the knowledge base. I agree this is a nice little low power receiver. Very simple design, fun to work on and own. Are any of you guys familiar with a C1445 transistor? I have 6 of those on hand that I bought and never used because frankly I found them suspicious. I was expecting to get a 2SC1445 transistor which is a TO-66 and what I got are these TO-220 transistors labeled Sanken (SK) 1445. Here's a picture of one of them. Are these anything that would be a good sub? Couldn't find any data sheets online for these.
americannigh
Active Member
By the way I ordered the KSD1408YTU transistors and the Nichicon KL caps to upgrade the coupling caps. I'm also going to up the filter cap by 500uf to 1500uf so got KL series for that. I think this is in the range of what would be considered safe from an inrush current standpoint and probably provide just a little more reservoir to improve dynamics in the bass register.
two.dogs
Active Member
I see Nichicon UPW recommended more often in power supply and filtering. UKL series are low leakage that typically get used in the signal path when the cap value is too large to go with polypropylene (around 3uf and up). However, I'm not aware of any disadvantage in using UKL for power supply. Cost? Reliability? Maybe someone will chime in.
The KL series from Nichicon has lower-than-all-the-rest leakage. The specs from the datasheet are 1/3 the leakage of the next-best electrolytic cap. The leakage is bad for audio signal, so the lower you can go the better. Film caps will have zero (or near zero?) leakage, so that is the better choice compared to an electrolytic but it'll be more expensive. So, if you're replacing an electrolytic cap or getting rid of a tantalum cap in the audio path, the best choices would be as follows and you'd pick based on how much expense you're willing to have for that cap and how much physical space you have available:
- Film cap, metalized polypropylene
- Film cap, metalized polyester
- Electrolytic cap with very-low leakage
- Electrolytic cap
The PW series (and also the FW, HW, others) have higher ripple current and lower ESR. For use in the power supply side of circuits, a lower ESR means less of the passing current will be converted into heat. For use in smoothing out rectified AC into flat DC, the higher ripple current is better.
So, KL electrolytic caps or WIMA MKS/MKP/FKP/FKS film or Panasonic ECQ film for audio path and PW electrolytic caps for everywhere else. In general.
americannigh
Active Member
americannigh
Active Member
OK so this is interesting. The original "scratchy scratch" sound on the right channel which prompted me to re-transistor the whole preamp and amp sections has returned. Curious if you all think my inclinations are correct. Follow me here. I've already replaced all the transistors in the audio path. Granted the outputs are not optimal and are too fast for this circuit but this same problem presented with both the original and new outputs on the same (right) side. I have also replaced most but not all of the caps. I have a Mouser order coming with the 8MHz outputs which will be a better match and caps to complete recapping the electrolytics. This "scratcy scratch" sound (sounds like a rat clawing at the inside of a shoe box lol) presents itself when the volume is either all the way down or just slightly up so music is barely audible. My inclination is that when the volume is down, the amp is "resting" and thus giving a leaky cap opportunity to discharge and present this sound. When volume is up, the cap is getting more of a charge so doesn't have opportunity as much to leak. The scratchy sound does NOT get louder with volume turned up. My inclination is to complete recapping the board and replace the outputs too once the new ones arrive from Mouser and see if any of those things fix the problem. Who knows, it could even be one of those "no name" 1000uf caps I put in the coupling cap position that is leaking and those will be replaced with Nichicon KL when they arrive. Anything else I should be looking at as a possible source of the scratchy sound? Diodes?
americannigh
Active Member
Well shoot, spent the better part of the evening trying to chase this down. Started by replacing the coupling cap on right channel with a Nichicon I had on hand. It wasn't an ideal cap, had axial leads which had been cut short but I made it work. This didn't fix it. Tested and compared resistor values between right and left channel. Nothing stood out as being problematic. Then just as quickly as the problem cropped up again, it went away. At this point, I'm just going to wait for my Mouser order to arrive and then complete the recap and install the ouputs that @kevzep suggested. If the problem crops up again, it occurs to me that it could be RF or some other kind of interference. This receiver seems to have pretty shoddy to no shielding. It is very strange that the receiver behaved without a single hitch since Thursday and then all of a sudden, one evening, there is this noise in one channel that persists. Then a few hours later "poof" gone. Same thing happened last time I experienced the noise. Maybe I'm jumping to conclusions that it's heat related. This receiver can be on all day, no problems, and then just out of the blue, the scratchy noise comes back. If it's RF, maybe happens on the right channel just due to where components are placed on the board. I notice the preamp is shielded but the amp part of the board is not. Might explain why the noise amplitude doesn't vary with volume if it's some kind of RF being picked up by the amp circuitry. Thinking out loud here.
two.dogs
Active Member
The scratching you describe sounds like semiconductor noise, but also be a broken resistor or bad solder joint. If it doesn't get louder with volume, then its gotta be after the volume pot - somewhere from R703/4 back to the output. I don't believe you told us if this happens on multiple sources (tuner, and aux) but that can also help to confirm that the problem is in the amp section.
I say poke it with a stick. That is, take something non-conductive and gently push on components and slightly flex the board to see if you have a mechanical problem. You might also check solder joints with a magnifying glass. If it is semiconductor noise, and you've already replaced all the transistors, then maybe its a diode. Good news is that there are only 6 in the amp and power supply, but 2 of them are your SV3A (D801/2). If those are bad, others on the site have made replacements. Freeze spray might help locate a bad semiconductor.
http://audiokarma.org/forums/index.php?threads/missing-stv-2h-3h-4h-bias-diode-fix-recipe.696966/
It might help if you tell us what replacement transistors you used.
TR001 2SC971
TR301 2SC930
TR302 2SC930
TR601 2SC1312R
TR602 2SC1312R
TR603 2SC1312R
TR604 2SC1312R
TR701 2SC1312R
TR702 2SC1312R
TR801 2SC693
TR802 2SC693
TR803 2SC693
TR804 2SC693
TR805 2SC1364
TR806 2SC1364
TR807 2SA678
TR808 2SA678
TR809 2SD315
TR810 2SD315
TR811 2SD315
TR812 2SD315
I say poke it with a stick. That is, take something non-conductive and gently push on components and slightly flex the board to see if you have a mechanical problem. You might also check solder joints with a magnifying glass. If it is semiconductor noise, and you've already replaced all the transistors, then maybe its a diode. Good news is that there are only 6 in the amp and power supply, but 2 of them are your SV3A (D801/2). If those are bad, others on the site have made replacements. Freeze spray might help locate a bad semiconductor.
http://audiokarma.org/forums/index.php?threads/missing-stv-2h-3h-4h-bias-diode-fix-recipe.696966/
It might help if you tell us what replacement transistors you used.
TR001 2SC971
TR301 2SC930
TR302 2SC930
TR601 2SC1312R
TR602 2SC1312R
TR603 2SC1312R
TR604 2SC1312R
TR701 2SC1312R
TR702 2SC1312R
TR801 2SC693
TR802 2SC693
TR803 2SC693
TR804 2SC693
TR805 2SC1364
TR806 2SC1364
TR807 2SA678
TR808 2SA678
TR809 2SD315
TR810 2SD315
TR811 2SD315
TR812 2SD315
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americannigh
Active Member
@kevzep @two.dogs I am looking forward to seeing how your 310 comes along. I'll plan to pull down the schematics in case I can be of any help and return the favor for the info you've offered here.
So far today, I've been listening to the receiver here in my office for two hours and no sign of the noise. It sounds nice even with the wrong outputs I will definitely have a good look at the solder joints and board integrity again when I open it up to do the output replacement and recaps later this week. That is a good suggestion. Also if the problem returns before then I am going to try to test my RF theory by putting a blanket of tin foil over the receiver (without taking off the cover of course) and also looking around the house to see if there are any appliances on which could be causing line interference. With the filter cap being only 1000uf on this unit perhaps there is something running on my AC here in the evenings which is causing it. It does seem to happen in the evenings more often than not. But that may just be murphys law since that's when I like to settle down and listen to tunes.
You asked about the transistor substitutions I used. Here is the menu:
2SC693 = KSC1845FTA
2SC1312 = KSC1845FTA
2SC1364 = KSC1815YTA
2SA678 = KSA1013 (this is a PNP transistor)
I see the 210 board has spots for several components which are not part of the 210 design so I have a suspicion the board was also used for another model such as maybe your 310! Would enjoy seeing a picture of the 310 board when you get it opened up and I'll let you know if it's the same board.
So far today, I've been listening to the receiver here in my office for two hours and no sign of the noise. It sounds nice even with the wrong outputs
I will definitely have a good look at the solder joints and board integrity again when I open it up to do the output replacement and recaps later this week. That is a good suggestion. Also if the problem returns before then I am going to try to test my RF theory by putting a blanket of tin foil over the receiver (without taking off the cover of course) and also looking around the house to see if there are any appliances on which could be causing line interference. With the filter cap being only 1000uf on this unit perhaps there is something running on my AC here in the evenings which is causing it. It does seem to happen in the evenings more often than not. But that may just be murphys law since that's when I like to settle down and listen to tunes.You asked about the transistor substitutions I used. Here is the menu:
2SC693 = KSC1845FTA
2SC1312 = KSC1845FTA
2SC1364 = KSC1815YTA
2SA678 = KSA1013 (this is a PNP transistor)
I see the 210 board has spots for several components which are not part of the 210 design so I have a suspicion the board was also used for another model such as maybe your 310! Would enjoy seeing a picture of the 310 board when you get it opened up and I'll let you know if it's the same board.
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americannigh
Active Member
@two.dogs You asked about whether the noise happens on all inputs. Indeed, the scratchy noise presents itself on all inputs (Phono/FM/AM/Aux) and seems most prevalent if the volume is all the way down or just slightly up. That is, when it's happening. I have not replaced TR301/302 or TR001. Maybe I'm not reading the schematic right but I thought TR301/302 were part of the FM section and TR001 was part of the power supply. If I'm not reading that right please someone correct me. If those are something that could cause noise in one channel of the amp, I will replace them as well.
americannigh
Active Member
OK looks to me like TR301/302 are part of the AM section. That said looking at the schematic I don't see anything that would prevent noise from one of those transistors from being injected into the amp section even when AM is not the selected input. Transistor equivalents for 2SC930 look pretty slim picking but was able to find a source (not ebay) online just now. In a bit I'm going to do an experiment and try listening to some AM to see if that makes the problem come back. For now I'm enjoying music so I don't want to ruin a good time. Thanks everyone.
two.dogs
Active Member
Sorry if I injected confusion. That transistor list was one I was making for my own receiver - its not intended to represent the list of what you need to replace. But now we know that you didn't replace TR001. That transistor supplies the 21V to the collectors of TR701/2 located just behind the volume pot at the beginning of the amp stage. It could be the culprit. Forgot to ask if the scratchy sound was in both channels or just one? If both channels, then TR001 is a prime suspect, followed by ZD001 or maybe D002/3 in the power supply. Those are the only semiconductors behind the volume pot that are common to both channels. But look for bad joints or cracked resistors first.
If it were a lack of shielding, then everyone would be complaining about how the Sansui 210 is noisy and badly designed. But that isn't the case - it has a great reputation for a low powered amp. I'm putting my money with dlucy that it's not RF noise.
If it were a lack of shielding, then everyone would be complaining about how the Sansui 210 is noisy and badly designed. But that isn't the case - it has a great reputation for a low powered amp. I'm putting my money with dlucy that it's not RF noise.
