petehall347
the brandy coffee man
yes NPN and PNP ... obviously not interchangeable .
SA-900 with major issues
- Thread starter EastPoint
- Start date
- Status
Watthour
Electron Rancher - JS3600
VR3/4 appear to be 50Ω. Reading 40-60Ω from end-to-end might be about right. The failure is sometimes at the riveted connections between the solder legs and carbon traces, and re-staking the rivets after a bit of de-oxidizer might restore the connection. It would still be better to replace them. The killer is going to be that most modern replacements are going to have a lot closer lead spacing than the original at about 12mm centers - Common replacements are often only a 5mm lead circle. In short, get long leads, bend, and pray. Maybe THIS would work.
CTS Electrocomponents' Series 201 would be a better fit, but they don't offer a 50Ω version.
I don't know about Nichicon, but Bournes' resistance code for a 50Ω pot is "500" just as you are reading.
CTS Electrocomponents' Series 201 would be a better fit, but they don't offer a 50Ω version.
I don't know about Nichicon, but Bournes' resistance code for a 50Ω pot is "500" just as you are reading.
Last edited:
Oldsansui441
Super Member
It wouldn't hurt anything to use the 100ohm bias trimmers but they will be too sensitive to adjust being only single turn. If you are going to replace the centre voltage trimmers may l suggest using slightly higher range parts for these. I did an SA-900 a while back and found that the centre voltage was just outside spec when pots were fully one way.
OK, now I feel stupid. I replaced the bad bias pot and no change. I randomly checked the rear fuses and both were blown. I replaced them and I get sound out of both channels. However, the left channel is much quieter than the right, and distorts when I turn it up.
One channel I can get the DC balance set to 41v with no problems. The bias will not go above 5 mv or so. However, if I increase the dc balance to 45v, then I can get the bias to 10-15 mv. That is the channel with the new bias pot.
The other channel the DC balance is at 78v and will not adjust. Seriously. On that channel the bias will go up to 15 mv. Thoughts?
One channel I can get the DC balance set to 41v with no problems. The bias will not go above 5 mv or so. However, if I increase the dc balance to 45v, then I can get the bias to 10-15 mv. That is the channel with the new bias pot.
The other channel the DC balance is at 78v and will not adjust. Seriously. On that channel the bias will go up to 15 mv. Thoughts?
RobinTW
Well-Known Member
This may be late in the game, but anyways.
Have you checked VR3/VR4? You can measure them in circuit. I am also restoring a SA-90 (Japanese domestic version of SA-900) with the main amp both channel not working. Both VR3/VR4 are bad. They are supposed to be 50R, but measure 7.3M and 3.4M, and they don't adjust. Surprisingly, they are Nichicon's.
Oldsansui441
Super Member
Good job on finding the cause. They are a beautiful amp and were TOTL at the time, l wish l still had the one l let go about 18 months ago. In my opinion they make the ever popular Marantz 1060 and others sound lacking in comparison.
The Fuxtor
Addicted Member
I agree! I sold my SA-1000 not tat long ago, and truly miss the sound it had...... great era
Oldsansui441
Super Member
Yes it was a great era, l agree.
The trimmer thing was important--I think I had to up the 50-ohm to 100-ohm and may have had to increase the others as well. Otherwise just swap caps and transistors. Those boards are a CHALLENGE to work on--lots of wires to break, lots of weird solder connections with multiple parts in them. If you know what you're doing, you are good. I had no clue when I got into that one, so it was not easy. It had also been messed with before.
My preamp section works fine, on the amp side one channel flares the DBT and the other has weak, garbled output. (power supply is good).
It's going to take some time.
- Status
