Pioneer SA-1000 repair help

ViperZ

AK Subscriber
Subscriber
Hi all,
I have been working on this Pioneer SA-1000 on and off for a few weeks now with no luck.

One channel output was completely blown - Q15, Q17 (2SC1080) were both blown collector to emitter, R57 0.5 Ohm resistor on Q17 was blown open. Q9 2SC984 looks also shot at least through one junction.

So I originally replaced Q15, Q17 and R57 (Q9 stayed original). Turn it on, Q15 goes hot over ~10 seconds.

I shotgunned at that point and replaced every transistor as per consolidated list:
http://www.audiokarma.org/forums/index.php?threads/sa-1000-transistor-list.546251/#post-7155137

I also replaced the electrolytic caps on the board, and 2nd 0.5 Ohm resistor (R49).

Still have exactly the same problem.

I cannot adjust idle current at all through VR3 (I have 2A across those resistors in the bad channel).

All resistors are exactly the way they are supposed to be. Diodes and zeners measure ok. Capacitors are not shot through. I did not replace the variable resistors. VR1 definitely adjusts offset voltage.

I have not replaced VR3.

All power supply voltages are present. From measurements table, Pin to Pin 5 is 1-2V (depending on VR1 value), but not 0V (as in good channel).

I am also doubting why Q9 2SC984 is supposed to be replaced with KSC2383YTA, as current values for 2383 are three times higher than 984.

Any ideas are welcome. Thank you.
 
A quick update:
- 2SC984 replaced with 2N2222A instead of KSC2383.
- installed original 2SA572 matched pair, as it was working, and I have no means to match KSA992 transistor pairs.
- There was no need to replace variable resistors.

Still have lots of work, but amp is working now, relay clicks, etc. Yay.
 
So I'm finishing this amplifier. Recapped protection and power supply boards, cleaned the pots and switches.

One thing, which is very noticeable - there is noticeable hiss coming out of both channels - a bit more from one than the other. DC offset is 6mV on one channel, 4mV on the other, so no problems there. Any ideas? Thanks.

This hiss is independent of volume setting (i.e. volume dial can be at 0, his is pretty much the same as when volume is at max).
 
Last edited:
One update for myself - the hiss was cleaned up with new transistors installed on the preamp board.
 
Let me the first to respond to your thread.
Wow, you are going it alone on this one but making headway. A testament to your persistence.
The diff pair on a set with a DC Balance trimmer can be matched but the trimmer makes up for any mismatch in the HFE. I will match them if it does not have the DC Balance trimmer. You will notice that amps without the trimmer will have a higher margin for the offset. Also I found that the Fairchild 992's are pretty close in specs and will usually work randomly paired up, giving a acceptable tolerance. As a general discussion.
 
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