SA-9100 recap problem

bzb882

AK Subscriber
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I’m in the process of recapping, etc. my SA-9100. I first did the two equalizer boards, all was fine. I then did the left and right Power Amp Assy boards (AWH-023-C version in this case). I replaced all the electrolytic caps, Q1 thru Q5 as well as VR1 and VR2 (both set to their midpoint). At first the right channel had very low sound, and unless my mind’s playing tricks on me after a few minutes it was ok again. FF to last night I adjusted VR1 and VR2 on both boards to spec (no problem doing that and they weren’t that far off). Now the right channel initially has very low sound and after a while no sound. Any idea as to what could be wrong? I DBT tested each step of the way, no issues with that. Comparing the two boards I don’t see anything amiss. Maybe I should replace Q6 & Q7, I have the replacements on hand,
 
Did you deoxit all the switches? There are plenty in line that can do this to you.

And have you tried criss-crossing the channels at the pre-out / amp in jumpers (which is ALSO controlled by switch contacts!!) to see if it is the power amp or the preamp?
 
I didn’t deoxit all of the switches last night, I did the ones I could get to easily. I did work all the switches (including the one by the pre-out/amp jumpers) and that had no effect. I had the amp serviced twice about two years ago and that was done both times. My plan for tonight is to double-check my work again, deoxit the switched I didn’t do last night and if that doesn’t work I’ll criss-cross the jumpers.
 
Tonight I checked over my work, everything looks ok. Deoxited all the switches, no difference. Criss-crossed the jumpers, the problem stayed with the right channel...
 
The 2sc1451's are still in both channels?

Those are the FIRST things to go.

Replace them. PLEASE!!!!
 
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I replaced both 2SC1451 on the right board with 2CS3503. Now there's no sound at all from the right channel and the dc offset is 2.47 V and adjusting the VR has no effect. Idle current was 11 mv once I replaced the two transistors, I adjusted it back to 25 mv. No idea what to check next. I did check over my work while I had the board loose, everything looks ok. I took voltage readings this morning; first column is the right channel, second column is the left channel (which still works):



1 23.8 23.74
2 0 0
3 0 0
4 0 0
5 0.01 0.01
6 -42.3 42.3
7 0 0
8 41.9 41.8
9 2.7 0.013
10 0 0
11 -46.2 -46.3
12 2.7 0
13 2.7 0.01
14 46.1 46.2
15 2.7 -0.01
16 46.4 -46
17 2.1 -0.6
18 2.7 0.01
19 46.3 46.2
20 3.2 -0.6
21 .005 to 3.5 to OL 0.93
22 .005 to 1.4 -1.2
 
After reviewing the SA-9100 threads here on Audiokarma and checking the SM, I went back and checked the voltages on pins 6 and 16. Both pins should have shown as negative on both boards in my previous post. Other than that, I couldn't find anything as to what to do next.
 
The 2SC3503's are e,c,b, Better check the install. It's easy to install the TO-126's in backwards. And make sure you soldered the transistor in. I know how I am!
 
Thanks, Zebulon! The 2SC3503’s are in correctly; I’ve double and triple checked that. They were a little tricky, the holes were not quite big enough (reamed them out a tiny bit with a pointy surgical scalpel). The pin layout didn’t help matters either. Your comment about forgetting to solder things got me to thinking. I had put everything back together and had forgotten to solder VR2 in place (found it on my final check before the dbt). I tried to solder it with the amp in the normal position. When I realized I may be dripping solder down the board I repositioned the amp so that couldn’t happen and soldered it in place. My plan for now (barring any other ideas) is to change out the last two transistors (Q8 & Q9) and double check all solder connections and reflow them. I’ll also check for drips below VR2. I probably won’t get time before Saturday. The only schematic I have is from HiFiEngine, and I’m pretty much an amateur…
 
I was wondering about your voltage readings as I only see 14 pins on the amp board AWH-023.
 
There's 23 counting the ground pin. 1 thru 14 across the bottom, 15 thru 22 across the top. From what I've read, that SM is one of Pioneer's worst.
 
I see, the other pins on top are the connections for the STV and outputs. I looked at some images on Google.
 
I am busy but one of the other members should chime in as we keep the thread at the top of the que.
 
Last night I reseated the output transistors on the right channel after squirting some deoxit in the holes. Checked the dc offset, it was 3.5 V but briefly dropped down to 60 to 70 mV then back up without me doing anything. Today I checked all the solder joints and reflowed them. I replaced all 5 diodes as well as Q8 & Q9 (noting that the pinout went from BCE to ECB and installing accordingly). Readjusted VR2 to 25 mV. Dc offset is still 3.5 V; and adjusting VR1 still has no effect. For a while after turning the unit on tapping on VR1 sometimes caused the dc offset to drop to around 90 mV, but after being on for awhile that no longer had any effect. Any ideas as to what to do next? I'm totally stumped. Still no sound from the right channel.
 
This morning I rechecked the voltages on the right channel. First number is right channel before replacing Q8, Q 9 and 5 diodes. Middle number is this morning's right channel voltages after those were replaced. Third number is from working left channel:

1 23.8 23.8 23.74
2 0 0 0
3 0 0 0
4 0 0 0
5 0.01 0.08 0.01
6 -42.3 -42.3 -42.3
7 0 0 0
8 41.9 41.9 41.8
9 2.7 3.7 0.013
10 0 0 0
11 -46.2 -46.2 -46.3
12 2.7 3.67 0
13 2.7 3.67 0.01
14 46.1 46.1 46.2
15 2.7 2.7 -0.01
16 -46 -46 -46
17 2.1 3 -0.6
18 2.7 3.67 0.01
19 46.3 46.3 46.2
20 3.2 4.25 -0.6
21 .005 to 3.5 to OL 4.6 0.93
22 .005 to 1.4 .005 to 1.4 -1.2
 
I also checked the 5 diodes I removed from the right channel board, they all tested good.
 
Any ideas as to what to try next? I tested the output transistors, they tested good. I've checked the parts I've installed multiple times and cannot find a mistake. I thought maybe I didn't have good contact from the pins I desoldered on the right equalizer board so I checked continuity from the pin to its solder pad. That all tested fine. I'm really stumped!
 
ran voltage checks on Q1 thru Q5 on both the right board and the working left board. If I'm reading the schematic correctly, from back to front on the right channel (and front to back on the left channel are Q1 Q2 Q4 Q3 and Q5.

RIGHT CHANNEL LEFT CHANNEL
AWH-023-C should read
Q1 512-KSA992FBU base 3.9 5.2 mV bad??
Q1 512-KSA992FBU collector -40.3 -40.1 ok
Q1 512-KSA992FBU emitter 4.53 0.543 bad??
Q2 512-KSA992FBU base 3.9 2.7 mV bad??
Q2 512-KSA992FBU collector 40.3 -40.1 ok
Q2 512-KSA992FBU emitter 4.46 0.541 bad??
Q3 512-KSC1845FTA base -40.4 -40.2 -40 ok
Q3 512-KSC1845FTA collector 5.7 1.73 bad??
Q3 512-KSC1845FTA emitter -41 protect bad??
Q4 512-KSC1845FTA base -40.4 -40.1 -40.6 ok
Q4 512-KSC1845FTA collector 0 - 0.3 mV
Q4 512-KSC1845FTA emitter -41 protect -40 bad??
Q5 512-KSA992FBU base 40.2 40.1 ok
Q5 512-KSA992FBU collector 37.1 1.76 1.2 bad??
Q5 512-KSA992FBU emitter 40.8 41 41.3 ok
 
Q3 collector and Q5 collector should be reading the same 1.2 volts. Your readings don't show that. I see you are getting crazy + volts there. Q6 or the diode D6? But the Outputs are getting to much base voltage and could be toast soon. (You should remove them (Big Outputs) and double check e'm for condition)

This is one of the toughest problems to trouble shoot due to the feed back circuit. The best method is to remove the outputs and install large resistors to fake out the circuit and simulate the outputs installed . This allows you to find and fix the cause without wrecking the expensive parts.

Easily said! I can't help you with that. MTF has the procedure that would ensure a positive result.

Lets see if Mark will chime in. In the mean time check these out this thread from "craxx6969".

http://www.audiokarma.org/forums/showthread.php?t=576175&page=10

This might be the procedure you will end up doing. I hope I am wrong.

Patience
 
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