Sa-9100 protect light.

CrispySqrl

New Member
Hello all this is my first post on here but it's gonna be a good one. I have been trying to fix a friends SA-9100 protect light we found some bad capacitors on the power board so we ended up recapping the the power b board and the protect board as well as replacing the transistors on both. After that the protect light still wouldn't go off. So we did voltage checks again and it lead me to believe the output transistors on the right channel were bad. So we ordered the MJ21193G and MJ21194G to replace them. Unfortunately the protect light is still on so we took some new voltage readings and am hoping that someone here can help.


Protect board (AWM-025)

1: -2.2v fluctuating
2: -12.77
3: 38.20
4: ground
5: -2.2 fluctuating
6: -2.2 fluctuating
7: 38.30
8: 32.00
9: 35.80
10: 35.80
11: 35.80
12:7.44 AC


Power B board (AWR-032)

1: ground
2:-21.62
3: -32.97
4: -12.82
5: -55.72
6: -56.84
7: 56.62
8: 43.74
9: 35.88
10: 24.87
11: 15.99

Right Power amp unit (AWH-023)

15: 31.70
16: -43.22
17: 28.95

18: 37.94
19: 43.10
20: 38.39


Left Power amp unit (AWH-023)

15: -2.2 fluctuating
16: -43.17
17: -2.2 fluctuating

18: -2.2 fluctuating
19: 43.06
20: -1.0 fluctuating




If there are any other test to run please let me know. I am pretty sure the problem is with the right power amp.

Thank you in advance,
Darrell
 
looks like an open or shorted transistor or resistor in right side amp .
i would start by testing the outputs and working backwards through the drivers etc .
pnp output might be open but that's a wild guess as it could be something else .like its not being driven .
 
Well I tested the .5ohm 5watt resistors in the power amp and one on the right board is open so replacements are on the way.

Thanks again,

Darrell
 
Traced back further the D358 and B528 transistors are both shorted and the 528 was 1ohm, and when following that circuit back on the collector side the 10 ohm 1watt resistor was cooked as well, couldn't see it since it was under the protective sleeve but upon testing it was open and when removed it fell apart.

Thank you again for any help.
 
sounds like a few problems then .
its recommended you change vr2 as it could be the root cause of the problem .
you need to check r24 r25 r26 . its best to check all resistors as it happens .
 
Ok we replaced all the transistors and a r23, r24, r25, r26 on both power amp boards. Still haven't bias'd all the way my friend took it home to do it and hooked it up, he says there is distortion on the low frequencies still. So I am gonna get it bias'd myself and take a listen to see what kinda distortion it is.


Thank you very much for the help it's very nice to get something working that you have never seen work and have no idea how or why it failed as an electronic tinker.

Darrell
 
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