dbxdx5
Super Member
A friend of mine asked me to take a look at his SA-8100. He said he had brought it to a tech because the protection light would randomly come on. The tech said the amp couldn't be fixed. Well, we'll see about that....
When I tested the unit with some sacrificial speakers, I initially got no sound out of the left channel. Thinking perhaps the balance pot was oxidized, I exercised it a bit while continuing to play music. After a minute or so, there was faint sound from the left channel, followed by the protection light going on and off, and then music from both channels. Then the I started getting static in the left channel, at which point I stopped the music. But before I could turn the amp off, the left speaker got a good hit of DC.
Left channel DC offset can be adjusted close to 0.00mV, but it's less stable than the right channel (no surprise there), spiking when the protection kicks in. I was able to set bias to 20mV for both channels.
My best guess at this point is that the 2sc1451's and 2sa726's may be causing issues in both the amp board and the protection board, so I plan to replace those, along with the light blue Sanyo caps. Suggestions for other areas to consider before I place my order?
Pin readings and a few transistor readings below.
Control Board AWG017 B
Pin 3: -16.73
Pin 4: 17.99
Q5
E: 16.82
C: 0.83
B: 17.44
Power Supply AWR030 A
Pin 1: 0.00
Pin 2: 0.00
Pin 3: 0.00
Pin 4: -39.2
Pin 5: 39.2
Pin 6: 0.00
Pin 7: 0.00
Pin 8: 0.00
Pin 9: 51.4
Pin 10: 0.00
Pin 11: 0.00
Pin 12: -40.7
Pin 13: -23.4
Pin 14: -16.6
Pin 15: -12.7
Pin 16: 12.8
Pin 17: 17.9
Pin 18: 24.3
Pin 19: 34.4
Protection Circuit AWM027 D
Pin 1: 0.00
Pin 2: 0.00
Pin 3: 0.00
Pin 4: 0.00
Pin 5:
Pin 6: -12.7
Pin 7: 0.00
Pin 8:
Pin 9: ~0.00 with protection off . Spikes and drops when protection kicks in.
Pin 10: 0.00
Pin 11: 0.00
Pin 12: 0.00
Pin 13:
Pin 14: 08.3
Pin 15: 34.5
Pin 16: 34.5
Pin 17: 0.00
Q1
E: 0.00
C: 19.1
B: 0.00
Q2
E: 0.00
C: 19.1
B: 0.00
Power Amp Board AWH022 D
Pin 1: 0.00
Pin 2: 0.00
Pin 3: up to 0.01 fluctuates during protection
Pin 4: 0.00
Pin 5: 51.5
Pin 6: up to 0.15
Pin 7: 00.0
Pin 8: 00.0
Pin 9: 00.0
Pin 10: 00.0
Pin 11: -40.8
Pin 12: -12.7
Pin 13: 12.9
Pin 14: 0.00
Pin 15: -40.8
Pin 16: 0.00
Pin 17: 0.00
Pin 18: 0.00
Pin 19: 0.00
Pin 20: 0.00
Pin 21: 51.5
Pin 22: 0.00
Pin 23: 0.00
Pin 24: 0.00
Pin 25: 0.00
Pin 26: 00.6
Pin 27: 39.3
Pin 28: 00.0
Pin 29: -00.5
Pin 30: -39.2
Pin 31: 00.0
Pin 32: 00.5 – 00.6
Pin 33: -39.2
Pin 34: 00.0
Pin 35: 00.7
Pin 36: 39.3
Pin 37: 00.0
Q3
B: 0.00 fluctuates when protection kicks in
C: -40.7
E: 0.6
When I tested the unit with some sacrificial speakers, I initially got no sound out of the left channel. Thinking perhaps the balance pot was oxidized, I exercised it a bit while continuing to play music. After a minute or so, there was faint sound from the left channel, followed by the protection light going on and off, and then music from both channels. Then the I started getting static in the left channel, at which point I stopped the music. But before I could turn the amp off, the left speaker got a good hit of DC.
Left channel DC offset can be adjusted close to 0.00mV, but it's less stable than the right channel (no surprise there), spiking when the protection kicks in. I was able to set bias to 20mV for both channels.
My best guess at this point is that the 2sc1451's and 2sa726's may be causing issues in both the amp board and the protection board, so I plan to replace those, along with the light blue Sanyo caps. Suggestions for other areas to consider before I place my order?
Pin readings and a few transistor readings below.
Control Board AWG017 B
Pin 3: -16.73
Pin 4: 17.99
Q5
E: 16.82
C: 0.83
B: 17.44
Power Supply AWR030 A
Pin 1: 0.00
Pin 2: 0.00
Pin 3: 0.00
Pin 4: -39.2
Pin 5: 39.2
Pin 6: 0.00
Pin 7: 0.00
Pin 8: 0.00
Pin 9: 51.4
Pin 10: 0.00
Pin 11: 0.00
Pin 12: -40.7
Pin 13: -23.4
Pin 14: -16.6
Pin 15: -12.7
Pin 16: 12.8
Pin 17: 17.9
Pin 18: 24.3
Pin 19: 34.4
Protection Circuit AWM027 D
Pin 1: 0.00
Pin 2: 0.00
Pin 3: 0.00
Pin 4: 0.00
Pin 5:
Pin 6: -12.7
Pin 7: 0.00
Pin 8:
Pin 9: ~0.00 with protection off . Spikes and drops when protection kicks in.
Pin 10: 0.00
Pin 11: 0.00
Pin 12: 0.00
Pin 13:
Pin 14: 08.3
Pin 15: 34.5
Pin 16: 34.5
Pin 17: 0.00
Q1
E: 0.00
C: 19.1
B: 0.00
Q2
E: 0.00
C: 19.1
B: 0.00
Power Amp Board AWH022 D
Pin 1: 0.00
Pin 2: 0.00
Pin 3: up to 0.01 fluctuates during protection
Pin 4: 0.00
Pin 5: 51.5
Pin 6: up to 0.15
Pin 7: 00.0
Pin 8: 00.0
Pin 9: 00.0
Pin 10: 00.0
Pin 11: -40.8
Pin 12: -12.7
Pin 13: 12.9
Pin 14: 0.00
Pin 15: -40.8
Pin 16: 0.00
Pin 17: 0.00
Pin 18: 0.00
Pin 19: 0.00
Pin 20: 0.00
Pin 21: 51.5
Pin 22: 0.00
Pin 23: 0.00
Pin 24: 0.00
Pin 25: 0.00
Pin 26: 00.6
Pin 27: 39.3
Pin 28: 00.0
Pin 29: -00.5
Pin 30: -39.2
Pin 31: 00.0
Pin 32: 00.5 – 00.6
Pin 33: -39.2
Pin 34: 00.0
Pin 35: 00.7
Pin 36: 39.3
Pin 37: 00.0
Q3
B: 0.00 fluctuates when protection kicks in
C: -40.7
E: 0.6