T&M SA8200 only 3 channels working!

Nanaimo

Member
2014-10-26 7:12 am
This HEAVY (25Kgs. Toroidal Coil PSU) 8 Channel amp has only 3 working channels! I am needing a Service Manual - or - Workshop Manual to help sort out this problem. Only User Manuals available but they are useless for my purpose. HELP!!
 
Last edited:

Nanaimo

Member
2014-10-26 7:12 am
T&M Systems SA8200 Solid State 8 CH. Audio Amplifier

I would probably start with no signal and checking DC voltages

Sounds like a Plan which I will hope to follow during the week-end. Thanks. The case is steel with each panel being attached to the other panels by c/s screws. The Toroidal is 'clamped' between top panel and bottom panel by two huge cross-head bolts so only one of these panels can be removed at any time. Front panel - with indicator lamps, on/off switch, pre-amps PCB attached, Back panel with 8 XLR inputs, push-buttons and PCB with more pre-amps attached, The speaker output sockets are attached to the bottom panel. in between front and back are the two Power Amps each with a large cooling fan. ManualsLib - Makes it easy to find manuals online! have a free pdf of the User Manual of the SA8200 with schematic block diagram and drawings of front and back panels - but there's no Service or Workshop Manual that I can find. Michael UK.
 

Nanaimo

Member
2014-10-26 7:12 am
Encouraging result on bench. The method used to connect all the PCB's is ribbon cables with self-locking connector blocks. We found one ribbon cable to one of the two Power Amplifiers came out of its soldered-in PCB mounting block. Strangely (since I don't have a Service Manual and cannot gauge any reason) re-connecting this multi-way ribbon connector made ALL 8 Channels operational. EXCEPT this has now revealed a noise and SIne-wave infidelity issue on CH8. We think this may be a possible capacitor or Transistor problem issue. We are removing one of the Power Amps to find what Transistors have been used and what the condition of any electrolytic caps is. This was the problem with my AKAI GX635-D NAB tape deck - now fixed, thanks to DIYAudio.
Michael UK
 
So the noise wasn't there before reconnecting the cable? The problem may be ahead of the power stage then. See if you can't short the ch8 power amp input for a test.

Excessive noise and distortion indicates severely degraded loop gain. Ahead of the power stage, this could be a bad opamp (or one with a bad joint anyway), in the power stage you'd have to look for bad transistors and other components... usually not the big output transistors but rather somewhere in the middle, maybe an input transistor.

This unit came out in 2007, so I would not normally expect bad caps to be too much of a problem... that said, these amps were made in China, so you never know what their idea of parts quality was. Anyway, it can't hurt to take a look at the soldering either.

FWIW, the user's manual has a coarse block diagram at least.
 

Nanaimo

Member
2014-10-26 7:12 am
So the noise wasn't there before reconnecting the cable? The problem may be ahead of the power stage then. See if you can't short the ch8 power amp input for a test.

Excessive noise and distortion indicates severely degraded loop gain. Ahead of the power stage, this could be a bad opamp (or one with a bad joint anyway), in the power stage you'd have to look for bad transistors and other components... usually not the big output transistors but rather somewhere in the middle, maybe an input transistor.

This unit came out in 2007, so I would not normally expect bad caps to be too much of a problem... that said, these amps were made in China, so you never know what their idea of parts quality was. Anyway, it can't hurt to take a look at the soldering either.

FWIW, the user's manual has a coarse block diagram at least.
 

Nanaimo

Member
2014-10-26 7:12 am
Many thanks for your informative and very useful reply,sgrossklass. As to whether the noise was there before reconnecting that displaced plug from its socket (which turned out to be the four pin PCB Output to two of the eight speaker terminals), I do not know - for the amplifier did not work and could not show this. Providentially I now have received pdf's of the T&M SA8200 from Germany - so we're in with a chance of finding the cause and your suggestions are extremely useful. Michael UK