I'm trying to troubleshoot the right channel on this amplifier, the right channel is triggering the protect with a DC offset of -350mv to -400mv. Must be on the border of voltage to trigger as it comes out of protection half the time? Anyway looking at the input IC 101 , I get normal values except at the output of pin7 ( right channel) which reads +14.36 v ? Pin 1 output for left channel is -154mv... Does this indicate a toasted IC or would it be a bad component feeding into it??
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Some IC info...
TA7317p pin voltage testing:
Service manual specs: pin1) -.6 pin2) 0 pin3) 0 pin4) 0 pin5) -.7 pin6) -.6 pin7) 0 pin8) 1.3 pin9) 3
TA7317p pin voltage testing:
Service manual specs: pin1) -.6 pin2) 0 pin3) 0 pin4) 0 pin5) -.7 pin6) -.6 pin7) 0 pin8) 1.3 pin9) 3
Check R118, R120, R122, and R124. The center point of R118 and R120 should be near 0VDC if all is working. Check to see if you have the proper voltages feeding R122 and R124, +/- 15.5VDC. Pins 5 and 6 are near 0VDC? If those all check OK IC101 could be kaput.
Craig
Craig
Check Q221-228 for shorts. Any 2.7K 1/2W resistors on hand? Any NJM4565s on hand? Pulling the IC opened up the feedback loop and I guess it didn't care for that. If the transistors check OK you can try installing the good resistors in the left channel, reinstall IC101 and check if the left channel is still OK. Are you using a Variac or DBT? You should have no load connected.
Craig
Craig
Transistors have no direct shorts, I have a couple new ICs on order. Not sure about half watt resistors? I probably have 1/4 watts?? They make due until I can order up some new half watt? I haven't been using a variac or DBT but I do have both.
Ok, finally received my order for this new IC. I installed but strangely enough , both channels exhibit high dc offset now? They both are around -350mv..... It appears that the voltages for ic101 are good now tho?
I'm getting closer! I found r222 and r223 were no good. Replaced those and now the offset is down to 75mv on left channel and 140mv on right. They start very low MV , but gradually increase to the stated voltages. Seems as the right channel "surges" and occasionally trips the relay. Would replacing the transistor pairs on the input board help out here?
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Found the recommended drivers for this , installed new drivers and replaced components required in service bulletins. Upon power up, R 244 & R 246 both went nuclear!! Q214 , Q218 and Q226 outputs are gone...? Not sure why this happened ? I had no apparent shorts before I replaced drivers and the service bulletin resistors. Never powered up with DBT as I was testing without prior to... Lesson learned. Assessing damage. As for outputs, am I better to replace damaged transistors first and if the unit is appearing healthy, replace all outputs on this channel?