My m-70 failed tonight

bktheking

Gitter Done!
I've been using it for the last week, get home, press the power button, think I saw a flash and stuck in protection.

DC measured before the relay at tp0 is 29v per channel and all the voltages are messed up. I'm thinking ground.............to be continued.
 
I've been using it for the last week, get home, press the power button, think I saw a flash and stuck in protection.

DC measured before the relay at tp0 is 29v per channel and all the voltages are messed up. I'm thinking ground.............to be continued.

Or perhaps you lost a rail.
 
I measured 79 and -80 on the PE+ and PE- , 42 and -42 on B+ and B-. All grounds test good going to the predriver board and the amp board. PE+ voltage going to the transistors on the rail are supposed to be 67v according to the voltages found in the schematic. The pre drive has it's own power supply and I do believe I found a suspect cap tonight, supposed to be 1000uf and measured 500uf, the other 600. I'm going to try and get caps tomorrow when I go to Syracuse.
 
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I noticed it also powers the AMP board as well. So- assume 70v is where it's supposed to be and i'm sitting 10v higher. This is an unregulated PS according to the schematic, is close to 80v ok?
 
I noticed it also powers the AMP board as well. So- assume 70v is where it's supposed to be and i'm sitting 10v higher. This is an unregulated PS according to the schematic, is close to 80v ok?

Have you went through or rechecked the -B voltage adjustment and photo-coupler alignment ?
 
OK your 70v rail is a little high. Does the amplifier work?
 
It did, now in protection. I checked all the right channel transistors with my cricket, all passed.
 
Desoldered all outputs, tested 3 with leaking junctions, one was really bad. Guess that will do it. It will be shelved, just bought the board with a all outputs from the bay, with 2 set of outputs I should be able to make it work again.
 
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I wonder if it's something to do with the style of transistor? I had an A-1000 that I believe had the same type - and it failed in an odd way too that was hard to find - I ended up putting in all new drivers and outputs. I think leaky outputs was the problem.
 
Just my opinion but from what I've seen the C-XX/M-XX are some of Yamaha's worst; mass produced and chalk full of bad solder joints. Shame on Yamaha when it comes to these. :thumbsdn:

There, I said it. :D
 
Just my opinion but from what I've seen the C-XX/M-XX are some of Yamaha's worst; mass produced and chalk full of bad solder joints. Shame on Yamaha when it comes to these. :thumbsdn:

There, I said it. :D

If you're referring to the M-70, it seems to be unusually problematic for many who have owned them. I wonder if or how much that is related to it's fairly unique X-Power design, which was not used in Yamaha's successive amps. I'm not sure that it is necessarily a good representative of the whole series. Then again I have had my C-80 in the shop twice so far, for solder issues... thankfully both quick and inexpensive repairs.
 
If I can't fix it with what I just ordered it's getting the baseball bat treatment, there, I said it.
 
I wonder if it's something to do with the style of transistor? I had an A-1000 that I believe had the same type - and it failed in an odd way too that was hard to find - I ended up putting in all new drivers and outputs. I think leaky outputs was the problem.


a-1000 has the wider style plastic package, not the same outputs.
 
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