Yamaha M-70 output DC levels

phatterplatter · Mar 9, 2015

Hi...

I have one here that is ALL adjusted according to factory spec service manual

yet , when you add in a signal source and increase input to ANY appreciable level , there is DC also increasing on the outputs, following the input level.

Idle spec DC offset is 0.00 +/- 5mv

Adding signal and output has 100mV..then 200mV...then 400mV

Any ideas??

Thanks:thumbsdn:

Obviously , the protect circuit sees it and shuts the outputs "Out"

avionic · Mar 9, 2015

phatterplatter said:
Hi...

I have one here that is ALL adjusted according to factory spec service manual

yet , when you add in a signal source and increase input to ANY appreciable level , there is DC also increasing on the outputs, following the input level.

Idle spec DC offset is 0.00 +/- 5mv

Adding signal and output has 100mV..then 200mV...then 400mV

Any ideas??

Thanks:thumbsdn:

Obviously , the protect circuit sees it and shuts the outputs "Out"

Check your rails both regulated and unregulated. If there stable. Then perhaps a transistor has developed excessive leakage.

avionic · Mar 9, 2015

BTW when you did adjustments steps 1 & 2. Did you use two multimeters ? This it the adjustment for the +/- 70 vdc rails. Ya really need two meters.

phatterplatter · Mar 10, 2015

Thanks

I'll check the power supplies again

The thing is ...is that BOTH outputs do the same thing.

Must be something in common

avionic · Mar 10, 2015

phatterplatter said:
I'll check the power supplies again

The thing is ...is that BOTH outputs do the same thing.

Must be something in common

Maybe power supply rails...

avionic · Mar 12, 2015

Hows it coming along?

phatterplatter · Mar 16, 2015

I found out that the feed lines from the Volume Controls are also supplying a small amount of DC proportional to volume level.
That aint good....Maybe some caps that arent true anymore

avionic · Mar 16, 2015

What does the +P & -P voltages look like. C705 and C706 are the main filters for the P regulated P/S.

Yamaha M-70 output DC levels

phatterplatter

Active Member

avionic

" Black Knights "------- F-15 " Wizard "

avionic

" Black Knights "------- F-15 " Wizard "

phatterplatter

Active Member

avionic

" Black Knights "------- F-15 " Wizard "

avionic

" Black Knights "------- F-15 " Wizard "

phatterplatter

Active Member

avionic

" Black Knights "------- F-15 " Wizard "

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