Moog sonic 6....

[sam]

I want to recap the power supply....I see two large old caps, What can i replace them with ...?

Modern replacements ....?

[sam]

Anyway the main fault is this....

The keyboard always sustains, The pitch is fine but the keys always play.

I first looked at the envelope generator and replaced ic 14 but it has made no difference.

I now look at IC 4 and 5.....

Any idea's would be very appreciated ....

[sam]

I have replaced ic 4 (741)....But no difference.
Should i look at ic 5..?
BTW..The schems are easy to google...

I restore my own synths and have a good knowledge of electronics...I have not worked on a sonic 6.

So any info would be great.

[sam]

I think i have found the root of this problem.....The -ve rail is reading 22V and should be 15v.
The +ve side is ok...I think the ic 1 (741) could be at fault.

Anyone..?

[schmidtc]

A bad op amp shouldn't give you a voltage rail out of whack like that. But, replacing those 723 voltage regulators is certainly a good idea. -22V sounds pretty close to the unregulated voltage coming off the rectifiers. Dropping in a new IC11 should put it right.

[sam]

OK...Thank you the new chip solved that problem but it still hangs on the last played note as if the bypass switch is on.

Very strange....Any ideas...?

[sam]

I have found the main problem...Q7 TIS97 transistor in the ad circuit.

But where can i find one....Or is there a replacement...?