Electro Harmonics Electric Mistress no effect

[pontiacpete]

This has no effect, it passes signal but nothing happening. I got voltage around the board on the 741, 4558 and 339, not sure what needs to be seen on the 4013 and thE 1026. Just to throw a few parts at it, I changed the 741 and the 4558 and 1n914. Is there a way of testing the big ICs? Or any ideas that might help to get this going. Thanks in advance and happy holidays!

[Mick Bailey]

Full test voltages and waveforms are shown here: http://www.metzgerralf.de/elekt/stom...-volt-v2.shtml

[mozz]

Owww,..... those SAD chips are known to go bad, and are very hard to find without spending some good money.

[Mick Bailey]

For what people ask for them I think they're too expensive to take a gamble on, as they're usually pulls from old equipment. There are conversion boards that use relatively inexpensive ICs and whilst not maybe as good as the originals will give a workable fix.

Hopefully pontiacpete's is OK.

[pontiacpete]

Thanks I’ll look into a conversion board.

[mozz]

Well try to narrow it down to that chip before you buy. I try not to shotgun parts unless i am at my wits end.

[Mick Bailey]

A quick check of the SAD1024 would be: DC voltage to supply pins, presence of audio on input, presence of clock on clock pins, audio on output. If any one of the first three are missing, the IC won't operate. If the first three are there but no output, the IC could be bad.

Except - if I recall correctly - there's a bias voltage that has a narrow range and if it's out the chip won't work even if it's good.

[Mick Bailey]

Edit: VR1 is the bias setting. Probably wise not to make any adjustment and assume the circuit was previously working with is where it's currently set. If you have the means, also check the electrolytics for high ESR.

[pontiacpete]

Ah, it works!! This came to me with a weird wiring in the power supply. I sorted that out but in the process wasted out a couple of 9v batteries. Finally cobbled up a supply using two 9v wall warts. Then found a solder joint that was joining two traces that weren’t suppose to be connected. And so it went. Thanks for the help and valuable info about this pedal.

[Mick Bailey]

That's the sort of fix that I like. Good result.