Need Service Manual / Schematics for Allen ADC-220

[timnc]

Looking to fix a problem with one of the keys not working on an Allen ADC-220--cleaning did not help it. Looks like a resistor behind the reed switch is deteriorating.

[jbird604]

Post a pic of the part. I don't think there are any resistors in that area. Could it be a tiny diode?

[timnc]

Sorry. Yes, diode, not resistor.

[timnc]

Also, I should have added: The other keys on the swell sharing the same wire back to the controller are working fine. Also, running a cloth between the reed contacts did not help. My post with the pic should show up as soon as the moderator approves it.

[jbird604]

If the little diode looks bad, you should replace it. It's a standard little glass signal diode, type # not even important. They are available in packs of 100 for around $5, but of course you only need one. I told someone else recently to check Amazon, and I believe there are several different packs available. You can choose a type that looks similar and it will work.

Be sure to observe correct polarity when you replace it. Align the "band" end the same as all the others and you will be correct.

[timnc]

Thank you jbird604! I soldered in a new signal diode and now Swell C3 speaks! Although, if someone does find the manual, it would be good to have going forward as well as just interesting to read.

[jbird604]

Glad you were able to get that fixed. A dead note can be highly frustrating! And now you see that many such repairs are actually not that difficult. The great thing about organ repair is that in most cases, a given circuit is duplicated dozens of times within the instrument (one per key, one per stop, one per division, etc.), so you can usually just look at the adjacent component for clues about testing or replacing something.

Allen service manuals are sometimes seen for sale on ebay. That would be your best bet, as Allen has never released any service manuals for their digital models for sale to the general public. They were passed out to dealers as the models were introduced, and for a while were available for purchase on the tech site, but nowadays the technical info is only distributed via the private tech site viewable only by dealers and authorized techs (hand-picked by the dealers themselves) with secret log-in credentials.

Here on the forum, we sometimes share a scan of a page when somebody really needs one, but all this material is fully copyrighted and Allen is quite aggressive at enforcing their patents and copyrights, as you may know, so we have to be careful about what we share.

As a true organ nerd, I enjoy reading service manuals, having a deep interest not only in organ music, but in the workings of organs, pipe, analog, digital, or whatever. During the ADC period Allen's service manuals were very well done, with complete schematics of many components, especially amps, power supplies, analog audio processors, and the like, along with extensive drawings of the keying systems and other wiring details. There were never any schematics of digital tone generator boards though, as those are closely guarded secrets, even to this day, and repairs are only done by returning defective boards to Allen, where they have people who can repair them.