ADC-8000 power distribution

[clhammonds]

I recently began to smell a strong electrical odor coming from inside the console. I removed the back and sniffed around the various components and determined that the source of the odor was the control power supply adjacent to the power distribution box. Although everything was still working normally, I assumed that the large transformer was probably breaking down and about to go. It would get slightly warm after a few minutes of operation although the organ worked normally. I looked around and found an exact used replacement on Ebay. I bought it, received it and installed it today. I powered everything up, check the voltages and everything seemed good, the organ worked normally. I turned it off, put everything back together, turned it on again, and now, everything was dead; no power, no pilot, nothing. I was in the process of checking incoming power just upstream of the main distribution box. In a few seconds, there was a loud pop, and what I thought was a flash of light somewhere in the vicinity of the box, but the power came on. I turned it off in an effort to check for any sign of a short or blown component. Nothing obvious but now when turn on, everything was dead. I assumed that maybe a main power relay inside the distribution box had failed and so preceded to open it up to see. The relay (I assume that's what it is, seemed ok, but there was a small disc capacity on one end of the board that had blown and shorted out. Sorry for this long story............anyone know the specs on that component? I'm not a trained technician with only enough basic knowledge for simple tracing and component change. Any ideas?

[you795a]

I am not an expert on these but I would suspect an electrolytic capacitor popped.

[jbird604]

That little round thing inside the AC distribution box is probably the "inrush current limiter." It was probably the source of the smell, the pop, and the flash of light, and now that it completely burned up, it makes the whole organ dead. Not a big problem. See the attached PDF of the AC distribution box. The device I'm talking about is the thing that is drawn like a resistor at the lower left in the picture.

Trace the electrical current path inside the AC distribution box. If I'm right, that little device is simply in series with the incoming AC power from the power switch. It only serves to slow down the inrush of power when the AC switch is snapped on. In other words, it acts like a resistor for a fraction of a second, then it just becomes a short circuit until the organ is turned off again.

I've seen this device burn up in other ADC models, but it's been several years. I think I ordered the part from Allen, but it is surely available somewhere else.

If you can make absolutely sure that this is the part in question which burned up, it is safe to just replace with with a piece of wire, about #18 I'd guess, bare wire if possible, until you can get one. It serves only to "soften" the inrush of current in the first few milliseconds of operation, possibly helping to lengthen the life of the switch. But the organ will work just fine if you simply replace it with a piece of wire.

AC distribu box ADC.pdf

[clhammonds]

John, as usual, your knowledge is amazing. I need to go back and trace the wiring, but I am all but positive that the component you described in the circuit is the one in question. It is a small ceramic capacitor about the size of a nickel. Unfortunately, the values and polarity were destroyed when it burned up. I assume if there is polarity on a new capacitor, the + would be attached to the incoming power and the negative to the load. The good thing is I now have a spare control voltage power supply. The capacitor in question was within a couple of inches of the power transformer on the adjacent power supply and my nose was not that selective when sniffing out the source of the odor. After confirming this for sure, I will try the bare 18 gauge solid wire. Thank you so much for your help.

[clhammonds]

I traced the wiring and confirmed that the capacitor in question is in fact the inrush current limiter. In the process of examining the wires wires, I noticed that the insulation on the switch cable was very brittle and cracked in multiple places exposing the bare wire. On further examination, the entire cable from the chassis to the switch is very brittle and any pressure on it along the way cracks and insulation falls away. Just with moving the cable during the dismounting of the chassis, all the insulation of the switch wire had cracked and fallen away just before it entered the chassis. I feel I must replace the entire cable since I believe it is severe enough to cause current leaking across no telling how many internal breaks in the black and white wire insulation of the cable. Have you ever seen this? None of the other power cables in the console are brittle and show this kind of deterioration. Must just be a bad run of cable from the beginning. Not at all typical of Allen quality.

[jbird604]

I have seen this exact thing in a few ADC models. Not sure why, perhaps as you say, a bad run of cable. But it would be wise to replace the cable. A suitable cable can be found at any electrical supply or hardware store.

The inrush current limiter is a specific type of device, not a capacitor, though it has the general appearance of a disc capacitor. It's more like a resistor that heats up almost instantly and becomes non-resistive (i.e., becomes equivalent to a simple piece of wire). It serves to protect the power switch and your household wiring from the large current the organ could draw at the moment of power-on, due to the several power supplies in the console that have to charge up their large capacitors.

I looked it up in the Allen parts catalog, and they want $32 for the part. But here is an item for under $10 that would surely be equal to if not better than the original. It offers 20 ohms cold resistance, handles up to 10 amps (the organ surely doesn't draw over 5 amps), and looks like about the right size, best I remember:

https://www.digikey.com/en/products/...5-20010/749866

There is not polarity to these things that I'm aware of. The power flowing through it is AC anyway, so it has no polarity either.

[clhammonds]

Thank you John. I will get that on order right away. As for the bad wire, I guess after over 35 years, that isn't much to complain about. Hope to see you guys one of these days in the Village. thanks again!

[jbird604]

Good luck! Let me know how it turns out. I do hope to come for a visit one of these days.

[clhammonds]

Here is an update on the failed power link. I received and installed the component you recommended and everything is working normally. The one I received was much larger than the original, so I had to relocate the terminal block to make room inside the box. I also replaced the power cable. Very strange how the entire 3' cable would just crumble to the touch. So, my pride and joy is good as new, thanks to your help. Thanks again John!

[jbird604]

Good news! Glad to have been helpful to you, my friend. To be honest, I've never ordered one of those devices from anywhere except Allen, and that was many years ago. The one I suggested on digikey just seemed to have plenty of capacity, so I thought it should work without any problems. Interesting that it was so large.

If I ever get the chance, I'll check out one in an ADC distribution box to see what the actual ratings are, and perhaps find a closer match on digikey. Thanks for the report.