What's wrong with my Baldwin 632?

[troyillinois]

I have had this Baldwin 632 organ for about 7 years now. When I bought it, a few keys didn't work but everything else functioned just fine. About a year or two ago, it started rapidly transposing through different keys every time I turned it on (link to a video demonstrating this is below), which made me think something was wrong with the transposer. I had repairmen in to come take a look but they did nothing useful and couldn't figure out what was wrong. Does anyone have any ideas what is wrong with the organ or how I can fix it/if it can be fixed?
I have the technical manual for the organ but know little to nothing about electronic organ parts or repair.

Video of the problem: https://youtu.be/kX5cVKCno6Y

Thankyou!

[jbird604]

This is one of Baldwin's organs from the 80's using a CPU to control an elaborate system of gates and filters to produce the stops. The CPU interfaces with the rest of the system with a large number of latches and logic chips. All this stuff, including the CPU, can be found in a stack or "sandwich" assembly of three or four boards, usually located right behind the stop tabs or possibly on the upper side wall. Don't confuse this with the "tone color" or filter stack, which merely filters the signals ahead of the amps in order to make the flutes flutey and the strings stringy, etc. The CPU stack is quite large and has a great many IC's on all the boards, while the tone color is smaller and has only ordinary resistors and capacitors for the most part.

Once you locate the CPU stack, try to make sure that all the plugs that attach to the sides of the boards are fully seated on the little pins sticking out the sides of the boards. It's a bit of a fragile system for connecting up so many cables. (There are probably 30 or more of these spaced around the stack of boards.) But if they aren't making good contact, the system will malfunction in various ways.

Also, you'll see down lower in the console the three sets of "daughterboards" standing upright on "motherboards." There are six or eight large daughters and maybe another six or eight small ones standing atop each motherboard. These all plug into the motherboard with connectors, and the solder joints underneath can be fragile. GENTLY press on all of them to make sure they are well seated. Also check the various connectors that attach to the tops and sides of these boards in similar manner to the CPU stack.

Take a look deep inside, underneath the tab rail, using a flashlight to inspect the transposer button board. It is attached with a plug or two that can also work loose in time. And there is a master generator board, possibly labeled as the "transposer board" (because it changes the frequency of the master oscillator by sensing the button presses on the transposer switches). This board has several plugs on it as well.

As you may guess, these old organs can prove unreliable. Not long ago we had to junk one out because it had become so unreliable. The church was having to call us every few weeks to come back and try to chase out some more bugs. Not only do the plugs work loose on the boards, the crimped wires (hundreds or maybe thousands of them in there) also eventually work loose inside the plugs themselves! So one of these days, it may become impossible to make it work right again. But until that happens, you may be able to keep it alive with some regular poking around inside.

When it gives up the ghost, the keyboards and pedals are quite nice, and the console is sturdy, so this can serve as a good base for a MIDI organ/VPO setup.

[jbird604]

After watching you video, I'm inclined to think you should focus on the master generator board (AKA the "transposer" board). Sounds like the frequency of the master clock is wavering all over the place. This could be due to a loose connection on that board somewhere. You can ID that board by looking for the board with a round metal "can" about 2" tall with a round hole in the top for tuning. The board also holds a few IC's and some other components and has three or four plugs on it with wires leading away. The board could be on the left sidewall (as you look in from the rear) or it could be in the middle of the large shelf that holds all the gate boards (daughter boards on top of motherboards).

Once you find that board, block down a key so you can hear what's happening, make sure you are wearing no metal jewelry and that your hands are dry. Then touch various places on the board. Gently try to wiggle the metal round can, press on the various sections of the board, touch various components, etc. You may find a part that provokes the trouble or that stops it when you touch it. That might be your bad part.