I had a recent repair job that I thought was hopeless. I’m not a fan of a million wires, and when I heard about this repair, I knew that if nobody else wanted to repair it, I was going to be challenged.
Well, I accepted the challenge. I went to the owner’s house and began disassembling the organ to gain access to the inside. I found gaining access to be easy, but I was instantly overwhelmed by the number of wire wrapped connections inside. This was a very complex design.
I flipped on the power switch, and I noticed that the baffle around one of the speakers spun a little, so I knew something was working. I tried everything to make some noise, but nothing happened other than making the speaker baffle spin faster.
I turned the power back off and unplugged the organ. I unbolted the power supply and checked the fuses. I found a fuse that was blown. I had no idea what it was connected to. I plugged the cord back in and turned the organ back on. [Do not attempt this!!! Death or shock or death from shock may and will occur.] I took my multimeter and set it to measure AC current. I placed the leads across the fuse and heard a 60Hz/120Hz hum and saw the current spike to about 6 amps. I released the probes to allow the system to return to its non-working state. I probably could have done without this test, but I had to take the risk. I don’t recommend doing it because that is enough current to ruin good parts.
As I’ve always stated: Troubleshooting starts at the wall and works its way forward. I gave up for the night that night, but I did make one mistake. I should have taken the power supply home with me. I had to go back to get it. I knew that the problem was in there. While I was there I checked all of the rectifier diodes. They seemed to work alright. I checked the transformer, and the leads had continuity. I checked the big capacitors and they all had good tolerances. Tha took about 1.5 hours.
I got the power supply home and gave it a semi-good dusting. I found some schematics and troubleshooting guides online and read through them. Then I started checking resistor tolerances first. If they had a value, I left them alone. Then I went back and checked the diodes one more time. Then I checked the caps again. Then, I tried to test the transistor leads. They were tricky to get to, and making these measurements without breaking anything took a while. I had to be sure not to break the boards. During this test I found a transistor that had a 15 ohm resistance between two leads. I suspect this is my problem.
I looked for a datasheet on the part number, but it wasn’t valid. Then I checked the schematic and found the Holiday part number and Googled it. I found another list of all the parts and found a good part number. Come to find out, this transistor had, in fact, gone bad. I found the part on the schematic and traced to check all the parts in line of it from the transformer to ground. The first part checked was a power transistor. It had a short from collector to base. Everything else checked out.
I ordered the parts and replaced them in the circuit. I reassembled the whole thing, and took it back to the owner’s house. I installed it back into the organ, and I plugged the organ in. I made sure all of the switches were off, and then I powered the unit up. It was fixed! Somehow the power supply had a fault that cause huge amounts of current to flow. The cause is unknown, but replacing the two transistors got it up and running again.
In your repairs, remember that most problems start at the wall. Good luck, and remember that it’s more than just a project.