Conn Theater 650 - no reeds.

[Lommylomz]

The fuse in question is on the left. These 1 amp fuses look like fast blow fuses to me, but please correct me if I'm wrong so I don't install the wrong part!

[tucsondave]

Correct. Fast blow.

[Lommylomz]

I have replaced the fuse successfully, turned on the organ and it hasn't blown. I've unplugged plug P3, turned the console speakers on, the loud hum went away. I've also found that the ground wires going into plug P2 pin 3 have been disconnected from the socket (plug P2 was in the socket for the test, only removed for better detailed picture), I'll have to fix those somehow as well. Whether that's what's causing the hum, I don't really know.

[ukmusicman]

If ground wires have been disconnected, that would probably cause a hum. The question is, why are they disconnected. If you manage to reconnect them, switch on the organ and be ready to switch off very quickly in case something sounds wrong.

[Lommylomz]

I haven't been able to reattach the ground wires yet. As the picture shows, there is still some wire left in there that I haven't been able to get out. I don't know if I should be soldering inside the plastic connector. I'm thinking of just getting a new octal connector, cutting the wires off the old one and reinserting them into the new one. I've learned more about the hum. The hum gets louder as more stops are turned on. And when I flip the reverb 1 or reverb 2 switches, there's a momentary scratching sound for the instant when the switch is being flipped. The hum isn't affected by anything else. One of the things that is different from the type 1 and type 2 conn 650s is that they added a spring reverb box, so the tabs on the left hand side of the great manual are reverb 1, reverb 2, chiff, and tibia harmonic. The supplement in the back of the manual said to insert into the block diagram a box labeled "reverb amplifier" in between the complex expression controls and the complex power amplifier. I still need to investigate the reverb amplifier, but I found that there was a loose ground soldered to one reverb connector pins which I had to re-solder.

I've also found that when I stick one end of my multimeter into the tibia input on socket S3 closest to the speakers, it makes a hum and when I touch the other lead of the multimeter with my finger, the hum gets louder. The exact same thing happens if I stick the multimeter into the complex input socket. I think this means the power amplifier works fine, and the problem is now before the power amplifier. When I conducted test 2 from page 33 on the preamp collector voltage, I got 0 volts instead of 24.

As I was checking voltages in the organ, the same fuse blew again, unsure if it was my doing or if it's something else inside the organ, guess I'll try again after I reconnect those ground wires because that I know has to be fixed. I'm also unsure weather it was my doing if the ground was disconnected or if I got the organ like that.

[Lommylomz]

I've reattached the ground wires, the hum persists. Same problem now as before with the preamp collector voltage being 0.

[tucsondave]

Check the voltages on Q27, the electronic filter. It is supplied by the +30 volts which is fused by M3.
Since those parts are on a terminal strip just below the post amp, perhaps you shorted something there causing the fuse to blow.
If Q27 is open or C136 is shorted there will be no 24 volts.

td

[Lommylomz]

On the electronic filter I checked the voltages for transistor Q27. I measured 30.4V on the collector, 30.4 V on the base, and 0 V on the emitter. I tested capacitor C136 with an ESR meter and it was in good condition.

[tucsondave]

Then it's time to replace Q27.

[ukmusicman]

I was looking at that, but TUCSONDAVE got in before me. See if he comes back on that. It suggests to me that thr transistor Q27 has gone down. In order to test that, you will need to remove that filter unit and lift two transistor legs from the board. Better still, remove the transistor completely making sure you have a note of which legs went where in case you need to replace it. It seems that you have been studying the course, so you should be able to test the transistor. I have found a useful little gadget for testing transistors called the PEAK ATLAS DCA Model DCA55. I've found it very useful, if you can get one of those, it would be a great help. While you have the filter removed, you could remove the C136 electrolytic capacitor and check the capacitance and if you have an analogue multi-meter, the charging and discharging as described in the course. Also, while you're at it, check the two resistors. If you need to replace the transistor, the Conn number 71819-1 is a SE6026, see page 78 in my manual and possibly yours.

[tucsondave]

Here in the colonies the 71819-001 crosses to a 2N3569 which crosses to an NTE123 or NTE128.

td

[ukmusicman]

I haven't got into transistor updates or alternatives yet. I know that some people advocate changing suspect components regardless, but for people like me and the guy we are trying to help who want to learn as much as we can about electronics, we need to know what item is faulty and why it's faulty, so testing is something we need to do to take our education forward. Just throwing stuff out in case it's faulty isn't going to teach us anything.