M3 Percussion won’t retrigger

[PN4A]

I recently acquired and starting modding an early model M3. I am very new to Hammonds but comfortable soldering/following tutorials etc. I added a Tek2 aux out, and removed the pedals (they were bent anyhow) and the pedal tube (it was humming).
Anyhow here is the dilemma, as I was testing the percussion I noticed it would not re-trigger. If I pull out just the last drawbar and hold a key down, when I throw the on/off rocker switch for the percussion it makes an initial tone (both in the 2nd and 3rd position), but when I play another key it will not re-trigger. I get the same results in the normal/soft positions and in the fast/ slow decay positions. The other rocker switched modify as they should. Anyone experience this. Anyone know a fix. Look forward to y’alls collective wisdom.

Thanks in advance

[tmccann]

For the sake of the obvious, you are playing one key at a time, correct? Upper manual only? The percussion won't trigger again until you release all keys and let it charge up.

Also set the percussion cut-off per the service manual.

Check the 6C4 tubes and the 12AU7 tube for the percussion. You can swap the 6C4 tubes V7 & V8 and the 12AU7 in V9 for the 12AU7 tube in V3.

Check the C30 cathode bypass capacitor also. It's electrolytic and likely to be way out of spec by now.

[Admin]

As pointed out by tmccann, the percussion will sound only when all other keys are released. Try turning the percussion on an off with no keys pressed. If the percussion sounds, it means that there is a short in the manual. Often this is caused by dendrites. Search the Forum using that term for more information and remedies.

[PN4A]

tmccann Thanks for the prompt response. In response to the obvious, yes I am playing 1 key at a time, yes on the upper manual only and yes fully un pressing and waiting. As for the tubes, cut-off and cathode that trouble shooting will have to wait until I have more time. If I had a pretty good idea what to fix I could jump in, but I just got it up and running and want to actually play with and record it before I disable again.

In response to Admin, when no key is depressed it does not sound. Only a single percussive note when a key is depressed and the on/off is toggled.

Attempted to link a video clip of the problem, apologies for the camera work and the buzz, but hopefully it will help illustrate the problem.

thanks

[tmccann]

Attempted to link a video clip of the problem, apologies for the camera work and the buzz, but hopefully it will help illustrate the problem.

From what I see if the video it looks as if percussion only triggers when you toggle the percussion switch on and a key is held down. Correct? I thought what you were saying is it triggers once and then not again. If you turn the percussion on with no key down, and then press a key, does it trigger once and then not at all? Or does it only trigger when you toggle the percussion on and off?

I would definitely check the percussion cutoff and the tubes. The percussion cutoff takes only a few minutes to set:

[enor]

What you're describing is the classical case of a short to ground, either in the manual or in the percussion switch assembly. Something is causing the trigger wire (=the signal from the highest drawbar) to short to ground. Likely crystalline hair growth. This is without competition the #1 most common problem with the percussion circuit.

[tmccann]

What you're describing is the classical case of a short to ground, either in the manual or in the percussion switch assembly. Something is causing the trigger wire (=the signal from the highest drawbar) to short to ground.

Yeah, I can see how this makes sense. With percussion off, there is maybe no short so the C31 cap charges up. When you hold a key down and flip on percussion, and it is shorted inside the switch from whiskers, you would get exactly one trigger and then the cap won't charge up again until the percussion switch is turned off.

I'd still check the easier stuff first but I can see how this would be the likely problem.