No percussion decay

[johnny b3]

Since the percussion switch wiring harness is tied with string, there is no way for these to be hooked up to the amp incorrectly - furthermore they are color coded to match the amp terminals. The shielded wire from the switch connects to terminal P, correct? Inside the amp each terminal is wired correctly; P to T6 and H to T4.

The only other thing I can think of is the White, Green and Yellow (two of each) wires which exit the percussion switch box and intercept the 4th, 5th and 9th drawbar connections at the B preset drawbars. Is there an incorrect way to have these wired? Since they are the same color would it matter which one intercepts the drawbar feed and which returns it to the corresponding drawbar?

[Tim_at_Jonas]

I've had your symptoms come out of nowhere. A flash fixed it (can't guarantee it for you of course).

Percussion Problem: Failure to decay, or sounds only when a key is held and the percussion tablet is switched to ON.

The problem is most likely in the manual or in the percussion switch assembly.

Test 1:

Power the organ. Depress the B preset key and turn percussion the tablet to the OFF position. Using a VOM/DMM, measure between ground and the preamp's K terminal (blue wire). You should have 30 Volts (plus or minus a few).

Turn the percussion tablet to the ON position. There should be no change in the voltage reading. If it drops substantially, there is likely a dendrite problem.

Press any playing key on the upper manual. The voltage reading should drop to 0 as the percussion sounds and decays (if the above was ok). If not...




Test 2:

Turn the organ off.

Locate the terminal block on the back of the manuals that has white, green, yellow, yellow, red, orange, red, and brown wires. Connect an Ohm meter between ground and the terminal that has the white wire.

With the percussion in the OFF position, you should have about 0 Ohms.

With the B preset key depressed and the percussion tablet in the ON position, you should have about 120k Ohms. If it is subtantially less, there is likely a dendrite problem.


There is a short procedure for "zapping" the dendrites with DC voltage. It can repair the problem for a while, but dendrites will continue to grow and the problem will eventually return. However, if it clears the problem it is easier to do this a number of times than remove the manuals to get at the buss bars.

This procedure requires a DC voltage source (9 volt battery may work). Using aligator clips, attach the ground terminal to a chassis ground point. Attach another clip to the positive terminal.

Locate the white wire coming off the 1' drawbar, B preset. Turn the percussion tablet to the ON position. Briefly touch the clip to the terminal where the white wire connects to the busbar. Turn the percussion tablet to the OFF position and repeat.



Check your meter (or just play the organ) to see if you have the correct results. If not, try again, touching the lead to the terminal for a bit longer than briefly. Recheck.

If this does not clear the problem you need more voltage. You can tap off the Leslie kit and get about 290 Volts from it. Be "real careful" if you do this - don't short it to ground! (A bit easier is to remove V4 and tap off of socket pin 1 for about 140 Volts.

If this does not clear the problem, remove the wooden cover from the drawbars, remove the fasteners for the drawbar & switch "chassis", remove the percussion switch box, and remove it's bottom cover.

Remember that white wire? Trace it into the switch box and to the percussion switch. Find the wire that this gets connected to when the switch is in the on position - I think it is black. Turn the switch off. Touch your DC voltage source to this terminal. This has cured a couple of organs.

[johnny b3]

Locate the terminal block on the back of the manuals that has white, green, yellow, yellow, red, orange, red, and brown wires.

Thanks Tim, I'll get on this soon. in the mean time can you please clarify which aforementioned wires you're talking about? Where are they going/coming from?

[Tubejack]

If none of these symptoms were present before you recapped the amplifier, I wouldn't recommend any more "flashing." It's curious that the two symptoms are contradictory. The fact that "K" is constantly grounded whenever percussion is on should prevent percussion from sounding. Yet, percussion sounds as long as a key is pressed. Considering that removing percussion amp V7 doesn't change this, the percussion tones might be getting back into the amplifier through the matching transformer. This would involve a couple areas of the circuitry that aren't easy to interpret, such as the switch contact annotated with a circled "4". The note says "Preset percussion switch under 'B' adjust switch only." I have no idea what that means. Maybe you can find a way to trace back the "K" wire to whatever is grounding it. That may point to the cause of both problems (I still suspect miswiring). Don't know what else to suggest at this point...

Jack

[Tim_at_Jonas]

Thanks Tim, I'll get on this soon. in the mean time can you please clarify which aforementioned wires you're talking about? Where are they going/coming from?

The terminal strip that's in the middle of the upper manual. They may all go to the perc switch box, but I'm not sure. I think it's the white wire that's the one that most needs to be flashed.

[Guest]

Apologies if done already but why knowing the little beast was awaken after nothing else changed but a recap job, the recap job is not checked as such on the first place, step by step, component after component... That could be just a bad/wrong soldering etc... Or some wire, component leg or soldering that sends to ground where it shouldn't and can be finger fixed? I hope this suggestion can help.

Cheers
Boyan