T-233 percussion sounds have very low volume

[Gjesse]

Hello all,
I’m new here and new to Hammonds. Just brought home a T-233 and am getting the bugs worked out. It’s almost fully functional, with one stubborn issue...the percussion sounds all work , just very quietly. When the upper manual controls are in the up position, or if the Drawbars selector is down(but the Drawbars all in) I can faintly hear the keys when played, and the sounds change when I toggle through the percussion selections, even the reiteration tab (not much change with the rate pot though). The upper manual is plenty loud with Drawbars out, or the other tabs selected. But percussion alone is barely audible. There is a slight increase if I press the Leslie or pedal rockers just right, which is interesting. Any ideas what my issue is, or what general area I need to poke around in?

[Gjesse]

Also, it should be noted, that the percussion sounds I can hear do not fade out as I understand they should. It’s just a steady tone that persists as long as I hold down the keys.

[Brendon Wright]

Ahh... That second bit's interesting. I'll have to do a bit of digging to remember what's responsible for the decay.
But first, check out the trims on the Percussion board (have you downloaded the service manual?
http://captain-foldback.com/Hammond_...schematics.htm it's not quite complete, but should get you started.
It pays to have the T500 one handy too:
https://archive.org/details/T500Serv...PAGESREORDERED)
Use a marker pen on the trims to show where they are positioned now. The one in the middle of the board is the Percussion level. Does that effect the perc in any way?

[Gjesse]

So helpful...thx! I'll see what I can figure out from the manuals. I'll try and find those trim pots and report back

[Gjesse]

Well I found the four trim pots on the back of the percussion board, one on one of the other boards, and a larger different type on the top board behind the reiteration pot. I cleaned them all with contact cleaner, as well as all the other contacts I could find, and marked the original positions on the pots. Then I fired it up and played percussion sounds only, and started playing with the pots. One of them on the Perc board raised the volume a lot. The others had no effect. The one pot on its own board also raised the volume even more...maybe an overall volume trim? Didn’t check it yet with non Perc sounds. The one on top behind the Reiteration pot did nothing. The reiteration switch and control pot also had no effect. And again, there is no decay with the Perc sounds. Just rings out at steady volume. So I guess that’s my remaining problem. Any ideas? I’ll keep reading the 500 manual and see if anything jumps out at me.

[Brendon Wright]

Ah- good!
That's that one then. In my own T I've had infinite perc happening before but can't remember how I fixed it- it pays to write all the working solutions down cos you never WILL remember everything!

Because it's a T200, try this page here:
https://www.keyboardpartner.de/hammond/t-mod-skill2.htm
Scroll down to "shorten percussion length".
Is the original 1meg resistor there? Is it still working? If there's a break in it the perc should ring forever, though it may not be the only cause for that.

[Gjesse]

I checked the resistors behind the reiteration tab and they are all good, the one that stretches across the terminals of the switch reads 1 meg, so I guess that’s the one you mean. R551 trim pot on the Perc board is all the way up, and the Perc sounds are much louder than before, but not as loud as the Drawbars. Not sure if that’s supposed to be that way.
I verified the other pot on its own board (preamp board?) also affects the drawbar volume, so I guess it’s an overall preamp volume being sent to the power amp?
Also to note, the Reiteration tab does affect the sound of the marimba and xylophone Perc sounds, but the rate control does nothing I can hear, and of course, still no decay. I really appreciate your advice Brendan, it’s helping a lot... If I can just get the decay/rate control working , I can stop tinkering and start playing!

[theseacowexists]

You know, this happened to my T-200 once before. Exercising the pot that's right behind the volume soft and brilliance switches set everything straight. It's not one of the pots on the percussion board, but rather the one that faces upwards.

[Gjesse]

Thx for the advice seacow! I played with it before with no luck...I’ll try again, for lack of other ideas currently...

[Gjesse]

Still no action with the big pot in this photo.
I assume that’s the one you mean.
The reiteration tab seems to act as a high pass filter when activated, cuts the low end, that’s about all. Maybe that is a clue?

[Gjesse]

I keep reading about this zapping procedure… Does this sound like a candidate for that?

[Brendon Wright]

Nah, zapping's just for dendrites inside the vibrato scanner.
The ol' T500 doesn't have a pot behind the tabs, I'll have to find out what it is!

[Brendon Wright]

Try Carsten's mod out and see if it makes a difference...
solder a much smaller resistor in parallel with the 1meg and also one with the 3.3meg and see what happens.
Did you find a 3.3meg in behind the reiterate tab before? if that was missing or broken it would give infinite perc when switched to "long perc."

Looking at my T500 notes I realised I haven't touched it since struggling with a major percussion issue myself...
Had written pages and pages of notes combing over the T500 board and still failed to nail it.
I see in the end I had my beady eye on a spare L100 perc module but knew if I went onto that I'd NEVER have solved my perc board!
Since you guys are getting me running again I should give it another go.

I have a secret weapon Hammond Tech on another forum I'll send you to if the Carsten Meyer mod doesn't make a difference.

[Gjesse]

You’re awesome Brendan! I’ll let you know if the mod helps. BTW, I’m not sure mine has a ‘long Perc’ selection...

[Gjesse]

I put in a .5 M resistor in parallel with the 1M behind the reiteration tab, making 330k. No effect.
Not sure what the target is for the 3.3M position ...(it is still there and good). I could just try something and see what happens.
These are mods though, right?...seems the Perc should be operating correctly in the first place before mods will do much good?
I wonder if it’s worth replacing components on the Perc board (others too?)that are most likely to have failed, like electrolytic caps?