Hammond H395 Percussion

[mdrehkopf]

Dear organforum

After several fixes I did in the last weeks on the H395, the probably last to do is to fix the percussion. The organ has a transistorized percussion preamp, that is easily accessible from the back.

I checked all caps today, the electrolytic ones were 60% off nominal value, therefore I replaced them.

The percussion itself just works on the 2nd voice registration, I can adjust the volume level then wihh one of the Potis on the frontside of the preamp. If u turn the 2nd voice tab off, I should hear the 'ping' percussion, but there isnt any sound then. I tweaked the cutoff poti on the preamp, which did not result in any audible ping....

Does someone know, how to fix that? Is the 'ping' generated in the preamp board or in the reiteration board, that is directly behind the tabs?

Attached a photo of the board
Thanks and greetings from Germany
Matthias

[mdrehkopf]

Dear Forum

in the meanwhile the search for the missing "ping" progressed, but I am not done yet.
Through some good help I learned, that the "ping" is coming from the reiteration board, therefore I replaced both caps, that are, according to the service manual, responsible for the ADSR curve (013-010142 - C201 and C202). These are film capacitors, I replaced them with 0.1uF/100V electrolytics, but the change did not accomplish what I wanted.
I measured, that the reiteration board has sufficent voltage coming in at pin12 (25 V). However I did not get a 6V Keying voltage input on Pin3 (orange wire) as the drawing tells me on the H100 service manual.

I am not sure at this point of time, if I am on the right path:
a) the service manual is H100 and my organ is a late model H395, with transistorized preamps -- not sure if this would make a difference on the 6V expecation on pin3
b) if the 6V should be on pin3, I do not know where the voltage should come from

I did read some other Organforum postings, that were indicating a specific busbar, with resistors on it. I understand that the percussion keying and the "brush & cymbal keying" is coming through the same busbar. I checked now:
a) brush and cymbal work on most (not all, but most) keys of the upper and lower keyboard
b) percussion does not work on any key (once percussion is not in the 2nd voice modus)
c) in the 2nd voice modus all works fine

Please get me some ideas

Thanks
Matthias

[Drawbar Dave]

I have a similar issue on my R100. The reiteration works on all percussion tabs but does not work in the other mode. I have 25 volts instead of 6 on the orange keying wire. I do not have time to work on it at the moment as I have a lot of customer's organs to repair first but will be interested to see what people make of this. I am not familiar with the H series organ but imagine that there will be similarities in the circuits from the features that you have mentioned.

[Admin]

Hammond percussion problems are often caused by dendrites that have formed on the keyboard contacts and short the percussion keying signal. Second voice and reiteration aren't affected by this so they continue to work.

To test for dendrites, turn all percussion tabs off, press the upper manual B preset, then, without pressing any keys, turn on one of the percussion stops. If you hear a note sound when activating a percussion tab, without any keys pressed, you have a dendrite short within the keyboard. Search the Forum for info on how to zap the dendrites without having to remove and open the keyboard chassis.

If percussion isn't working and you don't hear a note sound when activating the percussion tab with the B preset selected, the problem lies elsewhere in the circuitry.

[mdrehkopf]

Thanks so much for your support - I tried to figure out the mistake in the H100 reiteration board, but I was not successful.
The issue is:
a) The 7th contact should deliver 6V when percussion is switched on, 2nd voice being off and a key is pressed - I just record 0.x volt, which, according to the manual and drawing, is not enough
b) The D205 - 001-026050 Silicon Control Switch is one of the first receivers of the keying voltage, which I do not know any commercial replacement for.

Therefore I have 2 assumptions:
a) Somehow the power supply of the H395 (which is a late H100 with transistorized pre-amps) has a bug. I do not know which voltage I should expect from the individual contacts in the power supply, therefore I would be glad if someone has the drawing for the H395 PSU (it may be different from the H100 PSU)
b) 2nd assumption would be, that the voltage keying is ok and the chain of transistors and the programmable unijunction transistor (which is the 001-026050) is including a failure. In this case I will need a replace of the PUT .... and need the commercial replacement equivalent. In order to prove this assumption, it would be a great help, if another "late H100" or H395 owner would measure the orange wire on the reiteration board (looking from the players side the 7th from the top contact on the right side of the PCB) - picture see attached

Thanks in advance for any help or support
Matthias

[Jyvoipabo]

Hello,

001-026050 = 2n6027 is a PUT widely used in oscillator circuits.

In the diagram you give, very difficult to read because overloaded, I suppose that the cathode of this transistor must be grounded by the darlington Q202 Q203. Under this condition, it oscillates and produce a saw tooth..

This implies that this transistors are saturated by a high voltage (6V) at the input control.

If the control voltage stays at zero, it can't work.

JP Redeconfined

[enor]

Most often, these things are caused by a short to ground in the manuals, as has been previously suggested. Have you ruled that out?

[mdrehkopf]

Thanks Enor, I tested for dendrites as described and did not hear any percussion sound.

Is there any other test that i could make to test for shorts to ground?

Thanks

[mdrehkopf]

Hi again, on the "search for the 6V" I decided now to recap the power supply unit, it has the number #127-000037, will keep you posted

[mdrehkopf]

Great.... I got percussion today. I measured the entire audio signal path of the ping signal at the reiteration board and figured out, that the path was stopped at one of the electrolytic capacitors.

Obviously I mixed polarity when I replaced it earlier. Now the percussion is back, works with 2nd voice. Reiteration does not work yet, but there are a few days left over before we enter 2021!

I am still confused by the 6V, that should arrive at pin 3 of the red plug prior to the reiteration board. On my board, that is built into a very late H395, just 0.6v arrive, but obviously there are different resistors built in, as after the 1st resistor all voltages are according to the schematics.

The power supply unit indeed seems to be OK, all voltages are available.

Thanks for the help so far
,

[mdrehkopf]

Dear Organforum,

the percussion is gone again. I made now several measurements and .... please ... if anyone that has a late H100 (with transistorized percussion amp) of H3xx ... would like to locate the issue better.

The percussion keying path has been measured and is included in the picture below
PSU
First question:
Can anyone measure on his H395 the third pin on the PSU (it is the left white connector, that is a 9 pin connector, starting to count 1 at the left top, then to the right) ... is this also in the 32V range ? My PSU is labelled with #127-000037

Second question:
Is is realistic, that the percussion busbar resistance WITHOUT any key pressed is 6.7K Ohm, WITH a key pressed 6.3K Ohm ? This looks very high to me .... nonetheless the 0.3V remaining are not enough to trigger the few transistors on the reiteration board (they would require min 0.6V as stated in the schematics). Two weeks ago at least 0.6V arrived and then the percussion worked

Thanks, once the H395 is fixed, I promise to stop asking all that questions

Cheers
Matthias

[enor]

If you have 14V at the supply point to the keying busbar, but only 0,3V on the other end of the keying busbar, then you have a short to ground in the keying busbar - most likely because of zinc hair growth in the manual. Not quite sure what you mean by "6.3 kOhm" under the busbar - is that the resistance to ground, or the resistance of the busbar (+contacts) itself?

[mdrehkopf]

Thanks Enor
- the 6.3 KOhm is the resistance of the busbar + contacts (measured between the supply point of the 14.4V and the "other end" of the keying busbar)
Matthias

[mdrehkopf]

Thanks again
- the 6.3 KOhm is the resistance of the busbar + contacts, when a key is pressed (on B preset, percussion on, touch off, reiteration off)
- the 6.7 KOhm same thing, when NO key is pressed
- the and resistance to GND is exceeding 7K Ohm (measured between the supply point of the 14.4V and GND)

I fear that it could be the zinc hair / dendrite issue - do I really need to remove the upper manual then ... ? Is there an "easy" way to fix .... ?
Cheers
matthias

[enor]

You're measuring with the busbar and contacts lifted out of circuit, right? As in "supply desoldered, and molex connector taken apart"

Supply terminal to ground should be open circuit.
Supply terminal to trigger busbar output (one of the pins in the white molex from manual) should be open with no key down, and good continuity when playing a key.