Hammond A100 Percussion Trouble Shooting Guidance Needed

[Von R. Colborn]

I have a 1960 A100. The percussion is not working properly. By that I mean that, with one exception, the percussion never sounds. That one exception is when percussion is OFF, a key (any key) is held down and the percussion is placed in the ON position. At that time I hear a "bonk" percussion sound. After that, repeated key presses do not generate percussion "bonk" sounds. The other tablet switches seem to be working properly. The Harmonic switch does, in fact, change the frequency of the "bonk". The Long/Short switch does change the length of the "bonk" sound. Soft/Loud does change the volume of the organ (Loud does lower the overall sound of the organ, which I understand is correct behavior).

So, the bottom line, as it seems to me, is that the Percussion is not triggering properly. If it would trigger on a key press the other functionality would be observed. As a side note to be put into another post, Chorus/Vibrato is not working, but seems to be trying. I don't know if these two functions are closely related.

What I am looking for is guidance on how to troubleshoot Percussion problems. Is there a sequence of things to check (I'm thinking of a troubleshooting flow chart that guides one through the "Check this, Yes - go here, No- go there sort of an approach. I've read all that I can find on the subject, have studied the block diagrams and schematics that are in the 2016 version of the Hammond service manual. I am hoping that some of you experienced Hammond repair people can provide some guidance as to where to look for the problem, resistance measurements, theory of how percussion works, Tubes that may be the problem, etc.

I'm out in the Hammond support void of Utah. There really is no one to contact locally, that I can find at least.

All help will be greatly appreciated.

Thanks,
Von

[muckelroy]

There is no flow chart that I know of, but ample resources online (the forum included.) Please do your due diligence in searching for resources, and we are happy to answer questions.

As a hint to help you get started, I would recommend 2 things:

1. Read the Hammond Service Manual carefully, in the paragraphs which explain how the percussion circuit works. We can answer specific questions you might have about it.
2. This problem is almost always caused by a short, in the form of:
-- Dendrites in the percussion switch assembly
-- Dendrites in the manual contact bins.

Remedies abound, some safe, some dangerous. Some effective, some not. Some long lasting, some short-term lasting. If the problem is dendrites and you temporarily solve by "zapping" them, you will find the issue returns, which will require removing the manuals, and opening up the upper manual contact bin, and cleaning the areas between each row of contacts to remove errant dendrite growth.

Good luck.

[Von R. Colborn]

Yes, I've been researching both on-line, and in manuals. Actually, I'm not surprised that there is no flow chart. I would be surprised, however, if there is not enough combined knowledge and experience on the is forum to create one. I would be willing to put together such a diagram and troubleshooting guide and upload them to the gallery area.

The organ was never used heavily (given to a 16 year old girl who played it for several years then married and moved away, leaving the organ at her parents house. There it sat, abandoned until around 2001, when it was moved to year aunt's house for storage. It's entire life was in the house in a smoke-free environment. I purchased it in an estate sale. The TG was frozen solid. I oiled it and kept it warm for about five weeks, occasionally testing the stiffness of the TG. Last week it broke free and has been starting fine, noise-Free since then.

Do dendritic grow more in situations where the organ is not being used?

Based upon your response, is it reasonable to say that the first thing to do is is disassemble and clean the four tablet switches for percussion?

[muckelroy]

Based upon your response, is it reasonable to say that the first thing to do is is disassemble and clean the four tablet switches for percussion?

That is the easiest and safest thing to do by far, and could work.

[Bobmann]

The zinc whiskers form on all zinc plated surfaces, this is something that is not an issue just for Hammonds.
NASA has done research on this problem.
If I were you, I would certainly disassemble and clean all the tablet switches as well as the vibrato switch box while you are in there. Even if you are not having vibrato issues right now, it is just a matter of time and this will keep you from taking it apart again.


Benton is a wonderful resource for Hammond.
Here is the klink to the preamp page:
https://bentonelectronics.com/servicing-the-hammond-b-3-type-pre-amp/

This may also interest you
https://www.youtube.com/watch?v=vnwO0m7eEpg

Bob

[Bobmann]

There are only a few wires to unsolder, and typically they are wrapped in order.
If I am working on ones that either have wires that are not in the string loom, or some of those older fabric covered wires that are hard to determine colors, I will number them with those wire markers that are available in the electrical section of your big box store.
Also mark the terminals on the line box, RD, BL, and either GN or BN.
Rather than run the risk of miswiring, I label every wire, even though I know the locations by heart. It serves as a double check as well, and does speed things up when putting it back together.

[Von R. Colborn]

BobMann, thanks for the advice on the wiring. It sounds as if you've refurbished many a Vibrato units. I have a couple of questions:
1. How long does it take you to do the removal, disassembly, clean, reassembly, and reinstall? Should I double or triple the time for a first-timer?
2. How long should the parts be soaked in lacquer thinner? Is the stuff that can be purchased in the paint department of a good enough quality?
3. As part of the reassembly should any of the Hammond oil be applied to the bearings and oiling wicks?
4. Are the wires solid core or multiple strand?

[Bobmann]

Hard to sayy how long it will take anyone, obviously some people are more meticulous than others. As with anything, efficiency comes with practice, and I plan on 1 to 1.5 hours, start to finish. You should plan on spending an afternoon.
Soaking is not necessary to clean any of the parts. Neither the phenolic nor the metal parts are porous, so you are just removing surface contaminants. I use lacquer thinner from the local big box store, it is pretty much all the same. I put the phenolic parts and screws, washers, etc. in a small dish, (make sure it is resistant to the thinner) then pour enough thinner in the dish to just cover the parts, swish around or use a small brush to agitate, pour the thinner out and lay the parts out on a paper towel to dry, usually a minute or so. If the parts are unusually oily, I may repeat the rinse.
The wires could be either stranded or solid, I have seen both. Be patient when unsoldering the wires at the terminal strip. These terminals are not very robust, and I have broken a few. This would not be a problem other than it could take a little longer to fix.
I typically clean the scanner pretty well, so as SOP I put a drop of oil on all the bearings. It can't hurt, for sure.
Not to be dismissive of your abilities, but I should emphasize to mark every wire that you remove in some manner. It will help speed the process of reassembly and eliminate miswiring. Nothing more frustrating than trying to track down a unit that does not work after putting it back together.

[Tonewheel]

If it helps, I had a similar problem. I really cleaned the rocker switches and sprayed them well with contact cleaner. I also taped 2 9V batteries together and zapped the supposed dendrites. It was successful. The pain is taking so much apart and getting it back together again with no extra screws. It is amazing how fixable these things are, and the help that is so freely offered in the forum. My 2 bits. Dave

[Von R. Colborn]

I did see a video on the Poor Man's Vibrato Repair where someone had a little black box with a couple of leads with alligator clips and a pushbutton trigger. I didn't know if it had a step up transformer or was just doing a quick spark if 18V. That seems like a pretty good device to use in trouble shooting. Zap the usual suspects; If it helps take the action necessary to correct the problem properly. :-)

[Bobmann]

Zapping is something that may or may not work. It can fix it for days, weeks, months, years. Depends on the whisker infestation.
The only way to fix permanently IMO is to disassemble and clean. I coat the inside of the switch box with a thin coat of lacquer for added protection and to assure that I will never have to clean it ever again.

[Jaim]

This is a fairly common problem. The reason the tone plays on the 1" DB is the matching transformer provides a very low input impedance. When percussion is selected, the 25VDC on terminal K is grounded through the TWG filter. The transition from 25VDC to ground is what triggers the percussion. Terminal K presents a higher impedance so if you have a dendrite short of 200 ohms say, this is enough to pull the trigger voltage down and no transition will be seen. Current flow will always take the path of least resistance.

Jim

[Von R. Colborn]

Jaim, are there any disassembly instructions for getting to the switches so that they can be disassembled and cleaned? Recommendations on contact cleaner? I bought some from Home Depot (CAC QD Contact Cleaner). Is that a good choice for cleaning the switches, drawbar contact, etc.?

[Von R. Colborn]

Would those dendrites be in the switches for percussion control?

[Bobmann]

Go back up to post #5 and look at the video. It shows the disassembly of an A100 switch box.
As I said before, go ahead and clean out both switch boxes.
I use CRC QD cleaner as well, it is plastic friendly.

[Sweet Pete]

Would love to watch a two year time lapse of garage vs living room,insofar as the common unplayed atrophy;to witness the dendrite growth.
In my collection,the ones stored the best,and played the most?Work as intended.
The one with perc switches that did need cleaning,also a 1960 A100,already had new e-caps on the genny filters.......say what Bobmann....?
Don't know the story there,nice organ plays well looks great.Maybe it just sat around too long,nothing the last 100 hours didn't look after though.
After a 're aquaintance' break in period,it now works as intended.
People are quick to jump in with repairs that might not be as good as actually playing the darn thing.
Things do start working again,usually.Next up,ten hours on the B2.

[Von R. Colborn]

I like your thoughts Sweet Pete. I've been turning it on every day, playing it, playing with the switches, etc. I guess, as with lots of things, time can be a healer.

[Von R. Colborn]

Pete, here is a time-lapse video of dendrites growth. Not on a Hammond but was the best that I could find.
https://youtu.be/COMTYzqe_XE

[Bobmann]

It is impossible to know what work has been done on any Hammond. Perhaps the tech recapped without cleaning the switches.
I am pretty sure that the environment plays the biggest role in whisker growth. It is believed that heat and humidity helps create the ideal environment for whisker growth.
I have seen a CV that was in a living room all its life with hardly any whisker growth at all.
I have also seen a C3 that was also in a living room all it's life that had more fur inside than my dog's back.
Since these whiskers are really very fragile, they can be vacuumed or blown off easily, it is possible that the action of playing knocks the whiskers off. It is also possible that the heat generated from playing may keep the humidity levels inside the cabinet down.
The most common problem with organs that are not played enough is that the key contacts get dirty, and playing does indeed fix lost tones in most cases. If contacts are shorted with whiskers, no amount of playing will make it better.
Bottom line is that these instruments have been around 60 years or so, and it is impossible to know what environment they have existed in, and which pieces and parts may have been serviced. So, at this point all we can do is deal with each organ and it's condition and treat each issue accordingly.

[valotus]

Couple of weeks ago I opened vibrato rotary switch box from -73 A100, that suffered occasionally motorboating vibrato when c/v knob was turned. That was a typical dendrite issue as bottom plate was covered by thick fur of dendrite. Longest single hairs were easily over one millimeter tall. Now imagine similar view every zinc coated surface; inside switch boxes, amp housings, keyboards...

[Sweet Pete]

Bobmann has been a great help with his Youtube video's.Very informative,comfortable delivery of things we need to know!
Geo Benton has helped me out on many occasions as well.If you need help sorting out Hammond issues,you've found the right place!
Countless others as well!

Those zinc whiskers sure grow big in Finland!

That time lapse says it all.Thanks for posting.Sitting around unplayed,unplugged is a recipe for disaster.
Getting in there and cleaning is not impossible.Removing gooey foam from manuals is not impossible.
For someone who doesn't thoroughly play it the 'repair process' can go on .....I played my B2 back into shape before actually 'repairing' it.
George and Bob S in Oakland coached me through it on Hamtech.
That organ is a true survivor,so glad I played it back into the condition it should be.
Will be firing it up for a few sessions later this week.
I spent most of the last year tech time working on Leslies.....repairing,rebuilding,refurbing.
Haven't turned over the gig A100 in a few months either,it's winter....
spring just around the corner and it's Hammond time again.
A nice sunny day to take a few pics of the boxes too! Maybe a 'family' shot,LOL.

[Tim_at_Jonas]

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 that comes out of the back of the drawbar base behind the right end of the percussion switchbox and goes to the left tab of the terminal strip on the back of the upper manual (wires are white, green, yel, yel, red, or, red, brown - there's a resistor on there too) . Turn the percussion tablet to the ON position. Zap the wire. Turn the percussion tablet to the OFF position and repeat. If it does not work, try a higher zapping voltage.

------------

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 (or one of the tube socket pins) and get about 290 Volts from it. Be "real careful" if you do this - don't short it to ground!

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 is what
finally cured the one I was working on.

[Sweet Pete]

Thank you Tim for the methodology!
Que "Been A LongTime Since i Rock-N Roll" but yeah,
that's how that issue is dealt with!
Traced an M3 right back to the black wire in the switches more than once.
And that 12AU7 perc amp tube 'pin' has more than enough juice to zap them with.
I keep one arm behind my back on that procedure.

[Von R. Colborn]

Tim_at_jonas, Is the dendrite problem to which you refer in the percussion switches? I took the assembly apart and cleaned the percussion switches, as well as the Soft/Normal, ON/Off and Chorus/Vibrato Manual switches and the contacts on the rotating Vibrato/Chorus contact groups in the long, cam-controlled contact box (My Vibrato/Chorus is not working either). It made no difference for either the percussion or vibrato problem.

To recap, on my A100 the percussion problem is that percussion triggers on the first key press after turning it on. Subsequent key presses (after releasing the previous key, of course) do not trigger the percussion effect. Apparently, there is one particular tube in the pre-amp that is dedicated to the percussion?

Thanks for the troubleshooting techniques post. I would love to see more of those types of posts from the experts on here. Simply shotgun Ning by replacing all tubes, tearing things apart, etc. Without first doing some basic troubleshooting is not a great approach, in my opinion. Without understanding the problem it will be unclear how the problem was resolved. If someone else has a similar problem the only advice is to try a the b then c until the problem goes away. In software we call that hacking a solution.

Thanks,

Lonely in Utah. ( no Hammond support)

[RogerRabbit]

Von, I had the same problem in my C3. I followed the guide here http://www.dairiki.org/HammondWiki/P...roubleshooting and it turned out to be a dendrite problem Working fine after zapping - follow the instructions carefully for that part.

[Von R. Colborn]

So Roger, the dendrites problems that were cured by zapping were in the console switches for percussion? I actually took the top of the A100 apart and physically cleaned the switches for both the Tremolo and the chorus/vibrato. That exercise made zero difference.

The article was very good and informative. I have swapped some of the tubes and will do to the remaining today to see if anything changes.

Thanks

[RogerRabbit]

Not 100% sure they were in the switch box, but I followed that procedure 18 months ago and the problem hasn't come back.

[fmbeaumont]

Hello, I have an M3. The percussion is not working. I've searched for specific information about how to zap an M3, but all posts are for other models. I just want to make sure I zap the right points on this organ. Can anyone assist me here. I'm planning on using three 9v batteries in series. Need to things like....
1 do I remove the tubes
2 do I disconnect the wires an which ones ( ie K, etc.)
3 which wires do I zap
4 switch positions when zapping

Thank you in advance!
kind regards,
Fred

[tomboy]

hello, i also own a hammond a organ but mine is a a102 .first check the tube marked 12au7x it hangs up side down right below the tone generator.take the tube out clean the pins on it ,spray some deoxit 5 contact cleaner in the tube socket and while you have the can out spray all the tube sockets and clean all the tube pins .just make sure to take them out one at a time so you dont get them mixed up.but remember the tubes are marked with numbers and letters on them and also the amp chases are marked with what tube goes where. also get you self a tube tester so you can check the tubes and fine someone that has one to have them all checked out. last take a screw driver and turn the percussion adjust screw ,its the amp box that hangs upside down below tone generator .its marked percussion cut off .you cant do anything bad here it just adjust the ping sound.hold a note down upper manual no drawbars out,but black preset down that says upper draw bars and percussion .turn screw driver till ping sound just fads away.this should solve you problem .this adjustment does get out of wack over time or you tube might be weak or bad for this sound.hope this helps .terry