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Hammond A100 dead percussion (not even a ping!)

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  • Hammond A100 dead percussion (not even a ping!)

    Hi everyone,
    After reading numerous posts here about A100 percussion issues, learning tons of information, I finally joined the forum ... with the hope of solving my percussion problem.

    Mine is an English A100 from the early 60s (ca 1963). I see on the maintenance chart that it has been serviced in 1973. I bought it in France in 2006, with a Leslie V770. Percussion was working just fine until last October. I suspect no particular event, or shock, or anything, it just sopped working.

    Many people here do have a "ping" when turning the percussion tablet ON; I don't, it's "fully dead", if I may say so!

    Prepare for a long reading, here is what we did so far:

    - move all the percussion tablets back and forth repeatedly, spray some deoxydant.
    - change all the percussion tubes (12AU7, 2x6C4 + 2x6AU6AW), clean all the pins and sockets with deox.
    - move the percussion cut off screw (far left, far right, back to initial position, a lot of times).
    - opened the percussion "box" to clean the inside: there were some dendrites on the inner sides, we removed them. Meticulous cleaning, deox. We didn't dismantle the whole thing, just cleaned meticulously "from the bottom".
    - did all the testing we could, following Tim Padrick's test (post#11) & The famous troubleshooting page.
    - test: organ turned on / B preset / percussion OFF / maintaining several keys down --> percussion ON = no ping at all
    - took some measurements:
    organ turned on / no presets : ca26V at terminal K
    organ turned on / B preset / percussion off : ca 26V at terminal K
    organ turned on / B preset / percussion on (no key depressed) : 0V at terminal K
    - zap the WH-GR-YEL contacts of the resistor panel, following this tutorial:https://www.youtube.com/watch?v=f53EnpKKrYA.
    - zap the K terminal
    - unsold and resold blue wire at terminal K (it was old and ugly)
    For the zapping procedures, we used 2 9V batteries in series. I won't be as brave as some of you are, using 200V & more. Life is short, I don't want to make it shorter!

    None of this brought my beloved percussion back :-(

    I had the opportunity to talk to a Hammond tech on the phone (there are only 2 In France, to my knowledge). He advised not to do any more zapping, as it could damage other circuits. He thinks the problem most probably comes from a short in the upper manual, caused by dendrites or a broken palladium thread in a busbar. He would also inspect the A028 preamp.

    He won't come to my place, he doesn't want to. I live some 140km from his workshop, which is not much, but my organ is located on the 3d floor of the building, my health condition doesn't 'allow me to lift the beast and, being relatively new to the city, I have no friends that I could "trap" with apple cider and a good meal to do this delicate lifting job ... So moving the organ to the tech and back would cost approx. 800 to 1 000€. The repair job would be at least 2 000€ I guess.

    So here I am.

    I'd love to send my organ to the tech, but I'm afraid my budget won't allow me.
    I'm ready to dive into the guts of the organ, but need some step-by-step guidance to do so. I have Alain Kahn's DVD "Hammond inside", but he's working on a B3, I don't know if the A100 would imply the exact same manipulations. If I can avoid to unsolder every single wire, I would be very happy!

    Do you think I can/should do anymore testing? Where, how?
    I have never seen a step-by-step guide to get access to the contact box of the upper manual. Do I have to fully remove the upper manual from the organ to access the contact box, or can it be done just by removing the keys?
    Can you guide me through this? Like tell me what I have to put out of the way, what to unscrew, etc.

    Your help would be very much appreciated. Actually it is already: the forum has already taught me a lot.
    Not hearing the percussion is so depressing.

    Thanks for reading this long piece of writing!
    Last edited by SoSu; 02-25-2021, 10:01 AM.

  • #2
    organ turned on / B preset / percussion on (no key depressed) : 0V at terminal K
    This usually indicates a dendrite problem. On back of the upper manual you should see the colored wires coming from the manual to the preset tabs. As you look at it, the wires in the left most set should come from the b preset key. Follow the white wire to the resistor panel. Un-solder and with the b preset engaged, measure the resistance to ground. If you read something, the problem is in the manuals. With the presets cancelled. Try shifting the busbars to see if it helps.
    It it reads open, then the problem is in the percussion switches.



    • #3
      Like Jaim said: 0V with percussion on but without any keys down means that you have a short to ground, either in the switch assembly or in the manual.

      Start by desoldering the wire from terminal K. Push all drawbars in. Switch percussion on and select 2nd harmonic. Now, what you should have is a continuous tone that sounds just like drawbar #4 on full volume. Two things might happen:

      1. You get no tone. This indicates that you have other problems, either with the wiring or with the preamplifier itself.

      or 2. You get a tone. Now, keep holding the key while shorting terminal K to ground with a short piece of wire. Did that cause percussion to decay? Good - you now know your preamp is working as it should, and your problem definitely is the short to ground, and nothing more.

      But no matter how the above turns out, regardless if the preamp is operating right or not, you still need to adress the short.

      Since you didn't take the perc switch assembly apart for cleaning, you really only cleaned half of the assembly (the bottom half) and potentially missed dendrites on the top half of the casing. Get back in there and finish that job first.

      Then, if the problem persists, you're lucky you have an A-100 because it is possible to clean out the manuals with compressed air without taking the manual out. But it's not the easiest job out there so do the switch first!
      Current organs: AV, M-3, A-100
      Current Leslies: 22H, 122, 770


      • #4
        Thanks very much Jim for taking the time to respond!
        Your diagnosis concords with the tech's: he suspects we do have dendrites in the upper manual (and we found many dendrites on several other places). He doesn't believe that the problem is located in the percussion switch box which I already cleaned. I don't understand why, but the test he made us perform (ie organ on / no preset / 26V at terminal K) narrows the problem to the upper manual.

        We now plan to access the upper manual's contact box. On the A100, do you know what we have to put out of the way to do so? Is it absolutely necessary to unsolder everything (preset panel, resistor panel, etc.) or can we do the job in a less intrusive manner? I don't know exactly what has to be removed and in which order. My dream is to see a step-by-step guide for dummies of this procedure in the A100!

        Thanks in advance for your help

        Sophie & Patrick


        • #5
          The test you describe does NOT narrow it down to a fault in the manual, the possibility of a short in the upper section of the switch is still very real (and in my experience, much more common than in the manuals anyways).

          Also, it is very weird that you don't get that initial ping when turning percussion on - if your problem was ONLY a short, you should be getting one ping. Thus the amp check I was talking about.

          You shouldn't need to unsolder much, but perhaps unscrew a couple of items and lay them to rest on the generator (put a towel on the generator first). Then remove all keys, and you can access the "lid" over the contact assemblies. This page has a lot of good pics on the matter: http://hammond-c2-restoration.blogsp...on-part-1.html
          Current organs: AV, M-3, A-100
          Current Leslies: 22H, 122, 770


          • #6
            The big advantage of the A-100 is that the top comes off, offering much easier access than on a B3/C3
            Current organs: AV, M-3, A-100
            Current Leslies: 22H, 122, 770


            • #7
              Enor is absolutely correct. Exhaust all possibilities before you dig into the manuals. Let us know what the results are.



              • #8
                Enor & Jim,
                Thank you so much for taking the pain and time to respond. It's overwhelming to receive so much help, with such detailed info and advice.
                The last few days have been a rollercoaster of enthusiasm, disappointment, hope, discouragement, etc. Your help cheers us up!
                It's now 11pm here, it's too dark in the organ's room to make sure I don't desolder M instead of K :-)
                We'll try your suggestions tomorrow and let you know how it goes.
                Thanks again!

                Sophie & Patrick


                • #9
                  Hi everyone,
                  Here is today's update:

                  - We did what Jim suggested on post #2:
                  Unsoldered WH wire of B preset on resistor panel, took some measurements.
                  [I write down everything I did: I probably took some useful and some silly measurements, as I'm a total noob in electronics, please be gentle on my lack of knowledge, I'm here to learn! Ohm meter was set on 20K]

                  B preset engaged / perc OFF, mes. taken between "resistor tab" & ground -> 0
                  B preset engaged / perc OFF, mes. taken between WH wire & ground -> 0,36
                  B preset engaged / perc ON, mes. taken between "resistor tab" & ground -> 0
                  B preset engaged / perc ON, mes. taken between WH wire & ground -> 0,36
                  resolded WH wire back in place.

                  - We did what Enor suggested on post #3
                  Unsoldered BL wire on terminal K
                  B preset engaged / all drawbars pushed / perc ON / 2nd harmonic / normal volume -> no sound at all

                  Took some measurements, just in case [Ohm meter set on 2000]
                  B preset engaged / perc ON, mes. taken between BL wire & ground -> 65
                  Any other case, taking the mes. between K tab & ground or BL wire & ground, result is 0.

                  - cleaned the percussion box

                  - shifted the busbars (upper manual, no key or preset engaged) -> terrible FAIL; now many notes are "coughing", or coming long after I hit the key.
                  After turning left and right, I set it, in a totally blind fashion. That brings a new problem: on B Preset, 16’ drawbar, harmonic notes are not all coming on some notes. Some other notes are like having a bad cough: busbar must not be in the right position and it creates bad contacts. Same with the other drawbars.
                  Have no clue on how to set it back to its original position to get all the notes clean.

                  What do you think should be the next move?

                  After shifting the busbars a little bit (one last time !), it got better. By doing staccato on the coughing keys, the notes sound again, almost 100%.
                  Last edited by SoSu; 02-26-2021, 09:19 AM.


                  • #10
                    Shifting dirty busbars is like playing the lottery. Yes you might get lucky and find a better working, clean spot but odds are strongly against you. At this point, I'd say that cleaning the busbars is the only good way to remedy the situation.

                    Also - your preamp needs attention. Your little experiment proves that your amp has some sort of problem, unfortunately so although you still need to clear your short, that alone isn't going to fix your issue.

                    So in summary - your best path is to take the manuals out, clean the busbars and remove dendrites while you have easy access to everything. Then, find and fix the problem in the amp. George Benton's site has excellent service info for the AO-28: http://bentonelectronics.com/servici...-type-pre-amp/
                    Current organs: AV, M-3, A-100
                    Current Leslies: 22H, 122, 770


                    • #11
                      Thanks very much Enor.

                      As you say, busbars and contacts must be super dirty.

                      Some questions:
                      - would it be sufficient to remove only the upper manual, or do we have to remove the upper & lower manuals?
                      - can you guide us through the whole process, meaning: what should we remove (with minimal unsoldering)? in which order?

                      We are very inexperienced with electronics & mechanic (well...you could guess that). We try our best to learn and are scared of making things worse.
                      The first link you gave has fantastic pictures, but like A. Kahn, the man dismantles everything to make it new, so it makes sense that he takes every single screw and wire apart. We're just trying to remedy the issues with no additional damage of our own.

                      We'll follow your advice: take care of the busbars/contact box first, then the A028 (although we don't understand the diagram from Benton electronics, but we'll address that later).

                      Thanks ever so much for your time, knowledge, energy and kindness!


                      • #12
                        I'm not sure how you want to proceed. I agree with Enor that the manuals should be remove to clean the buss bars.
                        However ...
                        You could try and get the missing tones to sound by repeatedly hitting the key to see if the footage comes back and live with the percussion problem.
                        Remove the keys from the upper manuals to see what's going on. I'll add a procedure (from memory) and you can use your best judgement.

                        Access to the upper manual key contacts can be gained without unsoldering any wires.
                        1> Remove power.
                        2> Use thin plastic or cardboard to protect the sides of the cabinet from scratches from the drawbar base and front rail.
                        3> The drawbars should be pulled out.

                        Top removal:
                        1> Remove know off reverb control and remove hex nut holding pot.
                        2> Remove 4 screws holding the start/run switch plate and gently lift to expose switches. Back off the hex nuts and remove the knurl nuts on top by hand. If you use a pliers on the knurl nuts you may scratch the plate.
                        3> From the back, remove 2 screws holding pilot lamp. Upon installation, make sure lamp contacts are not shorted.
                        4> The top is held on by 2 screws on each side and 3 screws in the back rail. The big flat washers are used as spacers.

                        1> Remove big slotted screw on both sides. This screw also holds the manuals together. Remove 2 small slotted screws. Gently raise Drawbar base.

                        1> The bar which has the dust felt on the back of the upper manuals is held on by 2 small screws. Remove.
                        2> Raise the upper manual and prop up with 1" spacer. (1x2 works good)
                        3> Remove the screws front black rail. The rail has an adhesive so be careful not to bend it.
                        4> Keys are held by a 1/4" slotted hex screw. I generally use a nut driver. You have to be creative by the preset panel. Loosen about 1 turn. Do not remove screws.
                        I number the keys so they go back in the same order. Remove keys. The little dimples in the key spring steel help align the keys.

                        Key contact Cover:
                        1> Remove screws.
                        2> Pay attention to the location of the felt used to seal the back.

                        The key contact stack follows the drawbars. 16" on the bottom and 1" on top.



                        • enor
                          enor commented
                          Editing a comment
                          You don't really need to remove the front rail to get the keys off (and therefore you don't need to raise the top manual either)

                      • #13
                        Jim you're an angel!
                        Your step-by-step guide is precious, we'll print it for tomorrow's operations.
                        It's perfectly clear; we're amazed that you did it by memory.
                        Fortunately, we got the missing tones back, by hitting the keys repeatedly, as you recommend.
                        We'll try to be creative around the preset panel :-)

                        We'll start by cleaning the inside of the key contacts "box" and will come back here for the next step: cleaning the busbars (so lifting the upper manual completely, I guess?)

                        Many many many thanks Jim🙏!


                        • #14
                          So, we only did some thinking today, studying the organ to see how we'll proceed to remove the keys to access the contact box (I guess we'll have to remove the preset keys as well).
                          3 places we'll be tricky (see pics here):
                          - the preset panels https://i79.servimg.com/u/f79/20/13/80/10/img_7612.jpg
                          - the resistor panel https://i79.servimg.com/u/f79/20/13/80/10/img_7610.jpg
                          - the vibrato line box? (red cylinders) https://i79.servimg.com/u/f79/20/13/80/10/img_7611.jpg

                          We finally fully understood the preset panel's wiring. We made a short document to make it clear for us, using this link as a reference (standard presets).
                          Might be useful for other noobs like us!

                          Do you think we should remove what we think is the vibrato line box (removing only the cardboard on top, or the screws on the chassis?) & resistor panel (removing the 2 screws)?


                          • #15
                            When you say "remove the keys", do you mean "remove the keys" or "remove the keyboard assemblies"? Because there's no need to remove preset panel, resistor panel or vibrato line box in order to just take the keys off.
                            Current organs: AV, M-3, A-100
                            Current Leslies: 22H, 122, 770