I've been servicing an M3 at a nearby studio, everything works except the percussion does not decay properly (decays very slowly but never stops sounding), and does not reset unless you switch the percussion off and back on. All the tubes have been replaced and i've had a peek at the percussion control panel, I can't see anything awry. The percussion cut-off pot is fully Counter-Clockwise, even a 1/4 turn clockwise makes the percussion completely in-audible. It seems to be controlling the percussion volume, not cutoff. </p>
It's my understanding that a meter best checks for a shorted capacitor but not for a leaky one. There are a lot of good articles on electrolytic capacitors. Check Wikipedia or Google and do some reading. It'd be best to replace it and all it's capacitor brethren while you're under the hood. Pull the tubes, unbolt the amp, take some close-up pictures, and make a list of every cap, mfd. value and voltage. As you shop for parts, write the values of the replacement caps next to the originals on your list in case some of the replacement values are not exactly the same. Take notes as you work and draw diagrams to help you remember how to put things back. Also, pay attention to polarity as you remove old parts.
I've been servicing an M3 at a nearby studio, everything works except the percussion does not decay properly (decays very slowly but never stops sounding), and does not reset unless you switch the percussion off and back on. All the tubes have been replaced and i've had a peek at the percussion control panel, I can't see anything awry. The percussion cut-off pot is fully Counter-Clockwise, even a 1/4 turn clockwise makes the percussion completely in-audible. It seems to be controlling the percussion volume, not cutoff. </p>
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Flash the percussion circuit first. There is a very common problem with dentrite causing tiny shorts in metal enclosures. Take a 9-volt battery and connect one terminal to ground. Take the other terminal and touch it to the "K" terminal on the preamp/amp chassis. This is near the percussion cutoff pot. After flashing, check the percussion. You will have to re-adjust the decay pot. If it doesn't work, try two 9-volts in series.</p>
Right on George, that sounds like a very interesting fix. I'll give it a go and report back. </p>
By "ground"...what does that mean exactly? Piping in the building? or the amp's chassis? (btw, the amp still connects to AC with two prongs, No ground pin on the plug)
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Just to confirm, the two battery set-up would be as follows? </p>
GND to negative on battery one, positive on battery one to negative of battery two, Positive on battery two to K terminal? (btw, which colour wire connects to K?)
George - I was skeptic at first, but the battery trick worked!...somewhat, though it did make an improvement.</p>
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The percussion now works as normal but not indefinitely. I get it working for about 5, 10, sometimes 20 seconds and then it dies - I need to re-set the on/off switch to get it back. I noticed it never lasts as long (usually 5 seconds) if I change between the fast/slow positions on the decay switch. </p>
OK. I would try more voltage. We technicians routinely use the DC voltage already in the amp circuit to flash the percussion and vibrato. This isn't for the faint of heart though. I typically pull the 12AU7 tube on the right end. Then, I take a clip lead wire and connect a small screwdriver to it. The socket has a "key" which is the area with no holes. Counting counterclockwise from the key, the first pin is pin one. There is a couple of hundred volts DC there. I place the screwdriver with the clip lead attached into that hole. The other end is touched to terminal "K" briefly. There will be a spark so be ready. As long as you don't touch any metal you will not feel a thing. The percussion should start working.</p>
In some extreme cases I will do this with the percussion switches in each position. Now if that doesn't fix it, you have a problem other than the dentrite issue. BE CAREFUL! :o)</p>
I found the HammondWiki article about flashing and I have a few new concerns - </p>
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First, the author(s) say this procedure may cause problems with other areas of the organ (even if done correctly), and Second, sometimes the procedure is carried out on other terminals (H, J, M, and N wires) AND sometimes the wires are to be disconnected at the terminals before flashing. Thoughts?
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The article mentions that this is a shorting problem - and I should check the resistance between K and ground to find a few hundred ohm reading (supposibly, if this is actually a dendrite problem), as well as normal operating voltage readings at this point. However this article was written with a console in mind - can I follow its instructions precisely? (i'm not sure about the discrepancies between the AO-28/29 in regards to this procedure).
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I have serviced Hammonds for over 30 years. I will never intentionally give out incorrect or misleading info. I may accidentally do that though :o( </p>
I have flashed percussion and vibrato circuits for decades. The only failure this ever caused, was to blow out the rectifier tube because of a larger than typical short. That it why I don't advise people to get the High Voltage from the 6x4 circuit. By getting it from the 12AU7 percussion socket, you have enough isolation to prevent rectifier damage.</p>
Yes, the other terminals may be flashed too but I always do the K terminal and then check it. That usually fixes it.</p>
Dentrite is a metallic growth that forms on metal surfaces that have a lot of tin in it. You can go to NASA's site and actually see microscopic pictures of this problem. These growths occur inside the preamp, percussion switch box, vibrato switch box, vibrato scanner etc. Even in the manuals themselves. Flashing is a technique of applying a voltage that can "burn" away any shorts caused by the growth. Of course you could fully disassemble all these metal boxes etc. and clean them manually. In fact, that kind of repair would likely last longer. Many will disassemble the vibrato scanner for example and after cleaning, paint the metal surfaces to prevent this growth from returning. I have rebuilt many scanners but never painted one. I still have not had to rebuild any scanner that was already rebuilt.</p>
BTW. The new standard adopted by EU and coming soon to a technology product near you is the complete removable of lead from solder and parts. RoHS is the standard and you will find this label on products already. The idea is that when these products are throwned away, the lead "could" leach into the ground water and raise the lead levels. Sounds right, but studies have shown that lead in solid form does not do this. I would never advocate any practice that worsened our water supply but I am dubious of this idea. I believe it's a typical over reaction to a perceived problem. Guess what, NASA and other Governments are exempt! Why? Because they made the case that lead makes better products. As you know, solder is usually a mixture of lead and tin. Well, as we know, lead lowers the melting point of solder but it turns out that another benefit of lead is it reduces the metallic growth in the tin. Solder with no lead has no natural way to supress the growth meaning that products made with no lead content won't leach lead into the enviroment and also won't last very long.</p>
I went back today to hook up my cheapo 147 kit, when it came time to add the power section I took off the protective cover at the AC terminals on the M3, and proceeded to check to the switched/unswitched connection points with my multimeter. I don't know what happened but I ended up blowing out my test probe leads a large blue zap and some sizzle and smoke. I thought at first the meter was fried (I realized the + meter lead was not plugged in the correct location - 10A instead of VOmA) however now i'm checking and the meter is fine, and neither test lead has continuity. </p>
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Now, I dont know if this came before or after me flashing the percussion circuit. (I used one of the meter leads to flash it - the pointy end in the tube socket (Pin 1 CC) and the stubby end on the K terminal). There was no spark, but only a click through the speaker. The percussion seemed to work in the 2 mins I had to test the organ. </p>
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I need Brown and Grey for switched power, correct?</p>
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