X77 Percussion Issues

[Beach324]

In 2011 I purchased this one-owner X77 with X77L Leslie speaker from the family of a church organist. She purchased the organ new in 1971. When I purchased the organ it had some issues and by working with various subscribers to this forum, I was able to fix everything that bothered me then. The organ plays beautifully. However, there is one feature of the organ that still has issues. That's the percussion section. I am not a big fan of percussion, but I could be if it worked properly. On some tabs there are notes that do not play. It's the same notes in each octave, but could be different notes for each problem tab.

I would not know where to begin searching out the problem, but I am real good at following suggestions and I have fixed a few things on the organ this way. In 2011 I purchased all new caps and electrolytics but have never replaced any of them. I don't have hum or other noises from the speaker other than a squeak in the lower assembly arm that moves back and forth.

If someone would care to walk me through some places to look for percussion problems, I would be grateful.

Thanks !

Larry

[Admin]

There are two percussion systems in the X77, the Harp, and everything else. The Harp is different in that the notes continue to decay after the key is released while for the other percussions the note decays only while the key is down and is cut off entirely when the key is released.

So the first question is which percussion voices are not working?

If it's Harp notes, the problem is in the harp keyer wiring or circuitry, which is mounted to the back panel, or the harp keying contacts for those notes

If it's the main percussion voices missing notes, it has to be the percussion contacts for those notes that don't play since the percussion gate is common to all notes.

Percussion problems are often to due to dendrite caused contact shorts, but it's best to eliminate dirty contacts, broken wires, and malfunctioning circuitry as possible causes first.

[Beach324]

The harp works perfectly. Marimba does not work at all. All other percussions tabs have issues. Mostly there are notes that do not play. With chimes it is not possible, for instance, to play the Westminster Chimes tune because after about three notes the next note will not play. I cannot play one note after another with chimes because the chime effect fades away until I give it a second or two to recover. I'll make a short video of some of these issues. It would be easier for you to actually see what is happening rather than me trying to describe it.

[Admin]

Sounds like there is more than one issue, but I'm also wondering if you're misunderstanding the capabilities of that percussion system. Perhaps a little background would be useful.

First, it's important to know that because of the way TWG Hammonds generate and key audio, Hammond percussion, and this true of all TWG Hammonds, does not work the same way as percussion voices on other organs. Here, and in what follows I'm referring to the main percussion system, not the Harp.

As I pointed out previously, the Hammond percussion voices only decay while keys are held down, whereas, typically on other brands, the decay either starts and/or continues when the key is released. In addition, the X77 has four different percussion modes: "Normal", Touch Response, Reiteration, and Second Voice.

In the Normal mode the percussion is triggered with each keypress, even if other keys are being held down. Using Chimes as an example, if you play a single note, it is necessary to continue holding that note while the tone decays. Once you release the key, the chime ends abruptly and unnaturally. It won't sound much like a chime if you play the key and release it immediately because there will be no decay. This makes playing a sequence of chime notes difficult because the only way to get each note to properly decay is to continue holding it while you play the next notes in the sequence; however that doesn't work because each new key press re-triggers the other notes being held down. So if you are holding C while it decays, playing the next note in the sequence, say E, will re-trigger the C as if it was struck again, and it will be like the C and E were struck simultaneously. This is a limitation of the system.

The Touch Response mode, which is a holdover from the earlier -3 models, works differently. You still have to continue holding keys down to allow the decay to occur, but the percussion is triggered only by the first key pressed. So, if you play and hold the C and next play the E, the held C is not retriggered and continues to decay, but the E and other subsequent notes will sound at the level the C has decayed to. If the C has decayed all the way out, no other percussion notes will sound until it, and all other held keys, are released, in effect, re-arming the trigger. Perhaps that explains your Westminster issue.

In the Second Voice mode, the percussion voices don't decay at all. They sound, without decay, for as long as the keys are held and stop when the keys are released, just like the regular voices.

Problems with individual percussion voices are likely problems with the tab switches. Dead notes that are common to all voices are likely the result of bad contacts.

There is also another percussion mode on the X77, the reiteration mode. Two voices, the marimba and xylophone have a "twin-mallet" feature in this mode which involves additional circuitry, but problems with twin-mallet would not affect the other modes.

[enor]

Are you sure? On the E-100, the percussion trigger signal always comes from the reiteration module, regardless of whether reiteration is switched on or off. I was under the impression that the H-100 percussion worked in the same manner.

[Admin]

enor Yes, the percussion triggers originate in the same circuitry regardless of the mode. I was referring to the twin-mallet reiterating percussions which involve additional circuitry to accomplish the effect. That circuitry should not affect the operation of the triggering of other percussion voices or other non-reiteration modes.

[Beach324]

Sounds like there is more than one issue, .

I have uploaded to files a spreadsheet in .pdf format that illustrates the problems I am having with the percussion tabs. The file is located in Larry's Hammond X77GT in the files section. There are six notes involved - D, D#, F#, G, A# & B. The uploaded file illustrates for each percussion tab which notes fail to play when the tab is down. I played each note on the upper keyboard for each tab and recorded which notes are not playing. Second Voice and Touch Control tabs UP. I then put the Reiteration tab down and performed the same exercise, recording which notes for each percussion tab are not playing. There are a few differences.

I would like to eliminate dirty contacts as a first step, but I need some instructions on where to find these contacts and how to clean them. Thanks for all the assistance !

[Admin]

The first thing to do is to get all the notes playing properly on the upper manual with drawbars on and the percussions off. The percussion voices are keyed with the same contacts as the drawbars, so if the drawbar harmonic doesn't play, the percussion harmonic will not play either. Play every note with each of the drawbars drawn individually. Note which notes are dead for each drawbar and remedy the problem. Dead notes can be caused by dirty contacts or broken wires from the tone generator. You can expect to have the same working and dead notes whether the A# or B preset is pressed. If the dead notes differ between presets, there are bad contacts under the preset keys.

Contacts can be cleaned by striking the dead note repeatedly or by shifting the manual bus bars. There is a brass colored screw accessible from the back at the end of each manual for this purpose. Hopefully, that will get the dead contact notes playing again. If not, you'll have to remove the manual chassis to remove and clean the bus bars. Not an easy task. It is not practical or recommended to attempt to clean the individual wire contacts under each key. If you open the manual chassis, the reason will be readily apparent.

Search the Forum for info on shifting and cleaning the bus bars.

Once you've eliminated the dead drawbar notes, you can revisit the percussion issues.

One other diagnostic tip. Start with the all the drawbars pushed in, the percussion tabs up, and the B preset selected. Next turn on a percussion tab, e.g. Guitar. If you hear a note when you activate the tab, the percussion keying contact for that note has a short, probably due to dendrites and will require zapping or manual disassembly to remove the dendrites wherever they occur.

[Admin]

It also probably be a good idea to clean the contacts on the percussion tabs by using a contact cleaner such as DeOxit. Hammond cut some corners in wiring those contacts and daisy-chained some of the connections through the contacts. If the contact is bad, it can affect the other percussion voices as well.

[bnelson218]

Another problem could be the 220k (or possibly 100k) voltage divider resistors which are in the manual assembly and are tacked at one end to an external, common buss, and to a TG frequency wire on the other. It's been my experience, with X77s and H100s that the welds to the common buss can break, or the resistor can become brittle and crack. If the same notes are dead, no matter what percussion voice is selected, I'd bet this is the reason. Unfortunately, getting at the innards of the manual means extensive disassembly and the unsoldering of a hundred or so wires. And in the end, your work would be futile since other welds and/or resistors are likely to fail. Bad news, I know, but while some Hammond designs were ingenious, and meant to last decades, others not so much.

[Beach324]

The first thing to do is to get all the notes playing properly on the upper manual with drawbars on and the percussions off. The percussion voices are keyed with the same contacts as the drawbars, so if the drawbar harmonic doesn't play, the percussion harmonic will not play either. Play every note with each of the drawbars drawn individually. Note which notes are dead for each drawbar and remedy the problem. Dead notes can be caused by dirty contacts or broken wires from the tone generator. You can expect to have the same working and dead notes whether the A# or B preset is pressed. If the dead notes differ between presets, there are bad contacts under the preset keys.

Contacts can be cleaned by striking the dead note repeatedly or by shifting the manual bus bars. There is a brass colored screw accessible from the back at the end of each manual for this purpose. Hopefully, that will get the dead contact notes playing again. If not, you'll have to remove the manual chassis to remove and clean the bus bars. Not an easy task. It is not practical or recommended to attempt to clean the individual wire contacts under each key. If you open the manual chassis, the reason will be readily apparent.

Search the Forum for info on shifting and cleaning the bus bars.

Once you've eliminated the dead drawbar notes, you can revisit the percussion issues.

One other diagnostic tip. Start with the all the drawbars pushed in, the percussion tabs up, and the B preset selected. Next turn on a percussion tab, e.g. Guitar. If you hear a note when you activate the tab, the percussion keying contact for that note has a short, probably due to dendrites and will require zapping or manual disassembly to remove the dendrites wherever they occur.

Ok. I have only one drawbar that does not play. It's the 2', upper manual, B preset. None of the notes sound with just this drawbar pull out. All other notes and drawbars work perfectly. There were a few keys that I needed to strike hard a few times, but now they play consistently. Here comes the glitch. This 2' drawbar does work with the percussion tabs.

I will admit that I don't use percussion and I am not at all sure how it is supposed to function. I have discovered that ALL notes on ALL percussion tabs work just fine if I staccato the notes. I can play a chromatic scale from one end of the keyboard to the other using staccato on every percussion tab and all the notes play. Now, if I stop and strike the same key more than once it begins to fade away after about the third strike.

I did "shift" the bus bar using the brass turning shaft, but I don't think that had any effect on anything. I could only find one brass turning shaft. It's on the left end of the organ when viewing from the back.

With all drawbars in, I don't hear any note when I activate the percussion tabs.

[enor]

If a drawbar voice plays thru perc, but not thru the drawbar itself, the likely cause is poor connection/dirty contacts in the percussion switch assembly. I've seen this a lot on E-100s and T-100s which use the same type of switch as the H-100.

What happens is - the clear plastic switch actuator bar (the "cam shaft") gets slightly bent and consequently the switches don't make a good enough connection. The solution is to bend the switch reeds slightly to compensate as there is no good way of straightening out the actuators. The correcting little bend has to be made in the lowermost portion of the switch reed, below the actuator bar, in order for the fix to work well.

[Admin]

The important question is whether the 2' drawbar plays with A# preset. If it does, the problem may be the percussion switches, as enor suggests, or broken wire on the drawbar or somewhere. Looking at the schematic, I don't see that the 2' drawbar signal is routed through those switches, but as I said, Hammond did daisy chain some of that wiring through those switches, so it's possible, and those switches are a source of trouble. I'd try cleaning those switch contacts as the easiest thing to start with. If the both upper manual drawbar presets lack the 2' harmonic, the problem is around connections to the 2' manual bus and, unfortunately, I don't have any suggestions on how to further isolate such a problem.

The problem with the decay sounds like the Touch Response tab is on. With Touch Response tab in the up position, turn on the Guitar with no drawbars drawn and play middle C holding the key down until the sound completely decays. While continuing to hold the middle C key down, and press any other key and hold it. This should cause both notes play and decay. If the second note fails to sound when you play it, this could be an indication that the percussion is in the Touch Response mode. Clean the contacts and check the wiring on the Touch Response switch.

[Admin]

I was incorrect. The 2' pitch for the B preset drawbars is routed through the percussion switches as are the pitches common to the percussion voices for all pitches.

[Beach324]

The important question is whether the 2' drawbar plays with A# preset. If it does, the problem may be the percussion switches, as enor suggests, or broken wire on the drawbar or somewhere. Looking at the schematic, I don't see that the 2' drawbar signal is routed through those switches, but as I said, Hammond did daisy chain some of that wiring through those switches, so it's possible, and those switches are a source of trouble. I'd try cleaning those switch contacts as the easiest thing to start with. If the both upper manual drawbar presets lack the 2' harmonic, the problem is around connections to the 2' manual bus and, unfortunately, I don't have any suggestions on how to further isolate such a problem.

The problem with the decay sounds like the Touch Response tab is on. With Touch Response tab in the up position, turn on the Guitar with no drawbars drawn and play middle C holding the key down until the sound completely decays. While continuing to hold the middle C key down, and press any other key and hold it. This should cause both notes play and decay. If the second note fails to sound when you play it, this could be an indication that the percussion is in the Touch Response mode. Clean the contacts and check the wiring on the Touch Response switch.

The 2' drawbar plays on the upper A#, lower A# and B presets. Does not play on upper B preset. How do I clean the switch contacts?

The guitar tab operates normally as you described above. Keys being held down repeat with the next key depressed.

[Beach324]

If a drawbar voice plays thru perc, but not thru the drawbar itself, the likely cause is poor connection/dirty contacts in the percussion switch assembly. I've seen this a lot on E-100s and T-100s which use the same type of switch as the H-100.

What happens is - the clear plastic switch actuator bar (the "cam shaft") gets slightly bent and consequently the switches don't make a good enough connection. The solution is to bend the switch reeds slightly to compensate as there is no good way of straightening out the actuators. The correcting little bend has to be made in the lowermost portion of the switch reed, below the actuator bar, in order for the fix to work well.

I would like to do what you suggest, but I don't know how to do this. Can you give me some detail on how to access the parts you mention? If it involves taking the organ apart to reach these parts, then I won't bother since I could mess up something else and create a larger problem. Been there, done that 10 years ago. Back then it took a full week with indianajo's help to fix what I messed up.,

[Admin]

You can spray the percussion tab switch contacts with contact cleaner by opening the back of the organ, removing the screws that hold the top in place, unplugging the music light, and removing the metal cover over the switches.

[enor]

I would like to do what you suggest, but I don't know how to do this. Can you give me some detail on how to access the parts you mention? If it involves taking the organ apart to reach these parts, then I won't bother since I could mess up something else and create a larger problem. Been there, done that 10 years ago. Back then it took a full week with indianajo's help to fix what I messed up.,

Take the top off the organ, and you should see the switch assembly. You may also need to remove a metal cover. Then use a small screwdriver to do the bending.

[Beach324]

You can spray the percussion tab switch contacts with contact cleaner by opening the back of the organ, removing the screws that hold the top in place, unplugging the music light, and removing the metal cover over the switches.

To remove the top, is it the two screws on either side, on the side wall of the case? Or are the screws underneath the top?

[Beach324]

Take the top off the organ, and you should see the switch assembly. You may also need to remove a metal cover. Then use a small screwdriver to do the bending.

OK. Got the top off and Marimba is now working. Just needed to clean the contacts. Now I need to figure out why the 2' harmonic is not working on the upper B preset. The 2' harmonic sounds steady with the harp, glock, or guitar tabs down. This must mean there are no broken wires, TG problems or other components which would prevent it from sounding at all since I can get 2' harmonic to play under those circumstances. So, what could cause it to not play when only the 2' drawbar is out?