Allen ADC-6000 Mystery Repair

[myorgan]

Hello all,

A couple of days ago, my wife and I reconnected the Symphony's Allen ADC-6000 to re-voice it and make sure it was in working order for the upcoming season. It wasn't!!!

Problem: When we tried the organ, half of the Swell was out of tune, and B below Middle C sounded the same note (just a few cents off). This was consistently true throughout the range of the keyboard, and the notes appeared to be random--no pattern so we could predict what would be out of tune or a wrong note.

Diagnosis Steps:

• We switched speakers--the issue just switched speakers.
• We switched amplifiers--the issue just switched with the change.
• We switched cage outputs/amp inputs--the issue just switched with the change.
• Now what?

Problem Clarification: The problem is ONLY on all stops of Channel 1 (including the Alterable on that channel). With that information, and knowing that channel spans 5 groups of stops over 3 cards, I'm pretty sure it's nothing to do with the cards in the cage.

Where do I go next? Thanks in advance for y'all's help.

Michael

P.S. I may not be able to respond until Sunday due to other engagements until then.

[toodles]

Michael,

I'm no expert, but I would suspect one of the FG (Frequency Generator) cards. It's definitely an issue within the cage, and since your channel voices spans 3 TG (tone generator) cards, it's most likely the Frequency Generator that they share in common.

You might be able to determine which FG card by looking at the voicing chart for the organ, as those usually identify which TG cards are supplied by which FG card.

I can only guess how the cage cards work, but FG = frequency generator, EG = envelope generator, TG = tone generator, from what I know; thus the FG produces the frequencies needed, EG give the speaking envelope, and TG plays the sound at the frequency determine by the FG--that my limited understanding based on the functions that have to occur within the cage.

Toodles.

At first, try unplugging it and replacing. It could just be a connection issue.

[myorgan]

Toodles,

You are a genius. I had forgotten about the FG cards and was totally baffled. I'll see if my local repair man has a copy of that card in his kit and will exchange it to see if it solves the problem. I'm quite positive that's what the problem probably is.

We discovered the troubles upon first connecting the organ. I had gone in to maintain it and do the vaseline trick JBird604 talks about (worked wonders on my organ at home--got rid of the Snap, Crackle, and Pop!), and it continued even after 2 re-seatings of the card. I have a static bag somewhere and can send it off for repair or replacement.

One thing I've noticed on both ADC organs, though. When re-seating all the cards, evidently there's some "give" on the backplane because I've discovered that when I take out a group of cards and replace them, the card(s) next to the one I insert become slightly dislodged. Consequently, I've taken to giving them one last nudge to make sure they are all seated properly before I replace the cage cover.

Toodles, thanks again for your reminder.

Michael

[jbird604]

Michael,

Toodles is right. There are USFG-1 boards in slots 17 and 18. The one in slot 18 is probably the one acting up. To test this, pull out both of them and swap slots. The problem will now move to the opposite set of Swell and Alterable stops.

There may be a socketed chip or two on each FG board. If so, use a very thin screwdriver to carefully pry the chip(s) from the sockets. Take note of the orientation of any chip you pull -- there is a notch or big dot on the #1 end of the chip which corresponds to a notch or other marking on the socket and you MUST put the chip back in the same way it was installed.

With the chips out (I'd pull only one at a time), clean the legs of the chip by scraping gently with a pocket knife blade, then coat with Vaseline and wipe most of it off before re-inserting into the socket. Be really careful not to bend any legs of the chips! You may need to straighten the legs out before re-inserting if any of them got bent in the process of being pulled out. As you insert a chip be absolutely sure that all the legs are actually going into the socket and not curling up underneath the chip.

Of course, you'll want to put a bit of Vaseline on the board's connector as well before re-installing in the cage. I'm not sure that FG boards have any socketed chips on them, but if they do this might help.

To be doubly sure that you have located the defective FG board, you can move the suspect board into slot 7 and you'll find that the problem moves to some of the great and pedal stops.

You know, of course, that there's little likelihood that you'll find anyone to repair the FG board, so you'll have to send it to Allen for exchange. It's even possible that they no longer exchange those boards and will force you to buy a new one outright.

But if you follow this process you will have done your part of the job! Good luck!

BTW, there are also some USFG-2 boards in that organ, but you can't swap them for FG-1 boards. For testing purposes, swap only FG-1 for FG-1.

[myorgan]

John,

As always, thanks for your guidance. I didn't realize the FG boards could be swapped between them, but I guess that makes sense since they're only producing the frequencies--not the tones (TG).

Thanks again.

Michael

[myorgan]

There may be a socketed chip or two on each FG board. If so, use a very thin screwdriver to carefully pry the chip(s) from the sockets. Take note of the orientation of any chip you pull -- there is a notch or big dot on the #1 end of the chip which corresponds to a notch or other marking on the socket and you MUST put the chip back in the same way it was installed.

Of course, you'll want to put a bit of Vaseline on the board's connector as well before re-installing in the cage. I'm not sure that FG boards have any socketed chips on them, but if they do this might help.

BTW, there are also some USFG-2 boards in that organ, but you can't swap them for FG-1 boards. For testing purposes, swap only FG-1 for FG-1.

John,

From your note, can I assume that the FG-1 from the ADC-6000 cannot be put in an FG-2 or FG-3 slot on the ADC-4300 for testing purposes? I pulled the offending board today and have it at home for repair, but don't have anything to test it on here. It's supposed to rain tomorrow, and I hate to be in the cold garage testing the board.:-(

You were right, in that the FG-1 board of the ADC-6000 DOES have 1 socketed chip on each FG-1 board on the Swell. Should I assume this is where the voicing also comes from (i.e. Romantic, Mean Tone, Equal Temperament, etc.)? I have noticed that on the ADC-6000 the Swell appears to be Romantically voiced, while the Choir appears to be Classically/Baroque voiced. I wonder if switching that chip out would change the voicing of the Swell--or if I even want it. In some sorta weird way, it makes sense to have one manual voiced for Romantic literature (Swell, in this case), while another is voiced for Baroque or Classical literature (Choir).

As always, thanks for your help.

Michael

[jbird604]

Michael,

The socketed chip on the FG-1 board is a "frequency number" chip which contains a table of frequencies for assigning pitches to all the notes of all the stops in that division. These numbers are computed to produce varying styles of tuning, such as a fairly broad de-tuning for a romantic sound or a tight and precise tuning for a baroque sound. You can swap the boards around without removing the chips if you want to see what difference it would make, though the differences may be subtle.

Most problems with FG boards have to do with the connection between the socket and the chip, so be sure to carefully pry out the chip with a small screwdriver, clean the chip legs by scraping with a knife, clean the socket with WD-40 and canned air, then apply a tiny bit of Vaseline to the legs of the chip with a Q-tip before re-inserting and making absolutely sure that every pin is straight and goes straight down into the socket.

Of course, the card edge connector will also need to be cleaned and lubricated before re-installing the card in the cage.

If all that does not solve the problem, and the problem definitely moves with the board from one division of the organ to another, you have a bad board. Let me know how it turns out and maybe I can help you.

[myorgan]

You were right, in that the FG-1 board of the ADC-6000 DOES have 1 socketed chip on each FG-1 board on the Swell.

I hate to admit this, but I was wrong.:-( The FG-1 board's chips are all soldered through the board. When I wrote the post, I was remembering the TG boards I pulled.

Sorry.

Michael

[don60]

The FG-1 does not have any EPROMs on it, so the frequency tables could not reside there. Since the trem adjustments for FG-1 channels are located on the MA (Master) board for the card cage, and since the MA board does have an EPROM on it, I am guessing that this EPROM contains the frequency tables and should be investigated for bad connections per John's advice. Michael, before you give up, pull your MA board and try reseating its EPROM. Maybe you will be lucky. (Or, as Spock said, perhaps random chance will operate in your favor.)

Don

[circa1949]

The FG-1 does not have any EPROMs on it, so the frequency tables could not reside there. Since the trem adjustments for FG-1 channels are located on the MA (Master) board for the card cage, and since the MA board does have an EPROM on it, I am guessing that this EPROM contains the frequency tables and should be investigated for bad connections per John's advice. Michael, before you give up, pull your MA board and try reseating its EPROM. Maybe you will be lucky. (Or, as Spock said, perhaps random chance will operate in your favor.)

Don

Yes. In the Great "How the ADC System Works" thread of a couple summers ago, I think I raised the likelihood that the "Frequency Generator" boards actually take streams of numerical frequency values coming from somewhere else, and collates them into the stream of 12 multiplexed sample point addresses that allow 12 notes of polyphony when that stream enters the TG board. Something about the picture of that board, with many rows of the same chips, gives the impression of something that's just performing a series of digital logic math operations. So it's not generating what we think of as frequency, but what frequency means for the tone generator board.

[don60]

On the other hand I believe the FG-2 boards, which do include EPROMS and trem adjustments, are complete frequency generators that contain the tables. They were probably used for certain tone generators that needed unusual frequency tables--perhaps mixtures and percussive stops such as chimes?

Don

We will probably have the ADC systems figured out just about the time they become hopelessly derelict and obsolete--or about the time we all become hopelessly derelict and obsolete.

[circa1949]

On the other hand I believe the FG-2 boards, which do include EPROMS and trem adjustments, are complete frequency generators that contain the tables. They were probably used for certain tone generators that needed unusual frequency tables--perhaps mixtures and percussive stops such as chimes?

Don

We will probably have the ADC systems figured out just about the time they become hopelessly derelict and obsolete--or about the time we all become hopelessly derelict and obsolete.

Haha you are probably right about that. Agreed about FG-1 vs. FG-2. Looking at a cage chart, it seems the FG-2 was required for mixtures, the primitive multisamples like the trompette, and mutations. The former 2 I can understand because you'd need a way to control the mapping over various notes to different sets of sample addresses. Thus the EPROMs could control mixture breaks. The mutations are a little harder to figure out. But aren't mutations supposed to be tuned slightly different from the rest of the organ? In other words, a 2 2/3 is not exactly in tune with the note it would correspond to? Perhaps the FG-2 kept that in order too.

[jbird604]

Well, you guys are into this deeper than I have ever been! I used to wonder why some of the stops had their tremulant adjusted on one board, and some on another. Now it's making a little more sense.

If you still haven't fixed your problem and if swapping the FG boards around does not cause the problem to move around too, you could have a problem with one of the EG boards in the system. The organ will actually play without the EG boards installed, but the attacks and decays will be plain off and on like a Hammond or something. You can try pulling loose one EG board at a time and see if the trouble clears up.

In spite of the fact that each EG board affects only one group of stops, a bad EG board can in fact cause problems in some other, apparently unrelated portion of the organ.

[don60]

The mutations are a little harder to figure out. But aren't mutations supposed to be tuned slightly different from the rest of the organ? In other words, a 2 2/3 is not exactly in tune with the note it would correspond to? Perhaps the FG-2 kept that in order too.

On the color spec sheets for the ADCs, Allen made a point of telling prospective customers that mutations are correctly tuned. I interpret that statement to mean that they are true overtones of the parent notes, not the nearest equally-tempered tones that would be used on a more elementary organ. So yes, special frequency tables would be needed for the mutations because their frequencies would not correspond to any notes on the equally-tempered scale (the notes that would be stored in the main frequency table on the MA board).

I will have to look at the cage chart for my 7000 when I get home tonight to see whether this supposition is borne out by the board assignments in that organ as well. I'll bet that it is--another piece in the ADC puzzle falls into place.

Don

[don60]

All of the mutation and mixture stops for the ADC-7000 use FG-2 boards for their frequency generators. The FG-2s do serve other stops as well in many cases, presumably because they have some spare "capacity."