ADC Capture Board

[John Vanderlee]

So I just acquired this nice 2 manual ADC organ. Everything perfect, but one tab refuses to return on general cancel. It sets but won't cancel. Hours of trouble shooting led me to the capture board. I had one on another organ so I swapped them. To my chagrin it was the board at fault. Does Allen still repair those? If not maybe someone has a schematic or block diagram? Is there a common failure on these boards? I suspect one driver output maybe.

Can't find any to buy on the internet either. I heard that an MD4 board is a universal replacement. Is that true?

Any and all advice would be appreciated!

John

[samibe]

Admin's Zuma group also sells a Midi DM board replacement that can function as a normal DM board or detect and control the stops and pistons via MIDI. I'm not sure how much a replacement DM board from Allen is. So, I don't know how the MIDI DM board compares.

Just curious: Is there any visible damage to the DM board?

[John Vanderlee]

Admin's Zuma group also sells a Midi DM board replacement that can function as a normal DM board or detect and control the stops and pistons via MIDI. I'm not sure how much a replacement DM board from Allen is. So, I don't know how the MIDI DM board compares.

Just curious: Is there any visible damage to the DM board?

No Damage visible. I suspect there must be driver outputs going to the action, my hunch is that one is defective. A schematic would help.
That ZUMA looks tempting, but don't know if I can justify its cost.

John

[Admin]

It might possible to solve your problem by moving the sense and control wires for that stop to an unused pin on the DM board, assuming that there is one. If you'll post the ADC model and the stop that isn't working, we might be able to supply some guidance.

The "universal" DM capture board is the DM4. I don't know if Allen still repairs these boards as I understand that they no longer repair some boards due to RoHS compliance issues. DM boards do show up on eBay and our forum classifieds from time-to-time. I have an older 4 division DM board available, in fact, but it requires an external battery backup cage assembly, that I'd include in the sale, but I think you'd have to wire it all up. Anyway, the point is that although all the DM boards are functionally the same and plug compatible, there are differences in how they deal with battery backups. The DM4 board does not require battery backup as I understand it.

[John Vanderlee]

It might possible to solve your problem by moving the sense and control wires for that stop to an unused pin on the DM board, assuming that there is one. If you'll post the ADC model and the stop that isn't working, we might be able to supply some guidance.

The "universal" DM capture board is the DM4. I don't know if Allen still repairs these boards as I understand that they no longer repair some boards due to RoHS compliance issues. DM boards do show up on eBay and our forum classifieds from time-to-time. I have an older 4 division DM board available, in fact, but it requires an external battery backup cage assembly, that I'd include in the sale, but I think you'd have to wire it all up. Anyway, the point is that although all the DM boards are functionally the same and plug compatible, there are differences in how they deal with battery backups. The DM4 board does not require battery backup as I understand it.

It's an ADC3500. while it's a theater model, it has a floating division which makes it useful for classical as well. I was going to supply it to a young student for practice since it is relatively small and self contained - with a headphone amp!
The woodblock tab is the offender - not needed but a pain if it can't be cancelled. Besides I like to have it 100 % functional.
I'm interested in what you have, You say: "external battery backup cage assembly" is that more than just a battery pack? and would the board be a direct plug in replacement? If you like we can continue privately. This forum is awesome!

[Admin]

Unfortunately, my documentation for this model doesn't include a diagram of the connections between the stop rail and the DM board, so I'm unsure if there are any unused pins that could be pressed into service, nor can I tell you what connector and pin the woodblock is connected to.

The backup battery assembly I referred to is a small power supply containing several D cell NiCad batteries. It connects to the DM board through pins on the J80 connector. Later model boards had smaller batteries mounted on the board itself or in separate battery holder. In order to use one of the older boards, you would likely have to run wires between the external battery power supply and the J80 connector to the DM board. Not rocket surgery, but not a drop-in replacement either.

[samibe]

John would you post a picture of your DM board and of your stop tab layout?

It's not super difficult to narrow down which pins sense and control which tabs.
I would start by setting up a general piston to activate all of the stops (opposite of cancel). Then turn off the organ.
Remove one of the plugs from the DM board (J-81 to J-83 or 4). Make sure it is out of the way and won't bump into (short out or damage) anything. Don't mess with the J-80 plug.
Turn on the organ and press the general or cancel piston. Whichever set of tabs does not move with the rest of the tabs on the organ (except for the few that are not driven by the capture system and your problematic stop) are the stops controlled by that plug.
Turn off the organ and reattach the plug. Repeat with different plugs until you find the plug that controls all of the tabs around the woodblock tab.

On my organ, the stops are in order on the J-plugs. My pedal/Acc division is all on J-81. The tabs (in order from left to right while seated at the console) are wired to the J-plugs in ascending order. (i.e. The leftmost tab is controlled by pins 5 and 6 on J-81. The tab to the right of that is controlled by pins 7 and 8. etc.)
On my organ, there are enough Ped/Acc stops that they fill up the entire J-81 plug. So, all of my percussions, generals, and trems are on J-84 with extra wires for expansion where the block spacers are. Depending on how many other stops are on your Ped/Acc division, all of your percussions might be on J-81. This should help you get close.

Once you know which plug controls the stop and about which pair of sense and control wires/pins might run the stop, you can test them by using an alligator clip to short the sense and control pins together and pressing the cancel piston. The tab controlled by the shorted pins will be the only one down. Find the pins next to the problem stop to figure out which pair of wires are the ones controlling the problem stop. If there are some extra pins on the same plug, you can carefully unwrap the wires (with the organ off) from the pins and move them to an open pair of pins. There are about half a dozen pins on each end of the J-plugs that are not used and will not control anything (so don't put the wires there). If there are no spare pins and/or you don't mind the stop not being controlled by the DM board, you could leave the wires unattached. If you do that, make sure you insulate the ends so they don't damage other stuff. I think if the wires are disconnected that the cancel will still cancel the tab, but none of the general or divisional pistons will be able to activate the tab.

Edit: I found the specification insert. My guess is that the woodblock tab is on J-81 probably pins 53 and 54. There is probably room on pins 59/60 or 61/62 or J-81.

[AllenAnalog]

Are we sure that this organ has a DM model capture board and not a USCP-2? As I recall later instruments, including theater models, used the newer capture card. A photo of the capture board or verification of the model number on the board ID sticker is important to getting the right information to John.

[Admin]

Are we sure that this organ has a DM model capture board and not a USCP-2? As I recall, later instruments used the newer capture card. A photo of the capture board or verification of the model number on the board ID sticker is important to getting the right information to John.

That's a good point and one I checked before responding. That model is spec'd as having dual memory capture, rather than the quad memory capture typical of the later multiplexed replacement. On the other hand, most of the ADC x500 models are quad memory capture, so it is possible that the DM board is not being used and a scaled down version of the USCP is being used.

The DM capture board looks similar to this:

[samibe]

I think the ADC x600 models are the ones with quad. I haven't seen any x500's with quad memories and the Mem B tab is mentioned in all of the manuals I have.

[John Vanderlee]

It's definitely a DM Board like the one pictured above. Except that it has a blank area since it has only 3 divisions. I had already determined that the bad tab tab is part of the top right plug. Now if I understand Samibe I can move the wires to an area on the plug that is not used? And it will work normally?

At his point I am trying to learn how the tab assembly works. What I have learned so far, I think: the orange and brown wires supply the pulse that energizes the coils. Of the two reed switches one is what activates the voice, the other has to do with telling what position the tab is in. The transistors on the tab assembly switch the proper coil, directed by a signal (how?) from the DM board.
Do I also understand that the DM board sends a reset signal to ALL tabs simultaneously and they only react if they are in the "on" position as told by the reed switch?

To Admin, I can handle the battery part if the rest of the board you offer does what it is supposed to do.

I love this Forum!

John

[Admin]

There are two wires from the DM board to the stop tab. The wires on the even pins of the DM connector are the control signal (usually green) and the wires on the odd pins (usually white) are the sense wires. The pulse voltage is supplied to all tabs simultaneously whenever a general piston or cancel piston is pressed or for the all tabs in a division when a divisional piston is pressed regardless of their current and target state.

http://www.organforum.com/forums/sho...l=1#post476271

[John Vanderlee]

Thanks People, The DM Board is just like the one pictured above except 3 divisions only of course. Thanks to Samibe and Admin. I 'm going to the shop today and try the recommendations. I'll report back later.

I love this forum!

[John Vanderlee]

Well, I found there is definitely no cancel signal coming off the board for that tab. I studied the board and found that it uses a shift register SN74198 IC as well as a SN7405 Driver IC associated with that tab. Since the other divisions work correctly, I feel safe assuming either of the two might be at fault. Found them for a few bucks, and hope to find time to swap those guys out next week.

John

[jbird604]

Good luck with the repair! I'd change the driver chip first, it's the one most likely to fail. I've not done that myself, but sounds like it's doable if you have the soldering skills.

Before you go to that trouble though, is there an unused pair of pins on that plug? If so, you can simply move the white and green wires that correspond to that tab (since you have already determined which ones they are) to an unused opposing pair. As long as you transfer them to a pair of pins on the same plug they will work just as they should and will continue to respond as belonging to that division. That can be a permanent repair as it will not affect the operation of the system in any detrimental way.

If there are no unused pin pairs you might still sacrifice some other tab in the division, if there is something you could do without. Taking the wires off the pins for a tab would cause it to go down with any piston press, but in a pinch you can put a thick chunk of felt under a tab using double-sided tape to keep it from turning on. That won't hurt anything, but will of course make that tab unusable.

This kind of jerry-rigging might not appeal to you, but in my line of work we sometimes have to do what we have to do just to make an organ playable before parts can be obtained!