MDS-5 Sound generator problem???

[Happy Organ Owner MDS-5]

Hello everybody, I would like to find out if anyone has any experience with the following problem:

I just got a used Allen MDS-5, : all the stops in channel 2 work fine, all the stops in channel 1 are extremely out of tune (some tones are correct, some out of tune as much as a third). All stops in channel 1 are out of tune in the same way. Register-sound color all correct...
Any idea where the problem could be? probably the tone generator, but has anyone any more detailed idea? I will be happy to provide more information...

(I asked already in the alles organ owners group on facebook, so if someone is also member, please excuse for crossposting. )

[Happy Organ Owner MDS-5]

Dear collective wisdom at the organ forum

After not receiving any answer at this forum, I would like to once more ask for help from the knowledgeable members, that wrote so interesting analyses and repair suggestions for many Allen organs (unfortunately not so much for my model MDS-5).

I do not have the possibilities to ask a certified dealer to come in from another city, but I am willing to try to fix it myself.
Even if the reason is unknown, that could have caused this strange behaviour, any technical details (service/repair manual), schematics, and the structure/architecture of the tone generator box would be of great help.

Thank you in advance, and I wish everyone a blessed weekend.

[toodles]

I am not familiar with the specific details of the MDS 5, but all the Allen digital organs of the MDS and earlier generations have tuning controls inside the console. There may be 2, as the organs use 2 generators to provide for shifting one against the other for celeste. The metal enclosure around the tone generators is usually marked in ink to show the various adjustments. Tuning should be marked on it. You probably need a special tuning stick to make the adjustment.

It may be that one of the generators has drifted out of tune.

[Happy Organ Owner MDS-5]

Thank you, I found only one tuning control which should work for the whole organ, both channels. I did not try to turn, because "half of the organ" is actually in tune

[you795a]

Can you take some photos of the Tone generator cage? We might be able to help you better then. It would have been built somewhere around 1992. I'm not sure what tone generating system was used in that model.

[samibe]

Another shot in the dark, is the transposer knob set to 0? I don't know that it's possible for the transposer to only affect one channel but it might be worth ruling out.

[Happy Organ Owner MDS-5]

Thanks, yes, the transposer is on 0.

[toodles]

Also check, does the celeste stop affect the tuning? Perhaps it is stuck "on" and so you get celeste when you don't want it.

[Happy Organ Owner MDS-5]

Thank you for the suggestion. There is no celeste stop in MDS-5. But there is a reverb stop, which works just fine in both channels.

[Happy Organ Owner MDS-5]

Thank you so much for the answers and suggestions, I attached the links to the photos, which can be downloaded or viewed.

The sound generator has two panels, the input comes from two data cables (one for tone, one for register information)
and the output goes as two channels to a mixer and the amplifier.

on the lower panel is one little screw for the tuning (left bottom), and another for the reverb (I guess speed of the reverb) (left middle)
on the upper panel the screws for the intonation.

There seems to be two pulse generators NE555P (lower panel, over the reverb screw and lower panel top middle ) . Could it be that they are one for each channel, or is the left one for the reverb?

It seems that all the other frequencies are derived from one basic frequency by use of flip-flops, (74HCxxx chips). However there have to be two different areas (each for one channel) that compute the tones, otherwise it would not be possible to have completely different tunings for the two channels. The question is where this separation occurs… ( on the upper panel it´s already very clear, but the separation might start already in the lower panel. ) This would be helpful, then I could compare the two parts and find out what´s wrong.

lower panel: https://yadi.sk/i/iyyiXfmmP3XEbQ
upper panel: https://yadi.sk/i/yYSoMGaMuafSzQ

I will post photos in a following post for those who are hesitant to click the link
Thanks!

[Happy Organ Owner MDS-5]

[Happy Organ Owner MDS-5]

Upper panel

[Happy Organ Owner MDS-5]

[Happy Organ Owner MDS-5]

Lower panel

[toodles]

The Celeste stops on the MDS-5 are the Swell Viola Celeste 8 and the Great Viola Celeste II 8, borrowed from the Swell. Does turning the Swell Viola Celeste 8 stop on and off change the tuning of the other stops? It might be stuck on, making some of the other voices seem out of tune.

[Happy Organ Owner MDS-5]

Thank you! Yes, you are correct there are two celeste stops, I didn't look carefully enough.
No, turning on the celeste doesn't have any effect. Swell Viola celeste is in tune, viola celeste II on great uses both channels, so it is out of tune.

[you795a]

That is a W4 system. You don't want to mess with the tuning coil unless you have a proper way of re tuning the organ. That tuning coil should control the organ as a whole. Can you give a list of the stops that are out of tune?

[Happy Organ Owner MDS-5]

Thank you, here it is:

Pedal
OK: Bourdon, Lieblich Gedackt, Gedackt, Choral Bass, Trompette
Wrong: Octave, Mixture II, Basson

Swell:
OK: Bourdon 16, Gedackt 8, Viola Celeste 8, Nasat 2 â…”, Blockflöte 2, Trompette 8
Wrong: Viola 8, Spitz Prinzipal 4, Koppel flöte 4, Basson 16, Clairon 4

Great:
OK: Gedackt 8, Octave 4, Blockflöte 2, Mixture IV
Wrong: Principal 8, Viola Celeste 8, Koppelflöte 4, Super octave 2, Chimes

It is clear; channel one is wrong, channel two is OK, so when I plug off channel one at the sound generator output, everything is in tune, but I have only "half the organ ".
Mixture II, Viola Celeste II and Chimes use both channels.

[jbird604]

Since you evidently didn't mind disassembling the W-4 sandwich, you might also remove the socketed EPROMs, one at a time, carefully observing the orientation. Clean the legs of each EPROM with a toothbrush, use some compressed air to blow out the socket, then carefully reinstall the chip, making sure that all the legs go back in straight (not curling up under the chip), and that the chip is firmly seated. It's a long shot, but I have known an occasional problem to be fixed by this cleaning/reseating of the EPROMs. Any other socketed chips on the boards should also be cleaned. I wouldn't remove those square chips though, unless you have the proper extractor. Just press down lightly to make sure they are seated.

Tuning on these W-4 organs is certainly a function of these boards, and I always start by cleaning chips and sockets and otherwise making sure all connections are tight. If that doesn't fix it, you likely have a defective board, which will cost quite a bit of money. There is only one tuning coil, which sets the pitch of all stops simultaneously, so I'm certain your problem doesn't relate to that coil.

Whatever you do, do NOT attempt to replace any of the chips on the board! These boards were not designed to be worked on outside the factory. If tampered with, Allen will not repair or exchange the board for you in the future.

BTW, there is also a chance that the power supply in the W-4 cage is defective, and I suppose that could cause a tuning issue, though that would be unusual. Verify the +5 volts and tinker with the adjusting pot if there is one. We routinely change out the old-style linear power supplies with a modern switching supply that can provide the same set of voltages with far more stability. That may not be a task for a non-tech though.

[myorgan]

So John, is the moral of the story to obtain an earlier MDS organ because the technology allows one to facilitate repairs of their own instruments? However, the later MDS organs with the W-4 or W-5 boards MUST be repaired at the factory?

Just my curiosity.

Michael

[jbird604]

This one IS a W-4 organ. He has successfully removed the entire assembly (a sandwich made of two boards connected with sockets and cables) and separated the two boards. Midway through MDS, Allen replaced W-4 models with W-5 models. The W-5 generator also consists of a sandwich assembly, the big difference being that the W-5 system fully integrated all the audio processing right onto the W-5. Whereas W-4 organs have a separate Audio Processor board and reverb unit (ADR-4), the W-5 system made those parts obsolete and put all that functionality right on the main board.

In reality, Allen never intended for us techs to dismantle the sandwich assembly. We were supposed to replace the entire assembly if there was a problem. This was the protocol, at least as long as the organs were in warranty. Nowadays, people do a lot of stuff that we wouldn't have done back then.

I think it's commendable that our OP here went to that much trouble. He may in fact find that it works once he puts it back together, since so many troubles are due to corrosion and poor connections. Or he may not, if there really is a bad chip on the board somewhere.

[Happy Organ Owner MDS-5]

Hello John, thank you for your extensive answer. I cleaned and reseated the EPROMs and other chips right away when I got the instrument, as that is what was suggested in another place in this forum for this situation. so that was not part of the problem.
I also measured the voltage /power supply which is very reliable with 5V

would you have information where the separation into two cannels starts?
Are the two pulse generators responsible for the two channels?

On some other service manuals that I managed to obtain (for MDC instruments) I saw some clear structural diagrams. If you have access to some similar information for MDS-5, I would really appreciate it.

This instrument is 30 years old and definitely out of warranty. I am also not able to spend a lot on a new sound board or some thing else, so the company will not loose any income by me trying to repair it on my own. In addition I just realized that I might not be the first one to fix this, several screws holding together the panels are of different kind, probably not Allen´s original screws...

There are some other major issues with this organ, that I did not mention yet because it did not bother me that much yet, but it might help the experienced technician to the real problem.

1: the right part of the stops GENERAL (Memory b, Add stops, Bass coupler, Melody coupler, Romantic tuning off, Console speakers off, External speakers off) are basically dead, show no response whatever.

2: MIDI connection is only available from computer to the organ (what I program on MIDI Channel 0 the organ plays with the Swell stops), but the the computer does not receive any input from the organ ( I did turn on the "MIDI stops") also anything on MIDI channel 1, 2, 3... is not recognized by the organ.

3: really low tones (16 foot) have "cracks" (sound interruptions)

4: the expression pedal is always on, does not react to the movement.

Thank you so much for your effort.

Albert

[myorgan]

Albert (& John),

Problems #1 & #3 sound like the issue I had with my Audio Processor board on an ADC. Could it be the same issue on this MDS?

Michael

[you795a]

Problem #4 could be a burned out expression bulb in the expression shoe housing.

[John Vanderlee]

Item 1 sounds like something disconnected maybe? Since these are all in essence switches, I would put a VOLT meter on the switch terminals and see if I read anything depending on the switch position. i.e. could be 12VDC in one position and zero in the other position. If there is no change, look for a disconnect somewhere.
Item 3 could be a speaker.
Overall, did this thing get hit by lightning or a power surge?

[Happy Organ Owner MDS-5]

Thank you John, I will try to measure.
About the prior history of the instrument I have no idea, I will try to find out, have no idea it went through
how many hands...

[you795a]

Just a shot in the dark here, but could it be something with the MN board. I am not sure but I think at this point Allen started using "loops" where the keyboards are in a loop and the stopboard is in a loop that goes to a small board like a stop driver and then to the MN board. That is how the W5 systems were. There would be an IC in the MN board that tells the organ what to think, called a stopmap.

[Happy Organ Owner MDS-5]

Thank you, you795a, there is in fact a board that collects the wires from the stops. I will look into it after a factory reset.