Gem Plenum Problem

[jgiddings]

My Gem Plenum will be playing along quite normally, and then suddenly there is an internal 'click' and the speakers (or headphones, if they're plugged in) begin to buzz (the buzz is like what you get when the volume is set way to high on any speaker), the organ plays with a tutti sound (irrespective of which stops are or were on) and suddenly the lights to the crescendo pedal all light up (irrespective of the position of the crescendo pedal). The tutti sound is similar in timbre to the sound the crescendo pedal gives on its highest setting but far louder. Nothing changes this until, after a time, it resets itself with another click (and that is quite variable - up to an hour!). Turning the organ off and on again doesn't necessarily reset the problem; immediately resetting never fixes it, but sometimes coming back to the organ after a day it has returned to normal (again, not always!).

Basically the organ is only good as a midi controller for Hauptwerk/GO with a jack to mini jack plugged in to the socket but with no headphones attached to mute the very loud tutti sound.

I don't have the cash to invest at the moment to make it into a good virtual organ (i.e. touch screen stops, a swell pedal) and although that is the goal eventually I wondered if anyone with some knowledge of digital organs might be able to point to a particular problem that I might be able to sort out.

Thanks in advance!

[jbird604]

This is a model that I have not seen, but the problem sounds like the kind of thing that might respond to some general maintenance and testing. I'd open it up, and wait for the problem to occur, then quickly use a voltmeter to test all the power supply voltages. It's possible you'll locate a voltage that is going off and causing this malfunction. The fix might be obvious once you know what is happening.

Also, while the malfunction is happening, block down a key so you can hear what's happening, then carefully poke around inside on the various boards and connectors, being careful, of course, not to touch any AC line voltage. If you find a spot on any board or connector or cable bundle that makes the trouble stop or start, you'll have to examine that area carefully and look for a bad solder joint or other defect.

Beyond that, with the organ powered off, I'd remove and re-attach every connector and plug. Remove any socketed chips from their sockets, check to make sure the chip legs are clean and straight, and carefully install.

If this organ is fairly modern and has surface mount components, it may be impossible to fix it yourself, but if the trouble is on a board or part with more standard construction you might be able to repair it yourself if you are handy with tools.

[jgiddings]

Thanks for this. I'll have a go at what you say over the weekend and report back.

[arie v]

Hi,

The GEM Plenum is the same organ as a Galanti Praeludium 2 organ. This organ was inproduction from late 1986 till about 1993.

The symptoms described tell me that most likely that there is a leaky battery problem. The battery is a solder in type cylinder, ni-cad rechargeable mounted on the CPU board. The battery acid leaks onto the CPU board, which travels down to the motherboard / daughter board right where the +5 v and grd connections are.
Generally I have found that once the symptoms start, they worsen over time, till eventually the organ does not work at all.

So, I suggest looking in the back of the organ, find the card rack, and look for the battery, and see if there are problems. If so, immediately remove the battery.

Once the condition of the battery is determined, we can discuss further.

As for using the organ for a MIDI controller, you will have to have the CPU running properly. Besides that the organ only puts out MIDI key data, does not put out stops or expression data. The MIDI implementation is also quite primitive as it dates from 1986.

AV

[jbird604]

Aha! That tells me a lot, Ari, that it is the same as the Praeludium II, which of course I played for a long time and serviced extensively. I didn't know what we were dealing with.

One thing that occurs to me -- both the expression pedal and the crescendo pedal use light-dependent resistors. If the voltage that lights the bulbs down there should go out, two things might happen: The crescendo goes to full AND the expression volume goes to the highest possible level, perhaps even higher than you'd normally get with the pedal wide open, if there is absolutely no light at all in the chamber.

This would explain what the OP says is happening, which sounds like full organ at super-loud volume.

If the cable that carries the lamp voltage is working loose or if there is a bad solder joint on the connector at either end of it, this could produce the situation, and it might not go away for a very long time. Maybe even persisting for days at a time, as he says.

So I'm going to suggest that he check that as well as the battery. Of course, we all know that the battery can leak and will do some very nasty damage on that model, so it should definitely be checked. I'm just suggesting the possibility of the lamps going dark.

[organman95]

One thing that occurs to me -- both the expression pedal and the crescendo pedal use light-dependent resistors. If the voltage that lights the bulbs down there should go out, two things might happen: The crescendo goes to full AND the expression volume goes to the highest possible level, perhaps even higher than you'd normally get with the pedal wide open, if there is absolutely no light at all in the chamber.

I remember having that issue with an Allen ADC-3100 seven years ago when the bulb on the Great/Pedal expressions went out. Glad we are past that stage of technology now :)

[jgiddings]

I've gone into the organ and think I've located the battery on the CPU. It appears that the organ has already had the battery replaced (or at least wired in so as to be at a distance from the board). It looks as though there may be a little damage as I have tried to capture in the photo below. The battery itself is wrapped in tape I assume to prevent leakages over the organ case.

Given the fact that someone has already replaced the battery, and despite next to zero knowledge about these things, the suggestion about the lamps going dark does seem a strong possibility as the entire organ remains functional when the issue occurs - i.e. you can hear stops like the chimes if you add them, the transpose function works etc etc - it's just all drowned out by the enormous volume, higher than the normal max, from the crescendo pedal.

The crescendo pedal is connected via a ribbon cable to a separate board along with the pedal and the pistons etc. I've tried re-seating this and pretty well everything that is in a socket near by and on the power supply/regulator board (?). I also swapped the swell and crescendo cables to no effect. Leaving the crescendo pedal unplugged also changes nothing, even when the organ is working normally with the pedal unplugged, the issue still occurs after a period of time. I've not gone as far as taking the board out to look at soldering on the underside - should this be my next step?

[jbird604]

If it's the bulb voltage that is disappearing and causing the problem, then it is being killed somewhere between the power supply where it is created and the expression and crescendo assembly. I say this because it is causing both lamps to go dark at the same time.

I'd just look for a loose connection somewhere in the system, and it could be lots of places. The power supply, of course, but also the motherboard and the mixer board are involved in sending this voltage to the lamps. Ribbon cable connectors are always suspect, as are wires held down by screws.

Best shot at finding it -- when the problem occurs, while it's going on, block down a key so you can tell if the trouble clears up. Then start methodically going from board to board on the main shelf and down at the expression assembly, poking gently, wiggling connectors gently, moving cables around, doing whatever you can think of. At the instant the trouble clears up, whatever you were touching or moving at that moment should give you a clue as to where to start your repair.

I know this is vague and difficult, but that is the nature of working on an older organ like this in which all kinds of things can and have gone wrong!

[jgiddings]

Finally got around to doing a thorough reseating of components and I found the issue - it was on the power supply and a component didn't have a good connection. That issue is solved.

However, after having fiddled with the organ's innnards, the stop tab lights and the lights beneath the manuals have stopped working...! The stops work fine, but there is no light to indicate what is on.

I've tried to check that I've put everything back in properly.

It's not as bad a problem as the previous issue, but does anyone have any ideas?

[jgiddings]

This is an old thread but I'm continuing to have difficulties with my Praeludium / Plenum.

The crescendo / swell problem gradually returns despite re soldering the problematic connection/component.

I read about wiring a 1.8k resistor over the input to the board which controls the expression, as per the following post in a thread about modifying the same type of organ:

http://www.organforum.com/forums/sho...-begins/page11

Would this work for my problem to remove the crescendo pedal from the picture entirely?

Thanks in advance.



Edit: The problematic part was/is the black square with the circle in its centre.

[Morrisek]

Hi!
I'll hook to the post. My organs (Gem Plenum) played without any problems for several years. But for some time now, there have been various issues in playing them. Sometimes it is a jam, sometimes some or all of the lamps turn on and the sound cannot be produced. Sometimes turning it off and then back on fixed the problem, and sometimes it didn't.

The problem increases with usage time. If the instrument rests, e.g. overnight, the problem disappears for a while.

I checked the supply voltage, and on the REG PWR & AMP board. I replaced two 470uF 63V capacitors, one FE6B diode and a 10K resistor. The battery on the cpu board was replaced before. I noticed that a slight movement of the cpu board could do a similar problem, so I improved the tinned connections with the motherboard. It improved for a while. After assembling the instrument, the problem returned after a few hours.

I still hope to solve the problem, but my wife is already losing her patience, because the instrument is in the living room and if you have to do something with it, you can imagine what happens.

[jbird604]

Yes indeed! Having to do organ repairs in the living room can make for some unsightly messes.

You are probably on the right track. Most intermittent organ problems are due to connector problems (such as the socket issue that you tried to address). Other connections to check include plug-in cables and sockets, wherever you find them.

Also look at the solder joints on the power supply and other boards that get warm. A weak solder joint can open up as the parts get hot and cause an organ not to play.

[korpen]

Hello! I have a problem with my plenum GEM.... It died on me and I replaced the fuses (wrong sort I now understand) i have a new cpu-battery (the old was leaking)

but the organ doesnot work propperly. no sound and half of the light bulbs are on, and cannot be switchwd off... no sound and so on....

can it be so with the wronge fuses?

I tried to take back the old ones on 3.7A but i cant find them all, so now I have two of them with a smaller number (800mA)

Do you know if I should take 3.7A on all fuses and maybe there is my problem?

//Lo

[arie v]

Hi,

The fuses required are 3.15 amp. Slo blow. The lamp supply requires an 8 amp fuse, again slo blo.

you need the following voltages, + 12 , - 12, + 5 volts.

the battery on the CPU board should be clean and read 3.6 volts

If the previous battery leaked, check out the the area around the battery and also the CPU board connection to the mother board.

This organ is likely around 30 years old, and is a fragile state.

To do anything on the organ, at least have a multi meter handy as well as the shcematics.

AV