GEM jumbo 61 - in koma... :-((

[sawatzki]

Hi folks,

I just bought a GEM jumbo 61.

When I hooked it up and turned it on for the first time, it worked although not flawlessly: All oscillators worked fine, but not all voices worked over all 5 octaves.

Out of curiosity, I plugged a (mono!) jack cable into the headphone output and hooked it up to y mixer.
What I heard then was an incredibly distorted organ - sounded kinda cool...
So I played a couple of notes.
And then it happened: Ffffzzzt.... and SMOKE!! A resistor burnt through on the left PCB (power supply, I suppose)... And then: silence.

Unfortunately, I have no idea what value the dead resistor was. I looked around for schematics / service manuals, but no luck.

I also suspect that one or all of the transistors on that took damage, right?

They are marked "BC301" (2x) and "BC303". I couldn't find these anywhere on the net...

How can I get this little GEM back to life??

I thought:
Step 1: Find out what kind of resistor died and replace that.
If that doesnt solve the problem (and I fear it won't),
Step 2: Find the corresponding transistors and replace them.
If that doesnt solve the problem,
Step 3: Try to rebuild that whole PCB and hook it up.

What are your thoughts on this?

Do you know where I could obtain those transistors? (I'm in Germany...)

Thanks for your help!

sawatzki from Berlin

EDIT:
Here are some pictures:

www.raphaelarmin.nl/_phpTest/index.php?/project/gem-jumbo-61/

[sawatzki]

Meanwhile, I figured that the PCB where the resistor burnt is not the power-siupply but the 25W amplifier... (I got the schematic of that part from a member of a (the?) german analogue-organ-forum...)

The question remains as to what caused the resistor to burn - obviously something else went kaputt aswell... (I replaced the 100 Ohm resistor and daringly switched the organ on: whoosh - there it went again - up in smoke! :-( )

I have no idea whether the failure occurred due to me plugging the mono-jack into the headphone-out or whether it was pure coincidence the the organ died on me while used the mono-jack.

I'm between total noob / eager beginner and hobby-electronic-tinkerer, learning and beginning to understand schematics and learning to use my multimeter... But I'm willing to LEARN! :-))

So hopefully, someone on this list can point me into the right direction as to what I should measure and how i could find out what caused the failure.

Greetings from Berlin,

Raphael

[brianjrobinson]

The short answer would be that you have a short circuit or other component failure somewhere and too much current is flowing through the resistor.

Have you located the resistor on the schematic? Trace it and see what could be causing the problem. Start with the components on either end of the resistor, and go from there.

[combonautfreak]

Hello sawatzki , I too just bought the Exact same organ, and the same thing happened to me (well, not quite, it's just the fuse blew out) I'm still waiting for my parcel to arrive, because I ordered replacement components.
Here's mine It's twin to yours:

i586.photobucket.com/albums/ss304/combonautfreak/GEM%20Jumbo%2061/DSC03221.jpg?t=1263204436

Before it went out, I had a constant AC hum and there is a big leaky 4700µF capacitor in the power supply here it is:

i586.photobucket.com/albums/ss304/combonautfreak/GEM%20Jumbo%2061/GEMJumbo61sickPowerSupply.jpg?t=1263204180

I ordered a bag of new fuses, a new capacitor, and a new SAJ210 divider IC, because I had quite a few notes missing.

But I think that plugging a mono Jack in the 'EARPHONE' socket is what caused my fuse to blow too. So you're not alone
But it's the only way to cut off the sound in the internal speaker while playing, and I don't even have a swell pedal

I have the schematics for this organ that I got at Musicparts.com, but it's not well scanned and half the oscillator drawing and capacitor value chart is cut out!

I'm willing to find a more reliable schematic, help needed

By any chance, do you know where could I found a volume pedal for this Jumbo 61? (5-pin DIN type) Help would be much appreciated

We both have to resurrect our respective Jumbos
So best luck to you, keep it up

Charles from Paris

[viggen]

Hi guys.

Found your conversation while googling some answers about a newly bought organ. It is a swedish built "Viggen" the model is a Jumbo-61... So I figured this would be the same as the GEM jumbo-61... And correct I was...

I bought it untested at a flee-market and brought it home just to find out that it was totally dead. I inserted a couple of new fuses and the old thing fired up. I only get this humming sound so I figured the fuses were not the only problem (something was causing them to blow). One of them had blown already when I started it. Seems to be the power supply / amplifier part (the one in your image). It could very well be the large capacitor, but it seems ok. It is hard to make any measurements while everything is on the board and without the proper schematics. So I figure one of you maybe has the schematics??

If that's the case, could you please share them with me?

I also have older Viggen from the 60's, a furniture model. So I figured if can't get this thing to work the case is a good start to make the old one mobile... But it would be nice to have both of them running.

Thanks in advance!

[domsless]

Hi all,
I've recently just purchased a Jumbo 61 at an antiques shop in brilliant condition but unfortunately it's missing the original speaker. I was wondering if anyone knew the details (ohm rating, mounting depth, diameter - i'm guessing it's a 8" driver with it mounting underneath the top?, wattage - i believe the amp outputs 25W?) of the speaker. Any help would be appreciated!

combonautfreak - I know this is an old thread but someone asked about the pedal over on the SoS forums, it might be of some use to you - www.soundonsound.com/forum/showflat.php?Cat=&Number=712670&page=23&view=collapsed&sb=9&o=&fpart=1

Cheers all!

[ctyler]

where did you get the SAJ210 divider IC? I need 2 for my GEM Caravan. Thanks

[ctyler]

no need to reply, i've found one now

[gianluca76]

does anyone have the gem jumbo 61 schematics?
thanks

gianluca

[Mtmbvd]

I last bougt a gem jumbo 49, and it wasnt too expensive because the bass part (and chord function) of the keys didnt work.

When I looked at the insides I saw that some things were resoldered and I think some parts were taken out of this machine.

Does anyone have some schematics, or detailed photos of this organ?

[combonautfreak]

I have a Jumbo GEM (version 3.1) and concerning the bass section, do only the lowest notes sound or none at all? For the chord function, Jumbo GEMs have fixed treble in the first octave and the Chords/Bass switch only adds the bass tone. I could help you have a schematic (I re-write them) but I first have to know what version you own. Could you post pictures? or send them to me at [e-mail]

Glad if I can help,

Charles

[combonautfreak]

For more info refer yourself to my thread: combonation.proboards.com/thread/914/gem-owners-schematics-bring-pictures

[gianluk]

Hi, how can you state the version 3.1? How can I distinguish it?
thanks