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Thread: Caravan (GEM?) compact organ - help please

  1. #1

    Caravan (GEM?) compact organ - help please

    Hello,

    i'm new to the world of home organs and new to this forum. I would appreciate some guidance on a repair issue for an obscure organ I just bought. As it's my first post please allow me a little time to introduce myself.

    I arrived at organs via synthesizers as I make and listen to a lot of electronic music. But i'm in also a band that does psychedelic rock style, and we have always used Native Instruments' B4 and other organ VST instruments to help achieve our sound. Recently I started looking at real organs to replace our software. Not only for the sound, but also for the pleasure of playing a real analogue instrument. So after some searching I recently bought two double manual "portable" organs: an Acetone GT-7 for the band and a Crumar Organizer T2 for myself (I said I liked synths!). Today I picked up my 3rd and (probably) final organ, a 49 key Caravan, from 1975 I think (the QC sticker says 75). I wanted a "cheesy" sound as an alternative to the "Hammond"-esque sound of the Acetone. It has a few problems and obviously hasn't been used in a while. I'm a total noob when it comes to fixing things.

    All the keys make a sound, but the B, A#, A, G#, F#, and F keys only play correctly on the top octave. The lower octaves (for those specific notes only) play the highest octave notes instead, so basically they are the same as the highest octave. I hope I explained that ok. Also, the "Chord Bass" switch doesn't appear to do anything (not sure how it should sound either!). Does anyone know anything about this organ, and more importantly which components are likely at fault and if I can easily get replacements?

    BTW, don't worry, I only paid 15 euros for the Caravan - thought it would be worth a punt.

    *EDIT* The only info I have about this organ was found at http://www.combo-organ.com/Gem/index.htm

    Thanks
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    Last edited by Charles Tyler; 09-26-2010 at 05:03 PM. Reason: added web link

  2. #2

    ps I also posted this on Combo Organ Nation as perhaps that forum is more appropriate for this kind of organ.

  3. #3
    Senior Member jimmywilliams's Avatar
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    Charles,

    I don't know this particular model but your symptoms sound like the tone generator divider boards. The way the work is they produce the highest octave for the pitch, and pass the signal down to a "divider" circuit to produce the same pitch an octave lower, and so on. These pitches are then keyed by the keyboard as needed. This saves money in parts costs because you don;t have to design an individual oscillator/filter for every single pitch that the organ needs to produce. The trade off: since each individual pitch/octave does not have an independnnt generator, if there is a problem somewhere up the chain, all the lower octaves will also malfunction because each is dependent on the previous divider working correctly. Does that make sense?

    It may just be a matter of dirty contacts or common failure parts (electrolytic capacitors, etc.) - hard to say. It would be strange to have that many divider boards just go bad but who knows? If there are no proprietary parts on the boards, you may be able to rebuild them ... but you would need the schematics.

    Some on this board have combo organs too but I think mostly Farfisa, Vox, etc. We also have people on the board with pipe organs on their houses and everything in between!
    So yes it was a good idea to post in the combo organ group too. I got "lost" on that site a few times....

    - jimmy
    Jimmy Williams
    Hobbyist (organist/technician)
    Gulbransen Model D with Leslie 204
    Farfisa Compact / Leslie 860 and Combo Preamp III / Hammond Porta-B

  4. #4
    Moderator andyg's Avatar
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    There's not much on that main board, is there! I'd look at those IC's. If they're the plug in type, then swap them around and see if the problem moves to other notes, then replace as required - IF you can get them and IF they don't cost an arm and a leg!

    E15 was worth a shot, so it's no real problem if this one eventually does end up in a bin. Let's hope that you can get it going. It sounded awful when it was new, by the way, but that may be exactly what you're looking for!
    It's not what you play. It's not how you play. It's the fact that you're playing that counts.

    New website now live - www.andrew-gilbert.com



    Current organ: Kawai SR6 + Leslie 760 Walnut
    Retired Organs: Lots! Including Hammond T402, T500 x 2, X5. Conn Martinique and 652. Gulbransen 2012 Pacemaker. Kimball something-or-other.
    Retired Leslies, 147, 145, 760, 710, 415 x 2.

  5. #5

    Yes, it really is a terrible sounding thing! But I was after that, a bit of cheese can be a good thing in a band full of otherwise good instruments.

    Anyway, thanks to you both for your replies. Everything on the board is soldered so i can't unplug things without unsoldering. But i do have a solder iron (as yet unused), maybe it's time i started experimenting with it. So, just to prevent me messing with the wrong parts, can someone identify which parts are which in the photo? I attach a close-up in case it helps.

    As I sid I am totally clueless at electronics projects, but if you give me a pointer then I can start un/resoldering the parts to see if it makes any difference. I will also get some alcohol solution to give it a proper clean. Maybe this would be a good simple project to get me familiar with basic cleaning and repairs in case i need to do something later on with the Acetone and Crumar. If it goes wrong on the Caravan then I won't be too upset.

    Finally, I am happy to report that the chord bass rocker actually does work - I just couldn't hear the difference through the awful internal speaker! Sounds quite good through real speakers, it's just a shame only a few of the notes work so far due to the octave divider problem.


  6. #6
    Senior Member jimmywilliams's Avatar
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    Charles, these look like newer divider circuits than I am familar with. From what I can tell those ICs may be the dividers and are possibly shared among different pitches (since I don't see 12 of them). How many IC chips are there? Are there three (which may mean that each chip controls four pitches)? You can do like Andy said and VERY CAREFULLY pop the ICs out of the white sockets and swap them - be absolutely certain that they have the same markings and that you put them into the sockets in the correct orientation. Then see if you get problems with different notes instead. WARNING: If they are not marked the same then do NOT do this. I'll let Andy take it from here. Before doing anything, please post a close up photo of the markings on the chip(s) and also take another photo that includes the circuits for all the notes - then Andy will have more information to work with. Wish I can help more but I don't want to be giving you bad information. I am curious to see how this turns out. Like Andy said I think it will give you that "cheezy" sound you are looking for.
    - jimmy
    Jimmy Williams
    Hobbyist (organist/technician)
    Gulbransen Model D with Leslie 204
    Farfisa Compact / Leslie 860 and Combo Preamp III / Hammond Porta-B

  7. #7
    Senior Member jimmywilliams's Avatar
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    Forgot to clarify about the orientation of the ICs ... you have to take note of where the little half-circle "notch" is on the top of the chip. You have to put it back the same way. If you put them in backwards the chip can be ruined.
    Jimmy Williams
    Hobbyist (organist/technician)
    Gulbransen Model D with Leslie 204
    Farfisa Compact / Leslie 860 and Combo Preamp III / Hammond Porta-B

  8. #8

    thank you, that answer was very helpful. I removed each of the black ICs from their white housings, in turn, and found that 2 of the 4 are functional and 2 are broken. Switching them around to different places made different keys work, showing that it's definitely the ICs at fault. More detailed pictures are below. The 2 ICs are the 2 broken ones. If anyone knows if these are available please let me know.

    Any other comments or advice welcome of course.






  9. #9
    Senior Member jimmywilliams's Avatar
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    Charles - are you in Europe (I guess you are becuase you paid for the organ in Euros). I came across this source (looks to be Italian?) - the SAJ210-AX7 chips are 10 euros each. I think these are the chips you need - though the second printed line on the IC looks different. Andy would know better. I know nothing about this source and there may be others you can research too.

    http://www.vintagechip.altervista.or...AJ210-AX7.html

    Click the "home page" link to see the price list for all their ICs.

    Hope this helps,
    jimmy
    Jimmy Williams
    Hobbyist (organist/technician)
    Gulbransen Model D with Leslie 204
    Farfisa Compact / Leslie 860 and Combo Preamp III / Hammond Porta-B

  10. #10

    It seems like a good find, he has a lot of stuff in stock. As it happens I have already found and contacted him, and he replied half an hour ago saying they are in stock. Additionally he offered a half price alternative: the "SAA1004N, fully working 100%, guaranteed and 100% equivalent to the SAJ210". He attached a PDF (see image below), which doesn't mean a lot to me. Anyone heard of these alternatives? They are 5 euros each instead of 10. BTW for anyone else interested his postage is 6 euros in Europe and 7 to USA.

    Thanks for your continuing help!


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