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Author Topic: Organ Problem  (Read 1849 times)
BlueBee
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« on: September 13, 2012, 08:19:55 PM »

OK Beeks, which wire do I need to tweak to fix this 1974 Conn Organ I bought in a garage sale?  Letís put some of that beek expertise to GOOD use  grin

Problem is the E keys produce nothing but static huh  The rest of the keys are working ok.  The other big problem is the bottom keyboard is not being amplified correctly; I can barely hear it.  

This is a transistor organ and has no vacuum tubes in the circuitry or the main amplifier.  The real organ aficionados really value the old vacuum tube sound, but hey, Iím just a beek.  All I want is sound!  Where do I start?






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AllenF
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« Reply #1 on: September 13, 2012, 08:45:18 PM »

Give it a good cleaning.   Dust can cause lots of problems.   
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BlueBee
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« Reply #2 on: September 13, 2012, 08:47:57 PM »

A good cleaning with what?  There is a LOT of wires and electronics in there. 

It really is remarkable the craftsmanship that went into these (American made) things.  It must have taken forever to build them.  The wiring alone would have been a nightmare.
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iddee
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« Reply #3 on: September 13, 2012, 09:37:54 PM »

Electro-wash. Just spray it like washing something down with a water hose. It dries without leaving residue and is safe on electronic boards and wires,

http://www.mcmelectronics.com/product/ITW-CHEMTRONICS-ES1603-/20-2080


PS. I thought all Obummer supporters had an organ problem.

 lau lau lau
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BlueBee
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« Reply #4 on: September 13, 2012, 11:06:50 PM »

OK folks, giving the thing a good cleaning is a good idea.  However it almost always takes more than a spray down to fix an electronic circuit.  Like I said, only the E notes are static.  What is likely to only affect the Es?  What might I need to worry about in an amp that is 40 years old?  Electrolytics drying out?  Poor DC rails?  Aging transistors?  Oxidation of the thin gauge wires they used to wire the keys to the circuitry?  There are literally hundreds and hundreds of small gauge wires connecting each key junction to the circuit boards.  The wires donít appear to be copper either  Sad  

I'll have to post a photo showing the magnitude of wiring in this thing!  It's a real rats nest in there.
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boca
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« Reply #5 on: September 14, 2012, 04:57:03 AM »

The best cleaning for an electronic circuit is a bath in isopropyl alcohol in an ultrasonic cleaner.
In this case the dimension of the panels make it close to impossible. Maybe the smaller panels can be cleaned in this way.
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sterling
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« Reply #6 on: September 14, 2012, 11:04:49 AM »

Do you play that thing a church? evil
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Geoff
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« Reply #7 on: September 14, 2012, 06:13:51 PM »

    Got similar problem with a Yamaha about the same vintage.
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BlueBee
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« Reply #8 on: September 14, 2012, 07:21:25 PM »

Sterling, Iím more of a preacher/teacher than a musician; you know that  grin

Geoff, I havenít figured out exactly how these things work yet, but there is a group of 555 based daughter boards that probably generate the base frequencies for each key in my machine.  Theyíre the 12 vertical boards you can see on the right side of the first 2 photos.  It looks like the keyboards are wired into those 555 boards.  The board on the far end is the one that generates the E notes.  Iíve already tried swapping the boards around but the problem still sticks with the E notes.  I think the next step will be to get out the oscilloscope and start back tracking the frequencies out of the 555 timers.

I would bet many of the electrolytics have little capacitance left in them after 40 years so my bet is that one of them is causing my volume problems on the lower keyboard.  I want to get this darn E note problem fixed before moving into the amplifier issue.

The sad thing about these wonderful old machines is they donít have much value right now in my area (the transistor based ones).  Many times people just send them with the garbage man or sell them for a few dollars.  Mine sold for $999 in 1974.  That was a lot of money back then.  I bought mine for $25 in a garage saleÖ.and I might have overpaid!!! 
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sterling
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« Reply #9 on: September 17, 2012, 07:06:46 PM »

Iím more of a preacher/teacher than a musician; you know that 

Or maybe a false prophet. evil grin
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deknow
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« Reply #10 on: September 17, 2012, 08:21:56 PM »

Start by replacing the caps in the power supply (it is probably bipolar +-15v for the organ).  You can use higher uf caps...but stick with the original voltage ratings.  Especially on the power supply and on all transistors (and any component that gets hot), look at all the solder joints under well lit magnification...look for faint circular cracks in the solder blobs around the leads...reflow the solder on any that are suspect.

My guess is that this has one oscillator per note....with frequency doublers for each octave...having an oscilloscope would help....but often replacing the big caps and fixing cracked solder mountain is all that is needed.

Deknow
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BlueBee
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« Reply #11 on: September 17, 2012, 08:35:12 PM »

Thanks deknow, that sounds like some good advice! 

I hadn't given much thought to cold solder joints, cracks, or reflowing any suspect joints; great idea!  You're probably right about the bipolar nature of the power supply back then, I haven't dug into the PS yet.  I do have a scope and am going to troubleshoot it one of these days when I get some more free time.  Will take some more photos then.

Luckily there only appears to be one custom IC in the machine and it seems to be working.  There was a mouse nest under one of the keyboards.  The mouse dug out padding from around the Leslie to make it's nest Sad  Luckily it didn't damage the Leslie and it didn't chew into the hundreds of wires around the nest.  Thanks God! 
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kingbee
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« Reply #12 on: September 18, 2012, 01:38:36 PM »

Start by replacing the caps in the power supply (it is probably bipolar...

That should be a snap for old BlueBee, he's bipolar too.  grin
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