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Cordovox CRD-0610 Combo Organ Service

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  • Cordovox CRD-0610 Combo Organ Service

    I just got a free Cordovox with "bad chips" and I just got it cleaned up and plugged in and all the tones seem to work. However, the tuning of the black keys only is way off...the trimmer just isn't in range to get the keys in tune but all the other keys seem to be in great shape tone-wise. I am somewhat curious as to whether or not the 12v supply to the TCA430N ICs is still really 12v, but that's for another day of testing. Worst case I'll rebuild the tone board with modern resistors and call it a day.
    The other main problem is the common tone leakage issue. I'll do a replacement of all the electrolytics for best practice's sake but wondering if anyone can chime in with other good maintenance items to do as long as I'm in the mud. I really wouldn't even mind doing a full rebuild but I'd much rather get to playing!
    Also, this thing can't really have 14KV capacitors on the transformer primary can it?! Looking forward to digging in.

  • #2
    Ah yes the 12v rail is a full volt low. Also noticed the preset buttons seem to not be doing their thing, but the associated percussion is pulsing through so might not be as clean a service as I'd hoped. Anyway, I'll replace all the elecros and report back with any improvements.

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    • #3
      Originally posted by kdmr View Post
      this thing can't really have 14KV capacitors on the transformer primary can it?
      Sounds like a misprint!

      -------

      Hammond M-102 #21000.
      Leslie 147 #F7453.
      Hammond S-6 #72421

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      • #4
        Yes, indeed. I found 1.4kv capacitors in the appropriate place in the power supply box. Re-capped all the usual suspects and the main issue seemed to be from the vibrato circuit. Still some tone leaking at maximum volume, but I think that is basically normal for these old italian units.
        The 12v rail is still a volt low and still no luck on the tuning. The whole thing runs on 9 and 12v so I've considered just replacing the whole power supply with something modern. It's got one of these transistor-based regulators for the 12v rail and I want to delete it out of spite mostly.
        You may only view thumbnails in this gallery. This gallery has 1 photos.

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        • #5
          Originally posted by kdmr View Post
          The whole thing runs on 9 and 12v so I've considered just replacing the whole power supply with something modern.
          When I was attempting to determine if there was a 5 volt rail problem with the Ahlborn SL-250 I was working on a while back, I replaced it temporarily with a supply consisting of a 12 volt motorcycle battery and an adjustable DC-DC buck converter module. That allowed me to see whether the problem symptom changed as I went below 5 volts or just above 5 volts. (It didn't -- the problem was somewhere else.)
          -------

          Hammond M-102 #21000.
          Leslie 147 #F7453.
          Hammond S-6 #72421

          Comment


          • #6
            Originally posted by gtc View Post

            When I was attempting to determine if there was a 5 volt rail problem with the Ahlborn SL-250 I was working on a while back, I replaced it temporarily with a supply consisting of a 12 volt motorcycle battery and an adjustable DC-DC buck converter module. That allowed me to see whether the problem symptom changed as I went below 5 volts or just above 5 volts. (It didn't -- the problem was somewhere else.)
            Interesting! I'm going to shoehorn in some DC supplies I have laying around to see what I can see. The B- rail is really just ground...not sure who they were trying to fool or if they originally meant to isolate from the chassis ground or what but either way it makes my work a bit easier for now.

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            • #7
              and success. I tied in a 9v and 12v wall supply to the appropriate pins and she fired right up with a noticeable decrease in bleed (still some though). Surprised at the lowered noise floor even with a switching dc supply. May whip up an ac-to-dc linear unit for comparison. Anyway, I fixed the tuning by auditioning new resistors around the tone generators. This organ uses the ITT TCA430n chips. Only two of the trimmers were out of range so I just tested a few resistors across the existing fixed resistors and soldered in the value I liked in parallel. I'll likely do this properly when I install the new power supply, but for this tier of combo organ I'm not overly concerned with making it super clean just for little ol' me.

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              • #8
                Originally posted by kdmr View Post
                I tied in a 9v and 12v wall supply to the appropriate pins and she fired right up
                Good to hear.

                That's a very rudimentary power supply -- not even full wave rectification. Installing a bridge rectifier and a couple of 3-pin regulators should do the trick.

                A recap of the usual suspects is always a good idea. The bleed though might be alleviated by some shunt capacitors from rail to ground in strategic places. May be worth poking around with a scope.
                -------

                Hammond M-102 #21000.
                Leslie 147 #F7453.
                Hammond S-6 #72421

                Comment


                • #9
                  The power box is so tight inside it honestly will be less work to just tear it out and rebuild the whole power supply circuit.

                  I had the same thought about adding capacitors. It may be from working so heavily with modular synthesizers but I was surprised that none of the tone generation ICs had any filtering near the rail connections. I think adding 100nf units from 12v to ground at least on those 3 chips would be a worthwhile experiment.

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