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Farfisa Compact Duo Lower manual volume

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  • Drawbar Dave
    replied
    Originally posted by David Anderson View Post
    I think Drawbar Dave and I have both completely replaced all electrolytic caps in our own Farfisas with no regrets.

    I did it because I didn't want to have to keep taking my Duo apart every time another one failed. The result of my work is that it's been quite reliable.

    When you have oscillator circuits, the caps have to be able to charge and discharge quickly to provide the necessary current demand for the circuit. Old electrolytic capacitors often can't do this, so the oscillator won't run. In some oscillator circuits in guitar amps, it's even necessary, after decades, to replace film caps.

    If you're playing a transistor combo organ in 2020, you have to accept the fact that they were not designed to be working 50 years after they left the factory.
    No regrets here! It just seems to be a safe approach. Combo organs do not want to be pulled apart regularly either. It's a question of replacing all the capacitors at once, tuning it once and putting it back together. I offer mine for rent to recording studios and pro-artists and I want it to be as reliable as a Farfisa can be.

    I have found it a satisfying and rewarding job when I have done a full replacement and returned it as close as possible to factory spec. The MK2 that I kept is in perfect tune and functionality six years later, even though it has been moved around quite a lot.

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  • David Anderson
    replied
    I think Drawbar Dave and I have both completely replaced all electrolytic caps in our own Farfisas with no regrets.

    I did it because I didn't want to have to keep taking my Duo apart every time another one failed. The result of my work is that it's been quite reliable.

    When you have oscillator circuits, the caps have to be able to charge and discharge quickly to provide the necessary current demand for the circuit. Old electrolytic capacitors often can't do this, so the oscillator won't run. In some oscillator circuits in guitar amps, it's even necessary, after decades, to replace film caps.

    If you're playing a transistor combo organ in 2020, you have to accept the fact that they were not designed to be working 50 years after they left the factory.

    Leave a comment:


  • Drawbar Dave
    replied
    On a Farfisa Compact it’s a pretty safe bet that a capacitor is the root of the problem

    Leave a comment:


  • ebo
    replied
    Originally posted by Drawbar Dave View Post
    I have never had to repair the percussion on my CD30, just the Tremolo. Firstly there are two separate percussion circuits. The bass/pedal one is totally different.

    The rotary selector for fast/medium/slow has capacitors attached to it to time the decay. You might replace the capacitors or check the solder joints. As for the lower manual not working, it does not behave in the same way as the upper IIRC. If you hold a chord on the upper and it has decayed, what happens if you then press a key on the lower manual? It should retrigger the chord on the upper manual.
    Thanks again Dave for your valuable advice. I took a closer look and some meditation, before changing two suspect caps (arrows) on the Perc-board. Voilà. Repeat is working properly again. I am so happy. Thank you so much 👍

    Click image for larger version

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  • ebo
    replied
    Originally posted by Drawbar Dave View Post
    I have never had to repair the percussion on my CD30, just the Tremolo. Firstly there are two separate percussion circuits. The bass/pedal one is totally different.

    The rotary selector for fast/medium/slow has capacitors attached to it to time the decay. You might replace the capacitors or check the solder joints. As for the lower manual not working, it does not behave in the same way as the upper IIRC. If you hold a chord on the upper and it has decayed, what happens if you then press a key on the lower manual? It should retrigger the chord on the upper manual.
    Thank you very much! A useful hint. First target to check: the rotary selector.

    Leave a comment:


  • Drawbar Dave
    replied
    I have never had to repair the percussion on my CD30, just the Tremolo. Firstly there are two separate percussion circuits. The bass/pedal one is totally different.

    The rotary selector for fast/medium/slow has capacitors attached to it to time the decay. You might replace the capacitors or check the solder joints. As for the lower manual not working, it does not behave in the same way as the upper IIRC. If you hold a chord on the upper and it has decayed, what happens if you then press a key on the lower manual? It should retrigger the chord on the upper manual.

    Leave a comment:


  • ebo
    replied
    Originally posted by Drawbar Dave View Post
    There are two bulbs in the knee lever unit. Do you have the original F/AR power supply with it? That should send 9 vac and 24vdc. The dc gets knocked down to 9 vdc by a diode as it enters the organ and then powers all of the boards. The 9 vac powers the knee lever bulbs, the expression pedal bulb and tremolo bulb. There's also a gizmo under the bottom right end panel that boosts the dc up much higher for the neon in the repeat circuit. Give me a shout if you need any help!
    Yes thank you! I would need some help/advice how to best approach that frequent Percussion/Repeat issue on CD MKII. Symptoms:

    • Repeat + Percussion fast (left position on rotary switch) on upper manual do not work (just straight sound)
    • Percussion medium-slow on upper Manual working.
    • Perc/Repeat on lower manual does not work.
    • Percussion on Bass manual/Pedals working (medium-slow)
    • Tremolo working
    • Knee booster working.

    Bulbs working or replaced. Some Facon-Caps replaced on the board. Heatsink-Transistor is warming up. I guess it should be somewhere in the Perc-Rep-Board.

    Is that the right track? How to proceed with this issue? Any idea is very welcome.

    Leave a comment:


  • Drawbar Dave
    commented on 's reply
    That rings a bell I think that’s what I used in mine too.

  • David Anderson
    commented on 's reply
    Much better.

  • Jaim
    replied
    Thanks David - I replaced it with a 1N4004. Fun little organ.

    Jim

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  • David Anderson
    replied
    I would use something larger than a 1N4148 for any kind of DC rectification. Those are mainly used for key switching in organs. Their forward continuous current rating is only 300mA. There are known cases in guitar amps where designers tried to use 1N4148 for low voltage supplies, and they did not survive long term.

    Leave a comment:


  • Jaim
    replied
    The 10 & 25uf caps on the PA-31 bd looked leaky. - one tested bad which was in the lower manual input. Replaced all. Manual volume is normal. On to the the divider and knee level.

    Jim

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  • Jaim
    replied
    The 9VAC is fine. The 9.8 VDC derived from the 9VAC is not. I disconnected the load to the diode and still nothing. The cap was replaced so I have a bad 2EQ5 diode. Replaced with a 1N4148. Now I have the 9.8 VDC. The volume is better and the tremolo works. The volume will vary by itself. Going to replace the electrolytic caps on the amp bd. Just a process of working through the issues.

    Thanks for the insight.

    Jim

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  • Drawbar Dave
    commented on 's reply
    Yes it should do. Check for the 9 vac on the tag strip bottom right when viewed from rear. Organ should work full volume without the pedal. You can make up an adapter for the expression pedal plug and use a stock single ended synth pedal if needed.

  • Jaim
    replied
    The knee lever will work with the expression pedal disconnected? The 125 VDC from the FA-28 bd under the right lower check block is ok. I'll start chasing the 9Vac.

    Jim

    Leave a comment:

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