[sdiy] Yamaha CS30 repair

[Kevin Walsh]

Thanks folks.
I ordered some 1N540x diodes last night.
I think I'll err on the side of caution and put those in for some extra headroom.
Better looking at it than for it...
Kevin.

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________________________________
From: Didrik Madheden <nitro2k01 at gmail.com>
Sent: Friday, July 26, 2024 4:22:30 AM
To: Kevin Walsh <kadub at outlook.com>
Cc: SDIY <synth-diy at synth-diy.org>
Subject: Re: [sdiy] Yamaha CS30 repair

I agree with the previous speakers.

Another more subtle perspective. You've replaced the diodes with schottkys. The diode drop goes maybe from 1.6 V (10DC-1 typical drop according to datasheet) to 0.5 V and the wasted power in the diodes is halved. Great. What happens next? The rectified voltage is now on average ~1 V higher, and the pass transistors in the 15V regulators have to drop slightly more voltage to keep regulation which results in slightly more wasted test there instead. (And also the pass resistors to be fair.) This is a pretty slight effect and might not matter either way, but given the choice, dropping a but more in the diodes instead of the transistors is probably preferable. Replacing the diode pairs with discrete 1n400x is a fine choice.

/Didrik


On Thu, 25 Jul 2024, 19:19 Kevin Walsh via Synth-diy, <synth-diy at synth-diy.org<mailto:synth-diy at synth-diy.org>> wrote:
Hi all,
I have a Yamaha CS-30 in for repair that was dead on arrival. It only needed the dual diodes (D1 & D2) on the PSU replaced to get it working again.
I got it working by using two pairs of 1N4001's:

  *   One pair configured in common cathode
  *   One pair configured in common anode

Both secondary fuses were replaced with 1.6A fast blow fuses as per the service manual instructions. Given this, I figured any 2 or 3 amp diodes should work fine.
Being such a nice synth, I'd prefer to have the best long-term solution. Should I replace them with Schottky diodes for their lower forward voltage drop and efficiency, or stick with regular silicon diodes and opt for a higher current rating?
Any tips or recommendations for specific diode models would be most welcome.
Thanks,
Kevin.


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