Odyssey, power supply upgrade

The negative power supply rail dropout that I experienced whilst repairing board B of my Arp Odyssey back in 2008 decided to become a permanent annoyance some months ago. When finally having the time for repairs, I decided to do the upgrade I had been pondering on during the 2008 repairs. So, 7×15 series regulators it is then!

I decided to use the original PSU board and modify it to fit the new regulators by removing or disconnecting old parts whichever appropriate. Switching to 7×15 regulators actually makes the circuit much more simple, besides these only bypass capacitors (100nF on both input and output) need to be added. For these, I decided to use ceramic SMD capacitors (10% 50V) as they fit neatly between foils on the solder side. To match the original pinout on the board, the positive rail regulator (7815) had to be installed back side up.

7815 regulator installed back side up.

100nF SMD bypass capacitors for the 7x15 regulators

My approach with removing parts not needed should be visible from the following picture :)

Heatsinks for the 7x15 regulators.

Whilst at it, I decided to make the PSU board detachable by adding connectors in-between both the power switch and the power socket. Both use the same type of connector, but the mating polarity is different to avoid mixing up connectors. I also replaced the fuse with a regular socketed one.

The new PSU connectors.

Mods complete!

And there it is! The next time the PSU blows up, maybe I’ll test making a switch-mode version :). On the modded PSU, the new negative rail regulator (7915) gives out around -14,8V but at least at a glance, this doesn’t seem to affect the tuning or such.

Best thing is of course, that fixing the PSU revealed more faults. Apparently, the power supply failure has damaged the VCF circuit (osc mixer output at VCF input, nothing on its output) so the Odyssey gets to spend yet more time on the “lab bench”. I also managed to break one of the sliders, its lever snapped off when I moved the synth uncautiously. Yay.

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7 responses to “Odyssey, power supply upgrade”

  1. Morten Tornes says :

    Hi. I just bought a Whiteface Odyssey, which I´m awaiting in the post from the US shortly. Found your blog when surfing around for info on the Odyssey, and finding it quite insightfull. I live in Norway, with 220v, and the synth comes from the US so it´s 110v. I´ve been told that it´s quite easy to switch the power supply from 110v to 220v, just moving some of the cables, changing the fuse and doing some adjustments to the trim pots. I was told the service manual describes this, but I couldn´t find anything in the manual about it. I see the powers supply schematics say 110v and 230/240v many places on the left side, but I can´t make out what they mean. Do you know anything about this? I was told this by a synth tech, but he has about a years waiting list to take new synths in, so I´m planning to have a buddy who has some background in electronics help me out and try to sort it.

    Another thing. I was recomended to change the caps in the power supply. As far as I see there are 2 tant caps (c2,c3) and 2 electrolytic caps (c4,c5) Correct? I found the tant caps in the catalog from the local electronic component shop, but I´m wondering about the electrolytic caps. The manual says these should be 250mf 50v. The highest mf they have is a 10mf. Is this some outdated description method? Should it actually be 250uf? They don´t have 250uf either, but could I use a 220uf?

    Can I use these?
    https://www.elfaelektronikk.no/elfa3~no_no/elfa/init.do?item=67-713-13

    https://www.elfaelektronikk.no/elfa3~no_no/elfa/init.do?item=67-789-30&toc=19198

    Any answers to my questions would be highly appreciated.
    Thanks

    • arto says :

      Switching between 110V and 220V is very much evident on the power supply schematic; cable connections, fuse types etc. are all there. What’s important here is to keep in mind that if neither you or your buddy don’t know how to interpret the schematic, you shouldn’t be modding the power supply modding either (hazardous voltages and all that). Sorry, this just is the way it is.

      BUT.. Just to point the way, type -1 is 120V and -2/-3/-4 are 220V on the schematic (higher voltage, less amperes on the fuse). Cable colors depend on the version of Odyssey you have, just identify and follow the schematic accordingly. Trimpots are used to calibrate the +/-15VDC outputs for correct voltage, measure both rails against GND and adjust trims accordingly. This can also be done with the power supply disconnected from rest of the boards, just remember to check that both rails remain on correct levels once re-connected.

      As for the caps, you’re quite right about the manual using a older/alternate marking method. I’m pretty sure 220µF will do for C4/C5, but I don’t see going for a higher value (say, 330µF or 470µF) a problem either. Definitely don’t go under the specced voltage level (50VDC) at least.

      • Morten Tornes says :

        Thank you very much. I wasn´t sure how capable my buddy was. I hadn´t shown him the schematic yet, but I showed it to him now, and he said it was super easy, so I guess that´s a good sign. Keep up the good DIY´ing :-)

  2. Synth Chaser says :

    But you didn’t change out the 40 year old capacitors!

    • Arto says :

      But you didn’t change out the 40 year old capacitors!

      Well their measured values were fine so I didn’t see the point :)

      • jonathan says :

        well – in my humble opinion – the ‘point’ is to avoid a trail of destruction downstream from the power supply board when your old caps blow… I promise – they will… and soon. It happened on my odyssey and on my mono/poly. Once your ESR starts dropping (it will have by now – did you measure it?) then the deterioration will escalate logarithmically – until **POOF**… but you may get lucky – and just blow a fuse… or lose rectifiers. I lost some 4000 series cmos chips in my mono poly…

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