Audio Systems: Korg SDD-3000, korg sdd 3000, step up converter

Question
Hello,

I recently moved to the UK from the US with all of my music equipment.  One of the units is a Korg SDD-3000 digital delay from the 80's.  The unit was bought from Germany and is stamped for 220 Volts on the rear panel.  In the US, I used a step-up converter to convert from 120 Volts.  When I got to the UK, I tried to hook up all of my equipment (properly with converters, etc.) and I plugged in the Korg SDD-3000 without a converter.  When I went to pick up my guitar, I got the biggest shock in my life.  This could be due to the fact that I was unknowingly using a faulty power strip for the equipment requiring conversion that had blown.  My amplifier (Vox AC30) required conversion and had a charge to it. If this was due to the faulty power strip, it could have kicked a charge back into the SDD-3000 as it was the last effect processor before the amp in the signal chain.  At any rate, the SDD-3000 does not work properly.  It hums loudly and numerous controls (mainly in the modulation section) are either dead or confused (controlling the wrong thing).  I took it apart and, although I sifted through it in much detail, could find nothing obviously wrong with it... all capacitors, transistors, etc. seem to appear normal and no fuses are blown.  I bought a multi-meter with the thought of measuring all of the transistors and capacitors to see which are blown.  This seems to be a huge undertaking and I wonder if there is any advice you can offer.  Taking it to an electronics repair technician is difficult for me as I live quite rurally.  Any advice you can offer is welcome.  One last related question... Britain is rated 240 Volts, the unit is rated for 220 Volts... I assumed it would still work properly with the slight voltage difference.  Would a difference that small cause any problems?  Thank you.

Answer
you need to isolate which unit is causing the hum first, by process of elimination, take pieces out of signal path to do this. once you figured which unit/s are humming, look closely at circuit board near input/output jacks (jacks coming loose are a common problem), resolder where needed, also check/replace large electrolytic capacitors in power supply section (should be 2 or more near where power transformer wires attach to circuit board)look at tops of caps looking for any 'bulging' of the metal cans and also look at the condition of the heat shrink label on cap. if looks like cap label has shrunk, replace cap. any more will require more indepth servicing techniques, re. checking voltage regulators for proper voltages. They are marked well, look like transistors but are marked 7805, 7905,7809,7909, 7812 7815, 7912, 7915. 78 numbered regulators are positive voltage, 79 series are negative voltage. normally, pin 1 is input, pin 2 is ground, pin 3 is regulated output. also make sure there is no ac voltage on the output pins. this means you have bad diodes off of transformer wires. hope this helps, i tried to be as indepth as possible.......garry