Roland SH1000 recapping

Sometime ago i bought Roland’s first ever synthesizer, for about a quarter of what it goes for these days-it was in dire condition, mind you. The control panel rusty and battered, the silkscreen on a couple of spots barely readable.

I always believed mint condition items belong to museums, not being fit for use, abuse and misuse.. i feel the same way about vinyl records-people who wrap them in polypropylene covers from day one and treat them as if they’re going to break anyday soon.. good grief

I must say that although i truly love the instrument- i also fit the Kenton cv/gate control board a year ago, i rarely ever used it.

The other day i took it out for a spin and the tuning was way off, it was drifting. It wouldnt even span an octave-it was that bad.

Time to recap, i thought, and pulled out the Elnas, the Nichicons and the soldering iron-i figured i’d give a refresh to the power filtering section, part of what the service notes call the “Pulse Sheet Assembly”..

Before
I also upgraded the caps from 35v tolerance to 50v

Just a note: although the unit was in working condition, albeit out of tune, most of the 1uF caps on this board, were off their nominal capacitance-the 2.2 uF cap measuring a whooping 8.5 uF! Of the big 1000 uF caps, two were measuring 1200something uF, whereas the other two were still closer to the 1000 mark-and they all showed low ESR (40+ year old caps!). The three tantalum capacitors on this board were still working great, their value as per specs.

I fired the synth after recapping this board-the sound was a bit more definite, but the tuning was still off.

I decided to check the VCO board, pictured above. But, alas, no electrolytics there to substitute. I checked very carefully the board-and there it was, staring at me:

Polarity is negative at diode soldering onto the board

The diode+resistor combination to the upper far right of the board: the diode was broken in two!

The schematic calls for diode, 1S2473.. i checked a few diodes I had, and landed on a 1N4148 as a fitting substitute!

And.. yes now it IS tuned! The snipped diode was the issue!

Assorted pics of the wiring at the back of the oscillator board