I have a strange problem with a VFX/SD that has been upgraded to an SD1-32 (ROM version 4.10). I bought it used and quite cheap too. It’s mostly working fine except that the aftertouch (both channel and poly) always rises to maximum shortly after pressing any key (provided pressure is activated in the patch). Velocity works normally though. When sending MIDI to the synth it also functions as expected.
Another SD1 owner posted a similar issue on two different forums a few years ago, but sadly both threads are dead ends.
At first I thought it might just be dirt, but the problem persisted after a thorough cleaning (it was quite full of dust and dead silverfish bugs).
The connector between the coil boards had already been replaced with a wire, continuity checks out fine.
I tried both a soft and a hard reset as described in the service manual, made no difference. I checked if the ferrite bead is clear from the mainboard and the flat cable is folded around the gate array, as described in Service Bulletin #12.
Since velocity does work normally and I don’t have any of the usual bad connector misbehaviour (random notes etc), I assume it has to be something else. Next suspect was the KPC board (rev D, version 2.33). Especially because for some unknown reason this board had been modified as follows:
-the trace between pin 1 and 2 of U4 (74HC00AN) was cut
-there was a wire running from pin 2 of U4 to pin 30 of U1 (MC68HC11A1P)
-there was a wire running from pin 3 of U4 to pin pin 6 of U3 (S38BC01PS01)
-the trace between pin 30 of U1 and pin 6 of U3 was cut
As far as I could figure out this means the clock line between the processor and the KPC chip was rerouted through a (normally unused NAND gate). I really wonder why ??? Anyway, I undid the modification but again it made no difference whatsoever.
I then tried booting up the synth with a “naked” keybed (all keys removed from the assembly). I had expected some kind of error but strangely enough, keyboard calibration passed without any problem. Maybe this is just how OS 4.10 deals with the keyboard? Or yet another clue to suspect the KPC?
When booting without the keyboard attached I get the message “KEYBOARD IS NOT ATTACHED” and booting freezes.
When booting with ONLY the KPC attached, I get “KEYBOARD CALIBRATION FAILED” but I do get the option to ignore and continue. Does that mean it could be something in the coil boards after all?
Is there anything else I can check before replacing the KPC board? There’s one up for sale in France (I live in the Netherlands) but before I spend any money on that while keeping my fingers crossed it will solve the problem, I’d like to make sure if the the issue is really with the KPC.
The main reason I’d like to fix and hold on to this synth is the poly pressure keyboard, so even though it works fine as a MIDI sound source that kind of defeats its purpose for me…
greetings from Holland,