This repair follows the Mattel Synsonic entry from my blog. Just found a non-working SD1 on craigslist in the mist of Carpiano in Italy, a very foggy village with zombies. The (undead) seller claimed the SD1 does not work due to internal battery, which sounded a bit weird, but ok: in Europe, the Ensoniq stuff is quite rare.
The overall shape SD1 is quite good, however some screws are missing and the floppy drive is dangling for some reasons-- Dangling and dangling.
Back home, the SD1 simply does not switch on but a quick flash on the display VFD. I tried the basic reset procedure (for fun) but this was a total waste of good time. However I managed to find out the service manual and PSU section schematics, better than nothing (you can find all documentation at the end). Note that the SD1 is basically the same as the VFX model and it shares quite all in common, including the PSU, but special 32 voices versions that requires different voltages.
Opening the SD1 is easy: some classic Ensoniq hex screws on the front board, finally a couples on the rear. Not a big deal, the main control panel just lift off quite easily.
UPPER - First task is to verify all voltages. The primary showed correctly the VACs on terminal from transformer. Following the +5V for analog, another +5V for digital, +12V for analog and its relative -12V. It's quite easy and well -ndicated on the main board. Also some 9VAC for the VDF display filament. Quite explicit stuff including: 7805, 7812, 7912 voltage regulators and a strange bird LM2925 a low dropout regulator with delayed reset that generates the essential reset for digital section IC and CPU. OH ! If forgot kind of disclaimer: don't play with primary voltage if you don't know what your doing; I feel stupid to write this every time, but it seems to be important for some Yankees laws.
A quick test to all 6 fuses, all ok, the diode rectifiers 1N5400 (CR1-6)seems ok. A quick ESR value to capacitors, but the seemed in excellent shape and low values. Special LM2925 is measured with black probe on pin 3 (ground), and either red probe on pin 5 (+5VDC for the VRES line) or pin 2 (+5VDC for the +5D line).
Checking the -12V and it is missing! nice! the voltage regulator 7912 is plain dead (after verify C14) the input V was good but output was out of value. The PSU board double sided soldered (like the motherboard), so cutting legs is the quickest way to change the bummer.
Once changed the 7912, all the tensions were there (without load) but the SD1 is still not waking up :( Time to check the LM2925 reset (after short ms delayed boot) at high VRES +5v (no really but it's in tolerance) anyway I changed the 16V big capacitors just in case. But still nothing, the serial communication (Motorola 68681P - DUART ) just freezes CPU boot if something wrong. Time to check the more complex digital board.
UPPER: To fully access the whole motherboard you have to remove the keyboard,it's about 20 screws under the hood (long and short , don't mixup)! An eye inspection revealed quite nothing: no joint solders, no broken tracks, just something really dirty between CPU 68000 and the custom OTIS chip. Note: there's another low dropout regulator with reset 2926 this time that sends also a reset other various chip (remember: there are NO schematics).
UPPER: The socket OTISR2 VLSI device had a bit of oxidation around the pins. Some intensive cleaning thenback in place ... and yes, the SD1 finally fired up! But the sound was distorted for some reasons and the slider was like having jumping value. That was probably a beginning of an oscilloscope pain session, but I checked twice the OTIS also the 5510 and the CPU, then I finally found an interrupted track at pin 1 of OTIS. The OTIS was giving ok at DUART but was not really working (note if you want to glitch and circuitbend the SD1, just cut the track on PIN1 or bend it - actually don't do it please).
--- and here we go! Perfectly working! a bit clunky keys, but I had no CALIBRATION error (for now) and no SELF TEST MODE. All buttons were working, outputs, slider is now ok. Now reset procedure:
RESET PROCEDURE: HOLD PRESET BUTTON AND PRESS SOFT #1 BUTTON (UPPER LEFT CORNER OF SCREEN). RELEASE BOTH, PRESS YES AT THE PROMPT.
If you need it, here's the english MANUAL
and here the SERVICE MANUAL (including PSU)
UPPER Just adding some information for floppy disk drive that is not working: the Sony mp-f63w is simply not detected by the SD1, but J4 gives normal +5V (RED) for logic and +12V for motor (white). Note that for old devices, the -12V is mandatory. I suppose the J4 cable has some troubles on the 4-pins connectors making not really a good contact on the pins. So I had to replace it with a standard from another PC molex. Then a good head cleaning and it perfectly worked.
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