Drumulator will not power up, outputs burst of drums.

[czaleschuk]

I recently purchased a non-working drumulator with the intention of repairing it to use in my music. It currently will not power up.

Upon switching on, however, it outputs a quick burst of drums, maybe 6-8 sounds in rapid succession, before they stop. They sound clean and clear, and respond to the front mix volume knob. But no segment display, no LEDs, no response on any of the buttons.


Ive tested the rectifier diodes, 5v, 15v and -15v rails and all seem good. I have pulled and cleaned the board(dirty, lots of ?dog? hair) with iso and visually inspected it for broken/missing traces and have found none. There is a lot of areas with lifted solder mask on the rear of the board(top side with buttons), but all questionable traces have been verified for continuity. I have gently pulled and reseated every IC that is socketed, including the Z80 and CTC without change. I have purchased a new OS 3.0 EProm in an attempt to get something out of the front panel and that has made no difference. Still no lights, no segment display. Dead. The Z80 and CTC both seem to receive the reset signal from the CA3086. I have been able to see some waveforms on the few data lines of the z80 I could test with a cheap, audio rate only(50us horiz.) oscilloscope I borrowed. None of the front panel buttons seem stuck closed, and the ones that i have tested work. I have tried the POOF sequence and reset command without illumination and no luck.


The 6116 ICs, 13K and 15K receive 3.1v when off, and 5.2v when powered on, and the rest of the ICs in the Digital side all have 5.1ish volts on their VCC.

P.C.B. is Rev 1, 11/30/82, Serial #1049

I am pretty stuck and in need of some assistance, and simplified information regarding the bare minumum requirements for front panel illumination, and  knowledge of typical Drumulator start up behaviour.

Thanks!
C.