Archive of the former Yahoo!Groups mailing list: Vintage Simmons Drums (UK) Users Group

I’ve recently had a couple of SDS-9’s in the workshop.  Both exhibiting the same problem, power itup, LED’s light, 7-segment display shows the software version, then nothing, everythingblank and not working.

It took a long time to get the first one working, but once Iknew what was happening, and found the test ROM, the next one was much easier.

The technical description says that the SDS-9 has a testmodebuilt in.  Unfortunately it doesn’t havethe full testmode – it does the tests but doesn’t tell you what the fault is ifit fails :-(  So on boot, the normal ROM doesa ROM checksum, RAM check, A/D check, fast interrupt (1KHz clock) check and serial receivecheck.  If any of these fail, it seems tojust hang waiting for the test to pass, which never happens!

I found on the first SDS-9 that it wasn’t getting an end ofconversion (EOC) from the ADC IC54.  The CPUwaits for an EOC before attempting to read what’s on the data bus, and if it doesn’tget it, it waits forever...  ReplacingIC54 fixed the problem.

For the 2^nd SDS-9, turned out the fast interruptfrom IC1 (555) wasn’t there.  The 555 wascompletely dead, no fast interrupt signal nor sawtooth.  Replacing it brought the unit back to life :-)

The testROM will show you (via the panel LEDs) where the fault is likely to lie,and makes troubleshooting so much easier. Otherwise check that the above bootup tests (ROM/RAM/A/D/interrupt/serial receive) are doing what they should.