Vintage Simmons Drums (UK) Users Group

I think this post will be of much use to "niners" in the future - thanks 
Phil!

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electronically yours, jesper

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philmurr@... [Simmons_Drums] skrev den 2015-02-28 19:23:
> I\u2019ve recently had a couple of SDS-9\u2019s in the workshop.Both exhibiting
> the same problem, power it up, LED\u2019s light, 7-segment display shows the
> software version, then nothing, everything blank and not working.
>
> It took a long time to get the first one working, but once I knew what
> was happening, and found the test ROM, the next one was much easier.
>
>
> The technical description says that the SDS-9 has a testmode built
> in.Unfortunately it doesn\u2019t have the full testmode \u2013 it does the tests
> but doesn\u2019t tell you what the fault is if it fails :-(So on boot, the
> normal ROM does a ROM checksum, RAM check, A/D check, fast interrupt
> (1KHz clock) check and serial receive check.If any of these fail, it
> seems to just hang waiting for the test to pass, which never happens!
>
>
> I found on the first SDS-9 that it wasn\u2019t getting an end of conversion
> (EOC) from the ADC IC54.The CPU waits for an EOC before attempting to
> read what\u2019s on the data bus, and if it doesn\u2019t get it, it waits
> forever...Replacing IC54 fixed the problem.
>
>
> For the 2^nd SDS-9, turned out the fast interrupt from IC1 (555) wasn\u2019t
> there.The 555 was completely dead, no fast interrupt signal nor
> sawtooth.Replacing it brought the unit back to life :-)
>
>
> The test ROM 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.
>