[sdiy] Ensoniq Esq-1 main board question

[Rainer Buchty]

On Thu, 25 Jun 2020, Mark G via Synth-diy wrote:

> I acquired copies of the schematics from buchty.net, but the ones of 
> the main board circuits are not great quality so some things are hard 
> to read, which makes troubleshooting more difficult.

That's why Tony Gonzalez redrew them some decade ago. These you also 
find on my page.

> Does anyone have any knowledge of common main board issues that I can
> check, or any tips? 

From your description: What your machine seemingly does is crashing 
right after the reset. It's alive for long ago so that the display 
processor gets a first message (and hence does not remain in diagnostic 
mode), but then dies.

This unfortunately is quite unspecific and can be anything and 
everything like mechanical issues (a contact problem due to corrosion, 
hair-cracked traces, cold solder spots), ROM/RAM issues, issues with the 
DUART (which does the bank switching of OSLO), with the DOC (creating 
E/Q clocks) and the arbiter circuitry (creating the CPU's switchable 
2MHz/1MHz clock depending on DOC or no-DOC access), memory decoding 
(some '139 having died).

The mentioned keyboard processor or the DAC, however, should not cause a 
crash as a dead keyboard processor just won't forward display button 
presses via the internal serial link (unlike the SQ80, where the CPU 
would wait for a start code coming from the polypressure controller 
indicating [un]successful keyboard calibration), likewise the DAC should 
cause no harm (unless it's that failed that it affects the A/D bus or 
brings down the 5V rail).

HTH,
 	Rainer