Ensoniq EPS issue

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Ensoniq EPS issue

Post by gkmaia » Sun Oct 13, 2019 6:03 am

I bought a second hand EPS (not the 16, the standard one).

Got the ALL leds no display issue.

Power supply is fine.
The keyboard to main pub cable has been re-crimped.
MC68000 MPU seems to be managing the control, address and data bus.
MC68440 DMAC seems to be also doing its job pulsing addresses to the RAM.
27C256 EPROMs are getting address calls and shooting data.

If I unplug the keyboard PCB and type on buttons the display place the characters only on the first column.
If I plug the keyboard PCB back and type on buttons the display then place one character per column.
Seems the keyboard PCB is alive in some way.

If you look at the attached screen you will see the 68000 try to call the buses with repetitive routines for a couple seconds then goes quite. But it does not bring RESET or HALT low.

My suspicion is that the processor is not getting valid boot instructions from the EPROM and then goes quit. But I never sealed with this keyboard before so not sure how it behaves.

Anyone out there with some reasonable experience at the EPS component level to give me some hints?
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Re: Ensoniq EPS issue

Post by Rasputin » Sun Oct 13, 2019 1:27 pm

gkmaia wrote:
Sun Oct 13, 2019 6:03 am
My suspicion is that the processor is not getting valid boot instructions from the EPROM and then goes quit.
Dump the ROMs and verify the checksums.

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Re: Ensoniq EPS issue

Post by blueknob » Sun Oct 13, 2019 2:31 pm

I have the Service Manual for the ESP16+ which goes into some detail in top level fault finding, but how relevant it is to the EPS. There is a Diag. Disk for the 16+, I wonder if there is anything for the EPS.... only Mr R will know.

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Gear: Ensoniq Mirage-EPS-EPS16-ASR10
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Re: Ensoniq EPS issue

Post by Hyde » Sun Oct 13, 2019 3:45 pm

You are speaking beyond my level but, having had these machines apart many times. I know that the two circuit boards in the keyboard assembly(in the earlier versions) are connected buy tiny little wires that often break at the connection. Caused me a lot of problems
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