Ensoniq VFX-SD stuck in display self-test mode

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Endeavour94
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Ensoniq VFX-SD stuck in display self-test mode

Post by Endeavour94 » Wed Jun 12, 2019 8:02 pm

I've got an Ensoniq VFX-SD that I'm fixing up and I could use some advice. When I got it, it had a dead display board (display would only ever light up from the filament voltage) so I followed the flow chart in the service manual till it said I should replace the entire board, which I did and it is now working in self test mode and responds to all the buttons. All the PSU voltages are within spec except Vres going to the mainboard which is 2.48VDC. My understanding is that this voltage resets the logic chips/microprocessors or turns them on per se, which would explain why it's not booting (logic chips need at least 3-5 volts to go high, and the service manual says at least 2.7V) The input voltage on the LM2925 regulator is only about 10.5VDC, which is a tad low I believe. Before I do anything, am I correct that the PSU caps would be in question if that input voltage is low?

Rasputin
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Re: Ensoniq VFX-SD stuck in display self-test mode

Post by Rasputin » Fri Jun 14, 2019 2:21 am

Endeavour94 wrote:
Wed Jun 12, 2019 8:02 pm
All the PSU voltages are within spec except Vres going to the mainboard which is 2.48VDC.
I think George already gave you a lot of good technical advice.

In other words, disconnect the PSU from any other boards so that the reset line cannot be dragged down by a fault from any other boards (display, main, etc.). If the reset line still stays down when the PSU is unloaded then check the supporting circuitry for the LM2925. If the rest of the circuit is behaving correctly then that points to the LM2925 having some issue.

Also, measure your ripple if you haven't done so. Your voltage readings could be significantly off if you've got high ripple.

LM2925 is old and slightly pricey but still obtainable these days. Let me know if you need one.

Endeavour94
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Re: Ensoniq VFX-SD stuck in display self-test mode

Post by Endeavour94 » Fri Jun 28, 2019 1:44 am

Okay, so the DUART was sucking the Vres down and after replacing it things are looking good now - but I'm stuck with the infamous Keyboard Calibration Error. I checked the keyboard connections, and someone had hardwired the connectors together already, but they used real thin of wire and they looked a bit blackened so I replaced them with a little thicker gauge to see if that'd do it. No luck, it's still giving me the Keyboard Calibration Error - any ideas?

Rasputin
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Re: Ensoniq VFX-SD stuck in display self-test mode

Post by Rasputin » Sun Jun 30, 2019 7:08 am

Endeavour94 wrote:
Fri Jun 28, 2019 1:44 am
Okay, so the DUART was sucking the Vres down and after replacing it things are looking good now - but I'm stuck with the infamous Keyboard Calibration Error. I checked the keyboard connections, and someone had hardwired the connectors together already, but they used real thin of wire and they looked a bit blackened so I replaced them with a little thicker gauge to see if that'd do it. No luck, it's still giving me the Keyboard Calibration Error - any ideas?
Replace keyboard ribbon cable, or at least redo the connector that everyone yanks on to remove the keybed.

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