Ensoniq ESQ-1 boots to self-test, but keyboard, MIDI and sound all work

[guyasaer]

I’m trying to diagnose an early metal-case ESQ-1 (serial ~82, OS 1.7).

On startup it shows the normal ESQ-1 screen, then goes into self-test. The self-test works normally — all front-panel buttons and the display work.

Interestingly, the keyboard and sound generation work normally, and I’ve also confirmed that MIDI input works, including pitch bend and modulation.

The synth actually worked perfectly once shortly after I received it. I could edit sounds normally, including filter cutoff and resonance. All patches had reset to Brass1, presumably because the battery was already dead. Unfortunately it has never booted normally again.

I’ve done quite a bit of scope testing:

• 6809 clock, reset, address and data buses all look healthy.
• The 2601 DUART is transmitting to the display on TxA (pin 11).
• I can see two bursts of data during startup, then nothing further.
• I don’t see any response coming back from the display.
• The display/keypad board works correctly in self-test.
• RAM reset and the 470 pF modification made no difference.
• The battery has been removed.

I’ve ordered a new set of OS EPROMs, and I’m also planning to reseat the socketed ICs and inspect/reflow connectors and suspect joints.

What I’m trying to understand is what should happen during the normal startup handshake between the 6809/2601 DUART and the display processor. Does the main CPU stop sending because it isn’t receiving the expected response from the display, or should the DUART continue transmitting regardless?

I’m particularly interested in whether anyone has seen this exact failure mode on an ESQ-1, or can suggest what I should probe next.

[Didier]

I had a similar experience, which I described in the following post last May :

Ensoniq ESQ-1 : Successful repair of dead keyboard

Hello, I wasn’t as lucky as you. The unit on my workbench was stuck on the second startup screen. None of the panel buttons had any effect. However, in the Keypad/Display board’s self-test mode, they were recognized. The keyboard wasn’t working either, but my ESQ-1 was working via MIDI. After some discussions with Rainer Butchy, we strongly suspected the 6500/11 Keyboard, for which there is no clone. Fortunately, I had bought a disassembled ESQ-1 for parts some time ago. Replacing it with t…

I am at your disposal if you need further information !

[natere2]

I have this same problem on an ensoniq dp2. The display and buttons work but are in self test mode. Let me know how the eproms swap works I have a similar thing with the serial bus ring or whatever it’s called. Have you unplugged the key bed and booted it on?

[guyasaer]

I fixed my ESQ-1. In the end it was a really odd problem. After going down many rabbit holes I discovered that once turned on, if I turned the synth off and back on within 2 sec it would start up fine. I found that the 50Hz signal on the display’s 6500 had a massive delay and only showed after the main board had sent the initial message. This is why it went onto self test mode as it never saw that message.

Now for the cause. It turned out that R1 on the display board was 100K instead of the required 10K. This was the reason for the delay. I replaced it with a £0.02 resistor with the correct value and now the machine starts perfectly. I guess the lesson is, don’t take anything for granted.