Ensoniq ESQ-1 Metal Scrambled Sound

Hello all, thanks for taking the time to read this. I am trying to revive 1986 metal Ensoniq ESQ-1.

I’ve created a video showing the current state of the synth. You can see it here:

When I turned it on initially, it did not make any sound and the screen was blank. Power cycling a few times resulted in a few characters on the screen, then a constant garbled tone from the machine after a successful boot of the OS. I can navigate menus and change setttings on different pages with the up and down keys. Pressing keyboard keys changes the tone coming out of the machine, but not musically. The pitch does seem to go down as I move down the keyboard. Changing settings such as the level of the overall VCA or the filter cutoff has no effect. I can see lots of different patch names and move between them, but the sound does not change. Trying to load sounds from tape mutes the constant tone. The volume slider does not make any difference when moved. Also, the value slider does not change settings. Cartridges are not recognized.

My first step was checking the power supply. The fuse at the bottom of the row of fuses had worked loose and was replaced. I checked all the voltages against the service manual. Everything seemed with the given parameters in the manual except the unregulated power which was 11.4VDC instead of 11.8VDC.

The internal battery is reading 0.03V, which is essentially dead. I’ve performed the soft reset accessed by holding the Record and Soft button 1. While reseting the constant tone is silenced, then returns. I’ve also performed the hard reset by shorting the ground of the battery terminal to C1. It did not seem to make a difference. Information for these routines was pulled from http://www.scoreforsale.com/html/reset_re-initialize.html.

I’m looking for advice on what to try next. I’ve got some experience building and repairing electronics. You can see my blog for an idea of where I am at:

You’re going to want to replace the volume and data sliders. The volume slider, in particular, can have lots of effects on the output for obvious reasons though that buzzing seems extra odd.

That unreg has a range in the service manual of 8-11. 11.4 would be overshooting. -11.4 barely fine for -12v and 11.7 minimum for +12V. Most power board components are moderately cheap, so knocking that into spec would be a good thing. Clean power to start can solve a litany of issues down the line with that many digital chips and related noise-sensitivity.

I’d likely replace the sliders, try to work the power supply to be in range of spec, then, if the noise is still there, start tracing it back through the chips. I can’t find a schematic quickly, but wondering about DACs as some were stereo on a single line (Kurzweil k2000 output from the DSP effects chip) and required a clock to split the signal into stereo. If that clock wasn’t doing the deal, the noise was awful - though it didn’t sound like your noise.

I think you have a digital problem there, and replacing sliders and battery won’t make any difference. You’ve done all of the obvious things (hard reset, etc.), and since it made no difference, I think it’s a main board issue. You can also try pulling the EPROM chips and then replacing them - that sometimes solves strange issues, but I’m not confident it will help. I think you’ll need to replace the main board, unless you have the skills for diagnosing the digital electronics.

After tracing through the board, the issue was a blown fuse in the F3 position. I believe one of the analog supplies was out. Also reseated all the socketed ICs and connectors. Removed the sequencer expansion as well, as this seemed to occasionally cause the keyboard not to boot. Everything is working now.

wonderful to hear that esq-1 is back up and running further research can be done for the battery replacement check out bradthx and the guys on you tube. enjoy the music playing i have an original 1988 esq-1 they are good