Vintage Synth Explorer Forums

Well, I got given a broken Ensoniq SQ-R by a friend. Figured I could get it working again, but after a few weeks of flying blind, I'm officially stuck.

Problem: no audio. Digital side works (display works and the unit receives MIDI). Audio side doesn't. It keeps blowing the two 2A 250V fuzes.

Does anyone have a schematic for this model?

I want to make sure I'm replacing PS caps with the right values, etc.

Thanks -

I know there's one kickin around the web somewhere; I found it a few weeks ago but never saved a copy. A persistent Google search should reveal it sooner or later. Sorry I can't help more than that.

Good luck!

www.midiworld.com/quadrasynth/qs_swlib.htm

Here is a rather good-quality PDF of the keyboard versions to get you a start.
First thing, check the minus-15-volt line (and it's regulator)

rhino wrote:http://www.midiworld.com/quadrasynth/qs_swlib.htm

Here is a rather good-quality PDF of the keyboard versions to get you a start.
First thing, check the minus-15-volt line (and it's regulator)

Thanks, man, but that's the Alesis QS, not the Ensoniq SQ...

I checked all voltages coming off the transformers, both old and new. 7VAC side read 12.30 both ways, 14VAC side read 17.86 both ways - again, both old and new transformers, so I assume I found the right replacements (even if the old ones were fine, they did look a little beat).

I assume that these are stepped down in some way on the main board to 7V and 14V, because that's where all the diodes and filter capacitors are. PS board has the choke and transformers only.

Since the digital side of the unit and the display work fine, I also have to assume that this portion of the PS circuit is working as designed.

There has GOT to be a short somewhere throwing the audio supply voltage straight to ground, because those little 2A fuzes blow instantly when the unit gets turned on. I just can't seem to find the short.

Aaaaawwww, s**t !!!
Old and blind. sorry.

In case anyone is still looking for it (posting here because this thread is above the archive.org link in DuckDuckGo search results), here's the service manual for the SQ 1 (Plus) and SQ-R: https://archive.org/details/sm_Service- ... _Plus_SQ-R

Does anyone happen to have the MIDI specification document for the SQ-1/2/R? Unfortunately the full MIDI specification isn't part of the regular manual, it had to be ordered separately "back then", and now I cannot find any traces of it on the internet. This makes it difficult to work with the SysEx dump format.