Ensoniq SQ2 trouble shooting advice needed

[Jesse Pearson]

Hey guys, I was given a blown up Ensoniq SQ2 synth to keep and fix. The SQ2 went out at a gig. I checked it out the next day and the screen still worked but showed a bunch of nonsense stuff and had no sound at the headphone out jack. The next day after that, the screen was completely dead. I looked inside and found that Q1 to Q2 and all the resisters and diodes between those two transistors had completely fried. There was also six traces on the back around Q1/Q2, as well as around the headphone jack that were also destroyed. After a lot of effort I found out what the values of all the destroyed components were and started trouble shooting the power supply and the board. I had to re-flow solder on the power supply board to get it to output power again. With the molux connector going to the board disconnected, the power supply board output had 18.12 volts, Gnd, 18.12 volts, all AC voltage on three output pins and 10.84 volts, Gnd, 10.84 volts, all AC voltage on the other three output pins. I used an ESR meter and tested and replaced all the electrolytic caps that were bad. I used my diode checker and replaced all the Bad 1N4148 type diodes. And I tested all the transistors with the diode checker and replaced the bad ones. I need some advice on how to test the little yellow caps, they have me stumped. Also, I just learned how to test the IC's for shorts/open if you have the pin out and data sheets using your diode checker. I have a CRT 100 MHz Oscilloscope that I'm new to and can only calibrate it at this point. Plus I need to learn the proper way to identify and test the op-amps and voltage regulators. I did the repairs that I've found so far and still have no sound. The screen however has a green back light now and will display "button #34" for example when I press a switch down, but that's it. Also, when I reconnect the power wires back to the main board, I only get 7.48 volts before the big black diodes at the molux connection where there used to be 18.12 volts when the molux connector was disconnected from the main board. The other three power pins are now 8.03 volts when connected to the main board when they used to be 10.84 volts when they were disconnected from the main board. Can someone please tell me what this means? I don't get it. I would be very grateful if some of you pro techs who worked on these Ensoniq's, could spell out a better systematic approach to trouble shooting this synth that I should follow. Point me in the right direction on what to study. I can't believe there is no schematic for these synths, but I guess it's a good practical application to develop the skills you need to fix something when there's no paperwork. Also, U9 on the main board is a muliplexer that is way too hot to touch. It's temperture is 95C. I was able to get 5+ volts from "pin 8" gnd to "pin 16" +v. All the in/out pins have a regular volatage drop except pin 3 which is showing .100 volts and is the common in/out pin, but I don't know what that means. That whole Q1/Q2 area still has no volage yet either. I have an isolated transformer floating side going into a Variac and then into a light bulb current limiter and that is what I have the SQ2 plugged into, tested for 110 volts. I plan on plugging the Scope into the grounded side of the transformer for the earth ground for safety. Anyways, thanks in advance for any help and advice you can share.

[Jesse Pearson]

Here is the main board that blew. And a close up of the Q1 to Q2 cascading failures and the burnt traces on the back of the board that were visually obvious. Those bad parts have been replaced with good parts now and the traces repaired as well. As you can see, Ensoniq really went to town on the many test points for diagnostics so their factory guys could do repairs quickly. This is probable a great machine for newbies getting into electronics repair to try and fix. There's a lot you need to know and try to figure out.

If you look at the far right of the main board pic, you can see the red bike tail light mod I did for the backup battery, which is attached to the middle bottom of the board where the old watch battery went. The tail light cost $1.49 and has two lithium AA batteries inside the tail light case for the 3 volts needed. The shelve life of the batteries are 20 years and very easy to replace with alkaline in a pinch. I've done this mod on two other synths I own as well. Just an idea I came up with.

[The Dude]

That's a well constructed post and gives us as much info as you probably can without a schematic. I used to be an Ensoniq warranty station, and for most of their gear, they didn't offer schematics. Their policy was to troubleshoot down to which board and then you'd order a replacement. There isn't much documentation for their stuff. I'm presuming your statement "18.12 volts, Gnd, 18.12 volts on three output pins" that one of those 18V supplies is negative? It's probably supply for the op amps. I would look for a bad regulator or shorted op amp since one of those loads down when the main board is connected to the power supply. Typically, but not always, an 8 pin DIP op amp will have supply only on pins 4 and 8. If you find voltage on other pins, it usually indicates a short. Note that this is somewhat guessing without the board in hand or a schematic. There's obviously something loading down that supply. See if you can trace where it goes.

[Jesse Pearson]

Thanks Dude...yes, the 18.12 volts is supposed to be + and - voltages but since it is ac voltage coming off the power supply, my meter is giving me the same reading. I was guessing it turns + and - when the ac gets rectified as it starts entering the main board, which has some voltages printed on the board where the ac voltage starts to enter. Here's a pic of what I'm talking about. Thanks for the advice, I appreciate it very much and will get right on it.

[The Dude]

Oh, yes. If the 18V is AC, it will likely feed a rectifier circuit and then a regulator circuit. You could have a leaky rectifier diode, shorted regulator, or something shorted after the regulator. Look and see if you spot a couple of 15V or 12V regulators- one neg and one pos, or maybe some 15V zeners. That'll get you in the area where the likely problem is.

[Jesse Pearson]

Cool, thanks Dude...

[Enzo]

I was an Ensoniq shop for quite a few years, right until they dissolved into Emu. Yes it was maddening their support. No schematics, and no parts. If I wanted so little as a jack or a volume slider, they wanted a board swap. I used to routinely rape the dead boards for parts before returning them.

After a time, they would not have stock on boards so I'd have to wait for a dead board to return to them from somewhere, they fix it, and THEN ship to me. And sometimes the new board was defective. I even repaired a few of them myself. And then bitched to the factory. Plus they charged us like $100 for a board swap. REfundable with warranty claim, but after warranty, my board swap for a new jack cost me $100, and they suggested charging $150 to the customer. Now there is a challenge, explaining to the customer why his new jack cost $150.

After like the third generation of models, they did publish schematics. They still wanted us centers to pay $100 for them. We did. But now I had the original piano, and the ESQ1 and EPS and others of the old lines. But understanding synth, I could see the lines of Curtis chips and SSM chips and figure what was going on, and was thus able to troubleshoot to a certain extent.

I do not know if SQ2 was in that set, they are buried in my storage.

[The Dude]

When I was an Ensoniq shop, I would routinely get new replacement boards missing parts. It happened often enough that I would give them a thorough once over before installing them. I remember having to remove parts from the old board to install into the new board hoping I wasn't moving my problems onto the replacement.

[Enzo]

Steve Coscia was the service manager, nice enough fellow. But he was bound by their policy. Yet he was the only face I had to yell at. He handled me but it got testy at times.

I had been at the music store for 8 years, where we were the authorized shop. On my last day, I called to tell Ensoniq I was no longer going to be there. I wanted to list off all my gripes before I left. Steve asked where I was going, I told him down the street to start my own shop. He asked if I wanted to be the Ensoniq shop in town. Damned if I didn't agree to it. As much as we butted heads, he realized I was looking out for the customers, and was doing a pretty good job of supporting the product.

[Jesse Pearson]

Cool stories...what surprises me about the SQ line, is that there is still no real resource collective on line that specializes in trouble shooting these boards, parts, info about home made schematics etc...I had to reach out to Germany, Canada and Texas on line just to figure out what my burned up components had once been. And I got a little info from all three of these guys which answered my question and got me started on my repair. "Synthesizer Keith" who has a YouTube video on a SQ mod wheel repair was kind enough to open his SQ back up and send me a pic of Q1 and Q2, which verified that they were in fact J110 NPN JFETS. This forum is a God send as well, with the collective mind set of knowledge that you guys have, doesn't get any cooler then that.

[The Dude]

If it helps any, I found this site with some decent pics- just in case you need to identify any other parts.

http://studiorepair.com/gallery/Enso...707130263.html

[Enzo]

Emu absorbed Ensoniq, and after not long, they got tired of supporting old models and so stopped. SOme guy (I think in Oregon) bought all the old Ensoniq documentation, boards, parts, etc. He then opened an Ensoniq repair shop. He won't - or wouldn't at the time - sell parts, or schematics or boards. You either sent him your instrument or boards, and he fixed them at his steep rate. If I called up and offered to pay $50 for a schematic, I would hear "no". So that is why there is so little out there.

[nevetslab]

Well, I now wonder if all this is why I was given an Ensoniq VFX a few years ago. I'm not a keyboard player, but as far as I know, this instrument works. At least I now know who has the expertise on Ensoniq around here.

[Enzo]

I appreciated they were very user friendly. And there were in fact some good diagnostics built in. But support was a nightmare.

One tip, on most of them there is a large board for the panel switches and display. And of course the main board down below. A cable connects the two. Power supply feed each board separately. If you unplug the cable between panel and main so they cannot communicate, it defaults to test mode on the panel. Each button causes something to happen on the display. Easy way to test all the buttons for functionality.

[Jesse Pearson]

Thanks Dude, that's Nicklaus from Germany and one of the guys I spoke with. He was kind enough to send me an HD pic of the section of main board I needed and that's how I got my resistor values.

Thanks for that info Enzo, appreciate it.