So I thought I would post a problem and the solution in one post as well as the methods I used to solve the problem. Sometimes it's hard to find portions of this long thread that resolve problems, so if it is all in one post it may make it easier for others.
I have built 3 SSL Compressors and had small issues with all 3.
The first issue I had was that I wanted to use the square illuminated pushbutton switches like the ones used in the original. I bought 12V bulbs and thought I would just tap the 12V from the switching board that is intended for an LED. I think this may have worked for the power bulb, but when I engaged the compression switch (which illuminated the bulb in the switch) the 12V regulator said.....NO I DON'T THINK SO! and shut down. I solved this problem but adding another voltage regulator that taps directly from the DC feeding the input to the existing +15V Regulator. I mounted the regulator on the PCB where the on-board transformer would have gone and used this 12V tap to feed all of the bulbs and a relay that I used as well. (The relay was also used for the compression switch because I needed 3 things to be able to be switched: The Compression On/Off, the Makeup Gain Bypass, and the Lamp for the switch). BTW making holes for those square switches was a time consuming process. I drilled a circular hole and slowly filed a square hole from that. It took about 20-30 minutes per hole. The flange on the switch isn't all that big, so I had to go slow and make sure I didn't take too much at once.
Another issue I had with a different unit was that when the compression switch was engaged it would make a super loud buzz/hum sound. I first checked to see if the unit passed audio without the compression engaged. It did, so I knew that the input/output section of the circuit was fine. I then went to check out the switching of the compression as well as the makeup gain. I desoldered the wires from the makeup gain section so that I could manually connect and disconnect them. I was using the relay for this switching, so I wanted to eliminate the possibility that the relay was causing the problem. The noise still happened when manually connecting the wires, so I knew the problem must be something in the makeup gain circuit. I consulted the schematic as well as the PCB layout art to measure voltages and check connections. I saw on the schematic that the makeup gain circuit was being fed 12V, so I checked that and all was well. I then checked the output voltage from the potentimeter and it varied from basically nothing up to 12V with the turning of the potentiometer. I then traced the circuit from there checking connections and voltages until I got to the makeup gain amplifier (the TL072). I did a search on this forum for voltages and found what the voltages should be on each pin. I found that the voltage was way too high on one of the pins (9volts instead of up to 1.9volts). I then began to suspect the resistor just before that pin and found that I had used a 20K resistor instead of a 620K. I changed it out and all was well with the makeup gain. I have to admit that it is a little tricky going from schematic to PCB artwork to PCB, but it makes the troubleshooting much more methodical and way less of a "shot in the dark" situation.
The third issue that I ran into with one of the units was that it wasn't compressing at all. (at least the meter showed no compression). I first checked to see if all of the meter connections were correct as well as the orientation of all of the caps on the switching board. Everything was just fine. My unit didn't compress in either channel, so I assumed it had something to do with the sidechain (although I do have the turbo board installed in this unit, I had no compression whether the circuit was in turbo or regular mode). I checked to orientation of all of the diodes and caps in the sidechain section (the portion of the PCB that says SIDECHAIN on it). Again, I used the schematic as well as the PCB Artwork to check this. Everything checked out just fine. I then began to check for solder bridges. On of my methods for this is to shine a flashlight from the topside of the PCB while checking the solder connections on the bottom. I also used the Artwork layout to see if certain pads were supposed to be connected or not. This can be tricky because the artwork is actually a mirror image if the PCB if you are looking from the bottom. I compared several suspect solder bridges with the artwork, and found one (the 10K resistor) in the very corner of the PCB. I am willing to be that this is a common one because it is very close to the 2 nearby pads and the ground plane. I used a copper braid to remove the solder and I carefully resoldered it correctly. Once I put it back together it worked like a charm in both regular and turbo modes.
I hope that this narrative can help a few people solve their problems. The thing to remember is that the problem is probably something simple and that you just need to be patient and methodical about searching for the problem. Use the schematic, use the search function on this forum, and take some time away if you get frustrated. Most of the problems that I solved took a few tries to find. The time in between gave my brain a chance to process stuff and come up with other solutions.
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