Finally got to this beast, I wasn't entirely sure of what I'd find, but my tests and everything else showed me that it was most likely a bad regulator causing the problems, it was pretty much the only thing that had not been replaced. I ordered the parts and they arrived a few days ago.
I started building the little boards and finished them in about a half hour, here is one:
Then I started working through the mess a previous tech had created. Traces were deliberately cut and a jumper run on the +80v regulator. The red line indicates where the jumper was. The circle is another cut trace on the -80v reg, but the last tech to work on it before me jumped it with a wire, the second photo indicates better where it is.
After repairing the +80v regulator traces, I tested and put the mod board in then moved onto the -80v regulator. This also had two cut traces, but the previous tech jumped them with a wire so it was following the original trace. The circles indicate where the cuts are and the line is where the wire was. I repaired them with solder bridges for a better look and less exposed surface. Q209 was shorted from collector to emitter (this was the reason Q211 was blowing up). I replaced Q209, Q213 along with D213 for the -80v reg and Q208, Q212 and D212 for the +80v reg, Q210 and Q211 were already replaced with the proper replacements and tested fine.
After replacing and soldering everything I went ahead and cleaned the board, as you can see in the photo above it's kinda gunky.
Ahhhh, much better. Top shot:
I checked everything else and it all looked good, so I set the bias on the power amp boards down and fired it up on a 150W bulb. Bright flash, then dimmed, soft start relay "click", then a few seconds later, protection relay "click". YESSSSSSSS.
Let it run for a few, everything seemed good so I shut it down, then powered it up on line current. Working great, so I reset the bias and offset and hooked up my test speaker. Sound; glorious sound from both channels. Proceed to do a victory dance.
One problem though, the soft start resistor is getting wayyyyy too hot. Powered it down, relays are original in this so they need replaced. I find that the soft start relay contacts are pitted and dirty, as I expected. Replaced the relays and fired it back up, soft start resistor now stays cool. Mission accomplished. :thmbsp:
This "dead horse" is dead no longer, I just had her playing with my Polk SDA's and she sounded wonderful. I just let pognoot know earlier that it was alive, you can imagine his reaction. So, another SX-1980 raised from the dead to play again!
