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Testing STK Modules?

No AC on either 6 or 8, but what I did find was right channel has -31Vdc at the terminals and the other side has 31Vdc. This receiver doesn't have a relay. It's like the power is going straight to the speaker terminals.

Still have to pull it apart to see what's happening with the filter caps.
 
JJCalvillo said:
No AC on either 6 or 8, but what I did find was right channel has -31Vdc at the terminals and the other side has 31Vdc. This receiver doesn't have a relay. It's like the power is going straight to the speaker terminals.

Still have to pull it apart to see what's happening with the filter caps.
Click to expand...
I stumbled across this thread last week while I was trouble shooting the left channel on my Sanyo JCX 2400 which has STK084s as the output ICs. That being said, I planned on coming back here once I figured out the problem. I love these JCX and the other late 70s/early 80s amps that have these STK ICs in them. There's just something about their sound that I really love.

My issue turned out to be the contacts on the speaker protection relay's left channel were super corroded. I tried removing the relay from the PCB, removing the clear plastic shroud, and sanding the contacts with 1000 grit sand paper, but that only helped a little. I ended up replacing the relay with a MY2-02-DC24 from Omron which completely resolved the issue. A year or so ago, the same unit developed a noticible buzz/hum on the right channel. Turned out the 1UF input cap and the 10uf caps connected to pins 6 and 8 were all bad. The caps used in these amps aren't vented, so when they start going bad the tops don't buldge like modern electrolytic caps. Instead, the bottoms buldge out, which makes the problem waaaay less visually apparent.

If you or some other random person who stumbles across this post in the future thinks they need to replace the STK ICs in their receiver, try replacing or at least visually inspecting the bottoms for buldges on the handful of support capacitors that essentially all of the STK ICs require. Additionally, it's really poorly documented online, but both NTE and ECG made 100% drop in replacements for most of the STK/Darlington Pack/Power Pack ICs. If you google something like "STK ECG Equivilant Replacement" you can find some german and (I think) Portuguese crossreference PDFs. In your case, the ECG1326 shuld be a drop in replacement for the STK 078. The reason that matters is because there seems to be a whole lot less fake listenings for the NTE and ECG parts, making it a whole lot easier and typically cheaper to source a ECG or NTE equivilant IC. Anyways, hope this info is help if you hadn't already got the issue sorted out.
 
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