Uni-Sync Model 50

[Logistics]

Good morning, friends! I saw an old, heat-sink-heavy unit on craigslist yesterday, so I decided to snag it as the owner only wanted $25. He says that one side powers up normally (lights up green), but the other side stays in clipping mode (lights up red). I haven't opened it up, yet. However, I'll post a picture of the guts from another owners unit so you can see what they look like inside. Looks pretty simplistic as it's all single-sided boards and through-hole components. What I am gleaning from my research is the first thing that should be done is the replacement of the large stiffening caps. Could a failure of the stiffening caps on one channel cause that channel to enter clipping mode?

Anyway, look forward to hearing from you all.

[CapLeaker]

Before you change things around. Look if all your voltages are there. You can compare the working side with the broken one. Could be anything from a broken solder joint, to a corroded connector, missing voltage, etc.

[Logistics]

Before you change things around. Look if all your voltages are there. You can compare the working side with the broken one. Could be anything from a broken solder joint, to a corroded connector, missing voltage, etc.

Ah! Good point. I don't know why this didn't cross my mind.

Thanks!

[CapLeaker]

Ah! Good point. I don't know why this didn't cross my mind.

Thanks!

I just looked at some pictures, this isn’t only the clip LED, also the protection one. So you probably could have DC on the output on that side and the protection is on. The nice thing here is you can easily swap one thing from one side to the other side.

[Logistics]

I didn't get to play for more than about 10 minutes today, but when I power the unit on both channels are red, in protection mode, and I hear the relays CLICK. After several minutes I noticed the left channel would erratically cycle back and forth between Green and Red, until it seemed to finally settle a solid Green. The right channel stays in protection mode. I'll dive into it more next week. Sounds like it would be a good idea to re-wet all solder joints.

[Logistics]

I just looked at some pictures, this isn’t only the clip LED, also the protection one. So you probably could have DC on the output on that side and the protection is on. The nice thing here is you can easily swap one thing from one side to the other side.

Wait a second, which things are you suggesting swapping? This is the behavior of the amp with nothing hooked up to the outputs so.

[CapLeaker]

First I would go after the interconnects on the boards. Then test if heat or freezing (can of air upside down) does anything. Take the transistors out and check them. I suppose it also could be a bad TO-3 holder. Put a little pressure on the board trying to flex it a little, or a little pressure on components. I suppose you could try to defeat the protect mode… there a various ways to go about it, but I would wanna check why this is in protect mode and if there is dc on the output while it is in protect. The problem is somewhere in the output section of the amp anywhere from the pre drivers to the final drivers. A bad input section does not make the amp go in protection mode. Once you identified suspected components, you can test them from swapping the same part from left to right channel.

[Logistics]

First I would go after the interconnects on the boards. Then test if heat or freezing (can of air upside down) does anything. Take the transistors out and check them. I suppose it also could be a bad TO-3 holder. Put a little pressure on the board trying to flex it a little, or a little pressure on components. I suppose you could try to defeat the protect mode… there a various ways to go about it, but I would wanna check why this is in protect mode and if there is dc on the output while it is in protect. The problem is somewhere in the output section of the amp anywhere from the pre drivers to the final drivers. A bad input section does not make the amp go in protection mode. Once you identified suspected components, you can test them from swapping the same part from left to right channel.

Just out of curiosity, could this behavior also be caused by aging relays?

[CapLeaker]

Just out of curiosity, could this behavior also be caused by aging relays?

As for the protection relay, NO. The protection relay is normally open. It only closes if all is o.k.
Your symptoms would be different. The amp would appear working normal, but yet nothing on the speaker. The problem lies with that channel clip. You got to figure out why that’s coming on.