PPI pro mos 450 pulses when powering on

[GEM 592]

OK I will check the clamps again. I find the back panel/clamp thing to be inadequate design wise. I am using compound at least, there wasn't any in there when I got it.

 

[GEM 592]

Played about a minute and died again. I'm beginning to see why the amp was sold!

 

[Perry Babin]

Are all of the insulators intact?

 

[GEM 592]

You mean the tape? Yes, but I will check again.

 

[GEM 592]

One of the 2n6487 in the original group that failed is shorted again.

 

[Perry Babin]

Make sure that all of the tabs are even.

Are you sure that you're tightening the cover sufficiently?

Have you looked into the ends of the amp (endplates removed) to confirm that the tabs are deflecting when the cover is tightened?

 

[GEM 592]

Both times it happened in bridged mode, 4 ohm. The speaker wires have been directly wired due to the common missing plug thing.

I checked for front L/R, rear L/R separately, then bridged the front side to one speaker and the rear side to the other, as you're supposed to.

But I wonder if mixing these up would cause this problem, and there is some other wiring mistake in the inputs or something that I'm not aware of. I labeled everything ahead of time but say if the RCAs were reversed.

 

[GEM 592]

I don't think it's that cover issue. I know what you're going to say I think but it just wasn't running very long at all. Barely started one song. I removed the cover right away and nothing was even the slightest bit warm.

 

[GEM 592]

Well actually one of the tabs on the cover, right by that output, is bent down a little, which would hamper its functionality it would seem.

 

[Perry Babin]

Before you clamp the cover down, press every transistor down and confirm that the transistor readily sticks to the heatsink without springing back up. If it's flat enough to be held down by the compound, it's likely flat enough.

Remember to look into the end of the amp to confirm that the tabs are being pushed up by the transistors when the screws are tightened.

 

[GEM 592]

I wonder if putting foam strip on the tabs would do more harm than good.

The thermal tape is non-adhesive. Perhaps compound under it would help.

Thank you for your help.

 

[Perry Babin]

You definitely need compound on the top and bottom of the tape if it's non-adhesive.

 

[GEM 592]

OK I straightened a few bent tabs, added heavy compound below tape, added heavy compound on each device, straightened all devices to lay flat (just pushing each with my finger they stick down flat and stay), torqued down back panel very well. Ready to test again.

 

[Perry Babin]

When you test, use a current limiter or a 10 amp fuse. It may save parts if there is still a problem.

 

[GEM 592]

Like 3 or 4 songs in, sink is warming up little. Never played this long at least, so if it fails again I probably just need to go back and improve the heat sink mating more. I think it is really really good now though.

Thank you very much Perry for your help, knowledge, and patience.

 

[GEM 592]

I've been rechecking the clamp screws when it warms up.

It seems like it is repaired. Sounds very very good, better than I was expecting honestly.

I don't suppose anyone has a solution for the speaker output plug problem. I remember seeing somebody did a custom deal.

 

[Perry Babin]

The spacing is a bit odd.

I know this probably isn't what you want but I'd remove and keep the terminal in case you find a mate for it.

Some people solder wires to the board and go out a few inches to a screw-type terminal strip. Something even easier, go out a couple of inches to male/female push-on connectors.

These aren't fancy but they do no harm, either.