Phase Linear 400 Latchup?

[frhodes]

Turn on my amp and the meter lights go dim, awful noise from speakers. Turned it off quickly, turned it back on and works fine, except
for hum. Put it on the dim bulb tester, when first turned on bulb stays dim. Has White Oak revision c board, transistors are original.

Time for new transistor set? Opinions?

 

[Gepetto]

Turn on my amp and the meter lights go dim, awful noise from speakers. Turned it off quickly, turned it back on and works fine, except
for hum. Put it on the dim bulb tester, when first turned on bulb stays dim. Has White Oak revision c board, transistors are original.

Time for new transistor set? Opinions?

Please read out what you mean by original transistors, each column. Starting from the bottom of each.

 

[Gepetto]

Turn on my amp and the meter lights go dim, awful noise from speakers. Turned it off quickly, turned it back on and works fine, except
for hum. Put it on the dim bulb tester, when first turned on bulb stays dim. Has White Oak revision c board, transistors are original.

Time for new transistor set? Opinions?

And check your bridge rectifier. The dim lights indicate an abnormal load on the power transformer.

 

[frhodes]

Please read out what you mean by original transistors, each column. Starting from the bottom of each.

I'll have to open it up again. The outputs are all XPL909's and the drivers are Not RCA 410's.

 

[frhodes]

Please read out what you mean by original transistors, each column. Starting from the bottom of each.

The drivers are Motorola SJ2741's

 

[Gepetto]

The drivers are Motorola SJ2741's

How does your offset measure? Is there any heat at idle being developed?

If you have a scope, look at the B+ and B- rails for abnormal waveform.

Have you ever posted pictures of the innards?

 

[frhodes]

How does your offset measure? Is there any heat at idle being developed?

If you have a scope, look at the B+ and B- rails for abnormal waveform.

Have you ever posted pictures of the innards?

I'll have to wait for my brother in law to bring his measuring equipment in a week or two. He is the engineer, I'm the taker aparter
and put back togetherer.

It seemed to me that the right side, opposite the transformer was running warmer but I could be mistaken. Pictures follow:

 

[laatsch55]

Jim, next time you're in there, put some .01uf poly caps accross those BR leads, all 4 of them...

 

[frhodes]

Jim, next time you're in there, put some .01uf poly caps accross those BR leads, all 4 of them...

Already have them on hand. (.01 x 670 volt).

 

[Gepetto]

I'll have to wait for my brother in law to bring his measuring equipment in a week or two. He is the engineer, I'm the taker aparter
and put back togetherer.

It seemed to me that the right side, opposite the transformer was running warmer but I could be mistaken. Pictures follow: View attachment 12652 View attachment 12653 View attachment 12654

Your bulk caps are rather tall and under stress, leaning together for some reason. Make sure the cap terminals are not making incidental contact with the first row of transistor wiring. The dimming load is apparently on the pre-fuse side of things or you would have blown one of the delicate AGX 5A instrumentation rail fuses. That would implicate transformer, bridge, bulk caps, pinched wires, loose wires, incidental contact as things to check out.

 

[frhodes]

Your bulk caps are rather tall and under stress, leaning together for some reason. Make sure the cap terminals are not making incidental contact with the first row of transistor wiring. The dimming load is apparently on the pre-fuse side of things or you would have blown one of the delicate AGX 5A instrumentation rail fuses. That would implicate transformer, bridge, bulk caps, pinched wires, loose wires, incidental contact as things to check out.

Thanks. I have some copper on its way for a new bus bar. Will check all items pre-fuse.