Antique Sound Labs Monoblocks stopped working

[Roscoe Primrose]

It is odd that monoblocks would fail at the same time. I wonder about a power surge that shorted a small cap across H and Neutral or maybe fried the SS rectification?

Exactly what I was thinking....

Roscoe

[dberning]

I suspect a rectifier diode has shorted, ironically in each one. I am guessing this because they blow the fuse even if the tubes are not installed if I understand you, bigthinker, correctly. Perhaps a line surge during a storm took them out?

[David McGown]

It is odd that monoblocks would fail at the same time. I wonder about a power surge that shorted a small cap across H and Neutral or maybe fried the SS rectification?

Looking at the photo, it is not clear if there is a cap between hot and neutral at the IEC, though I think I can make out a dark disc shape below the wiring. I agree that it is highly unusual for both units to fail in the same way at the same time, and an external event such as a power surge would be a logical cause.

David

[TubeDriver]

It is odd that monoblocks would fail at the same time. I wonder about a power surge that shorted a small cap across H and Neutral or maybe fried the SS rectification?

Looking at the photo, it is not clear if there is a cap between hot and neutral at the IEC, though I think I can make out a dark disc shape below the wiring. I agree that it is highly unusual for both units to fail in the same way at the same time, and an external event such as a power surge would be a logical cause.

David

I also noticed that disc shape near the AC input wiring. Could be a small value, cheap ceramic cap?

[David McGown]

It is odd that monoblocks would fail at the same time. I wonder about a power surge that shorted a small cap across H and Neutral or maybe fried the SS rectification?

Looking at the photo, it is not clear if there is a cap between hot and neutral at the IEC, though I think I can make out a dark disc shape below the wiring. I agree that it is highly unusual for both units to fail in the same way at the same time, and an external event such as a power surge would be a logical cause.

David

I also noticed that disc shape near the AC input wiring. Could be a small value, cheap ceramic cap?

That is what I suspect. The only problem is that if they shorted, they should take the breaker with them when plugged in. So it kind of rules that out as a possibility, since the fuse blows when turned on.

David

[Roscoe Primrose]

That is what I suspect. The only problem is that if they shorted, they should take the breaker with them when plugged in. So it kind of rules that out as a possibility, since the fuse blows when turned on.

David

Unless, and it's hard to tell from the picture, it's got one of those IEC receptacles with the fuse-holder built-in.... Need more

Roscoe

[Jim G]

Hate to stick my nose into these things, but..... Safe to assume both are correctly connected to a speaker load without any shorts in the wiring?

Jim

[randy warren]

is it safe to assume that the poster does not have much electronics experience? If so, someone more knowledgeable may need to look at these...

[Roscoe Primrose]

is it safe to assume that the poster does not have much electronics experience? If so, someone more knowledgeable may need to look at these...

Probably. Patrick - I should be available pretty much any time Sat, and Sun after about 1PM if you want to make the trek all the way out here...

Roscoe

Last edited by Roscoe Primrose on August 2nd, 2013, 5:43 pm, edited 1 time in total.
Reason: typo

[bigthinker]

I appreciate all the response to this post. I do not have a lot of experience but I do own an Ohm meter, so I can respond to some of your recommendations. I was thinking it was the mains transformer. If someone knows of a reputable place to get them repaired or knows for certain how to repair this, please let me know.

Again, thanks for all the positive suggestions and thoughts on this problem.