"Static" noise in Laney amp

[MoonBassAlpha]

This thread is copied from the Repairs and Technical Issues section:

Hi folks
I'm repairing a Laney BC30 combo.
It reproduces the input signal fine, but there is a constant volume static-like sound coming out of it all the time, punctuated fairly frequently by louder pops.
My first thought was a dry joint somewhere so I went all over the usual suspects (output transistors, big caps, bridge rectifier) with an iron to reflow them - nothing doing. I removed the preamp input and bypassed the send-return with a patch lead - still the same.
I'm now thinking it could be an odd failure mode with a cap across the supply rails, or a protection diode across the rails going "soft".
There isn't an undue amount of mains hum either.
Any comments?
Cheers
Jules

[Mr. Foxen]

Dying filter caps did that to my Carlsbro, replacing them sorted it, fair bit older than that though.

[MoonBassAlpha]

[quote name='Mr. Foxen' post='1040605' date='Nov 28 2010, 11:32 PM']Dying filter caps did that to my Carlsbro, replacing them sorted it, fair bit older than that though.[/quote]
It may still be that, but I'm not convinced(made in '94), as it went almost to nothing when the input to the power stage was grounded.
I think it may be the input transistor (part of a long-tailed pair) failing softly.
It's a little surface mount thing, and thought I'd fixed it when I reflowed it, It was perfect for a couple of minutes, then it came back again.
Then I reflowed it again, this time forgetting to turn the power off. New transistor should arrive tomorrow!!!

[MoonBassAlpha]

Replace both long-tailed pair and driver after it and all is now good, job done.
Unfortunately, during the repair I accidentally plugged my headphones into the speaker out when testing it, so that added a bit to my cost (Sennheiser CX200)

Edited December 12, 2010 by MoonBassAlpha