MoonBassAlpha Posted November 28, 2010 Share Posted November 28, 2010 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 Quote Link to comment Share on other sites More sharing options...
Mr. Foxen Posted November 28, 2010 Share Posted November 28, 2010 Dying filter caps did that to my Carlsbro, replacing them sorted it, fair bit older than that though. Quote Link to comment Share on other sites More sharing options...
MoonBassAlpha Posted November 29, 2010 Author Share Posted November 29, 2010 [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!!! Quote Link to comment Share on other sites More sharing options...
MoonBassAlpha Posted December 12, 2010 Author Share Posted December 12, 2010 (edited) 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 Quote Link to comment Share on other sites More sharing options...
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