Tube Amps / Music Electronics
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|8/21/2000 10:42 PM|
You won't like it.
A really good way to get electronics boards clean is to put them in a household dishwasher, detergent and all, and run a wash/dry cycle. Stuff that water will ruin or contaminate like relays should not be treated this way, but I have heard that most of the time, it produces pristine looking - and working! - boards.
By the way, rodent droppings and dribblings may carry the Hanta River virus, which causes symptoms up to and including death. Be real careful about what you touch or inhale around any rodent leavings.
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|8/22/2000 2:03 AM|
I often put amps into the sink and spray them off with the sprayer - have got really high water pressure here. Then warm them in the oven for a day. It's amazing how you manage to give a helpful concise answer under unsual circumstances - thanks. Am really at my wits end over this amp and grasping at straws hence the mouse pee theory (still don't see how it would conduct enough current to screw up things in a +/- 40 vdc amp situation, but.....when all of the possible/probable causes have been examined it only leaves .. the revenge of mickey).
|8/22/2000 4:46 AM|
Sounds like a weird one GW..i hate those meeses to peeesese.. I'm sure you have checked the speaker cable and speaker jack..Sounds like some intermitent..thing happening.. Could be a cap..rectifier,about anything..Power transformer??Microscopic trace line crack..Seen some weird stuff..Some SS amps won't work with replacement parts..even though they say it replaces them..just not up to snuff.. had a piece of wire once.. looked fine but had about an inch gap with nothing..still covered and looked like new.. I know the hardest 2 amps i worked on to fix were weird problem ones.A carvin.. that was sent to Carvin 2 times.. they couldn't fix it .. I fixed that one and a Marshall with a trace crack.So small you couldn't hardly see it.. those pc things can be a pain..
I don't mess with SS stuff..very much.So Not much help here..
|8/22/2000 1:40 PM|
OK, I admit it, I'm in a sick co-dependent relationship with my repair customers. No one else around here is doing the work and they're depending on me and I like to help folks out (and get paid to do it) so I wind up doing SS warranty work, yechhhh.
Well, as to other stuff, the MOSFET definitely shorts and the speaker on this cheapie is directly wired - as long as I didn't clip a speaker in circuit it idled fine. And the replacement parts are the SLM factory ones. When the parts come in again I'm going to replace the electrolytic caps and the IC that drives the output stage (although it isn't DC coupled to the output stage) after flushing the chassis thoroughly with water and drying it.
Then if it does it again I'm sending it to Ashland .
|8/22/2000 3:47 PM|
Was that with a dummy load or open circuit? Is there a DC offset on the output? Does it get hotter with a speaker connected? If it works with a resistive load and fails with the speaker it may be a high frequency oscillation you canít hear that kills the FET. It could do that if the Zobel network is open. Check the cap and resistor.
|8/24/2000 5:34 AM|
Then if it does it again I'm sending it to Ashland
So is Ashland the SLM factory? I was just wondering what the warranty policies are like... Will they send you a new board (presumably stuffed!) if you tell them about the problems with the old one?
You've been doing work for them for many years- right? so they can check their records to see that you obviously know what you are doing...
As for doing warranty work on these amps, I think that SLM needs you more than you need them... of course, they may view things differently! I hate to see you spending all of this time on this amp from hell if SLM is only going to pay a couple hours labor... (or is this not warranty work?)
P.S. When I was working in the parts department at Pacific Stereo in the 70's one of the service techs out in the field was having trouble repairing a Sony receiver so he ordered the main circuit board, copying the number off the board. It took us 6 weeks to get it and when it finally arrived it turns out that the board was unstuffed! I don't think that tech lasted very long...
P.P.S. As for the rat piss, is it possible that it may have damaged one of the parts in the amp that you haven't replaced yet? I really don't see the deposits on the board conducting much less than maybe 10 megs... then again I haven't studied rat piss as much as some people have.
|8/22/2000 5:45 PM|
Can u fire it up without the pwr Mosfets in circuit, and then get a reading on the gate connections to see what kind of voltage is showing up there?
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