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fender deluxe 112 plus- loud humm

Started by cwpeters, October 19, 2007, 11:00:08 PM

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cwpeters

Ive been working on a fender deluxe 112 plus -which has a loud humm as soon you turn it on.  with or without guitar plugged in or volume turned up.  The two large capacitors 50v- 4700 uf seemed to move alittle bit.  While the amp was on I moved the two capacitors which were connected together with a hot glue gun, and the hum stopped. I took both the capacitors out, checked them with a multimeter.  they seemed to be charging with the multimeter set on 20k ohms.  So I cleaned them up,along with the holes they went through, put alittle soldering paste on them and resolderd them back onto the board.  When I turned the power on, the hum was gone but I could hear another noise and then 30 seconds later the fuse blew. I dont think I shorted anything out with solder paste, if you even can,  but the noise I was hearing could have been the sizzle of soldering paste.  After the fuse blew, I shut off the amp, unplugged it and touched the capacitors and the were very hot.  Almost to hot to touch.  What damage could I have done?  Did I do the right thing? Any other thing I should be checking?  ect.

joecool85

Sounds like you put the caps in backwards.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

LJ King

Quote from: joecool85 on October 20, 2007, 07:54:14 AM
Sounds like you put the caps in backwards.

+1.

And very lucky they didn't explode all over you.

cwpeters

I just took it back apart and desolderd the caps.  I did put them in right.  I tested them again with my Dmm.  What other tests can I do on these caps to check their condition?
I had the schemadic once but cant find it and dont remember where I downloaded it from.  I've been to schematic heaven and the fender field guide but neither has this schematic.  Any sites I should try?  The board felt dry, I dont know if the paste I used could have squished together when I pushed the capacitors down on them to short out the caps.  Any paste would have to be a good electrical conductor, wouldnt it?  Dont know what I did wrong maybe I hooked one of the power lines on wrong.  I really dont think so but Im going to find the schematic and double check everything before I try to plug it in again. 

LJ King


What solder paste are you talking about?

Flux?

Flux is essentially a cleaning agent. I've never thought about it being electrically conductive. Can't answer that.

With rosin core solder I've never had to use any extra flux for any electrical connection.

teemuk

I believe the schematic can be found from Fender's website under the section titled "support - amplifier schematics". If not, PM me.

tonyharker

With that large amount of hum, and the Caps getting hot it could be that the rectifier is (partly) shorted and you are getting a high ac ripple.  Check it out using the diode function on your DMM.