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yamaha c-4 preamp problem maybe waterdamage?

aidynphoenix

aidynphoenix

Super Member
ok, so i found a yamaha c-4 preamp several years ago and its been in use since,, the lamps are burnt out, so its hard to tell when its on or not...

but yesterday i had unpluged it momentarely,, than when i plugged it back in, no sound,, untill i moved my stack of units so i could get to the back,, and it suddenty came on,,, i had this problem before,, and sometimes just letting it wait awhile did the trick,,, i thought maybe it had to be warm or something..

well today i opened it up.. and had my 1st look at how nasty and dusty it was inside,, i cleaned all the dirt on the top side i could with dexoit and a new toothbrush, and the other side of the board has all the components on it so i left it alone,, tryed it and it didnt work,, i gave it time, and moved it around like before,.. still no sound.. so i looked inside again and found a little heatsink under a board in the front,, real hard to get to and see.. it wiggles like no other,, and it looks black where it should rest on the board,, but i think it just might be glue,, because under the capacitors in it there is black glue also.. im not sure,, i have pictures,, of the insides before i cleaned the board and of the little heatsink that is moving around inside,.
here is one..

http://members.cox.net/cablefreak1/wheeeee012.jpg

sombody suggested it might be waterdamage,, im not so sure,, but i did find it sitting outside years ago. but it has worked without much trouble since then.. any ideas or suggestions?
 
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i cleaned all the dirt on the top side i could with dexoit and a new toothbrush
Click to expand...
Deox-it is a contact cleaner for switches , potentiometers and electro- mechanical contacts.Not a general purpose electronics cleaner..
 
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Another Yamaha model notorious for copper bus bars that need solder reflowing...

The spots in the (fuzy) picture at the upper left are suspicious, but if it's been playing for years, unlikely to be the cause.

The glue used also has a tendency to conduct after many years.
 
First then you need to do is verify "ALL" the power supply voltages are present at the power supply and there corresponding distribution points.
 
Actually it sounds like maybe it has cold or cracked solder connections probably in or around the power supply section.
 
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C-4

I recently had to build up (solder) a ground connection on one of the circuit boards where the screw passes through to restore operation. Prior to that, it would work... or not!
 
For starters . Pull the top cover off.Then have a real good look at the power supply boards solder connections.I use a bright light and a big ass magnifing glass . Especially the 19 links on the edge of the board.
 

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ok here is a photo i took, as you can see my board looks verry nasty, all the connections look good, but there is some kind of brown flakey stuff all around the connections, and the board itself looks wrinkley and unflat, as if it was warped or something... http://profile.imageshack.us/user/aidynphoenix/images/detail/#20/stuff1234567del007.jpg

also there is a heatsink that moves around alot, idk if it would have anything to do with it or not,
http://profile.imageshack.us/user/aidynphoenix/images/detail/#193/stuff1234567del002.jpg
 
also there is a heatsink that moves around alot, idk if it would have anything to do with it or not,
Click to expand...
Look at the solder connections under that heat sink..I´ll bet there is a loose TO-220 style transistor ie bad soldered connection.:yes:Wiggle the heatsink around while looking at the solder connections and you'll see what I'm talking about.
 
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ok well i moved it around slightly and nothing on the other side appeares to move at all, i even tapped in the connections near the spot where it was on the backside, i think maybe the glue isnt holding it down anymore,,

should i possibly scrape the old flux off with a toothpick and take a closer look at the connections?
and what would you reccomend for cleaning the board,, i dont like how nasty it looks.
thanks again!
 
With your pre-amp hooked to your power amp/speakers/sound source..Turn the volume up just enough to hear both channels. Tap and slightly flex the various circuit boards with a non-metallic probe ie plastic pen or something.And poke and prod to see if you can get the unit to act up.
Note: Some areas may have 120volts AC present so be extremely careful to keep your hands and fingers from contacting the energized circuit.
If you can get the unit to act up then note what area your in and try to narrow it down to the bad connection..
 
ok so i decided to plug it back in, upside down with the bottom open, and see if it would work still.. and i noticed that the 2 black heatsinks labled 26 and 27 right under where the pre out board is,, (are pretty hot) id say about 40-50c is that normal?
 
Alcohol or acetone with a small 2" paint brush works for me to clean the boards up. Use just enough on the tip of the brush to get the job done. The alcohol I use it " Everclear" ethanol. IPA or isopropyl will leave water droplets behind after the alcohol evaporates.
 
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ok so i used a wooden paintbrush and touched lightly, just about everything other than the resistors, including the wobbly heatsink and got no sound through my headphones.. i touched the black heatsinks that are hot though and felt a slight tingle,, is that bad? or should i not of have done that?
 
aidynphoenix said:
ok so i decided to plug it back in, upside down with the bottom open, and see if it would work still.. and i noticed that the 2 black heatsinks labled 26 and 27 right under where the pre out board is,, (are pretty hot) id say about 40-50c is that normal?
Click to expand...

probably...Thats why they are big black heatsinks...
 
ok well i turned the volume up some more, and i could hear a slight hum out of the headphones, depending on where the headphone volume was at.. and when i pressed with the brush. on the top side of the board above it (same side where the power switch is, at just about anywhere on the board it goes away,, ?? is this abnormal? or does it need cleaning?
 
ok i made a discovery!!that wiggly heatsink,, i tryed moving it a second time, but with it powered up and with the headphones on! i saw a little arc, inside it looked as if it was comming out the side of it, or from the diode next to it, right under the white wire to be exact, and also i heard a loud humm from the headphones,,, should i dissasemble the unit, to have a better look and see if possibly it has lost a connection at that spot? or do you thinki might of have just damaged it?
 
well it had been pluged in for more than 15, minutes, no spark just a arc, looked like the inside of a push start lighter when you press it down, really small and blue, i guess im going to leave it plugged in for awhile and see if it eventually starts working..
it had been plugged in since you suggested to tap with somthing non conductive,
 
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