dead amp

[ddoyle]

Advice? just picked up a pair of PSB powered sub's,(Century SubSonic 2i) one works great, the other dead. Fuse blows right away. Pulled the amp, looking it over looks like the op amp center pins are burnt. It is a LM324n, dont see anything else wrong. Worth getting fixed? What would be the most common cause for this to burn up? A bit of a novice at this level, any input would be helpful.

Dan

[drummer_Dave]

just a couple suggestions, not guarantying anything but if you are just going to throw it away you might as well try something (you cant break garbage right?). Those "Center Pins" are the supply pins to the chip

http://pdf1.alldatasheet.com/datashe...EMI/LM324.html


Try desoldering and removing the burnt op-amp, save this part just in case you do take the unit in so the techs can see what pins burnt. once the opamp is removed carefully look at the board and see if you can find any solder blobs or loose metal that could have shorted the pins and caused the chip to blow. Now try powering up the unit,

if the fuse doesn't blow we are making progress. measure the holes where the chips used to be with a multimeter, pin 4 on the chip (Vcc) and then measure pin 11 (Vee or GND) if there is another LM324 on the board reference that to see if the pins have the same voltages.

if the fuse still blows well then there is probably a short circuit somewhere. If you can disconnect the power supply section from the main board do so but be careful not to allow wires to short out each other. see if the fuse still blows (you may need a couple fuses )

if you can take some pictures of the circuit board(s) it would help.

good luck

Dave

[ddoyle]

Thanks Dave, will keep you updated.

Dan

[ddoyle]

Called PSB svc cntr, new amp, $500! Pulled board out, closeup exam no signs of something causing short. Did find 2 blackened areas on soldier side of board(TIP29c and TIP30c) transistors?

Dan

[drummer_Dave]

can you take some pictures of the boards? Its kind of hard to say what is wrong without a schematic or picture. If those tips are output transistors it may be possible that the output terminals were shorted and caused that transistor to blow. you really do need to check voltages to see what is happening.

[ddoyle]

seem to be having a bit of trouble attaching the pictures, I will figure it out!

Dan

[drummer_Dave]

you can sign up at photobucket.com then add your pictures there and then link them in your post

[Arx]

Originally posted by drummer_Dave
If those tips are output transistors

Those sound a little small to be output transistors on a sub. 1A 60V

Maybe a couple dozen watts tops into a 4 ohm load. Judging by ohms law and without looking at the datasheet, which probably gives plenty of other limitations.

I'm guessing they're part of the regulation or something.

-Nick

[drummer_Dave]

Excellent point Nick. I guess i shouldn't think out loud. By the way if they are used for voltage regulation it would help explain, well not explain but add reasoning to why the supply pins on the lm324 are burnt as well. Would be able to make a more educated guess with schematics or Pics

[ddoyle]

Thank you all. Tried the photobucket for the pics. Also got some service info from PSB. They had trouble with the voltage regulators failing due to ac line voltage increases. Looks like that is what happened here. Both low voltage regulators burnt, also took out the LM324 and a 1N5347. Not sure about the 2 mosfet's yet. I need my DVM from work for better testing.

Dan





http://s201.photobucket.com/albums/a...t=DSCF0634.jpg