help fix my powered sub..

[alex paik]

hello.. so this is the background of my sub.. this used to be a friends sub that he got off ebay.. he used it and it blew, so he was going to throw it away but i took it off his hands.. being a noob, i thought it was the sub, so i bought some cheapo $10 8" sub.. replaced it still doesnt work.. so i emailed jbl and they sent me the service manual on this thing.. i printed it out and looked at it and noticed one of the capacitors were blown.. i replaced the blown .1uF 50v +/-10% bipolor mono-ceramic capacitor with a similar electrolitic capacitor.. nope.. kept reading the manual and it said that maybe a different capacitor might have blown if this one blew, and sure enough, it looked blown.. so i went ahead and replaced this electrolitic radial with a non radial cap and still doesnt work.. can anyone help me fix my sub?

i know its a cheapo sub but im a poor college student that wants cheap stuff.. this was just screaming my name.. now its just ticking when i plug it in.. when i read the troubleshoot section, it says that "if you hear a mechanical clicking noise from the amp module, this indicates that the short circuit protection has been engaged. check that q3, q4 and q5 are soldered correctly. also check that q3 is not shorted to power amp case." im not that mechanically inclined but these transistors look fine.. here are some pictures.. and you can totally tell what i replaced..

if anything, can i send it to one of you guys close to san luis obispo, ca to get it fixed for a small fee?? please help me out here guys..

thanks!!!

 

[sreten]

Hi,

blown transistors generally look extremely healthy,
very rarely is it externally obvious they have blown.

They can go short or open. A healthy bipolar transistor will
measure as a pair of diodes between the connections.

/sreten.

 

[Bogie]

Okay - you're in college...

See if the speaker works - hook it up to a full-range signal, and see if it moves in/out, makes the funky noises...

Okay?

Now, figure that your amp's hosed, and you're not working on an electrical engineering degree. Darn. Now, you can either find a little chinese fellow if you can catch him halfway between class/lab/bed, or you can just call either MCM or Parts Express, and order a replacement amp. Check that the speakers in the thing work okay tho...

 

[ocool_15]

if you disconnect the outputs the clicking should stop. then you've isolated the problem and need to see if its worth buying the parts....

 

[alex paik]

i disconnected everything and plugged it in.. it ticks and i was looking around and touched something.. gave me a pretty bad shock..

i tried out the speaker, and it does work.. goes in and out..

no electrical engineer here.. so no help there..

can anyone take a look at it for me?

 

[Bogie]

Nothing looks like the magic smoke was let out?

Odds are, if you take it in, they're gonna charge you to look at it, and tell you it'd be cheaper to buy a new plate amp than to fix it. If you want to trace what's wrong, you're going to need a multimeter, etc.

 

[alex paik]

if i have a multimeter, can you explain to me how i can trace it to the root of the problem? step by step info please, for a noob.. thanks!

 

[ocool_15]

... like i said before disconnect the outputs. They will be black and attached to a large metal heatsink. if its discrete there with be individual black devices with 3 terminals un solder them and the clicking may stop.

 

[clem_o]

Suggest posting the schematic. 'Discrete Digital Amplifier' - class D ampli?

Cheers!

 

[Infinity buff]

If it is within your budgett, Rythmikaudio.com has a 150watt plate amp for $60 or a 250watt for $109. Might save you a lot of time and agrivation. Good luck.