calling all amplifier gooroo's

[HOPES AUDIO 10+ year member]

ok for all you amp repair gooroo's ,was wondering if any one could help me get started . i am trying to fix this amp myself without taking it to a shop. basically

learning how to work on some. with this amp some where around the

Transformer area when i stick 12v to it . it starts making a hissing noise like air blowing. so i quickly remove the 12v . the protection likes blinks soon as i touch power but goes out and then the noise starts . also the power light does not come on. if anyone has any idea please let me know

Click to read more...

 

[HOPES AUDIO 10+ year member]

bump

 

[05fronty 5,000+ posts]

what was the amp not doing in the first place? no sound, no power?

 

[HOPES AUDIO 10+ year member]

yes no power no sound , the protect light or the power light dont even come on

the protect will blink once then it starts making that funny hissing noise. a friend give it to me so i am just trying to gain some extra brain power on the internals and repairing amps.

 

[00poop6x 10+ year member]

Sounds like a leaky capacitor to me.

Does your powersupply show you current draw? If, after the prot light goes out, the current draw is high (>5A) at idle(no input signal) then your powersupply section is pooped for sure. Further diagnoses requires instruments. Also measure the collector leg of the FETs to see if it's shorted to ground.

And before you power that amp on again, reattach the metal bars that strap the transistors!!!! If anything is shorted in that amp you could overheat those to the point of no return in a few seconds.

 

[HOPES AUDIO 10+ year member]

something must be shorted in their like you said because i noticed the top first 3 above the biggest tranformer and the bottom 3 transistors were starting to get hot so i took off the power. whats the best way to see if theirs a bad cap.

on the bottom of the board their are no signs of damage like burn marks or any thing.

 

[HOPES AUDIO 10+ year member]

is their a book or a special class somewhere that will teach you how to work

on amps?

 

[05fronty 5,000+ posts]

get a ohm meter and ohm out the transistors in the power supply

 

[00poop6x 10+ year member]

something must be shorted in their like you said because i noticed the top first 3 above the biggest tranformer and the bottom 3 transistors were starting to get hot so i took off the power. whats the best way to see if theirs a bad cap.on the bottom of the board their are no signs of damage like burn marks or any thing.

A good way to test to see if a capacitor is bad is to literally take it out and measure farads. But even that won't always give you a surefire way of making sure it's bad, most of the time it will, though. Also if the capacitor gives off a foul odor that means it's leaking and it's going to fail. The hissing noise is a pretty good indicator of leak as well.

Getting hot is normal, especially without those metal strut bars going across them. Unless they're getting hot, changing colors, and smoking. Like I said, measure to see if the collector legs of the transistors are shorting to ground.

I'm not sure of any guide to repairing amplifiers, maybe someone on here might know. Maybe someone who's not an '07 or '06, because they seem to know everything.//content.invisioncic.com/y282845/emoticons/blackeye.gif.66a1670f5aaf7f406e783a63e3387dc5.gif

 

[thch 10+ year member]

there may be a short on the secondary, possibly a wire or lead touching the heatsink. this can cause certain overcurrent protection to kick in. in this case, the power FETs might get hot, even though they work fine otherwise.

 

[HOPES AUDIO 10+ year member]

so will a leak in a capacitor cause everything not to come on ? and basically just

very carefully unsorter them and test . and if one is bad should it read low or not at all and i can do these test with my fluke meter.

Thanks guys for the info.

 

[Decipha 10+ year member]

if you have a hissing noise i think you found your problem... make sure its coming from the transformers and after confirming that replace them.... remembers you always replace both alike parts at the same time... its not necessary but will save you headaches later on... trust me i've been messing with electronics awhile now and i can tell you that if one part fails, the alike part on the other channel will be failing soon as well... better do things right the first time

 

[HOPES AUDIO 10+ year member]

so your saying that the big transformer on this board can cause that hissing noise

also ? how can i be sure , i know its coming from that area! so if its bad i need to replace it and also the small one . where would be a good place to buy these parts?

 

[thch 10+ year member]

good luck replacing the power transformer. (only one on amp from pic.)

i'd take the amp off the heatsink and make sure nothing is touching. while you probably could let the amp idle without the heatsink, i'd just look for parts that could be shorting on the heatsink, and fix it. you may be able to use a dremel or drill to remove some of the heatsink material in the offending areas.

something is causing excess current on the transfomerer. this could be a short on the secondary, or an imbalence on a primary if this circuit does not use current mode control of what appears to be a push-pull power supply. a faulty capacitor on the secondary could also cause this for the reasons stated. damage to components on the secondary side could cause this as well.

In this situation, the amp may not be able to work, but may draw low enough current to prevent the fuse from blowing. the power FETs may get very hot though.

 

[00poop6x 10+ year member]

...while you probably could let the amp idle without the heatsink, i'd just look for parts that could be shorting on the heatsink, and fix it.
something is causing excess current on the transfomerer...

... the power FETs may get very hot though.

I wouldn't remove it from the heatsink letting it idle, especially if it's drawing more current now just idling. They get hot pretty quickly.

The transformer is the only other thing I can think of that could be hissing, but I do not think there's a need to replace that transformer. Definitely one of the FET's pulling it that need to be replaced, or like you said the capacitor.

I would take the amp to someone with equipment to diagnose this and fix it, if it was a simple output problem you might be able to get it up and running.