Kole Audio TRAX1-5500D Missing Component?

[KilgoreCemetery]

I have a mono block amp that won't power on. It doesn't light up at all. I pulled and checked the fuses and verified that they are good. Also, when I supply power, they do have about 12V all the way across.

When I first started looking at it, I did find 6 swollen 25V, 220uF capacitors and one 25V, 100uF. I have since replaced those with known good caps, but the amp still doesn't power on.

Recently, I found one vacant spot on the circuit board. It's a 4-pin surface mount component and I believe it is in the driver section for the power side of the amp. The down side is, I have no idea where it went or what it was supposed to be.

I checked the pads for voltage with the amp in the "on" state (12V supply and remote wire connected) and found 600mV on the two center pads, 12V on one of the outer pads, and 9V on the other (see picture).



When I disconnect the remote wire, the 600mV pads drop to zero and the 9V pad jumps to 12V.

From there, I'm stumped. I haven't been able to find a schematic and don't even have a good guess as to where to go next. Does anyone have any information on what else I could test or what may go in that spot? Any help would be appreciated.

 

[kellys_eye]

One pad (opposite the three) is a soldered 'tab' - usually connected to one of the other three pins - but it could be a simple LM317 (or its equivalent) based on the resistors adjacent to the other pads.

Can we see a close up WITHOUT the red marking?

 

[Tha fios agaibh]

Q nearly always mean transistor. My guess is it's a mosfet used to switch on the amp?
The 600mv pad likely goes to the gate.

Yes, if we know where the other two traces go that would be helpful. Perhaps the power on relay circuit?

 

[KilgoreCemetery]

Definitely! Hopefully these help. It's hard to get a good amount of lighting without glare

 

[KilgoreCemetery]

Q nearly always mean transistor. My guess is it's a mosfet used to switch on the amp?
The 600mv pad likely goes to the gate.

Yes, if we know where the other two traces go that would be helpful. Perhaps the power on relay circuit?

I would guess transistor as well based on the other markings on the board. IC's and diodes have the IC and D prefixes.

Figuring out where the other two traces go may be tricky, but I'll see what I can do

 

[KilgoreCemetery]

Ok, I think I have some info..

The pad that has 12V all the time goes through a resistor and takes two different paths. One goes to Q4 (BE RJ) and the other path goes through another resistor, the positive side of a cap, along the underside of the board, and then to IC2. Which is an ST LM393 Low power dual voltage comparator. It's difficult to tell orientation since there's no notch or dot on the IC, but based on the pinout, the options are either V+ or ground. I'm guessing V+.

The other pad in question goes through a couple resistors as well, then branches off to Q16 (BR 39). I have no idea how to decipher the markings on Q4 and Q16

 

[Tha fios agaibh]

The pad that has 12V all the time goes through a resistor and takes two different paths. One goes to Q4 (BE RJ) and the other path goes through another resistor, the positive side of a cap, along the underside of the board, and then to IC2. Which is an ST LM393...based on the pinout, the options are either V+ or ground. I'm guessing V+.

The other pad in question goes through a couple resistors as well, then branches off to Q16 (BR 39). I have no idea how to decipher the markings on Q4 and Q16

Yes, I think you're right, the pinout of lm393 says Vcc so that's positive to the Q1 pad.

The other side with Q16 will be the load your mystery transistor switches but sorry I don't know what smd code BR39 means either.
Perhaps a BT3904?
I think you may be stuck until someone can say what Q16 might be.

 

[KilgoreCemetery]

At least that gives me something specific to research though.

My only other concern is, if I find the right part and put it in, how do I know it won't just burn it up? Are the voltages on the pads considered normal for where a transistor would go?

 

[Tha fios agaibh]

how do I know it won't just burn it up? Are the voltages on the pads considered normal for where a transistor would go?

You need to know specs of what your switching on (Q16) to be sure.
What does it connect to?

One thing you may consider is carefully un-soldering Q16 and hook it up to one of those (relatively inexpensive) lcd component testers. It can tell you wither its a bjt or mosfet, the Hfe, Vf, if its a N or P type transistor and even the pin connections.

Another thing I'd do is look at the circuit board for similar sized transistor pads. Sometimes they use the same transistor type in multiple places.

 

[KilgoreCemetery]

One thing you may consider is carefully un-soldering Q16 and hook it up to one of those (relatively inexpensive) lcd component testers. It can tell you wither its a bjt or mosfet, the Hfe, Vf, if its a N or P type transistor and even the pin connections.

That's a good idea!

Ironically, Q4 and the missing transistor have the same foot print. There are other identical "BE RJ" transistors in the area, but I don't know enough of what they're doing to tell what they are.

 

[KilgoreCemetery]

So, I pulled and tested Q16 (BR 39), and this is what I found:

 

[Tha fios agaibh]

Tested Q16 (BR 39), and this is what I found

Great start knowing its a NPN, but not enough info to figure out what your missing part is.
I hope one of our more seasoned members will chime in here. What does BR39 code mean?

What I'd do next, is trace out where Q16 emitter goes and try to figure out what its function is. If you know that, it should give you an idea of what Q1 ahead of it might be.