American Bass 200.1 protect mode.. Am I diagnosing these fast recovery diode's right?

[obscuremind]

Ok first things first, I hope I dont garble on and run on and on about useless stuff because Id hate to make you all mis-understand me more than I probably will.

Picked this car audio amplifier up for $10.00 yesterday. The boy said it had been sitting under his bed for a couple years after it went into protect mode, So I addressed it myself hooked only the power 12V+, Remote, Ground up. Red LED shines on and throws a *protect*. Next thing I do is open up the bottom to let me into the internal and expose the PCB. right off the bat, I dont see anything wrong. no raised caps, no darkened spots or anything.

So then I break it down to where I can address the POWER side and the OUTPUT side of the amp.

I know how to check a transistor with my volt meter. All of them read the exact same reading.. And showed the same across the board which lead me to believe since they were all showing the same resistance they were in-fact good.

POWER SIDE

OUTPUT SIDE

However, When I got to these 4 components
two are FMG33R and two are FMG33S
as they look like transistors when I put the leads on them it automatically goes to an Open circuit. will not read an ohm load which in turn to me, means dead short.

but they don't -look- like typical transistors which is why I was wondering if I was diagnosing these right and checking them right. As if I am Im pretty sure I found the culprit as to why this amp is not working. And found the replacement parts on ebay for a mere 2.00 apiece. (not a bad little investment for an amp that retails new for 1000 dollars on ebay)

anyways, I appreciate any help as you all can give me, and wanted to make sure I was steering in the right direction to fixing this beast.. as Im sure it will knock the hell out of a set of subwoofers lol.

 

[davenn]

hi
welcome

as they look like transistors when I put the leads on them it automatically goes to an Open circuit. will not read an ohm load which in turn to me, means dead short

ummm which is it ? that statement is a contradiction
if it shows 0L then its open or VERY high resistance. if it shows 0.0 or something close ( 1.0, 0.1) then its a short circuit

Dave

 

[obscuremind]

oh it shows 0.00 like in the picture.. like I said Im not good with electrical terms. So I guess Open or 0L was the wrong term to use there. but yes.. ALL 4 of these
both the FMG33R and both FMG33S both show 0.00 when I hold the leads on the outer legs see.. so that would in fact make them bad correct?

 

[(*steve*)]

both the FMG33R and both FMG33S both show 0.00 when I hold the leads on the outer legs see.. so that would in fact make them bad correct?

It depends. If they are mosfets, you may have turned them on by handling them.

Once you've done that they will read close to zero ohms. Ti turn them off you need to short the gate to the source. However. Handling them is also likely to destroy them, so... stop handling them until we know what they are.

Tell us what is written on the devices. You may find that there are more than one type, so check them all to determine what types of transistors there are. We can look them up for you as long as they are not "secret" house numbered parts.

FMG33... They're a fast rectifier. With 3 leads, it's possible that 2 are common, so a reading of 0.00 is not unlikely. It's also possible they're shorted, but if you get the datasheet first, you may find the correct pins to probe and that may tell you something.

OK, datasheet is here. The two outer leads are likely to be connected together in the circuit.

Measure from the middle lead to one of the edge leads, then reverse the probes and try again. You should get two very different readings.

If you have a diode test range on your meter then one way should measure around 0.6 and the other way much higher (or even 0L)

But the problem is unlikely to be these devices. Check other part numbers for those devices that were mounted on the heatsink.

 

[obscuremind]

ok so, I done everything, and tried to explain best I could of the readings I got.. heres my turnouts.. hopefully the pictures best decribe themselves.. And even got a close-up of all the different chips for you all.
the weird thing is, You said I would be getting different readings on them FMG33 chips 3 of them read 406, while the one chip read in the 1400's on both legs while it was still continuing to climb on the Diode setting of my volt meter..

LEFT LEG

RIGHT LEG

the only one that done this LEFT LEG

the only one that done this RIGHT LEG

 

[(*steve*)]

Firstly, you did try with both the red and the black lead on the centre pin, right? The difference between the S and R versions is that one is common anode, the other is common cathode.

Your images show you with the same probe on the centre of the S and the R. SO the reading you got on that lat one is wrong. Put the black lead on the centre pin.

Oh, and great photos by the way. It helps to see what you're doing