Blown Keying transistor near Fatboy Amp Relay?

[yota167]

Hi all. Thanks for a great site:

Maybe someone can help me out here:

What happened:
My truck had the battery installed on reverse polarity. Blew a bunch of fuses in my truck. I replaced them all and the truck runs great. No problems. Now my FATBOY 4pill 2879 amp is another story. It seemed to survive the reverse polarity issue upon initial inspection. There was NO amp fuse inline with the hot unfortunately. Spare me the finger pointing. I realize I should have one....ok anyhow: The wire beneath the keying relay in the box has melted aka seperated. This is a wire that is directly near the bottom of the board and exactly in front of the relay....this is the wire that has melted. They are no longer connected. What was between that wire; What blew? Any help? I will post pics soon.

Note: I keyed it up, looked at my DOSY and NOTHING. Nothing showed up at all. Turned it off, and checked my Radio with the amp still inline: perfect SWR readings 1.2/1.3 and showing the correct amount of wattage and DK from radio as always. Soon as the amp is turned on: NOTHING. I keyed it twice just to see WTF and smelled that terrible electronic burning smell.


all PILLS in amp are fine.

Thanks gang.

 

[Robb]

As a pure guess, I would start looking/checking out all of the diodes on the board. One of them has popped. Usually on most amps, as soon as the power leads comes on to the board, they go thru a diode. That is probably the one that has popped - IMO.
Or it also popped an electrolytic cap as well. Check out the diode(s) first with a meter that is equipped with a diode test - as most are...

 

[yota167]

As a pure guess, I would start looking/checking out all of the diodes on the board. One of them has popped. Usually on most amps, as soon as the power leads comes on to the board, they go thru a diode. That is probably the one that has popped - IMO.
Or it also popped an electrolytic cap as well. Check out the diode(s) first with a meter that is equipped with a diode test - as most are...

Ok, whatever was between this wire is no longer there. It may have been either a electro cap, a diode, or a disc capacitor. I did find small fragments of BLACK PLASTIC.

Thanks for such a quick reply.

If your still here I will go take a pic and post it in like 10 minutes!

 

[Robb]

Non-polarized(disc) caps, resistors, coils, and wires aren't going to affected by a reversed current.
However, polarized caps, diodes, transistors will be affected. I would start from where the power comes on to the board and work my way inward twards the output. Perhaps the relay may also get fried; but don't quote me on it. The transistor that is in the relay circuit may also very well be gone - too.

Usually, if there was a diode where the power comes in, they usually just fry the inside of the diode and looks like a dead short on a meter. They are usually intact, but it is possible for it to shatter into shards.

The amp should still work if the protection diode is removed from the board, as its purpose is to protect it from improper polarization to the board. If it doesn't, then many other parts have been affected.

A lot of the better radios also come so equipped, and it is usually the first part to replace and usually fixes the problem in a jiffy when this happens. After you fix this amp, I would put in a protection diode - if it didn't have one put in by the mfr. Without this part in any 12v radio or amp, you may have to replace $60-80 worth of parts plus the time it takes to replace them. With this protection diode in place, you only need to replace a $.50 diode. They should have that part in every piece of 12v equipment - but some mfr's are just too cheap to include it.

You will probably have to check all of the diodes and electrolytic caps - and the output transistors as well. Since amps are basic and simple circuits, this shouldn't be too time consuming...

 

[yota167]

Damn. Dead batteries in the Digital Camera. Gotta go hunt some down !

 

[Dustydude]

Hello,

If this photo works lol.
The cap is a 10pf
The diode is a IN4148
The polerized cap is a 22uf
The transistor is a PN2222a
On the left side of the pic is the negitive side of the 22uf cap with the diode, That solders to ground.
The lead on the left of the 10pf cap solders to the center of the input so239 connector or to the relay from the input so239.
The right lead (positive)from the 22uf solders to the relay. left lower terminal.

 

[9C1Driver]

Actually an in-line fuse would only protect you from a dead short, not reverse polarity. Thats why radio's have both reverse polarity protection and a fuse. Hope you get er figured out.