This amp was in my sons truck. He said it just quit putting out sound. The amp gets power with no protection light coming on. The amp is not pulling excessive current. So I pulled the cover off & checked the outputs. 2 of them are shorted, which are FQA28N15 board location q218 & q222. Also there are 2 transistors(I think that is what they are) that are also shorted. 1 of them has # lm317t board location q13, the other #lm337t board location q12. I did a search on Mouser but could not find them. What would be a good cross for these 2.
This amp is different from amps that I have worked on before. I am used to working on old school amps. So I am a little lost as to what what else I need to check. I would like to try & get this up and running asap, because he is supposed to be going to a comp show in a couple weeks. Any help would be great
This amp is different from amps that I have worked on before. I am used to working on old school amps. So I am a little lost as to what what else I need to check. I would like to try & get this up and running asap, because he is supposed to be going to a comp show in a couple weeks. Any help would be great
I tested the regulators again. On the 337 with neg probe on pin 2 & pos on pin 3 got 3k and started rising rapidly til 8.45k then slacked off to a slow rise. Same thing with pos on pin 1. On the 317 with pos on pin 3 started at 3k Rose rapidly to 120k. With pos on pin 120k constant. This is with them in circuit. Does this sound right?
Get the schematic diagram from Rockford, email me a copy and I'll tell you what else to check.
It's likely that only one of the 28N15s is shorted. Measure the resistance from leg 1 to leg 2. The one with the lowest resistance is the shorted one. Cut it out of the circuit and see if the amp will power up.
It's likely that only one of the 28N15s is shorted. Measure the resistance from leg 1 to leg 2. The one with the lowest resistance is the shorted one. Cut it out of the circuit and see if the amp will power up.
You should be able to identify the shorted one without pulling either of them from the board. From leg 1 to 2 there should be one very close to a dead short, and the other will read slightly higher. Only cut out the one that reads very near a dead short.
Perry, I have seen several of these amps with negative rail on the speaker output and come on and remain on untill the smoke comes out of the speaker.
Perry check your email I sent you the schematics, for this amp.
With meter set to diode check both q218 & q222 reads .02. With meter set to ohms q218 reads 18ohm & q222 reads 37.8ohm. q217 & q221 read 19.7m ohm.
I also checked q122 & q118 in ohms read open in diode reads 1.15, q117 & q121 read open in ohms & 1.12 in diode check.
These readings are the readings that I am getting . When I checked the first time I checked these I had my meter set on the audible mode. Sorry about any confusion.
With meter set to diode check both q218 & q222 reads .02. With meter set to ohms q218 reads 18ohm & q222 reads 37.8ohm. q217 & q221 read 19.7m ohm.
I also checked q122 & q118 in ohms read open in diode reads 1.15, q117 & q121 read open in ohms & 1.12 in diode check.
These readings are the readings that I am getting . When I checked the first time I checked these I had my meter set on the audible mode. Sorry about any confusion.
I think you're reading across the defective Q222.
It appears that both N-channel FETs have failed so you'll have to order them before you can do any further testing.
Have you replaced transistors on the MEHSA insulators before?
You need to check the emitter resistors. Desolder one leg of the resistor to check it.
It appears that both N-channel FETs have failed so you'll have to order them before you can do any further testing.
Have you replaced transistors on the MEHSA insulators before?
You need to check the emitter resistors. Desolder one leg of the resistor to check it.
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