Rockford Fosgate RF? - Model unknown sync clips

Dr Zeus

Member
2010-10-17 5:12 am
I think this is an RF series amp; and I personally had one of these when Rockford failed to sell them back in 1997-ish. its a Rockford 4 channel amp, likely 30w X 4 RMS. I remember it ran my whole system at the time, but this amp was never considered to be anything more than entry level and likely costed only about $150 brand spanking new back then.

Needless to say I have one in for repair, which I believe has bad power fets as it draws too much on REM. Unfortunately I cannt test the fets because the clips are in the way, and I just dont know how I can remove the clips. The whole bottom of the amp is part of the sync and nothing seems to budge.

Any tricks to getting the PCB outa this one? It seems imposible and I'm out of ideas.

IMAG0087.jpg


IMAG0088.jpg
 

Dr Zeus

Member
2010-10-17 5:12 am
This amp has both of one out of four channel output transistors shorted so I clipped them off the board (540 and 9540). All Power supply fets (MTP 50n06v) were shorted so I clipped those off the board. I dont know if the TL494 is working right because I get iratic DC voltage from each of the supply fet Pad/Leg 1.

The surface mount TL494 is not looking so good measuring the following:
Pin 1: 0vdc
2: 4.47
3: 0.035
4: 1.325
5: 1.5
6: 3.320
7: 0
8: 10.9
9: 10.4
10: 5.71
11: 11
12: 9.97
13: 4.97
14: 4.97
15: 4.97
16: 0

Pad/Leg 1 of 2/4 the power fets measure 5.87vDC. The other 2 fet pad1s measure 0vDC

Pad/leg 1 of the power fets are going to a circuit series of ~8 surface mount transistors. Of the Punch series amps I've worked with, this amp circuitry looks similar.
 
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Dr Zeus

Member
2010-10-17 5:12 am
Testing these little ones between collector and emitter, I thought it was Q1 with is a 1G transistor so I carefully removed it. To my surprise, it actually turned out to be Q2 which is reading 33ohms from collector to emitter even off the PCB. Q1 and Q2 collectors and emitters are wired in paralell on the pcb.

Its really tough to read; because the transistor possibly defaced itself when it failed. I only see a 2 on its back, and then a brown/black spot right next to that. The only other transistor with 2 is a 2G at Q3 which is testing alright.
 

Dr Zeus

Member
2010-10-17 5:12 am
Man you are the best! Q4 is a 1G and its shorted to 33ohms between center and top right. You think that would cause 10v on pin9?

I dont know what a 1G or 2G is. How can I look these up without having to ask all the time?

So far, this amp needs:

4 power fets 50n06v (I'll likely use IRF3205ZPBF-ND cause I have a big order coming in of them)
2 output fets 540, 9540
4 source resistors (3w, 0.1ohm)
4 Power fet gate resistors SMD 100 (10 ohm)
1G
2G
 

Dr Zeus

Member
2010-10-17 5:12 am
New readings

IC# TL494C
Pin 1: 0.003
Pin 2: 4.47
Pin 3: 0.060
Pin 4: 1.449
Pin 5: 1.491
Pin 6: 3.298
Pin 7: 0
Pin 8: 11.48
Pin 9: 1.79
Pin 10: 2.88
Pin 11: 11.46
Pin 12: 10.39
Pin 13: 4.93
Pin 14: 4.93
Pin 15: 4.93
Pin 16: 0.000

Old readings:
IC# TL494C
1: 0vdc
2: 4.47
3: 0.035
4: 1.325
5: 1.5
6: 3.320
7: 0
8: 10.9
9: 10.4
10: 5.71
11: 11
12: 9.97
13: 4.97
14: 4.97
15: 4.97
16: 0