Rockford 250a2 Won't turn on - diyAudio
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Old 29th July 2007, 12:37 AM   #1
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Default Rockford 250a2 Won't turn on

I have a Rockford Fosgate 250a2 that will not turn on. I have inspected the board and haven't found any burn damage. I wired it up to a working configuration just to check to see that it is the amp and not the wiring. Any thoughts on what to do first?
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Old 29th July 2007, 02:20 AM   #2
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If the amplifier doesn't power up, measure the resistance between the 3 legs of the FETs in the power supply (the two transistors on the end near the power/ground terminals). If there are no readings near 0 ohms between any of the legs on either of the two FETs (checked individually, not from one FET to the other FET), you'll need to measure the voltage on the TL494 IC.

Connect the amp to a power source (including remote) with a 10 amp inline fuse.Connect the black meter lead to the ground terminal of the amp.Look up the datasheet of the TL494 to see how the pins are numbered and measure the DC voltage on each pin of the TL494 IC. Post the voltage for each pin in a list like this:

Pin 1:
Pin 2:
Pin 3:...
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Old 29th July 2007, 05:15 PM   #3
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Does anyone have a service manual for the 250a2? I will do the testing and let you know. I am assuming you are talking about the mosfets at the ver end on either side toward the LED/grnd/B+ side of the board?
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Old 29th July 2007, 05:15 PM   #4
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Quote:
Originally posted by Perry Babin
If the amplifier doesn't power up, measure the resistance between the 3 legs of the FETs in the power supply (the two transistors on the end near the power/ground terminals). If there are no readings near 0 ohms between any of the legs on either of the two FETs (checked individually, not from one FET to the other FET), you'll need to measure the voltage on the TL494 IC.

Connect the amp to a power source (including remote) with a 10 amp inline fuse.Connect the black meter lead to the ground terminal of the amp.Look up the datasheet of the TL494 to see how the pins are numbered and measure the DC voltage on each pin of the TL494 IC. Post the voltage for each pin in a list like this:

Pin 1:
Pin 2:
Pin 3:...

I had my multimeter set to 20v. I checked the numbers not once, not twice, but thrice and they were the same each time. the chip is the TI version as it has the tiny logo on it. Please let me know what you think. I suspect the two mosfets nearest the power block on either side are the problem. Thanks for your help.

1. 0
2. 4.46
3. .05
4 .44
5. .44
6. 3.22
7. 0
8. 10.14
9. 0
10. 4.79
11. 4.79
12. 4.79
13. 10.14
14. 10.14
15. 3.90
16. 3,90
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Old 29th July 2007, 05:15 PM   #5
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I screwed up the numbering

9. 3.90
10. 3.90
11. 10.14
12. 10.14
13 4.79
14. 4.79
15. 4.79
16. 0
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Old 29th July 2007, 11:11 PM   #6
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Quote:
Originally posted by Perry Babin
If the amplifier doesn't power up, measure the resistance between the 3 legs of the FETs in the power supply (the two transistors on the end near the power/ground terminals). If there are no readings near 0 ohms between any of the legs on either of the two FETs (checked individually, not from one FET to the other FET)
Did we check these? And yes they are the top component on either side of your picture. Also did you take the amp apart after it quit working or were you running it with only one screw in each of the strips of transistors?????
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Old 29th July 2007, 11:18 PM   #7
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It looks like the chip is operating and it has output.

With the same setup you used last time...

Measure the DC voltage on the first pin of each of the power supply FETs.

Measure the DC voltage on the center leg of the rectifiers (circuit board designation CR1 and CR2 -- part number u1620 and u1620r possibly).

Also measure the DC voltage on one IRF540 and one RF9540 in the audio section. Post the voltages for all three pins and make a note of the transistor part number (540/9540). If both channels are the same (within 10%), you only need to post a total of 6 numbers from the audio section.

Your post should include:

Voltage from the first leg of the two power supply FETs (2 voltage readings)

Voltage from the center leg of the rectifiers (2 voltage readings)

Voltage from the output transistors (6 voltage readings). List them like this:

IRF540
1
2
3

IRF9540
1
2
3
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Old 30th July 2007, 12:47 AM   #8
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Join Date: Jul 2007
Quote:
Originally posted by I Am An Idiot


Did we check these? And yes they are the top component on either side of your picture. Also did you take the amp apart after it quit working or were you running it with only one screw in each of the strips of transistors?????
I took the screws out after it quit.


Quote:
Originally posted by Perry Babin
It looks like the chip is operating and it has output.

With the same setup you used last time...

Measure the DC voltage on the first pin of each of the power supply FETs.

Measure the DC voltage on the center leg of the rectifiers (circuit board designation CR1 and CR2 -- part number u1620 and u1620r possibly).

Also measure the DC voltage on one IRF540 and one RF9540 in the audio section. Post the voltages for all three pins and make a note of the transistor part number (540/9540). If both channels are the same (within 10%), you only need to post a total of 6 numbers from the audio section.

Your post should include:

Voltage from the first leg of the two power supply FETs (2 voltage readings)

Voltage from the center leg of the rectifiers (2 voltage readings)

Voltage from the output transistors (6 voltage readings). List them like this:

IRF540
1
2
3

IRF9540
1
2
3
Power supply Fets both had the same measurments

12.15
12.15
0

CR1
0
.15
0

CR2
0
0
0

IRF540 Grnd
.15
.15
.15

iRF 540 B+
.15
0
.15

9540 GRND
0
.15
0

9540 B+
0
0
0
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Old 30th July 2007, 01:28 AM   #9
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Location: Louisiana
The FETs in the power supply are shorted. You should have found this earlier. They will have to be replaced.

You need to check the outputs for shorts between the individual pins of each transistor.

IT may be cheaper to pay someone to repair it than to attempt the repair yourself.
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Old 30th July 2007, 01:32 AM   #10
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Thanks for your help. Pardon my newbie ness. But how can you tell from those numbers that they are shorted?
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