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Old 20th September 2012, 06:21 AM   #1
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Default Rockford Fosgate Punch 250M

Hello everyone.

I have an old school Rockford Punch Power 250M board number PC-0776-G

When I received the amp it would not power up. I removed the cover and found R8 burned in half. I replaced R8 and the amp powered up fine with no excess current draw.

The amp has -10.85 vdc on the + output terminal.

The amp idles fine and the bias sets fine.

The op-amps all have positive and negative voltage.

The regulators have output.

The rectifiers have output.

The + rail has 50 vdc and the - rail has 70 vdc

The drivers Q110, Q109, Q107, Q106 are getting very hot.

LM339 reads as follows:

pin 1: 4.96
pin 2: 4.96
pin 3: 26.80
pin 4: 0.442
pin 5: 2.633
pin 6: 4.35
pin 7: 5.01
pin 8: 5.01
pin 9: 5.33
pin10: 5.01
pin11: 8.22
pin12: 0.002
pin13: 4.96
pin14: 22.07

TL594 reads as follows:

pin 1: 2.321
pin 2: 2.319
pin 3: 3.494
pin 4: 0.003
pin 5: 1.515
pin 6: 3.430
pin 7: 0.002
pin 8: 26.81
pin 9: 0.659
pin10: 0.639
pin11: 26.81
pin12: 26.81
pin13: 5.01
pin14: 5.01
pin15: 5.01
pin16: 0.002

Does anyone have any ideas? The lm339 and tl594 have some strange readings.
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Old 23rd September 2012, 09:55 AM   #2
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HHHMMM
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Old 23rd September 2012, 12:38 PM   #3
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+12v or +15v regulator shorted? Whatever supplies the opamp and 494.
That tied directly to remote voltage?
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Old 23rd September 2012, 12:44 PM   #4
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200m schematic

https://sites.google.com/site/brande...edirects=0&d=1
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Old 23rd September 2012, 08:00 PM   #5
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The 200M schematic is not the same.
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Old 23rd September 2012, 08:13 PM   #6
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The 500m schematic diagram has the right board.

These amps are a bit different than other amps. Confirm that the secondary center-tap of the power transformer is directly connected to the positive speaker terminal.
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Old 24th September 2012, 04:56 AM   #7
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It appears that one leg of the transformer is connected to the + speaker terminal. It is a little different than the 250m2 which has 2 legs connected to the + speaker terminals.

I attatched a photo so you could look at the bottom of the board, keep in mind this pic is of a parts board but its the same board.
Attached Images
File Type: jpg 250M parts board pic 001.jpg (861.4 KB, 93 views)
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Old 24th September 2012, 01:30 PM   #8
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If you measure the resistance from the positive speaker terminal to the secondary CT, do you read 0 ohms?

The 10v or offset and the 20v of difference for the rails are directly related. The output stage drives the rails up and down with the audio. If you look at the rails with audio driven into the amp, you will see audio but will not see normal audio on the output transistors.

Lift Q125 and 126. Does the offset go to 0v?

Be careful when applying power. I don't think the current draw will increase but be prepared to shut it down if it does.
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Old 26th September 2012, 06:22 AM   #9
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Quote:
Originally Posted by Perry Babin View Post
If you measure the resistance from the positive speaker terminal to the secondary CT, do you read 0 ohms?

The 10v or offset and the 20v of difference for the rails are directly related. The output stage drives the rails up and down with the audio. If you look at the rails with audio driven into the amp, you will see audio but will not see normal audio on the output transistors.

Lift Q125 and 126. Does the offset go to 0v?

Be careful when applying power. I don't think the current draw will increase but be prepared to shut it down if it does.
With Q125 and Q126 installed from the CT to the positive speaker terminal reads 56.1 k ohms, with Q125 and Q126 removed the CT to the positive speaker terminal reads 0L.

With Q125 and Q126 removed the offset drops to -2.968 vdc
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Old 26th September 2012, 08:22 PM   #10
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Please post a photo of the top of the board showing the secondary center tap and the area around it.
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