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Old 4th February 2013, 09:55 AM   #1
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Default Rockford Fosgate T40001bd

Perry

Sorry for the delay in getting back with you. Turns out after replacing the FETs and replacing all the components of the 4 drive circuits it powered up and played perfectly. Thanks for all your help...Now, for the next one.. I have another T40001BD that someone else repaired and they're work is somewhat questionable. I first opened the unit up and diode check the outputs and the powersupply chips. Everything seems fine. So i powered up the amp and everything is fine. No protect light until about 10 seconds. Amp meter on powersupply is around 1-3 amps and then jumps to 10amps. Nervously, i power down and check for hotspots. Nothing obvious, I power up again and check output voltages. I read 110v on half the outputs and then the unit goes into protect. I remove power and remove the +hv, gnd, -hv from the output board and power up. Unit stays out of protect mode now but i seem to have higher voltages from the previous amp. I am reading 184v from +hv and -hv. Does this seem normal or high? I was expecting around 120 or 110V.
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Old 5th February 2013, 02:03 AM   #2
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120v is what's spec'd on the schematic diagram. If it's really 180+, you have to test quickly to prevent blowing the rail caps. They're only rated for 160v.

What is the DC voltage on pins 1, 2, 3, 17 and 18 of the SG3526?

You need to gt them quickly bit not so quickly that you let your probes slip and short between pins.
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Old 5th February 2013, 11:26 AM   #3
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Pin voltages

1- 4.43
2- 2.516
3- 4.19
17- 26.50
18- 5.00
With 17&18. Opposite side(across) of chip for pin 1

With 17&18 at the bottom of the chip..
17- 2.5mv
18- 2.171v
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Old 5th February 2013, 01:39 PM   #4
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I don't understand the second set of numbers.

With the red probe on the anode and the black probe on the cathode, what is the DC voltage measured directly across D11 and D12?

With the black probe on the emitter, what is the DC voltage on the base and collector of Q36?
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Old 6th February 2013, 01:19 AM   #5
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D12 = -2.561v
D11 = 0.4140v

Q36 emitter to base = 0.638V
emitter to collector = 23.4mV
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Old 6th February 2013, 01:25 AM   #6
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Perry,

at what part of the circuit can the two banks combine voltage to cause this type a scenario? just curious..
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Old 6th February 2013, 02:27 AM   #7
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If you lift D11, do you get the proper, regulated rail voltage?

Be careful, I've never tried this but I don't see any way it could cause any harm.

I don't understand the question (#6).
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Old 6th February 2013, 12:16 PM   #8
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Perry I lifted the D11 and measured ~100vdc. I also diode checked D11 abd got 0.532vdc. The rail voltage seems to be regulated properly.

Just for curious, how long have you been doing electronic repairs?
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Old 6th February 2013, 01:32 PM   #9
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Perry I lifted the D11 and measured ~100vdc. I also diode checked D11 abd got 0.532vdc. The rail voltage seems to be regulated properly.

Just for curious, how long have you been doing electronic repairs?
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Old 6th February 2013, 04:41 PM   #10
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Check Q12 carefully (leakage, open junctions...).

Too long? Since about 1986.
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