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Old 28th July 2014, 02:52 PM   #1
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Default Rockford Fosgate T20001BD

I got a rockford fosgate T20001bd in for repair. I have checked the powersupply fets and the audio outputs, these all test fine with diode check feature. The unit powers up fine, no protect light, and very little current draw. After applying a 100hz sine i expect to see some output but have none on ac or dc or very little to nothing on dc. there are no burns or blown components. I dont have a schematic so i cant tell where to see the carrier wave and my fluke 97 has complications moving from MO to NC this month. any help would be appreciated. Perry i didnt mean to post this in the rockford 801s. I was doing it from my phone when i was reading the post and hit reply ot post instead of start new thread.
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Old 28th July 2014, 03:01 PM   #2
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Sounds like the problem is in the output if you are seeing little current draw. Try desoldering the rectifier diodes then test the supply for proper voltage, if you don't already have it with the output stage connected. Once that is ruled out, and if it is, I would suspect the driver board. These go frequently in car audio amps, usually due to heat build-up in the chassis. They are small and usually on a separate PCB standing on the mainboard somewhere. I will not be surprised if your issue is here. You could also try to trace the signal path from the RCA jack onward. Ignore the crossover controls for now if you can disable them. You may have a burnt a signal diode or resistor somewhere.
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Old 28th July 2014, 03:08 PM   #3
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I have found some internal pictures of this model online and it looks like there is a small SMD op-amp based input stage you could check out quickly. Look for power supply voltage to the proper pins and if you have the means check for signal, if you know where to look. If there is a service manual or schematic be sure to find it, but you know that. I can't see well enough to tell you where the switching driver is, looks like it is near the fan in the center, to the far left, or to the right of the RCAs. So my guess is as good as any as far as that goes. It's probably by the fan, since it will have some ICs in it. You could look up the part numbers on some of the ICs and check for proper supply voltage and output if possible. This gets difficult quickly without a scope.
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Old 28th July 2014, 03:58 PM   #4
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What's wrong with the scope? Is it something that you can repair (broken lead, dead battery) or do you mean that you don't have access to it?

To measure the rail voltage... Red probe on center leg of Q419 and black probe on 3rd leg of Q428.

Also confirm that you have ±regulated voltage on the op-amps.

Do you have all of the screws in the board in the power supply area?
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Old 28th July 2014, 05:18 PM   #5
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There is a open cell in the battery pack. It has a power adapter but will not turn on. I am wondering if the power adapter charges battery and not run off the adapter.
It had rail voltage of 101 on all of the outputs for the center leg and leg 3.
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Old 28th July 2014, 05:34 PM   #6
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It had rail voltage of 101 on all of the outputs for the center leg and leg 3.

I don't think that's possible since the center leg of half of the transistors connects to the 3rd leg of half of the transistors.

Confirm that the power supply for the scope has the rated output.
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Old 28th July 2014, 06:08 PM   #7
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I will double check tonight. The power adapter has 21 volts out. It is rated for 15 or 18 out
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Old 28th July 2014, 06:23 PM   #8
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That's probably OK. Most AC adapters overshoot the rated voltage when unloaded.
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Old 29th July 2014, 01:19 PM   #9
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Quote:
Originally Posted by Perry Babin View Post
That's probably OK. Most AC adapters overshoot the rated voltage when unloaded.
And by a good margin at that
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