Rockford Fosgate T40001BD Repair

RockfordFIx · 2012-12-04 5:07 pm

I am repairing a T40001BD and having a little trouble find a schematic. Can someone please email me a copy of a T40001BD schematic to matt76.brooks@gmail.com

I have replaced the output FETS and the powersupply FETS checked out fine. When powered up my +HV is around ~9v and my -HV is ~110v.

Perry Babin · 2012-12-04 5:55 pm

Check your email. You can get most Rockford schematic diagrams from Rockford.

RockfordFIx · 2012-12-04 6:25 pm

Perry,

Thanks for your help....might have a few questions for you after get home and check some test points to find out where i am losing my high voltage at.

matt

Perry Babin · 2012-12-04 6:59 pm

BD amps don't have static rails. In this amp, there is one 120v rail. The rail is shifted up above ground by 120v or driven below ground by 120v as needed by the output stage.

If you have a scope, that will be helpful when troubleshooting.

RockfordFIx · 2012-12-04 8:47 pm

Perry,

I have been meaning to buy a scope. Should i also invest in a signal generator too?

seankane · 2012-12-04 9:35 pm

You could buy one but I would save your money. You can download test tones and burn them to cd's and just use a head unit.

You can also load test tones on your i-pod or phone and use the 1/8" jack to male rca and plug it directly into the amp.

These options would work great for amp repairs.

Perry Babin · 2012-12-04 10:01 pm

I agree that you don't really need a signal generator.

I'd suggest a proper head unit with the proper protection. You can use an ipod but some amps will not work properly with any audio source with a floating ground (like an ipod). You can ground the shield to make it usable but you have to protect the shield ground like a standard head unit.

If you use an ungrounded signal source, you'll also miss problems like intermittently shorted transformers. If you are repairing an amp for someone and you miss an intermittently shorted transformer, you may be asked to pay for the damage to the vehicle or to the head unit when they connect it and cause damage to their vehicle or equipment.

RockfordFIx · 2012-12-06 7:23 pm

Perry,

should i be getting ~120 for both -HV and +HV at the same time. With the ground wire only connected to the output board i read ~110 on +HV and ~-5 on -HV. When connected i read ~5 on +HV and ~-110 on -HV.
matt,

Perry Babin · 2012-12-06 9:23 pm

You don't measure rail voltage referenced to ground on these amps. You measure across the red and blue wires.

RockfordFIx · 2012-12-06 10:51 pm

thanks for clearing that up. bringing home a fluke 97 scope meter this weeking and will hookup a descent headunit. I have a pyramid 52amp powersupply i purchased off of ebay but the output is at max for 14.5v. used my droid for pandora for an input to the amp hooked up to the powersupply. seemed to clip/distort a little with gain up and thats what made me look at the rail voltage. But now i am wondering if the powersupply is not producing enough power. Will get a car battery and check and see.

RockfordFIx · 2012-12-08 3:38 am

Perry,

i seem to have ~110v on the drain and source for 10 of the outputs and ~8v on the remaining. Any ideas come to mind. should i remove the outputs that have the lower voltage readings and start working my way back.

Perry Babin · 2012-12-08 3:47 am

What is the DC voltage across the speaker terminals?

RockfordFIx · 2012-12-08 4:21 am

i have 0.5 volts. I have some sound but it is distorting. I think there is an open transistor or diode somewhere. Don't think it is a shorted one or i would be seeing some other issues.

Perry Babin · 2012-12-08 4:30 am

If you don't have any significant DC, it sounds like it's in protect mode. Is the protect LED lit?

If not, measure the DC voltage across it to see if it's open.

RockfordFIx · 2012-12-08 5:57 pm

the protect light has a faint bit of light but it only can be seen with the lights off. I don't think it is in protect mode because if i hook my scope probe to pin 7 on U304 it sends the amp into protect mode and the led fully lights up as long as the probe is touching.

Perry Babin · 2012-12-08 7:03 pm

Confirm that you have a good triangle waveform on pin 7 of U303 and that it has essentially no DC offset.

RockfordFIx · 2012-12-09 5:51 pm

perry,

i measured the voltage across the protect LED and got 0.532V and a nice triangle waveform output B pin 7 with no baseline offset with max peak of 2.12v

RockfordFIx · 2012-12-09 8:12 pm

Perry,

I removed Q401 for troubleshooting the driver circuit for that bank of outputs and powered the circuit. unfortunately i didn't have my current limiting resistor installed and blew that bank of outputs. Can i remove the blown bank and power the amp to troubleshoot the bank that is not powering up

Perry Babin · 2012-12-10 2:36 am

The current limiting resistor in the B+ line would not have saved the FETs. There is too much secondary capacitance. When working on these amps, the only protection that I've found is either adding fuses or resistors in the red and blue wires.

You shouldn't power up any FET circuit with any of the driver components out of the circuit unless you know the circuit well enough to know that the FETs will be held 'off' when power is applied.

RockfordFIx · 2012-12-10 4:25 am

Perry,

should both banks of FETS be powered at 110 v or do they alternate? I noticed that T400 and T401 are both hooked to U202 and U204 which have a toggle A and B for the input. could one of the secondary output be open on t400 pin2, 3?

Rockford Fosgate T40001BD Repair

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