I have a Rockford Fosgate T20001 Power series amplifier, board ID PC-4755-A.
It powers own, without going into protect. As soon as it does, there is a clipped signal coming out of the output at rail voltage. It also drains the rails very quickly as soon as you power off, roughly 30 second. It makes a little screech sound when you power it back on ONLY when it has drained the rail voltage.
I can hear a slight buzzing sound coming from the output area, but I can't pinpoint it.
This is all with no audio input, RCAs are unplugged, and the amp board is still mounted into the chassis.
I did not have any shorted FETs, and the power supply gate drive looks normal (tested without 12v input, just remote and ground). Once 12v and remote are applied, it looks terrible.
Any ideas on what to check?
It powers own, without going into protect. As soon as it does, there is a clipped signal coming out of the output at rail voltage. It also drains the rails very quickly as soon as you power off, roughly 30 second. It makes a little screech sound when you power it back on ONLY when it has drained the rail voltage.
I can hear a slight buzzing sound coming from the output area, but I can't pinpoint it.
This is all with no audio input, RCAs are unplugged, and the amp board is still mounted into the chassis.
I did not have any shorted FETs, and the power supply gate drive looks normal (tested without 12v input, just remote and ground). Once 12v and remote are applied, it looks terrible.
Any ideas on what to check?
Attachments
With the scope set to 2ms and 1/2v/div, do you see any signal (OR DCV) on the RCA shields or center conductors?
Short the center conductors to their respective shields. Does that change anything at the output?
You'll need to look at the signal through the signal path to see where it's starts to show up.
Do you have the diagram?
Do you have the diagram?
It's up to you. For some circuits, it's more efficient to start in the middle of the audio path but this circuit is fairly simple.
Have you operated all pots and switches through their entire range (other than the 3-position switch) to see if anything changed at the output?
One end of the resistor is connected to the inverting input and that terminal may not show much signal.
What does the signal look like on R139? Check while operating all switches and pots through their entire range.
One end of the resistor is connected to the inverting input and that terminal may not show much signal.
What does the signal look like on R139? Check while operating all switches and pots through their entire range.
I had cleaned and worked all the switches with de-oxit. I'll check that signal again while working the switches
No I can't. I plugged my signal generator into the Pass Through RCA jacks and it wouldn't do anything.
Yup. Thanks a ton. I just cleaned it again, ran it a few hundred times while flushing it with de-oxit. Should I replace it to prevent this from happening again down the road? Or just put some de-oxit lube/protect?
I'd replace it if it was available.
So, if it produces audio that way, you know it's in the preamp section. The crossover filter circuit will commonly do this if the circuit is broken (defective pots are common).
Bear in mind that the entire filter circuit relies on every component working normally.
So, if it produces audio that way, you know it's in the preamp section. The crossover filter circuit will commonly do this if the circuit is broken (defective pots are common).
Bear in mind that the entire filter circuit relies on every component working normally.
Thanks for the help. I have 2 more of these (and a stash of 1k/3k/4k) series of amps that I am going to try and work through, so I'm really trying to learn how they work.
The switch seems to be a SK43D05, found a datasheet but I'll have to do some looking to try and find an available replacement. Does Rockford ever sell replacement parts like this, if still available?
The switch seems to be a SK43D05, found a datasheet but I'll have to do some looking to try and find an available replacement. Does Rockford ever sell replacement parts like this, if still available?
Try contacting the forum member seankane. He has some parts.
Side note... The op-amps are in series and DC coupled so they can build a lot of offset. In some instances, especially in the crossover/filter, all need to be replaced.
Side note... The op-amps are in series and DC coupled so they can build a lot of offset. In some instances, especially in the crossover/filter, all need to be replaced.