Rockford Fosgate T30001

[Perry Babin]

Do you have two low value resistor (2 ohm or 4 ohm dummy load resistors) that you can insert in the red and blue supply wires to protect the output transistors?

 

[seankane]

I may be able to come up with something, But I have the output board unplugged from the power supply board, red-white-blue-and both ribbon cables. The amp should power up even being not connected to the output board. Thats why I was thinking the fault is on the power supply side.

It does the same thing hooked to the output board or unhooked, so until I can get the amp to power I didnt see a need to have the output board hooked up.

Am I wrong to think the power supply board will power up not connected to the output board?

 

[Perry Babin]

I don't think that there should be a problem powering up the supply alone but I don't know if I've ever tried it on one of these amps.

Do you have all of the screws in the power supply side of the board?

Do you have a good drive signal on the leg of ALL of the power supply FETs?

 

[seankane]

Yes all the screws are in and yes I have a clean square wave on all the p/s fet gate legs. Pins 13 and 16 on the 3526 are also a clean square wave. I did this by just hooking ground and remote power.

 

[Perry Babin]

Have you disconnected the ribbon cables as well?

 

[seankane]

yes

 

[Perry Babin]

It could be that you damaged one of the rail caps. 20 amps of current draw isn't significant for this power supply if the FETs are clamped down and they are getting a good drive signal. I'd suggest that you let it remain on for a minute or so to see if anything starts heating more than it should.

 

[seankane]

OK but when I try to power it up the power light does not even attempt to come on it just squeels and draws about 20 amps on the power supply. It seems like something is shorted but its not the p/s fets.

You think I should just leave the power to it and see if it will over come the squeeling and power up?

 

[Perry Babin]

I wouldn't walk away from it but you may have to let it run like that for a minute or so to see if anything starts to get hot.

 

[seankane]

OK.......a few things did get hot and even smoked.

D33....hot
D34....smoked
D35....hot
D36....hot and desoldering itself

C78, C79, C5 felt warm.

It was hard to tell exactly which components it was but the heat was coming from one concentrated area. I cant find my heatgun and I was not sticking my finger on the board not knowing what voltage is where on this thing.

Can I or can I not clip those D33-D35 out of the circuit and then try and power up amp??

 

[Perry Babin]

I think they're probably OK but seem to indicate that there is a problem with the regulator for the rail voltage.

Check or replace Q36. Was it defective?

 

[seankane]

Changing Q36 made no difference, still same result.

If any of these D33 D34 D35 D36 were faulty could this cause this issue?

Can I clip them out of the circuit and safely power the amp?

D36 appears to have a crack in the component, not sure if it was caused by letting it try to power or previous from the huge spark from the red wire?

Looking at the schematic they seem to be connected to the voltage regulators.....if one of those was shorted could it cause this issue?

The wierd thing about it is the power light is not even attempting to come on or even flickering when trying to power up.

 

[seankane]

I removed D34 and D36 from the circuit and checked them with my meter and they read funny compared to the rest. I removed 2 BYV27-100's from a Punch 250M2 parts board I have.

I installed the used parts into the big beast......and it powered up!!!

Something is still not right. It powers up and idles and is drawing about 7 amps of current which I think is normal but one of the transformers is making a wierd frequency noise sounds like crickets chirping softly.

I no longer have clean output, there is bouncing DC offset on the output terminals jumping from 0.090vdc to 0.555vdc and sometimes as high as 1 or 2 volts DC. It will produce a audio wave but its real irratic and choppy, probably because of the DC.

Is there anymore components affiliated with the D34 and D36 that could be making the supply act strangely? It has steady current draw and seems stable but the noise was not there before.

The outputs are not getting hot bolted to the heat sink, but I can feel the heat sink getting warm around the outputs.

I know this is alot of info at once but I want to make the issues known and clear so maybe it will be easier to help. Please let me know what you think???

 

[seankane]

Please read post #52 and #53 first.

If I unhook the output board the power supply board idles great at about 2.5 amps with no noises or issues. I think the problem is on the output board.

I think replacing D34 and D36 has fixed the power supply board now?

I think Q410, Q405, Q404, Q403, Q432, Q420, Q419, Q418 are the fets that switch the rails?

I think Q403, Q402, Q411, Q431, Q433, Q429, Q428, Q427 are the fets that produce the audio?

Q433, Q429, Q428, Q427 all have the same bouncing DC on their drains so can I be wrong to say these could be leaky now after the big surge?

Q403, Q402, Q411, Q431 all have a steady drain of 0.000 vdc.

Maybe the transformer that has the noise with the output board connected is the one that drives the audio fets and if they are leaky could be causing the noise?

Just trying to enlighten all possibilties.

 

[Perry Babin]

Have you confirmed that all regulated voltage sources are now working properly and at the correct output voltage?

 

[seankane]

Do you mean all of the rectifiers and the regulators for the op-amps?

I dont know where they all are I just know the LM317, LM 337 and the MUR1520's. I will check all those is there anymore I need to be aware of?

Should I be checking all of the op-amps for DC as well again?

 

[seankane]

If any of those were defective would it only cause issues when the output board was hooked up?

Is there more that I should be checking than listed in post #56?

 

[Perry Babin]

You can check the LM3x7s at the regulator. If you don't know where the others are, check the supply voltage on all ICs to confirm that the positive and negative supplies are of the same magnitude (for example ±15, not +15 and -25 or -8). Come of the ICs will operate off of ±6 and maybe ±10.

 

[seankane]

Ok I will check all of those in the next day or so I am so so busy!!! If I find a fault in one of those components can that explain the bouncing DC on the output terminals and some of the outputs?

 

[Perry Babin]

When you have a failure like this and components fail for apparently no reason, you have to start with the basics... Confirm that all power supplies are as they should be.