Rockford T10001BD blown output fet

ComputerJLT · 2011-07-07 2:17 am

how much current we talking here? a few amps; a few mA?

grenadier · 2011-07-07 2:19 am

Amps. The driver needs to charge that capacitance in nanoseconds when running a fet at a high frequency.

ComputerJLT · 2011-07-07 2:21 am

ok; i think i get it...

asuming this amp powers up and sends signals to the fets still think it would be a good idea to start out with just maybe 1 fet per bank and then just test/add and maybe measure?

grenadier · 2011-07-07 2:25 am

The amp probably uses a full bridge (h bridge) to drive the speaker, so you'd need all four mosfets for it to work at all.

ComputerJLT · 2011-07-07 2:26 am

ahhhh

ComputerJLT · 2011-07-07 2:36 am

with no load (speaker) on the amp once i replace the fets are they still likely to fail catastrophically?

ComputerJLT · 2011-07-07 5:03 am

Alright small update....

I cleaned the board off finally to get some corrosion off and it looks like this amp HAS been into before. One of the LM339D chips closest to the trafo has been either replaced or unsolder-ed and put back on.

Also I got brave and connected the amp up to my 3a power supply to see if it even did anything.
I connected it up then applied power to the remote lead and the traffo made a buzzing noise as voltage increased and then when it topped out at 73v the protect light came on. I only had it powered maybe 5 seconds. In that very short time the 4 remaining output fets warmed up maybe 10f. just enough to notice that they're warmer than they were. Does that say anything (besides dont power it up with half the fets removed lol)???

Also while it was "on" but in protect i could hear/was aware of an extremely high pitch noise; i guess thats the traffo? I couldn't so much hear it but i knew it was there. Kinda like an old TV when they're on they make a very high pitch noise but most people cant hear it. I can't so much hear it as i know its there kinda like a pressure in your eardrum, very hard to explain without sounding crazy lol

Perry Babin · 2011-07-07 9:41 am

I wouldn't be concerned about the high pitched noise.

Which 4 of the outputs are out of the circuit?

gwada971 · 2011-07-07 10:56 pm

remplace les sfh 154 par des irfp250 et ça marchera il faut certainement changer les résistances de puissances de 0.1ohm 4w

kevinkr · 2011-07-07 10:59 pm

gwada971 said:
remplace les sfh 154 par des irfp250 et ça marchera il faut certainement changer les résistances de puissances de 0.1ohm 4w

This is an English language forum, as a minimum all foreign language posts must include an English translation.

gwada971 · 2011-07-07 11:07 pm

replaces by sfh154 irfp250 and it will work we need to change the resistance certainly power 4watt 0.1ohm

ComputerJLT · 2011-07-08 4:00 am

change what resistance?

ComputerJLT · 2011-07-08 4:01 am

oh and i removed the 4 blown fets perry; i just removed the 4 good oens so there are no fets in the amp and it still goes into protect; is this normal?

the power supply did come up instantaneously to 75v w/o the wine. crazy how this amp is the first i've heard that whines like that.

ComputerJLT · 2011-07-08 4:16 am

oh and this guy was blown apart too. its some sorta cap; the side and bottom were blown out i guess it expanded. i dont know if this was the cause of the amp failure or an effect.

gwada971 · 2011-07-08 5:35 pm

with a continuity tester to test all the transistor in the ouput stage to see if there are not short-circuit. because if there are short-circuit the amp goes into protection

Perry Babin · 2011-07-08 7:24 pm

It's a 4.7uf 250v 5% tolerance polyester/mylar capacitor.

Do you have any solder bridges between the pads of the transistors you removed?

Did you remove the entire MEHSA insulator or did you remove the transistors from the insulator?

ComputerJLT · 2011-07-08 11:19 pm

there were no shorts; i tested that first thing before I removed anything.

I removed the entire card with fets on it if thats the mehsa insulator; the daughter board with the remaining good fets had an extra 3 pins that i'm assuming were for some sort of thermistor. Even with that still intact it was going into protect.

So i'm guessing from your input with all fets removed the amp should not have gone into protect?

As it sits right now all of the power supply and diodes are on their daughter boards on the amp main pcb with the main heatsync removed. All output fets and their daughter boards are removed along with that dc filter cap. amp goes into protect now but power supply comes up immidiately, it took about 1sec with the good fets and that cap installed and the good fets got warm.

Also the samples i ordered from fairchild are in; one problem tho they're to-220 case not to-3. guess i shoulda checked that :-/ think these can be used?

grenadier · 2011-07-09 12:55 am

They can be used, but the problem is a TO-3PN has an insulated screw hole while a TO-220 does not. You'll have to get creative with mounting it, since the tab is connected to the drain of the mosfet and wouldn't like being shorted to the probably grounded heatsink.

gwada971 · 2011-07-09 2:32 am

if you want to repair your amp try to do what I tell you. if the power transistor is not shorted, check there must be 1 or 2 cms LM339 comparator it will then change. you have a multimeter that has the diode test function?

ComputerJLT · 2011-07-09 3:24 am

there are 3 LM339 the one on the right has been replaced or removed.

also what power transistor? output? there are no output transistors on the amp now.

also i'm not 100% sure it goes to protect; the protect light is VERY dimly lit; much less so than the power. also when power is removed the protect light gets brighter when voltage in the caps drop significantly.

i'm about to hook this thing up to my scope tos ee if there are any square wave forms getting to the output fets meaning its not actually in protect

Rockford T10001BD blown output fet

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