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Zaapp 17th November 2012 10:01 PM

Digital Designs M2a Repairs in process
Hello all, this is my first post and my first amp repair. Bare with me here, I'm not an electrical genius, and most of what I think I know is self-taught, so I may use incorrect verbage or component names, but I'm a quick study. My background comes from outside these cases we call High Current Amplifiers and more into the install world, but with my background in USAci, db-drag and several local to me leagues, it's a logical movement for me to look to diy repairs, and something that has always interested me. Now I'm willing to put in the time.

This is my amp, I've had it for several years now, one day last summer it let the smoke out, and the amp has sat since then. Last week I opened it up to find about 4 out of 16 irf3205 power transistors fried and completely broken, and all 4 fmu32u diodes with the legs broken from the board.
I was able to easily source and purchase the irf3205 transistors, so I replaced all 160f them. I was not able to find the fmu32u diodes anywhere besides japan, and they theoretically test fine with the meter so I simply soldered the legs back into the board after desoldering and removing the short broken off pieces.

Now the amp doesn't immediately blow the main power fuse when connected to a battery. success! no, when I apply remote power to switch the amp on, the protect LED will light for about 500mS then quickly turn off, and about 3 seconds later the internal relay clicks on, but the amp has no signs of life other than that.
At this point I have no clue where to go from here, or what else could be causing a problem, unless it's those diodes. it seems like I have no power on the output side of the board as all I show on the Volt meter anywhere is either 0.000 v or - 0.011v (negative voltage?)

Can someone help point me in a new direction so maybe I can successfully repair this amp?. Perhaps point me at a good replacement for the fmu32u's (can I use 2 similar diodes in each ones place?)
I'm willing to do whatever I need to do to get my amp back up and running again if possible ( I know it's possible )

Zaapp 18th November 2012 02:01 AM

I believe it to be the driver board at this point. After searching and reading several posts about the driver board in the DD amps failing. I used a dmm set to Hz and did not find the 22.5kHz that someone had mentioned I would need to see for an operational amp. also I am not seeing and rail voltage or anything above that of the battery voltage.

any help would be great as I now feel like I am in over my head, yet still wanting and willing to press on and get this bad boy repaired and working again

Perry Babin 18th November 2012 02:30 AM

What is the DC voltage on pin 1 of the 3205s? They should all be about the same.

Zaapp 18th November 2012 02:32 AM

will report back in about 5 minutes... don't go away.

also, very nice to see you here, I've pretty much read your entire site like 16 times and still over look it to sink stuff in.


Zaapp 18th November 2012 02:41 AM

q11 12.67v

Zaapp 18th November 2012 02:45 AM

oops... last post happened before I wanted it to.
q11 12.67v
q10 12.65v
q9 12.67v
q9a 12.65v
q12a 12.63v
q14 12.67v
q13 12.62v
q12 12.64v

q20 12.67v
q19 12.66v
q18 12.66v
q18a 12.66v
q15a 12.67v
q17 12.63v
q16 12.66v
q15 12.66v

both with the amp powered via remote wire and not powered... also seeing identical voltages on second pins of 3205's and nothing on the third pins

Perry Babin 18th November 2012 02:46 AM

It shouldn't be much above 6v. If it's at 12v. the center leg is at 12v and the 3rd leg is at 0v the FET is blown.

Zaapp 18th November 2012 02:47 AM

really? I just replaced them all... oh dang... there went 20 bucks in parts...

Perry Babin 18th November 2012 03:02 AM

Did you confirm that the voltages were as I listed them?

Zaapp 18th November 2012 03:06 AM


Originally Posted by Perry Babin (
Did you confirm that the voltages were as I listed them?

I think I verified that all of my power FETs are blown again after having been replaced.

Are there some other voltages that I should check? or should i just begin removing all of the FET's again and ordering parts?

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