# a/d/s/ P650 Amp: Need help removing FET Bracket



## bdub03 (Sep 17, 2010)

Hey Guys, my a/d/s/ amp started making noises last week. This morning when I got in the car each speaker went POP... thud, thud and nothing! I have some basic experience with electronics and decided to give it a look but can't seem to be able to remove the FET covers that hold the PCB in place.

Anyone have experience removing these in the past?

Picture for reference:










Thanks in Advance!


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## bdub03 (Sep 17, 2010)

I got it figured out last night. Took an old pair of needle nose pliers. Torched them to a curve which gave me access to unclip the retainers from the amp frame.

So here's my problem (well one of them so far)


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## envisionelec (Dec 14, 2005)

bdub03 said:


> I got it figured out last night. Took an old pair of needle nose pliers. Torched them to a curve which gave me access to unclip the retainers from the amp frame.
> 
> So here's my problem (well one of them so far)


What is the problem pictured? I see two Bipolar transistors that appear to be functioning as pass elements for zener regulation. It is on the preamp end, anyway.


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## bdub03 (Sep 17, 2010)

There is only 2 leads on that transister were there were 3. Some how the 3rd snapped? Not sure who that occured but I have the piece that fell off...

My question, do I need to use a Fairchild branded TIP42c specifically or can I replace it with any brand? My local Electronics shop in town (metro electronics) carries NTE.

Thx in Adv!


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## [email protected] (Jun 12, 2008)

Mouser or Digikey will have the Fairchild parts. If the other brand local has the same specs, I dont see what the problem would be. I have read that its best to replace both of them at the same time, not sure about that one tho, but the reason they stated seemed logical.


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## bdub03 (Sep 17, 2010)

again... I'm not an eletronics pro but that would make better sense if both run the same circuit. I'll pickup a pair, test 1 and if it works, replace the 2nd. Again I really appreciate the help here! I'm just an audio guy with a happy face that currently is frowned because his power house is down 

Cheers!


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## envisionelec (Dec 14, 2005)

BeatsDownLow said:


> Mouser or Digikey will have the Fairchild parts. If the other brand local has the same specs, I dont see what the problem would be. I have read that its best to replace both of them at the same time, not sure about that one tho, but the reason they stated seemed logical.



Not for these, you don't. They're not connected in any way that would require them to be matched and they're not in the audio path - they simply amplify the current for the zener diode.

I guess I figured the missing pin was in a shadow. I've never seen one completely fall out - usually breaks from improper lead forming.

You can replace them with any TIP42C - Fairchild, ON, ST... This is a non-critical application and it's unlikely that anyone would be faking a cheap TIP42C. Even the NTE replacement would be suitable for this application, but I think they're ugly.


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## envisionelec (Dec 14, 2005)

bdub03 said:


> again... I'm not an eletronics pro but that would make better sense if both run the same circuit. I'll pickup a pair, test 1 and if it works, replace the 2nd. Again I really appreciate the help here! I'm just an audio guy with a happy face that currently is frowned because his power house is down
> 
> Cheers!


The other one is a TIP41B - an NPN device. The TIP42C is an NPN.


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## bdub03 (Sep 17, 2010)

So like the idiot I am... I replaced the TIP42c with the NTE version along with the neighboring NPN that I thought was a TIP42c. Amp fired up normally and sounded great till I heard a pop! The amp kept working however the 2nd replacement NPN had snapped in half! I go back inside and audit the NPN I removed and noticed it was a TIP41c not a 42c  

So... no biggie, replace it back with the original working one, fire up the amp and no sound at all now  The PCB looks clean, see no blown caps or resisters. 

Any further advise before I seek out a pro?

Cheers and happy friday!


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