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Transistor or temp switch attached to heatsink? Crate PA-600 repair

newjeeper369

Aug 30, 2015
25
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Aug 30, 2015
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I am repairing a old PA mixer/amp, it has a transistor looking component that has aluminium wrapped around it and then is screwed on to the heat sink. i thought it was a thermal switch but it has 3 leads and a TO-92 style case like a transistor. when i removed it from the heatsink it had no identification markings on it. any ideas what this is? i can post pictures if needed i just dont have them right now. i bought a schematic off of musicparts.com unfortunately when i recieved the schematic it has the wrong PC ASSY drawing number, the schematic has some similarities but its not the correct one. when i bought it there was no description other than " Crate PA-600 " which is what i am repairing, i emailed musicparts.com today hopefully the have the correct drawing im looking for. Also if you have any suggestions on where to possibly get schematic for this it would be very helpful as well.
 

Martaine2005

May 12, 2015
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Hi newjeeper,
I think the answer to your question is BOTH.
It is a transistor used for temperature sensing.

Martin
 

dorke

Jun 20, 2015
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Jun 20, 2015
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What is wrong with the PA-600?
Photos can always help,
same goes for schematics .
 

newjeeper369

Aug 30, 2015
25
Joined
Aug 30, 2015
Messages
25
I found the part it is a 2N3404 http://www.ebay.com/itm/2N3404-GE-SILICON-NPN-TO98-WITH-HEAT-SINK-900mW-0-5A-50V-NOS-/141756210981?


When i got the heat sink under better light i found the part number. i didn't think the part number would be on the heat sink but i guess the heat sink is part of the component, they seem to come from the factory with it.


As far as the amp goes, when i received the amp it was taken apart in two parts, the mixer part which is the top piece and the amp and power supply, the bottom piece. it also was missing its main 5 amp fuse holder . (I will post pictures today when i get the chance) all i was told when i received it is that " it doesn't turn on right"..... I started by disconnecting the amp board and mixer boards from the power supply, i replaced the fuse holder and fuse and plugged in the power supply. output voltage was normal at ~+47 vdc ~-47 vdc, power supply work find. next i plugged in the power amp board, i found the power amp transistors (mj15002 & mj15001 two of each) were shorted causing the fuse to blow immediately. this is probably why someone removed the fuse and fuse holder.


I replaced the power amp transistors and connected the amp board to the power supply and all was fine, no fuse blow. i then connected the mixer boards and still all was fine. i connected a speaker and was getting a lot of noise. here is when things went wrong, the power supply and board are connected to the base of the mixer which is a metal chassis. the mixer boards are connected to the top of the mixer which is also made of metal so i thought maybe the need to be connected to ground correctly and the noise might go away. i connected a wire from the bottom chassis to the top portion of the mixer and as soon as i did the fuse blew and 2 of my power transistors got fried again and sorted. im not sure if me connecting the bottom half to the top half has something to do with it or it was just coincidence that it blew at the same time.


So where i am now is i installed new power transistors for the amp again and i am replacing all the preamp transistors on the amp board. keep in mind of my first post about the drawings i have and that they are not identical to my mixer. i still have not heard from musicparts.com about new drawings.


should i start a new thread for this repair????

DSCF8452.JPG
 

newjeeper369

Aug 30, 2015
25
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Aug 30, 2015
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25
i think i will start a new thread for this repair with good photos and schematics.. i will post link on this thread when i do. might not have the chance tonight.
 
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