# PPI A600 Question About Transistors Used?



## sleepy96 (Jun 30, 2017)

Hello All,

I've been lurking the site for a while and finally decided to make an account 

So I am currently repairing an A600, which recently stopped powering up.

Upon inspection it's obvious that one of the (what I assume is) power supply mosfets has blown. This is a RFP25N05 located at M2. I also noticed a diode on the same side was cracked in half. This is a 1N4936 located at CR26.

I plan to go ahead and replace all of the RFP25N05's with IRFZ44N's based on suggestions from others I've seen here. I will obviously replace the diode at CR26 and check other components for fault as well. 

But what really throws me off is: #1. why those components blew, but #2.- the output transistor arrangement/package numbers that I'm seeing on this. Which could be related to #1. From what I understand with the repair threads, both channels will have equal amount NPN and PNP transistors (per side). That is not quite the case on this amp:

The side with the blown components has a output transistor arrangement as follows: 
Q1 BDT81
Q2 BDT82
Q3 BDT82
Q4 BDT82
Q5 BDT82
Q6 A1011

Q7 C2344
Q8 BDT81
Q9 BDT81
Q10 BDT81
Q11 BDT81

*I would expect Q1 to be a BDT82 not an 81 right? Upon initial testing with a DMM, this lone BDT81 also appears to be BAD! (short between Base and Collector) I'm also thrown off by the A1101/C2344 pairs? Why are these used?

The other side is arranged somewhat how I expected (with the exception of the A1101/C2344 pair) :

Q32 BDT82
Q33 BDT82
Q34 BDT82
Q35 BDT82
Q36 BDT82
Q37 A1011

Q38 C2344
Q39 BDT81
Q40 BDT81
Q41 BDT81
Q42 BDT81


What could be the explanation for that lone BDT81? Is it bad/shorted because its the wrong transistor? Could that be the cause of the cracked diode and blown power fet? Im going to test the BDT81 of circuit to be sure that's the culprit.

When I go to replace this BDT81 (assuming that its bad or I need a BDT82), will I essentially have to replace all output transistors due to having to use a different component? I understand I'd likely have to replace them with 2N6488 and 2N6491's. 

Sorry for the wall of text, wanted to get all the info out there. I would appreciate any suggestions you wonderful people have for this. 

GO PPI!!


----------



## Dubstep (Apr 7, 2010)

Ive used a lot of irf3205's in place of 44's/48's with new 47ohm gate resistors.. im no tech, just know enough to get into trouble lol.. I do know some of the best around tho.. Those 3205's are really tough!


----------

