PPI amp

[mike49504]

Wondering if i pull the middle leg of the 7815 and 7915 will this seperate the power supply from the output side??

Im trying to figure out why this thing draws 40 amps of current when trying to power up.

I replaced the outputs the a06's and 56's and a afew resistors.

I checked all power supply fets irfz44 and the test fine.

[mike49504]

ok tracked it down and found the problem.

The problem is Q2 its between the 6491's and the 6488's in the output section.

Its either a mpsa56 or a 06 that belongs there but dont know which one and does the numbers face up or downwards towards the sink?

Its a ppi pc275 amp

[mike49504]

ok did somemore testing i have replaced all the a56's and 06's in this amp.

I put in the 2n6491's in the outputs

the hooked the amp to power and it comes on and idle's perfect.

then i go to put in the 2n6488's and thats when the amp goes crazy its trying to draw 40+ amps of current. ive checked all the a06's and 56's and the resistors all of them check fine.

wondering where i go from here

[Perry Babin]

Q2 is the bias transistor. It's likely to be an A06. You can look at the other channel to confirm. It has to be in the circuit.

[mike49504]

Thanks Perry,

I put the a06 in q2's spot and it powers up but as soon as i put even one 2n6488 in the amp it goes crazy. The locations for the 2n6488's are q4 q5 q6.

Say if i even put 1 2n6488 in q4 sppot the amp doesnt like it and pulls 40 amps of current. i checked all the resistor in it believe they are 100 ohms and all check fine wondering whats the next step?

[Perry Babin]

The most likely reason that it's drawing excessive current is because something is driving both the NPN and PNP outputs 'on' at the same time. You may have a leaking driver transistor.

How many of the A06s/56s have you replaced in that channel?

Have you replaced the outputs?

[mike49504]

ive replaced i think pretty much all of them maybe 1 or 2 06's i didnt replace and 2 mpsa18 i didnt replace and i replaced all the outputs

[Perry Babin]

Are you sure you didn't get an A06, 56 in the wrong location or reversed?

[mike49504]

im almost positive i have them right this is looking at the other channel

the a06's are connected to the 2n6488's q4 q5 q6
then q14 is a18
q15 is a56
q16 is a18
q59 06
q 17 56
q18 56
q19 56

this is how i recieved the amp wondering if you know are theese in the right locations?

[Perry Babin]

The attached diagram should be close to what you have in that amp. Follow the circuit confirming that the leg of one type of transistor goes to the correct type of transistor.

None of the circuit board designations will match.