polytone mini brute 378A no sound

[pontiacpete]

This amp came to me with a shorted output transistor ,Q4 an mj802. So I went and changed out Q1, Q2, Q3 and Q4. THis didn't stop the short in the amp so I went ahead got an LM391N-100. Put that in and it fires up without burning resistors, namely R17 and R16 nor R12 and R 14. The problem now is there's no sound.
I used for Q1 an MJE182 and MJE172 for Q2.
Here are some voltages
Q1
C 34vdc
B 1.6v
E 0
Q2
E 0
B -6.3v
C -34v
Q3
E 34v
B 34v
C 0
Q4
E 0
B -34v
C -34v
U1
1 0
2 0
3 -33v
4 -33v
5 -6.3v
6 -6.3v
7 -1.5v
8 1.6v
9 0
10 .6v
11 -1.3v
12 1.3v
13 .5v
14 34v
15 34v
16 -34v
All are DC voltage readings

Any help would be appreciated, thanks in advance.

[Enzo]

Well, did you check the speaker to see if the original failure has burned it out?

[52 Bill]

Well, did you check the speaker to see if the original failure has burned it out?

If not the speaker, check the speaker fuse on the top of the power amp chassis.

[pontiacpete]

I'm using a test speaker that I have under my bench. Actually tried another from another amp, also.

The fuse is good, checked it.

I realize it's probably something stupid simple but still haven't found the problem.

[gbono]

Check the preamp to PA connector - make sure all the pins are secure in the header. Where did you get the LM391N-100?

[pontiacpete]

The LM391 came from china, got it on ebay.

I will check that connection.

So I can assume the voltages are looking good, since no one is commenting on them.

[52 Bill]

So I can assume the voltages are looking good, since no one is commenting on them.

Q4 numbers look wrong, Collector and Emitter mixed up?

[pontiacpete]

Nope, that's what it is.

[Jazz P Bass]

That can't be correct.
Q2's emitter is tied to Q4's collector.
They should both be '0' volts.
At any rate, the driver bases look real good at + - 1.6 volts.
Pin 9 is at '0' volts.
Is the LM39 getting signal?
If so, what amplitude.

[pontiacpete]

The problem for me here is figuring out the pin configuration of Q1 and 2. The MJE172/182s I have are in a TO 225AA case and there are 2 different types, 1 and 3 style. I was going by the 3 style case. Now I think it's a style 1 case.
I tried changing them now the amp won't come up at all, the short is back.
What am I missing?
Again polytone is driving me crazy!

[pontiacpete]

Is there a way I can determine what kind of case I'm using for the mje172 /182. The ones I have were purchased a few years ago and all I have to go by is what it says on the bag - TO225aa?
What is being sold now at digi and mouser are style 1 but this pin out isn't working at all

[pontiacpete]

I went back to the style 3 case pin out and I 'm back to it starting up with no sound. The difference is that there is a mistake in the layout page, the voltages read:
Q4
C 0
B -34
E -34
So the voltages are correct now, I hope.

[52 Bill]

Is there a way I can determine what kind of case I'm using for the mje172 /182. The ones I have were purchased a few years ago and all I have to go by is what it says on the bag - TO225aa?
What is being sold now at digi and mouser are style 1 but this pin out isn't working at all

As far as I know and I'm probably wrong, as far as transistors in this case go, face up the right leg is the base, the center the collector and the left leg is the emitter.

Did you try using your meter to ID the leads?

[pontiacpete]

Havent' use an ohm meter yet. What are rough readings suppose to be?

I used these 2 data sheets and I think this is for a different case.

[gbono]

I'm looking at a 1974 Motorola data book and the MJE170-172 shows the pin out as 1= emitter, 2= collector and 3= base (reading from left to right with the exposed metal "tab" facing down). I think that agrees with your On Semi data sheet.

It's been a while since I've opened up a tiny mini brute but aren't Q4 and Q3 TO-3 packaged parts? Why not use MJ15003/4?