f5 power up issue

[specialidiot]

I had previously built cviller boards, this one is using Daniels boards.

At first power up, R11 and R12 went way over voltage and started to smoke... meters showed 4 or mover volts each.

Looking at the board, I think I installed Q5 and Q6 backwards, would that cause this issue? I managed to flip them over but I have the same results so maybe they are a dead short inside?

Any thoughts? Here's a picture, you can see the orientation of q6 on the board, and the print on the device is facing us.

[Nelson Pass]

Q5 and 6 are not usually conducting, and when they are, there
is little danger of frying the amp. It's probably something else.

[specialidiot]

Thanks for the response. What would cause such high current through r11 and r12? If it was one side, I could understand an assembly error, etc.

[Nelson Pass]

Full output to the negative rail would do it.

[specialidiot]

Since both R11 and R12 were at high levels and letting some of their smoke out, wouldn't it be full output to both rails?

So maybe the problem lies with q1 and q2?

[Nelson Pass]

You are right. Why wouldn't R9 and R10 burn up as well?

[specialidiot]

I just double-checked my boards.... both seem to be right. I'm using the Toshiba outputs so I though the pin out could be backwards or something like that but they appear to be oriented correctly. Q1 and Q2 are in there right, as were Q5 and Q6.

I only powered up one board, I'll saddle up the other one tomorrow evening and see what happens.

Any other ideas would be appreciated!

[eyoung]

any substitutions in your build on the transistor side maybe a different pin out on a sub part. your soldering looks great some times a cold solder joint can cause major pain....

Elwood

[Peter Daniel]

How did you set the trimpots?

[specialidiot]

Originally Posted by eyoung

any substitutions in your build on the transistor side maybe a different pin out on a sub part. your soldering looks great some times a cold solder joint can cause major pain....

Elwood

Q6 and Q5 are as called on the schematic, I'll double check Q1 and Q2. I verified Pin 1 of Q4 goes to R14 and that R14 is 47ohm.

My eyes are old(er) so I double check my soldering with a magnifier. In a former life as a tech I used to build and repair analog to digital devices so I'm pretty wary about poor solder connections.

Originally Posted by Peter Daniel

How did you set the trimpots?

Hello sir, thanks for checking in.

I set the trimpots to minimum, or what I figured were minimum based on which pins are shorted on your boards. After the initial wisp of smoke, I turned them fully the other way and had the exact same result.

I then measured across R4 and R3 in circuit to validate I had them set to minimum again.

For my first build using cviller boards, I did make that error. So initially I thought that I must of had them set wrong.