bad transistor? [solved]

[Karl5150]

After enjoying about four hours of uninterrupted music Sunday I figured all was well with the c4s equipped SEX.
I fired it up after work today and after about 10 min warm up all h*ll broke loose, thought it was going to blow out my little fostex OBs
On the bench I noticed that while all 4 LEDs light at first the D2 on the B side goes out after about 40 seconds. I reflowed the LED and transistor solder joints but the same thing happens.
There are no bridges but powered off I get a 500 ohm reading between the b and c legs on that transistor. The A side transistor gives no such reading.

 

[Paul Birkeland]

Voltages?

 

[Karl5150]

10 & 20 - 424V
0A - 74 V when lit, constant.
0B - 400+ before the LEDs light, drops to 220s when the LEDs light then creeps up and stops at 311 when the D2 LED goes out.
Yesterday I went through the original resistance and voltage checks and everything was good through A5.
B5 showed 311 and that's when I noticed the LED was out.
A6 - 2.35
B6 - 10.4
All the + & -3.15 were as they were on the orig. build: the +s reading 2.5 and the negatives reading -3.8

 

[Paul Birkeland]

I'd replace both transistors on that side.

 

[Karl5150]

Thanks Paul,
Guess I'll be ordering a care package.

 

[Karl5150]

Did as you suggested, 4 LEDs glow full time, voltages normal. 4 hours of run time and nothing but music.
Thanks