Driver Testing Voltage Help

[Alice B]

Halp!  Full disclosure - this is my first bottlehead project, so be please be gentle.

I'm working on my Kaiju 300B build and I've hit a roadblock with driver testing on the A-side of the amp (My D side testes within range off all expect outputs - especially after replacing the board and zener diodes when I accidentally caused a short the first time I powered it up for a test.  ).  All the LEDS are lit on the the board for the A-side of the amp, The IA and the OA are within the quoted spec ranges, but when I clip my lead to tab 32U, I'm only getting around 89-92 volts DC.  at a cursory glance I don't see any cold solder joints, but what do I know.  Can anyone help point me in the appropriate direction of where I might look for what would be causing the voltage to be so relatively low there?

Any and all help is appreciated! Thank you in advance.

 

[Paul Birkeland]

What voltage do you see at Kreg on the A side of the PC board on that side of the amp?

 

[Alice B]

About 2.92v it seems

 

[Paul Birkeland]

OK, I would try turning the blue trim pot ten turns one way, then remeasure Kreg, then ten turs the other and remeasure.

2.92V at Kreg and 90V at 32 tells us the driver half of the 5670 isn't drawing any current.  Some possibilities that come to mind are:

1. Bad solder joints on the PCB, socket, etc.
2. Improper R1 resistor values.
3. 10,000uF cap improperly installed.
4. 300K resistor between 3 lug strip and 9 pin socket wrong value.
5.  Jumper problem on the board, probably relating to the KregA quarter of the board.

Posting build photos could certainly help. Also, could you let me know the IA, OA, IB, and KregB voltages that you have?  That may present a clearer picture.

 

[Paul Birkeland]

Doc B. informs me that you're in our area.  I'm in Renton if you'd like to pop by for a visit.

-PB