On Tue, 18 Nov 2014 23:22:09 -0500, "Tom Miller"
wrote:


"Arfa Daily" wrote in message
news


"Tom Miller" wrote in message
...

"Arfa Daily" wrote in message
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Arfa

Useless bloody thunderbird, I remember reading the original of this
story but cannot now find it or could you at least repeat the model
number.
What was the failure in the board, could you tell whether over-current
or over-voltage, any deliberate track thinnings for tell-tales.


It's a Supersonic 100 head. The board failed to produce any 'controlled'
bias to the valves, and all four grids were at -89 volts. It looks as
though it works by measuring the voltage across four low value Rs in the
cathodes by using A-D inputs on the microcontroller on the board. The
bias is then produced by feeding PWM signals from four port pins to
driver transistors followed by filter caps. In the case of this board,
the supply volts, reset pin etc were all at correct levels, but the
micro did not produce any output. You could not even measure any clock
at the xtal pins. No evidence of any cause was visible. Board was
pristine. Double sided surface mount, and all examined under strong
magnification, but no signs of any damaged components.

Arfa
Any numbers on the cpu?


STM32F
101C6

This appears to agree with what it says on the schematic

Arfa

Put this whole number in a search to get the datasheet.

STM32F101C6

It is an ARM Cortex 32 bit CPU with 32k bytes of flash. I don't know how
successful you would be copying the firmware over to a new chip..

Believable. I wonder if the crystal itself died. Might check that
failure mode out if you are interested.

?-)