[hpsdr] Penelope

[Graham / KE9H]

Merv:
cc: Phil.

Although you will not like this answer, the most common reason
for a short to ground on the 3.3V regulator output is a shorted
FPGA. All of the I/O drivers in the FPGA are powered directly from
3.3 Volts. 

The regulator has a current limit/thermal overload circuit in it that
protects itself and the board.  So if the regulator is running hot
and the output dropped to a fraction of a volt, it is just doing
its job, and is not damaged.

Damage from static electricity, or plugging and un-plugging the
boards with power still applied to Atlas are the most likely
causes.  Observe anti-static precautions when handling, plugging
and un-plugging the cards to protect the FPGAs.

--- Graham / KE9H

==

Merv Thomas wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi Phil,
>
> I have removed U4 which is the 3.3v regulator chip-internal short as 
> pin(out)reads direct short to pin(gnd).
>
> More disturbing is that the pad that pin 2(output)solders to is a dead 
> short to earth and this seems to be as a result of the via, which is 
> within the silkscreen area for this chip, is connected to the output 
> pad and is probably meant to go to the middle pcb layer without being 
> connected to the bottom layer gnd plane.  If this is so then I appear 
> to have a dead short on all pins/components that access this 3.3v supply.
>
> Am I right in thinking the Penny pcb is at least a 3 layer board, one 
> of which carries the 3.3v supply to the various components?
>
> Regards,
>
> Merv  VK6BMT
>
> PS I'll also post this on the HPSDR Digest.
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