At 03:19 PM 3/31/2016, Ryan Stasel wrote:
I do know 74AC04s are horribly prone to ESD
damage
replaced more than a few when working on older bench multimeters.
You may need to get in there and probe a bit. In
my case, my bad RS232 driver was drawing about
350mA and getting VERY hot, VERY fast.
Good luck, and let us know!
Finally replaced the RS232 interface chip and the 'AC04 PPS buffer. Still dead.
Probing around, it looks like the UART output is
stuck in a break condition (232 out is at +9V,
and the input to the driver is near ground). The
32kHz CPU rock, the 3.684 MHz clock, and the 10
MHz OCXO are all singing. No PPS visible anywhere
on the 'AC04. I do see bus activity on the SRAM.
The CPU is getting very hot--it's the hottest
chip on the board, nearly as hot as the OCXO.
There is a ~60 kHz clock visible on the temp
sensor. I couldn't find anything that looked like
the GPS bitstream--maybe the CPU has to program the synth first?
I guess I can strip the OCXO off the board--it's
a good Trimble 37265 from the TAPR group buy.
Crap.
--
newell N5TNL
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