[time-nuts] Lightning 1, tbolt 0.

Scott Newell newell+timenuts at n5tnl.com
Wed May 11 20:48:54 EDT 2016


At 03:19 PM 3/31/2016, Ryan Stasel wrote:

>I do know 74AC04’s 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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