[time-nuts] Oscilloquartz OSA-4350 GPSDO

Robert LaJeunesse lajeunesse at mail.com
Sun Dec 31 14:56:26 EST 2017


Mark, best to use an adjustable current (current-limited) supply preset to voltage regulate at 5V. That way you can have some control over the power dissipated on the PCB. If you can, borrow a thermal camera and look for the heat with that. (FYI our local library lends them out.) Without a thermal camera I've used a 4-1/2 digit DVM set for 200mV full scale, or 20mV if you can do that. Often the low uV resolution will allow you to trace the current path, just start at the power and ground inputs to the board and follow the voltage drops to the short. Or go old-school with an HP logic pulser and current probe...

> Sent: Sunday, December 31, 2017 at 2:15 PM
> From: "Mark Sims" <holrum at hotmail.com>
> To: "time-nuts at febo.com" <time-nuts at febo.com>
> Subject: [time-nuts] Oscilloquartz OSA-4350 GPSDO
>
> I disassembled the unit and found that +5V is shorted to ground on the top board.   No shorted tantalum caps or obvious failed parts.  I am beginning to think it may be power/ground planes are shorted on the four layer board (all boards are four layer)... probably wasted $20 on a DC-DC.  It's not going to be easy tracking down the short.   Maybe apply a high-current 5V supply and see what gets hot.


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