Empathy List Archives

MS

Mark Sims

Sun, Dec 31, 2017 7:15 PM

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.

Are you going to swap out the DC-DC module?

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. ------------------ > Are you going to swap out the DC-DC module?

RL

Robert LaJeunesse

Sun, Dec 31, 2017 7:56 PM

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@hotmail.com
To: "time-nuts@febo.com" time-nuts@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.

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@hotmail.com> > To: "time-nuts@febo.com" <time-nuts@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.

GW

Gary Woods

Mon, Jan 1, 2018 12:12 AM

On Sun, 31 Dec 2017 20:56:26 +0100, you wrote:

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...

OK, I think, made an audible low-ohm probe "Shortsqueak?" That can
resolve an inch or less of PC board trace. You can't have mine!

This email has been checked for viruses by AVG.
http://www.avg.com

On Sun, 31 Dec 2017 20:56:26 +0100, you wrote: > 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... OK, I think, made an audible low-ohm probe "Shortsqueak?" That can resolve an inch or less of PC board trace. You can't have mine! --- This email has been checked for viruses by AVG. http://www.avg.com

AG

Adrian Godwin

Mon, Jan 1, 2018 7:09 PM

A similar product is the Polar Toneohm. I've been after one for a while but
they seem to go for high prices.

On Mon, Jan 1, 2018 at 12:12 AM, Gary Woods garygarlic@earthlink.net
wrote:

On Sun, 31 Dec 2017 20:56:26 +0100, you wrote:

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...
OK, I think, made an audible low-ohm probe "Shortsqueak?" That can
resolve an inch or less of PC board trace. You can't have mine!

This email has been checked for viruses by AVG.
http://www.avg.com

time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/
mailman/listinfo/time-nuts
and follow the instructions there.

A similar product is the Polar Toneohm. I've been after one for a while but they seem to go for high prices. On Mon, Jan 1, 2018 at 12:12 AM, Gary Woods <garygarlic@earthlink.net> wrote: > On Sun, 31 Dec 2017 20:56:26 +0100, you wrote: > > > 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... > OK, I think, made an audible low-ohm probe "Shortsqueak?" That can > resolve an inch or less of PC board trace. You can't have mine! > > > --- > This email has been checked for viruses by AVG. > http://www.avg.com > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. >

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Oscilloquartz OSA-4350 GPSDO