Empathy List Archives

AS

Alan Scrimgeour

Mon, Mar 15, 2010 9:46 PM

Here's a progress report:
Searching for a possible short circuited tantalum capacitor I tried to identify if any were connected to the 5V output of the overheating regulator. None on the visible side of the analogue pcb were. I dived in and removed the pcb and did a similar search of the tants on the rear. One, located right next to the regulator was connected. I replaced and tested it. It was a bit leaky, but ok, and the replacement made no difference.
I started probing around with a thermocouple looking for overheating chips connected to the 5V supply, but couldn't spot any. Then I accidently discovered that 5 electrolytics in the vicinity of the overheating 5V regulator were also overheating. Unfortunately the pcb does have buried layers so it's not easy to tell what connects to what, and I cant get to connections on the rear of the pcb when it's powered up, so the whole process is proving rather frustrating. I think I'll try removing the electrolytics and if they're still ok, putting them back on long wire legs to allow me to access the powered up connections.
Any bright ideas welcome!

Alan

Here's a progress report: Searching for a possible short circuited tantalum capacitor I tried to identify if any were connected to the 5V output of the overheating regulator. None on the visible side of the analogue pcb were. I dived in and removed the pcb and did a similar search of the tants on the rear. One, located right next to the regulator was connected. I replaced and tested it. It was a bit leaky, but ok, and the replacement made no difference. I started probing around with a thermocouple looking for overheating chips connected to the 5V supply, but couldn't spot any. Then I accidently discovered that 5 electrolytics in the vicinity of the overheating 5V regulator were also overheating. Unfortunately the pcb does have buried layers so it's not easy to tell what connects to what, and I cant get to connections on the rear of the pcb when it's powered up, so the whole process is proving rather frustrating. I think I'll try removing the electrolytics and if they're still ok, putting them back on long wire legs to allow me to access the powered up connections. Any bright ideas welcome! Alan

BC

Brooke Clarke

Mon, Mar 15, 2010 11:53 PM

Hi Alan:

I'm importing and selling a combined ESR and capacitance meter. See:
http://www.prc68.com/P/Prod.html#ESR <- ordering
http://www.prc68.com/I/ESRmicro.shtml <- description
http://www.prc68.com/I/Capacitors.shtml <- measured results using a
number of instruments

Have Fun,

Brooke Clarke
http://www.PRC68.com

Alan Scrimgeour wrote:

Here's a progress report:
Searching for a possible short circuited tantalum capacitor I tried to identify if any were connected to the 5V output of the overheating regulator. None on the visible side of the analogue pcb were. I dived in and removed the pcb and did a similar search of the tants on the rear. One, located right next to the regulator was connected. I replaced and tested it. It was a bit leaky, but ok, and the replacement made no difference.
I started probing around with a thermocouple looking for overheating chips connected to the 5V supply, but couldn't spot any. Then I accidently discovered that 5 electrolytics in the vicinity of the overheating 5V regulator were also overheating. Unfortunately the pcb does have buried layers so it's not easy to tell what connects to what, and I cant get to connections on the rear of the pcb when it's powered up, so the whole process is proving rather frustrating. I think I'll try removing the electrolytics and if they're still ok, putting them back on long wire legs to allow me to access the powered up connections.
Any bright ideas welcome!

Alan

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Hi Alan: I'm importing and selling a combined ESR and capacitance meter. See: http://www.prc68.com/P/Prod.html#ESR <- ordering http://www.prc68.com/I/ESRmicro.shtml <- description http://www.prc68.com/I/Capacitors.shtml <- measured results using a number of instruments Have Fun, Brooke Clarke http://www.PRC68.com Alan Scrimgeour wrote: > Here's a progress report: > Searching for a possible short circuited tantalum capacitor I tried to identify if any were connected to the 5V output of the overheating regulator. None on the visible side of the analogue pcb were. I dived in and removed the pcb and did a similar search of the tants on the rear. One, located right next to the regulator was connected. I replaced and tested it. It was a bit leaky, but ok, and the replacement made no difference. > I started probing around with a thermocouple looking for overheating chips connected to the 5V supply, but couldn't spot any. Then I accidently discovered that 5 electrolytics in the vicinity of the overheating 5V regulator were also overheating. Unfortunately the pcb does have buried layers so it's not easy to tell what connects to what, and I cant get to connections on the rear of the pcb when it's powered up, so the whole process is proving rather frustrating. I think I'll try removing the electrolytics and if they're still ok, putting them back on long wire legs to allow me to access the powered up connections. > Any bright ideas welcome! > > Alan > _______________________________________________ > volt-nuts mailing list -- volt-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > > >

RA

Robert Atkinson

Tue, Mar 16, 2010 7:44 AM

Hi Alan,
Have you put a 'scope on the 5V rail? overheating capacitors could be a sign of an unstable (oscillating) regulator. I'd just change the hot elecrolytics anyway, they have much reduced lives when they are hot. If you are testing them, you must include an ESR test of some sort (I've no connection to any vendors of ESR meters ;-)

Robert G8RPI.

--- On Mon, 15/3/10, Alan Scrimgeour scrimgap@blueyonder.co.uk wrote:

From: Alan Scrimgeour scrimgap@blueyonder.co.uk
Subject: [volt-nuts] Keithley 2001 Multimeter Fault - Update
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Date: Monday, 15 March, 2010, 21:46

Here's a progress report:
Searching for a possible short circuited tantalum capacitor I tried to identify if any were connected to the 5V output of the overheating regulator. None on the visible side of the analogue pcb were. I dived in and removed the pcb and did a similar search of the tants on the rear. One, located right next to the regulator was connected. I replaced and tested it. It was a bit leaky, but ok, and the replacement made no difference.
I started probing around with a thermocouple looking for overheating chips connected to the 5V supply, but couldn't spot any. Then I accidently discovered that 5 electrolytics in the vicinity of the overheating 5V regulator were also overheating. Unfortunately the pcb does have buried layers so it's not easy to tell what connects to what, and I cant get to connections on the rear of the pcb when it's powered up, so the whole process is proving rather frustrating. I think I'll try removing the electrolytics and if they're still ok, putting them back on long wire legs to allow me to access the powered up connections.
Any bright ideas welcome!

Alan

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

Hi Alan, Have you put a 'scope on the 5V rail? overheating capacitors could be a sign of an unstable (oscillating) regulator. I'd just change the hot elecrolytics anyway, they have much reduced lives when they are hot. If you are testing them, you must include an ESR test of some sort (I've no connection to any vendors of ESR meters ;-) Robert G8RPI. --- On Mon, 15/3/10, Alan Scrimgeour <scrimgap@blueyonder.co.uk> wrote: From: Alan Scrimgeour <scrimgap@blueyonder.co.uk> Subject: [volt-nuts] Keithley 2001 Multimeter Fault - Update To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> Date: Monday, 15 March, 2010, 21:46 Here's a progress report: Searching for a possible short circuited tantalum capacitor I tried to identify if any were connected to the 5V output of the overheating regulator. None on the visible side of the analogue pcb were. I dived in and removed the pcb and did a similar search of the tants on the rear. One, located right next to the regulator was connected. I replaced and tested it. It was a bit leaky, but ok, and the replacement made no difference. I started probing around with a thermocouple looking for overheating chips connected to the 5V supply, but couldn't spot any. Then I accidently discovered that 5 electrolytics in the vicinity of the overheating 5V regulator were also overheating. Unfortunately the pcb does have buried layers so it's not easy to tell what connects to what, and I cant get to connections on the rear of the pcb when it's powered up, so the whole process is proving rather frustrating. I think I'll try removing the electrolytics and if they're still ok, putting them back on long wire legs to allow me to access the powered up connections. Any bright ideas welcome! Alan _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.

AS

Alan Scrimgeour

Tue, Mar 16, 2010 11:47 AM

I think you're right, but the capacitors in question don't connect to the 5V
regulator (well, maybee one) so things are more complicated. By proximity
they appear mostly to be connected to bridge rectifiers. I guess an
oscillating regulator could put a high ripple current through a capacitor on
its input too.
. I've tested the overheating electrolytics and they all seem ok (ignoring
unknown ESR), but under a couple there's corrosion. There's also possibly
some heat damage to the pcb at one point that needs a much closer look. I
hope it's just more corrosion.
Unfortunately my scopes dead, which I'll have to sort that out, but for now
my meters ac range and frequency measurement mode should tell me what I need
to know.

Alan

----- Original Message -----
From: "Robert Atkinson" robert8rpi@yahoo.co.uk
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Sent: Tuesday, March 16, 2010 7:44 AM
Subject: Re: [volt-nuts] Keithley 2001 Multimeter Fault - Update

Hi Alan,
Have you put a 'scope on the 5V rail? overheating capacitors could be a sign
of an unstable (oscillating) regulator. I'd just change the hot elecrolytics
anyway, they have much reduced lives when they are hot. If you are testing
them, you must include an ESR test of some sort (I've no connection to any
vendors of ESR meters ;-)

Robert G8RPI.

--- On Mon, 15/3/10, Alan Scrimgeour scrimgap@blueyonder.co.uk wrote:

From: Alan Scrimgeour scrimgap@blueyonder.co.uk
Subject: [volt-nuts] Keithley 2001 Multimeter Fault - Update
To: "Discussion of precise voltage measurement" volt-nuts@febo.com
Date: Monday, 15 March, 2010, 21:46

Here's a progress report:
Searching for a possible short circuited tantalum capacitor I tried to
identify if any were connected to the 5V output of the overheating
regulator. None on the visible side of the analogue pcb were. I dived in and
removed the pcb and did a similar search of the tants on the rear. One,
located right next to the regulator was connected. I replaced and tested it.
It was a bit leaky, but ok, and the replacement made no difference.
I started probing around with a thermocouple looking for overheating chips
connected to the 5V supply, but couldn't spot any. Then I accidently
discovered that 5 electrolytics in the vicinity of the overheating 5V
regulator were also overheating. Unfortunately the pcb does have buried
layers so it's not easy to tell what connects to what, and I cant get to
connections on the rear of the pcb when it's powered up, so the whole
process is proving rather frustrating. I think I'll try removing the
electrolytics and if they're still ok, putting them back on long wire legs
to allow me to access the powered up connections.
Any bright ideas welcome!

Alan

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

I think you're right, but the capacitors in question don't connect to the 5V regulator (well, maybee one) so things are more complicated. By proximity they appear mostly to be connected to bridge rectifiers. I guess an oscillating regulator could put a high ripple current through a capacitor on its input too. . I've tested the overheating electrolytics and they all seem ok (ignoring unknown ESR), but under a couple there's corrosion. There's also possibly some heat damage to the pcb at one point that needs a much closer look. I hope it's just more corrosion. Unfortunately my scopes dead, which I'll have to sort that out, but for now my meters ac range and frequency measurement mode should tell me what I need to know. Alan ----- Original Message ----- From: "Robert Atkinson" <robert8rpi@yahoo.co.uk> To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> Sent: Tuesday, March 16, 2010 7:44 AM Subject: Re: [volt-nuts] Keithley 2001 Multimeter Fault - Update Hi Alan, Have you put a 'scope on the 5V rail? overheating capacitors could be a sign of an unstable (oscillating) regulator. I'd just change the hot elecrolytics anyway, they have much reduced lives when they are hot. If you are testing them, you must include an ESR test of some sort (I've no connection to any vendors of ESR meters ;-) Robert G8RPI. --- On Mon, 15/3/10, Alan Scrimgeour <scrimgap@blueyonder.co.uk> wrote: From: Alan Scrimgeour <scrimgap@blueyonder.co.uk> Subject: [volt-nuts] Keithley 2001 Multimeter Fault - Update To: "Discussion of precise voltage measurement" <volt-nuts@febo.com> Date: Monday, 15 March, 2010, 21:46 Here's a progress report: Searching for a possible short circuited tantalum capacitor I tried to identify if any were connected to the 5V output of the overheating regulator. None on the visible side of the analogue pcb were. I dived in and removed the pcb and did a similar search of the tants on the rear. One, located right next to the regulator was connected. I replaced and tested it. It was a bit leaky, but ok, and the replacement made no difference. I started probing around with a thermocouple looking for overheating chips connected to the 5V supply, but couldn't spot any. Then I accidently discovered that 5 electrolytics in the vicinity of the overheating 5V regulator were also overheating. Unfortunately the pcb does have buried layers so it's not easy to tell what connects to what, and I cant get to connections on the rear of the pcb when it's powered up, so the whole process is proving rather frustrating. I think I'll try removing the electrolytics and if they're still ok, putting them back on long wire legs to allow me to access the powered up connections. Any bright ideas welcome! Alan _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there. _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.

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Keithley 2001 Multimeter Fault - Update