[volt-nuts] Keithley 2001 Multimeter Fault - Update

[Robert Atkinson]

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 at blueyonder.co.uk> wrote:


From: Alan Scrimgeour <scrimgap at blueyonder.co.uk>
Subject: [volt-nuts] Keithley 2001 Multimeter Fault - Update
To: "Discussion of precise voltage measurement" <volt-nuts at 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
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