[volt-nuts] Keithley 2001 Multimeter Fault

[Alan Scrimgeour]

Thanks John, I plan to start the search in a few hours. Wish I had a thermal 
imaging camera!

Alan


----- Original Message ----- 
From: "John Lofgren" <jlofgren at lsr.com>
To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
Sent: Friday, March 05, 2010 4:09 PM
Subject: Re: [volt-nuts] Keithley 2001 Multimeter Fault


> Yes, check capacitors.  I has something similar happen to the -5V 
> regulator on HP 55300A GPSDO.  The symptoms were very similar to your 
> description, but with the addition of a discolored heatsink.  It turned 
> out to be a shorted ceramic cap on the regulator output.
>
> Good luck and keep us posted.
>
> - John
>
>
>
>
> -----Original Message-----
> From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On 
> Behalf Of Laurence Motteram
> Sent: Thursday, March 04, 2010 7:04 PM
> To: Discussion of precise voltage measurement
> Subject: Re: [volt-nuts] Keithley 2001 Multimeter Fault
>
> Don't be misled by the working display, as it has its own
> microprocessor.  The digital PCB has two LM2940CT devices, but it sounds
> like the one in question supplies the digital +5V.  Naturally,
> everything connects to this, but you might like to start by checking
> capacitors.  If you are lucky, you could find a shorted tantalum.
>
>
> Regards,
>
> Laurence Motteram
>
>
> -----Original Message-----
> From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
> Behalf Of Alan Scrimgeour
> Sent: Friday, 5 March 2010 11:32 AM
> To: Discussion of precise voltage measurement
> Subject: Re: [volt-nuts] Keithley 2001 Multimeter Fault
>
> The little functionality the meter had when I got it enabled me to start
> a
> self test, but now I can't even do that as functionality has dropped
> away
> rapidly. The display is fine and presumably the processor driving it,
> but it
> no longer responds to the keyboard.
>
> A smell of overheating plastic after a few minutes lead me to an
> LM2940CT -
> 5 volt regulator. It's located in the fan assisted cooling path but
> getting
> far too hot even allowing for that. It's output voltage is well below
> 5V.
> It's input voltage appeared to be reasonable given it's being
> overloaded, so
> I conclude that either the LM2940CT is faulty or more likely, something
> is
> overloading its output. A circuit diagram would show me what connects to
>
> this output so I can start searching for the culprit.
>
> Alan
>
>
>
>
> ----- Original Message ----- 
> From: "Laurence Motteram" <LMotteram at scientific-devices.com.au>
> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Sent: Thursday, March 04, 2010 9:34 PM
> Subject: Re: [volt-nuts] Keithley 2001 Multimeter Fault
>
>
>> IP issues aside, what seems to be the trouble with the 2001?
>>
>>
>> Regards,
>>
>> Laurence Motteram
>>
>> -----Original Message-----
>> From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com]
> On
>> Behalf Of Alan Scrimgeour
>> Sent: Friday, 5 March 2010 5:47 AM
>> To: Discussion of precise voltage measurement
>> Subject: [volt-nuts] Keithley 2001 Multimeter Fault
>>
>> I'm trying to repair a 7 1/2 digit Keithley Multimeter but can't get
> the
>> circuit diagram. Keithley say they don't release schematics any more
> due
>> to IP issues, whatever they are?
>>
>> Can anyone help?
>>
>> Thanks,
>>
>> Alan
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