[volt-nuts] Keithley 2001 Multimeter Fault

[Brooke Clarke]

Hi Alan:

I have a bunch of combined capacitance and ESR meters that I'm about to 
start selling.  See:
http://www.prc68.com/I/ESRmicro.shtml

Have Fun,

Brooke Clarke
http://www.PRC68.com


Alan Scrimgeour wrote:
> 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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>>
>>
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