[volt-nuts] Keithley 2001 Multimeter Fault

[Laurence Motteram]

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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