[Test-Equipment] HP 34401A DMM display problem

[DaveC]

Jim,
Thanks for your post.

Yes, the replacement display is orderable from Agilent @ US$83 ::

<https://onlinestore.tm.agilent.com:443/Agilent/en/US/partnerMkt/onlinestore?cmd=eFAPCatProductDetail>

The 34401-66512 display PCB has many components located on the front 
side of the board underneath the vacuum fluorescent display (VFD). 
These include the programmed processor, of course, and 7 support ICs 
as well as a handful of SMD caps and resistors.

But being the curious guy I am I want to see if it's something simple 
like a passive component or such. The processor on this PCB is the 
only custom component, so by process of elimination it should be 
possible to resurrect this as long as the VFD is good.

Did you ever try to repair one of these displays? I'm currently 
figuring out how to get the VFD out of the way so I can probe the 
circuit yet still have it connected so as to load the circuit.

FYI, Agilent service notes for the 34401A are here:

<https://litstation.marketing.agilent.com/litapp/SearchSN.do?method=openExternalSNSearch&prodNum=34401a>

Thanks again,
Dave

-=-=-=-

>Dave,
>
>I have fixed several of these meters.
>If I remember correctly, about the only
>other things on this board is a custom
>chip on the back. I do believe this display
>board is still available from Agilent, and
>I think the cost was about $90.
>
>There are about 3 different revisions of the
>main board over the years(only the first version
>is shown in the manual), but I think all the
>display boards are compatible.
>
>Jim,
>
>
>
>------- Original Message -------
>>From    : DaveC[mailto:davec2468 at aim.com]
>Sent    : 11/7/2010 1:47:08 AM
>To      : test-equipment at mailman.qth.net
>Cc      :
>Subject : RE: [Test-Equipment] HP 34401A DMM display
>problem
>
>  Bought recently, tagged as "needs new display". When
>I first powered
>on this unit the display worked. After pressing a few
>function
>buttons, display went dark.
>
>Now when powered on the display goes all-segments-on
>and stays like that.
>
>I swapped in a known-good display and the DMM works
>as expected: no errors.
>
>Anyone have any experience with the display PCB on
>this or other
>unit? The fluorescent matrix clearly works; it's
>something to do with
>the on-board support circuitry.
>
>Thanks,
>Dave