Fluke 8840A A/D Schematic Page

[Kjo]

I'm fixing one of several 8840As I have and I cant find the schematic to the A/D converter section any where. The only manual on the WEB is from the Fluke site and it is copied everywhere. But it is missing the schematic page containing the A/D converter (U101)! I dont see where anyone has flagged this in all of the discussions on the WEB either. Maybe someone has an original manual that could be scanned. The only manual I have ever seen in labeled "PN 879304 Dec 1991 Rev 3 5/97" on the front page.

[pelule]

Hi,
why not upload from the WEB?

https://www.elso.sk/media/download/pdf/fluke/man/Fluke-8840A-umen.pdf

/PeLuLe

[Gertjan]

Hi Kjo,

I have another version of the 8840A manual: Rev.2, 4/94.
You can download it from my webserver: http://www.miedema.dyndns.org/eevblog/FLUKE_8840A_Digital_Multimeter_Instruction_Manual.pdf

The schematic you are looking for in inconveniently split in two halves. But I checked against my paper copy (Rev.1), and it is complete.
(see page 183 + 184)

regards, Gertjan.

[pelule]

I need to apologize for a to fast look over. That PDF I referred to does not contain Sheet 2 (ADC) either.

I have scanned the schematic and the part of the ADC placeplan, but size exceeds the limits of attachments at EEVBLOG (600 DPI scan).

Thus I have uploaded it to my Dropbox: https://www.dropbox.com/sh/f9rwdmv1lzo2yyr/AAB6Lthhn2OzzIRNscTf_GZea?dl=0
As a special "sorry" I added the schematic to the manual (PDF) and uploaded it also (the complete document).
I will keep that link valid until Xmax (24/Dec) if someone else has an urgent need.

I have uploaded it to KO4BB, but it normally it need some time, bevor it is visible for the public.
/PeLuLe

[RobK_NL]

The 8840 uses the exact same A/D converter as the 8842:
http://assets.fluke.com/manuals/8842a___imeng0300.pdf

[TheDefpom]

I did a very short (and not very good) video a couple of years ago showing the digital signals on the ADC on the 8842A, it may be of interest to you if troubleshooting the unit, as it gives you an idea what to expect or check for.

This was using the Logic Analyser inputs of my scope, my notes from the time on the video:

Scope patterns of digital on ADC and TP101, triggering from TP201, troubleshooting incorrect readings on display, vs input voltages or resistances.
Scope shows the digital outputs for the resistor ladder, and TP101 output which is fed back into the A/D converter IC.