Fluke 8020A equivalent for A/D converter fluke part 429100 vs Intersil ICL 7106 - Page 1
Forum section: electronics / testgear

author: ek142
author_rank: Newbie
timestamp: February 09, 2021, 04:41:50 pm
content: Hi,I bought a Fluke 8020A. Unfortunately the Intersil IC (fluke part 429100) seems to be defect. I know there is an ‘equivalent’ the ICL 7106 from Intersil.I know that this is not the same. I read there is a difference concerning the autorange, but is that the only difference?Is it possible to use the ICL7106 in an Fluke 8020A without other changes?Thanks in advance

author: PaulSchmidt
author_rank: Newbie
timestamp: May 17, 2022, 08:52:54 pm
content: I know this is an old thread, but thought that I would weigh in on it now anyway.I have been working on a Fluke 8020A, which uses the Fluke-proprietary (albeit, made for them by Intersil) 429100 A/D Converter, purportedly originated for this model 8020A DMM. I have also been reading up on its history, and in a nutshell, it seems that Intersil just produced their own version of the chip as the ICL7106, and it is often cited that the 'only difference' was that the 429100 had limited auto-ranging whereas the 7106 had that section of the 'die' masked off somehow so it would not be functional.Comparing just the pinout of the 429100 from a Fluke 8020A schematic with the normal pinout of a 7106, only three pins differ:Pin 38: On the 429100 this is "RNG" and I have not yet divined its purpose, while on the 7106 this is "OSC3" for the 'C' part of an R/C oscillator that controls internal functions of the IC.Pins 39 & 40: On the 429100 these are "CL1" & "CL2", for connection of a crystal, while on the 7106 Pin 39 is for the 'R' part of the R/C oscillator, and Pin 40 is the common of that same R/C oscillator.Studying the schematics, it also seems that the nominal oscillator frequency of the 429100 may be considerably higher than what is normal for the 7106, although I have not definitively verified this.Also, the voltage range normally used for the 7106 (and 7107) "REF" differential voltage input seems to be a lot lower that what I am seeing from study of the 8020A schematic (I don't have an actual 8020A on hand to try). All of the 7106 designs I have seen, including a Heathkit meter that seems to have a lot in common with the 8020A, the external circuits seem to keep the V-Ref voltage around 0.1V, where on the 8020, with its 429100, that voltage seems to be in the Volts rather than in the fractions of volts. Since at least the 7106/7107 ICs are designed to display the ratio of the V-Ref and V-In differential voltage inputs, it seems that the 429100 might use a slightly different scheme. Again, I have not read a 429100 spec sheet nor done any actual empirical measurements of the 429100 in operation in regards to these voltage ranges.So, my caution would be that you almost certainly cannot just plug a 7106 into the socket for a 429100 and expect it to work. If you DID try that, and rearranged things to replace the crystal with the 7106's expected R/C oscillator components, you still would be without that Pin 38 "RNG" signal, that presumably the Fluke meter would need for proper operation. And no doubt the expected auto-range function of the Fluke meter would no longer work.

author: fordem
author_rank: Regular Contributor
timestamp: May 18, 2022, 03:13:20 pm
content: The 8020a doesn't have autoranging...