Fluke 8840A - AC reading PCB upgrade

[home_listening]

Hello Hello,

I purchased a Fluke 8840A last year, without the AC reading option, and have been a happy user since then. Curiosity got the better of me recently and I decided to open it up and poke around and noticed that it actually does have the PCB internally, without the ribbon cable connected.

Of course, I plugged it in to see what happens. The meter fails to boot up and do anything meaningful. Works perfectly again when the ribbon is unplugged.

Have had a look around the AC card itself and taken care of a few suspect looking capacitors and I'm getting sensible readings between all the power rails on the card itself - yet still having the same problem.

Does anyone know if there are changes that need to be made on the motherboard/main PCB to handle the AC option? Service manual doesn't mention anything but I'm hoping there is something I've missed.

Thanks and kind regards

[bdunham7]

Can you look very closely at the identifying marks and labels on the card?  It is possible that you have a card for an 8842A which is very similar.  If that is the case, I may want to swap with you!

EDIT:  Just noticed you're in Oz.  But look at the labels anyway.

[home_listening]

All research points to it being the correct card. PN# 728899 Rev. N - matches the service manual image and schematic.

Cheers

[bdunham7]

OK, that looks correct.  Some of the earlier revisions had hand-penciled notations on the circuit board and could be less clear.  There should be a separate number above that p/n that starts with either 8840 or 8842, but I think you have the correct one.

To answer your original question, no there is no modification or configuration of the main board that needs to be done when installing the AC board.  Without it you get '30' when you press any AC function.  Power down, plug it in, power up and the AC functions work.  One snag is that if you swap in a different AC board or add it to a unit that has never had one, your calibration constants will be incorrect and the AC reading accuracy will be suboptimal.

I have not encountered your exact problem, but I do have several of these units, both 8840a and 8842a, and if you need me to test anything for comparison I can do it when I have one apart.

[bdunham7]

Also, just out of curiousity, is the Option 09 box checked on the back panel of your unit?  And does it have the IEEE-488 interface?

[JasonB0020]

I just bought one from the auction site, hopefully it wasn't a bad screw up. Anyhow, I noticed after the fact it's lacking the AC option. Does that mean no ac period, or just no rms?

[bdunham7]

I just bought one from the auction site, hopefully it wasn't a bad screw up. Anyhow, I noticed after the fact it's lacking the AC option. Does that mean no ac period, or just no rms?

Without Option 09, you won't get any readings in the AC ranges, just a code '30'.

If you just bought it and don't have it yet,  you can't totally rely on the markings on the back, sometimes they have the board installed anyway.  And the A/AF models have AC  in their standard configuration.

[JasonB0020]

Maybe I'll get lucky and it will be in there, but the way my luck runs I doubt it. Edit: well, as expected it either isn't in there or it's not connected, and not sure whether it will hurt anything value wise trying to take it apart since one of the screws still has a calibration seal on it from MPC.

[wfdudley]

I've created a DIY Option 09 board.
Read about it and download the design files here:

http://www.dudley.nu/projects/Fluke_8840A

Bill Dudley
New Jersey, USA

[XenonEng]

Oh very nice DIY. I also made myself an AC09 a few years back when the price the auction site was more than the original unit. Wish Id has this resource back then! I may make another using your design in the future.

[Thrasherg]

I know this was originally posted 3 years ago, but I hope some of the posters might still be around. I have reached out to Bill to see if I can buy one of his version 2 PCBs, but this was all designed to go in a Fluke 8840, I just inherited a 8842 from my retired father but it doesn’t have the AC option so I was hoping to populate Bills board and fit it to my 8842, both boards for the 8840 and 8842 are referred to as 09 boards so I was hoping they are the same board, but more checking seems to imply that the boards are very similar but not the same. Can anyone tell me the difference? What would I need to modify on Bills board for it to work in my 8842? Thanks for all suggestions and advise.

Gary

[bdunham7]

The difference is just that the header where the ribbon cable plugs in has two pins swapped.  You can search the forum for this, the thread is several years back.  If I were designing (or adapting a design) I'd probably set it up with two jumpers so that it could be configured either way.

[TheDefpom]

I’m pretty sure I discussed the difference between the 40 and 42 in one of my repair videos where I worked on these units and got a ac board from a 40 and put it in a 42, this was several years ago now in one of my very early videos.