EEVblog Electronics Community Forum

Products => Test Equipment => Topic started by: mtdoc on December 26, 2013, 06:03:27 am

Title: Help troubleshooting Fluke 8842A AC board.
Post by: mtdoc on December 26, 2013, 06:03:27 am
I was happy to pick up this Fluke 8842A (http://www.ebay.com/itm/390723831959) meter on ebay for $90 (+ $15 shipping).   Sold "as is for parts" because it displayed "error 30" when trying to do AC measurements.   Well, knowing that this was the normal error on a functioning 8842A without the option 09 AC board it seemed like a good deal to me especially since I rarely need to do AC measurements and have other meters that I can use.

Well - sure enough - after arrival its DC measurements were spot on per my DMM CheckPlus voltage reference and my HP3478A.  AC functions do give "error 30"

Upon opening it up I was pleasantly surprised to find that it did have the AC board - but with a nice marking on it as seen in the photo.

It would be nice to get this working again.   I have the service manual (http://assets.fluke.com/manuals/8842a___imeng0300.pdf) but its trouble shooting section is not very helpful for this issue since it covers some malfunctions of the AC board but not causes of an Error 30 message when a board is actually present and connected.

I've checked the test point voltages and they are ok. No obvious overheating components (thank you Flir E4->E8!). ICs seated properly.

Any suggestions on where to look next would be greatly appreciated. :)

(BTW loose spade connector on right is just the AC input lead - connecting makes no difference)
Title: Re: Help troubleshooting Fluke 8842A AC board.
Post by: mtdoc on January 01, 2014, 09:04:15 pm
Bump. Thought I'd try again.


Any suggestions on where to look next would be greatly appreciated. :)


Anyone?
Title: Re: Help troubleshooting Fluke 8842A AC board.
Post by: rexxar on January 01, 2014, 09:14:02 pm
Well, if error 30 is for disconnected AC board, then something thinks the AC board isn't connected. I'd check that all the connections between the AC board and main board are good, then look at whatever components are communicating between the two boards. Hopefully that input on the main IC is not blown.
Title: Re: Help troubleshooting Fluke 8842A AC board.
Post by: mtdoc on January 01, 2014, 11:31:25 pm
Thanks. Yeah, the ribbon cable physical connections between boards appear to be fine - That was one of the first things I checked.

I guess the next step will be probing the actual connections. Pin 23 on U202 on the main board is labelled "AC sense" so obviously the logical place to start. Just not sure what I should be looking for when probing.... ::)
Title: Re: Help troubleshooting Fluke 8842A AC board.
Post by: lowimpedance on January 02, 2014, 12:39:17 am
U202 pin 34 (AC sense) is pulled low by plugging the ac option pcb in, thus telling the meter this option installed. Look for a low here when this module is plugged in.
Title: Re: Help troubleshooting Fluke 8842A AC board.
Post by: Jay_Diddy_B on January 02, 2014, 12:59:14 am
To the original poster,

Check the part number for the AC option board. The part number for the 8840A and 8842A board is different. Fortunately, the difference is the position of one of the signals on the connector. If you compare the two manuals carefully you should be able to find it. To save you the trouble I have attached a pdf document that shows you the differences.

Good luck !!

Happy New Year !!

Jay_Diddy_B


Title: Re: Help troubleshooting Fluke 8842A AC board.
Post by: lowimpedance on January 02, 2014, 01:02:21 am
To the original poster,

Check the part number for the AC option board. The part number for the 8840A and 8842A board is different. Fortunately, the difference is the position of one of the signals on the connector. If you compare the two manuals carefully you should be able to find it. To save you the trouble I have attached a pdf document that shows you the differences.

Good luck !!

Happy New Year !!

Jay_Diddy_B

 Now that is cheeky of them .
Title: Re: Help troubleshooting Fluke 8842A AC board.
Post by: mtdoc on January 02, 2014, 04:41:07 am
You guys are awesome!  :clap:

Indeed pins 34 and 23 were high.

Couldn't quite find board numbers in the manuals but switched pins 1 and 8 on the connector using ribbon cable and viola!

AC volts is even in within spec. (my DMMCheck Plus reference AC rms volts is 4.998)

No AC current measurement yet - but should be an easy fix - the fuse is blown... ::)

So it appears someone tried to install an 8840A AC board and when it didn't work assumed it was bad and wrote "error 30" on the board.

Thanks for the help!  Jay Diddy in particular - without your tidbit I likely would not have figured it out. :-+