Fluke 77-iv Repair - No backlight or continuity buzzer

[GeekPriest]

I've recently acquired a Fluke 77 IV. Everything works, EXCEPT the backlight and continuity buzzer.
Basically these are the same symptoms as here: http://mrmodemhead.com/blog/fluke-77-iv-copper-corrosion/ .

Indeed, my meter had the same white funk on the board. I've cleaned that off everywhere. Further, I can see that the trace from the +9V (direct from battery; unregulated) that powers the backlight and buzzer is corroded away on the bottom of the board. The damage on mine is more significant than that noted by Modemhead (link above).

However, my attempt to solder in a new wire failed. My guess is that I simply haven't made good contact with the remaining traces or the through-hole that goes from the bottom to top of the board.

What is my best way to make this connection properly and, hopefully, elegantly?

I've attached photos of what I'm looking at. If I need to provide more detail, I can try for better photos.

[retiredcaps]

1) Do you have continuity from the battery + to the top side of the board?

2) Do you have continuity from the battery + to the bottom side of the board?

Here is another modemhead repair that isn't published yet.  It is in draft format, but I will post it here.  The filename tells who what is going on.

[ModemHead]

For patching, I use 30 gauge wire-wrap wire with the kynar insulation stripped off.  It is tinned, and solder sticks well to it.  Scrape the copper trace with a semi-sharp hobby knife until you get down to bright clean copper.  Use plenty of liquid flux or a flux pen.  You can clean it up later with IPA.

Looks like you may need to patch through the via, so treat it like a lead in through-hole connection, and scrape the via pad on the other side down to bright copper as well.

And here's my secret for holding the tiny wires in place: poster putty.  With a little ball of it holding the patch wire down and plenty of flux, all you have to do is just touch it with a wet soldering iron.

[GeekPriest]

Does the poster putty melt, or do you remove it later?

[ModemHead]

If it gets hot it might get a little extra gooey, but it doesn't really melt.  I just pull it off after soldering.

[GeekPriest]

Re-worked the fix again today, and the Fluke 77 IV is back in action.

I had a moment of disappointment when it appeared that the buzzer and backlight work, but nearly nothing else did. Installation of a new Energizer 9V battery put everything right. (Note to self: Fluke 77 IV is quite flaky with a weak battery.)

Thanks to everyone's help, I have a meter I paid $45 for (including shipping) working, and worth a lot more.
 

[retiredcaps]

Installation of a new Energizer 9V battery put everything right. (Note to self: Fluke 77 IV is quite flaky with a weak battery.)

Good job on the repair.

The newer pcb revisions of the 170 and 77IV are supposed to display "Batt" on the lcd when the battery gets low and will not allow you to take a reading.

What version of the 77IV firmware is on your meter?

To get firmware ...

1) turn meter off
2) press hold button down
3) move rotary knob to DCV
4) release hold button

The meter will now briefly display the firmware version.

PS. Old weak 9V batteries will nicely work in the Fluke 27 as it has more double the battery life of the 77IV. I put my weak 9V batteries in my Fluke 7x series I, II and III meters (2000 hour battery life due to roughly 275uA current draw during normal operation).

[GeekPriest]

Appears to be 1.00 firmware, if I am doing things right.

I like the quickness of the Fluke 77, and its compact size. BUT, that 27/FM is just a beauty to use. That knob was easy to turn, the bail rock-solid. I didn't have an issue with the display. The young man I gave it to had better realized the awesomeness he holds in his hands.

[retiredcaps]

Appears to be 1.00 firmware, if I am doing things right.

I think there might be a 1.01, but I can't remember right now for sure.

Anyway, if you take an obviously weak battery (say 6V), it should display "Batt" on the lcd.

[radistx]

Hi.
I have two meters with the same problem. I re-soldered every contact on one of the multimeters and still has the same problem. I even swapped 14069UG between units.
Please help identifying the problem. 

[retiredcaps]

Please help identifying the problem. 

Clear focused pictures of your board will help.

[radistx]

Here are some pictures

[radistx]

More

[retiredcaps]

Service manual for the 77IV is now available as per

https://www.eevblog.com/forum/repair/fluke-77-repair-184173/msg2382876/#msg2382876

[dam234]

Need help deciphering the item marked in the photo?

Does anyone know what this item is?

Fluke 179


I soldered IRLML6302 and everything works