Another meter repair everyone! Anyway, as usual, I purchased a Fluke 12 off eBay listed as the buttons not working, but the meter itself worked as long as you were measuring diodes, or VDC. After a quick search online, this appeared to be due to the elastomeric strip between the buttons PCB and the main PCB being dirty, or failing. I contacted the seller to make sure the case wasn’t broken (as this meter seems to be on Fluke’s “Repair by Replace” list, I didn’t want to fall into that trap again), and after he said it was all intact, I ordered the unit for $30 + $6 shipping.
The meter arrived, and indeed, the buttons didn’t work. Nice “click” when pushing, but no registration. I pulled the screews from the back of the unit, and the main PCB clips into the case in a rather awkward way (really Fluke?). After getting that out, there’s a plastic/metal shield that holds the LCD and button board in place, and a cutout for the two elastomer strips to pass through. I cleaned the main PCB real well hoping that would help, but sadly, it still doesn’t work. I grabbed my meter, and checked the strip it came with, and it registered in 5 mega-ohms. Well, that’s not right. Online I found some references to stealing the elastomer strips out of a Harbor Freight cheapo multimeter. As luck would have it, I had one of those I got for free a while back. Indeed, it has two strips between the board and the screen, and while the height of them is right, the thickness is off (they’re just over 1/2 as thick is the stock strip). So, I cut two to the right length, and measured their resistance: about 5-10 kilo-ohms. Much better. I doubled them up and managed to shove them into the space where the old strip was, and closed the unit up. Once the screws were in (and therefore pressure applied to the strips), it worked! Total repair time, less than 10 minutes. Cost, free!
As some may have realized, I have a decent number ((10, by last count)) of multimeters now but since all of them have been purchased second hand (eBay, or Goodwill), and several of them have been repaired, I had no real solid confidence in any of them as being highly accurate. Though, to be fair, I didn’t have any real reason to doubt them either. I did check in to see what calibration of one of my Keithley 196’s would cost, but the number was much more than I’d want to pay (I believe it was about $450). So, I’ve been eyeing a product called the DMMCheck Plus for a while. It provides a 5V DC and AC, 1mA DC and AC, some precision resistors (100R, 1k, 10k, 100k), and a 100Hz frequency to check your meters against. All of these are calibrated by the guy that makes them with his 8.5digit HP meter, that’s NIST traceable. Meaning I should be able to check against it for how far out of calibration any of my gear is.