Fluke 190 Scopemeter repair

Late last week at work, our head of Maintenance at work had an older Fluke 190 Scopemeter at his desk. He said that something was wrong with it and he wasn't sure what to do with it - send it in for repair, or get rid of it and get a new one. At almost $5,000 however, he said his department didn't have it in the budget for this year for a new one. The scope was clearly beat up and showing its age. He said it wasn't powering up anymore and probably has a bad battery.

I told him I could take a look, but no guarantees.

I took it home over the weekend and started poking around. Upon plugging the scope in, sure enough nothing happened. I started with the power supply - 17.5V with center negative. The supply seemed fine - measured good voltage and when I opened it up, it was very basic - transformer, four diodes, and a capacitor (which looked good).

So then I opened up the scope itself. The battery voltage measure around 7.4V which was in line with the 7.2V rating. When I powered up the scope, the charging voltage was over 10V which seemed a bit high. I unplugged the battery and the scope powered right up. So it was drawing too much current to allow the rest of the device to run. I found the new battery on Amazon for $35, so ordered one.

Note - the bodge wires that were found on the PCB here:

Old and new triangular batteries -

The battery arrived on Monday and I was able to power it up. The charging voltage was now about 8V instead of over 10. But then I found another problem - and probably why the Maintenance department wasn't so sure if it was worth keeping around - the screen was messed up.

Here is the scope running while torn apart on the bench -

In looking for a battery, I actually came across an EEVBlog video of this exact scope with the same screen problem.

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Fluke 190 Scopemeter repair

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Since I was feeling brave, I decided that I should go ahead and attempt cleaning up the lines on the screen. The general idea is that the ribbon cable for the LCD is adhered to the PCB and over time the connection weakens. If reheated properly, the connection can be restored. I don't have a hot air reworking station (or a hot bar) so started by trying to hold a hot soldering iron just above the ribbon cable like shown below, then rolling a pencil eraser on the ribbon to press it back down.

This didn't work because I couldn't get enough heat into the ribbon to reflow the solder. My next attempt was to put a layer of kapton tape on the ribbon to protect it, set the soldering iron to a low 220 degrees, and press it on the kapton tape and roll it around.

It took quite a few tries and I ended up with a few vertical lines as well during the process; but after about 30 minutes, I was able to succeed! So it actually worked!

The scope went back together and powered right up; although the metal frame was tricky to re-secure to the PCB via the bending of tabs while keeping alignment of the LCD to the PCB.

Great success!