sencore fc45 frequency counter repair

I’m starting to fix up some of the test gear that I recently acquired and first up on the bench is a sencore frequency counter.

The frequency counter appeared to work, but the display wasn’t working correctly and the measurements seemed to jump all over the place.

First, I replaced most of the electrolytic capacitors and that seemed to settle down the readings.

Next, was the display.

Four of the seven segment displays were not lighting up correctly.

After I cracked it open. I found one of the seven segment displays had a broken trace to one of the leds, so I bridged that and it began working, but as you can see the three in the center still weren’t working correctly.

I checked the cathode resistors for those three numerals, and most of them were out of spec, so I replaced them all, but that didn’t help.

The displays were common anode, so the driver IC should pull each segment to ground, but that wasn’t happening, so I ordered a new one.

Digikey sent me the wrong part, so it took a little longer than I’d hoped, but I finally replaced the IC.

The new IC fixed the display problems and the counter seems to be working well now. I even have the prescaler for it that takes it up to 600MHz.