(Topic ID: 291876)

Gottlieb 6-digit display flicker

By DickHamill

6 months ago



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  • 8 posts
  • 4 Pinsiders participating
  • Latest reply 5 months ago by G-P-E
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displaylayout6 (resized).jpeg
IMG_2712 (resized).jpg
IMG_2714 (resized).jpg
IMG_2713 (resized).jpg
IMG_2711 (resized).jpg

#1 6 months ago

I have a Gottlieb 6-digit display that's showing flicker on the "h" segments, but only when the display is mostly blank. If the display shows 6 zeros, the "h" segments (on these, they're the vertical segments that create the 1s) are perfect. It's only when there's a single "0" in right digit that the other digits flicker the "h". My 60V is good and steady. I've tested the 6118s (segments & digits) and they're both good. The MPU is a new Pascal. This happens on this display regardless of what player position it's in.

Flickering "h" segments (looks worse in the picture than in real life, but it's not good in real life)
IMG_2711 (resized).jpg

60 V is clean (although it's a little over 61V).
IMG_2713 (resized).jpg

Here's the signal on the "h" pin -- it's the same on all four displays even when they're showing a single zero (which shouldn't use "h" at all)
IMG_2714 (resized).jpg

Here's the part I can't figure out -- when I hook up a scope to the "h" pin of the display, the problem goes away completely. This is the same display with a scope probe hooked up.
IMG_2712 (resized).jpg

A diode test of Z1 pin 11 shows OL, but is the current somehow leaking through? My oscilloscope probe is 1MOhm, and 15pF. I'm tempted to just hook up a 1MOhm resistor and 15pF cap in parallel between Z1:pin11 and ground.
Anyone have a better idea?

#2 6 months ago

Schematic shows pull up resistors on the displays but I don't see them anywhere on the display board itself? May be bad if they're there somewhere..... really strange unless the pullups are on the mpu board instead.

#3 6 months ago
Quoted from slochar:

Schematic shows pull up resistors on the displays but I don't see them anywhere on the display board itself? May be bad if they're there somewhere..... really strange unless the pullups are on the mpu board instead.

The resistor packs are for the variant with the Dionics driver. I should have mentioned -- I have the Sprague driver version. But yeah, that's essentially what I'm considering doing, although I would add a 1MOhm resistor instead of a 47k.
displaylayout6 (resized).jpeg

#4 6 months ago

It is an induced pulse from another signal. Hanging a scope probe puts a very tiny but just enough capacitive load to eliminate the narrow pulse.
Probably caused by a poor connection on that signal somewhere on the board. If you can't find it - get a 15-20pF capacitor (similar value to your scope lead which fixes the issue) with a 100V rating, attach between pin 3 and ground. Yes, a kluge but for a one-off fix...

#5 6 months ago

I hunted for a bit and couldn't find any bad connections or shorts.
I'm going to settle for a 15pf cap between "h" and ground.
I hate not finding the real issue, but it looks good now.

#6 5 months ago

Have you tried replacing all 3 capacitors on the display?

#7 5 months ago
Quoted from ForceFlow:

Have you tried replacing all 3 capacitors on the display?

No, I connected a 15pf cap between "h" and ground. It solved the issue and I decided to move on.

#8 5 months ago

Replacing the three caps wouldn't have been a bad idea. I imagine a bad bypass capacitor (especially C1) could have caused similar issues. These don't fail often but are sometimes physically broken.

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