Whilst waiting for the Mylar to arrive for my playfield I thought I would turn my attention to the 6 digit displays on my machine.
When I got it noticed player one flickered an the ball count numbers were not working.
I think I have atleast 3 different models of displays in my machine with 3 being Stern and 2 being Bally.
The one in the ball count position was a Bally AS-2518-15.
After doing a bit of reading on Piniwki and watching a couple of Youtube videos I got stuck in, first on the one with numbers not working.
With the initial visual inspection I couldn't see anything obvious, so I moved onto doing diode checks on all the transistors and they all looked ok, so it was onto the 100K resistors R1, R3, R5, R7, R9 and R11.
Testing these in circuit 4 of them were measuring around 120K and two open cct. The two measuring open cct I thought must of just been due to oxidation as I've never seen a resistor go open cct before that didn't look burnt, but as I had already bought new 1/2watt resistors to replace all the 100K ones I removed all 6 of them and then tested them again. Yes 4 were definitely measuring around 120K and 2 were completely open cct, so I guess that is why two of my numbers weren't working. I won't find out until I'm ready to power up the machine in a week or two time though.

Next I decided to test the 100K resistors in my Bally AS-2518-21.
All 6 of these resistors measured between 55K and 65K in circuit so I removed them all and yes the resistor had drifted down from 100K to 55K, so all 6 were replaced with new 100K 1/2 watt resistors.

I then tested the 100K resistors on my Stern display and found then all to be around 98 to 99K, so still within tolerance.
My question is what has everyone else found?
Did Bally use lower quality resistors that have drifted a lot more over time, or is it just my Stern displays are newer and not seen as much use?
I have not yet replaced the 1/4 Watt 100K resistors on the Stern displays with new 100K 1/2 watt ones.
Does everyone just replace these resistors as a matter of course, or only if they look heat damaged or the values have drifted?

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Thanks. I won't bother replacing the other resistors but may go back and have another look at the transistors again in the one that had the open cct resistors.
Yes I bought 1/2w metal film resistors