(Topic ID: 322769)

Bally 6-digit display segment out

By bayoubilly70

1 year ago



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  • 7 posts
  • 5 Pinsiders participating
  • Latest reply 1 year ago by MrBally
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#1 1 year ago

Bally 6-digit displays... I'm working on Star Trek. I have one display with the same segment out across it. I replaced the appropriate MPS-A42 transistor (Q18), and also the decoder chip. The segment "f":

http://web.archive.org/web/20071019004706/www.pinrepair.com/bally/index3.htm#display

is still out.

The problem follows the display if I change it in another location, so its not the inputs. Its the display board.

One could argue that I replaced the bad transistor and decoder chip with defective parts, but not likely.

Any ideas?

#2 1 year ago

Just for fun, double and triple check you replaced the correct parts. The way those things are labeled it is easy to pick the wrong one. I know because I have done it. The other thing to do is reflow the headers for the display. One little crack is all it takes.

#3 1 year ago
Quoted from Mk1Mod0:

Just for fun, double and triple check you replaced the correct parts. The way those things are labeled it is easy to pick the wrong one. I know because I have done it. The other thing to do is reflow the headers for the display. One little crack is all it takes.

Quoted from Mk1Mod0:

Just for fun, double and triple check you replaced the correct parts. The way those things are labeled it is easy to pick the wrong one. I know because I have done it. The other thing to do is reflow the headers for the display. One little crack is all it takes.

I did it correctly. If the link above is wrong then I replaced the wrong transistor. That's a possibility. I reflowed the headers. Bright... crisp... segment missing.

Could be crappy replacements... it might happen. I didn't resolder 2nd componets yet.

#4 1 year ago
Quoted from bayoubilly70:

Bally 6-digit displays... I'm working on Star Trek. I have one display with the same segment out across it. I replaced the appropriate MPS-A42 transistor (Q18), and also the decoder chip. The segment "f":
http://web.archive.org/web/20071019004706/www.pinrepair.com/bally/index3.htm#display
is still out.
The problem follows the display if I change it in another location, so its not the inputs. Its the display board.
One could argue that I replaced the bad transistor and decoder chip with defective parts, but not likely.
Any ideas?

1) does the BCD ic chip work in test... scope/logic probe...
2) if so does the transistor circuitry that drives the "F" segment work?...
3) if so then most likely the gas discharge display is bad...
4) it has happened to me...
5) best to get displays with missing digit position rather than segments.

#5 1 year ago

Are you sure that you installed the transister in the correct direction/orientation?

#6 1 year ago

The only other thing that comes to mind is this. I had a similar head scratcher that was keeping me up at night. I finally inspected the damn thing with my 10X Ott light and found broken connectors on the back side. It took some very careful soldering but I got it fully working again.

IMG_4230 (resized).JPGIMG_4230 (resized).JPGIMG_4231 (resized).JPGIMG_4231 (resized).JPG
#7 1 year ago

Besides what MK1Mod0 said, replace the resistors in the segment F circuit. You can try to ohm them out, but those 45 year old carbon film resistors sometimes open when any sort of current goes through them. They usually test good with an ohm meter though. If you aren't afraid of the 190 volt DC on the board, briefly jumper across the resistors one at a time while looking for the segment to light.

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