Help diagnosing Pinbot display problem

JackShandy

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My Pinbot has developed a problem with all of the displays. When the machine is first powered on, all the segments are working at full brightness. However, they rapidly fade until only a few segments are visible at a time. Which ones they are varies a bit but there's no obvious strobe pattern.

I've checked the cabling and everything seems to be secure. I've measured the voltage coming into the display board and it's +5, +90, -100, the +90 is a little below spec but from what I've read should be adequate to power the board, correct? However, the measurement was with display board disconnected, so it wasn't under load.

Any ideas on what to test next or what to replace would be greatly appreciated.
 
14049 Partial Segment Failures on Score Displays.
Sometimes only parts of a display aren't displaying or are locked-on, and only on certain numbers. For example, the top part of a "0" or "7" are not displaying or are always locked-on. It can even be so strange so that the missing segment will work on some numbers or letter, but not on others.

This can be caused by one of the hex input buffer 14049 or 4049 chips at U10, U11, U15-U18 or U7-U9,U10-U11 on 16 character display boards. Note on the schematics sometimes these are mis-labeled as 4050 chips! But these 4049 chips are CMOS and very static sensitive. You can check these with your DMM set to diode test:

* Red DMM lead to 4049 chip ground pin 8.
* Use black DMM lead and probe pins 2-7, 9-12, 14-15 of each 4049 chip.
* A reading of .6 to .7 should be seen. Any reading below this indicates a problem with the chip.
 
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Try testing the 39k ohm power supply resistors with a multimeter. If the the +100 and -100 volt DC power section of the power supply test open, the displays will not work correctly.

I had an issue with the display on my Whirlwind and changing the R1 and R4 resistors on my power supply with new 39k ohm, 1 watt resistors fixed it.

Steve
 
14049 Partial Segment Failures on Score Displays.
Sometimes only parts of a display aren't displaying or are locked-on, and only on certain numbers. For example, the top part of a "0" or "7" are not displaying or are always locked-on. It can even be so strange so that the missing segment will work on some numbers or letter, but not on others.

This can be caused by one of the hex input buffer 14049 or 4049 chips at U10, U11, U15-U18 or U7-U9,U10-U11 on 16 character display boards. Note on the schematics sometimes these are mis-labeled as 4050 chips! But these 4049 chips are CMOS and very static sensitive. You can check these with your DMM set to diode test:

* Red DMM lead to 4049 chip ground pin 8.
* Use black DMM lead and probe pins 2-7, 9-12, 14-15 of each 4049 chip.
* A reading of .6 to .7 should be seen. Any reading below this indicates a problem with the chip.

This really doesn't sound like his problem.
 
Try testing the 39k ohm power supply resistors with a multimeter. If the the +100 and -100 volt DC power section of the power supply test open, the displays will not work correctly.

I had an issue with the display on my Whirlwind and changing the R1 and R4 resistors on my power supply with new 39k ohm, 1 watt resistors fixed it.

Steve

I've seen many of these 39k resistors go bad over the years. All it takes is just one of the pair of them to go off value. You will need to unsolder and lift one lead of each resistor to test it properly. You'll get false readings if the resistor is tested in circuit.

If you find one of the 39k resistors bad, replace the other also. I've seen instances where one was replaced and a week later the other one failed.

The originals were half watt rating. I use one watt rating for replacement.
 
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