I just resurrected a -17 MPU and all is working fine with the exception of the credit display data showing up identically on the Player 3 display. U20, pins 2,7,9, and 11 are the display latch strobes. The U20 chip is socketed and it looks like pin 2 (player 3 strobe) is crispy at the solder pad despite continuity checking out ok. Checked for short between pin 2 & 11 (credit display), none. There's nothing obvious like solder splash and unfortunately I can't read what type of chip this is, but manual says hex buffer 14502 (B) or (8)? Can't tell.

I swapped the PIA's, no change. I have 2 other working -17 MPU's where this is not happening, so def on the board.

Has anyone run into this issue before?

#2 1 year ago

SLG

slghokie

Pinside+ Frequent

Cary, NC

7y 76,400 324 19 15

I have something similar on a Flash Gordon where player 2 mirrors player one. I tried PIA's as well but no change. Got a new connector to repin and see if it is the crappy push in connector for displays causing it. Have not had a chance to try. Otherwise it has to be one of the display chips on the MPU or bad components in the path to display connector.

#3 1 year ago

PSH

Phoerber

Pinside+ Frequent

Seattle, WA

7y 53,150 178 16

Quoted from slghokie:
I have something similar on a Flash Gordon where player 2 mirrors player one. I tried PIA's as well but no change. Got a new connector to repin and see if it is the crappy push in connector for displays causing it. Have not had a chance to try. Otherwise it has to be one of the display chips on the MPU or bad components in the path to display connector.

Agree 100%, I will let you know if I solve - please do the same. My issue is definitely on the MPU.

#4 1 year ago

IKE

DickHamill

Pinside+ Pro!

Topsham, ME

5y 68,550 722

OP
Quoted from Phoerber:
I just resurrected a -17 MPU and all is working fine with the exception of the credit display data showing up identically on the Player 3 display. U20, pins 2,7,9, and 11 are the display latch strobes. The U20 chip is socketed and it looks like pin 2 (player 3 strobe) is crispy at the solder pad despite continuity checking out ok. Checked for short between pin 2 & 11 (credit display), none. There's nothing obvious like solder splash and unfortunately I can't read what type of chip this is, but manual says hex buffer 14502 (B) or (8)? Can't tell.
I swapped the PIA's, no change. I have 2 other working -17 MPU's where this is not happening, so def on the board.
Has anyone run into this issue before?

Yes, that's a B (Motorola 14502B hex inverter/buffer).

Edit: ignore the rest of this -- Quench's answer is better.

What's the resistance between pins 13 & 1 on U20?
Since your U20 is socketed, to prove that the problem is U20 (or before), you could pull U20, bend pin 2 a bit, and plug it back in. Then, display latch strobe #3 should never go high. If the player 3 display still mirrors credits, your short is between U20 and the connector. If display #3 turns off, then your problem is U20 or before.

#5 1 year ago

PIP

Quench

Pinside member

8y 114K 8,035

OP
Quoted from Phoerber:
I just resurrected a -17 MPU and all is working fine with the exception of the credit display data showing up identically on the Player 3 display.

An open circuit on the player #3 latch signal causes it to float high at that displays 4543 decoder chip. It results in that display accepting all binary coded data written to any display. Since the Credit/Ball in Play display is written last in the refresh sequence, that's what you'll end up seeing on the player #3 display.

If you're saying pin 2 (display latch #3) on U20 looks crispy, the outputs for that pin in the chip might be blown out. Any standard 4502 logic chip should be suitable.

#6 1 year ago

ARD

Vector

Ardvark

Bellingham, MA

10y 30,650 101

This will happen if the switch wires at the coin door are grounded. As a quick test, you can unplug the switches from the MPU to see if the problem persists.

#7 1 year ago

PSH

Phoerber

Pinside+ Frequent

Seattle, WA

7y 53,150 178 16

Quoted from Quench:
An open circuit on the player #3 latch signal causes it to float high at that displays 4543 decoder chip. It results in that display accepting all binary coded data written to any display. Since the Credit/Ball in Play display is written last in the refresh sequence, that's what you'll end up seeing on the player #3 display.
If you're saying pin 2 (display latch #3) on U20 looks crispy, the outputs for that pin in the chip might be blown out. Any standard 4502 logic chip should be suitable.

Thanks Dick and Quench - I will have time this weekend to report back, sorry for the late reply, it's been a week.... More to come!

#8 1 year ago

PSH

Phoerber

Pinside+ Frequent

Seattle, WA

7y 53,150 178 16

Solved. Bad U20, thankfully it was socketed (that never happens!!) Appreciate the help Quench, Dick H, and all!

1 year later

#9 4 months ago

SLG

slghokie

Pinside+ Frequent

Cary, NC

7y 76,400 324 19 15

On mine I replaced U20, U11 but in my case it was a bad U8 5101. Thread is here in case it can help others...

https://pinside.com/pinball/forum/topic/bally-wrong-display-data-mpu-related

Quench was instrumental in helping there too

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