Pinbot tilts with bumper hit

I recently acquired a Pinbot, and when the top drop target is down, and the top bumper is hit, it tilts about 25% of the time the bumper is hit.

So far I have followed pinrepair's guide of pulling the connectors off of the MPU and testing pins, everything came back okay. Switch tests show nothing wrong. I have changed the diodes on the bumper, and the drop target. I have checked diodes and resistors along the entire rectangle between the top bumper, drop target, coin door, (and left outlane) and tilts.

I am pretty new to switch matrix Problems, and am looking for other ideas to check. Anyone have any thoughts?

#2 4 years ago

MSF

Nokoro

Pinside+ Frequent

If it is a rectangle on the switch matrix, it would seem like a diode or something acting like a shorted diode. Are you sure the diodes are going in the right direction? Is there anything else that could be acting as a short between the lugs that the diode connects to? For instance, I had a switch that was missing the insulating fish paper between the two lugs for the diode. It behaved just like a shorted diode even though the diode was fine.

You can also try to create other rectangles on the switch matrix with each of the switches in your rectangle acting as a corner but with different switches for the other three corners. If you find other issues, that may help you isolate the problem to a single switch.

#3 4 years ago

DEC

GRUMPY

Pinside member

10y 95,050 8,703

OP
Quoted from Pinfert:
Anyone have any thoughts?

Is this a system correct original cpu board?

#4 4 years ago

???

Pinfert

Pinside member

Quoted from GRUMPY:
Is this a system correct original cpu board?

Yes it is

#5 4 years ago

???

Pinfert

Pinside member

Quoted from Nokoro:
If it is a rectangle on the switch matrix, it would seem like a diode or something acting like a shorted diode. Are you sure the diodes are going in the right direction? Is there anything else that could be acting as a short between the lugs that the diode connects to? For instance, I had a switch that was missing the insulating fish paper between the two lugs for the diode. It behaved just like a shorted diode even though the diode was fine.
You can also try to create other rectangles on the switch matrix with each of the switches in your rectangle acting as a corner but with different switches for the other three corners. If you find other issues, that may help you isolate the problem to a single switch.

Thanks! I'll try creating other rectangles. I checked the directions of all of the diodes with known working switches, and saw nothing out of place.

#6 4 years ago

DEC

GRUMPY

Pinside member

10y 95,050 8,703

This can still be a CPU board issue. Since this only occurs 25 % of the time it wont be a reversed diode or miss wired switch. It could be a diode going bad but you have replaced two of them, you should also change the diodes on the plumb tilt and the right coin switch to be sure . SCR-6 could be failing causing random tilts. Look it over to see if it's cracked.

#7 4 years ago

???

Pinfert

Pinside member

Quoted from GRUMPY:
This can still be a CPU board issue. Since this only occurs 25 % of the time it wont be a reversed diode or miss wired switch. It could be a diode going bad but you have replaced two of them, you should also change the diodes on the plumb tilt and the right coin switch to be sure . SCR-6 could be failing causing random tilts. Look it over to see if it's cracked.

Thanks, I'll check this out and follow up!

#8 4 years ago

???

Pinfert

Pinside member

Quoted from GRUMPY:
This can still be a CPU board issue. Since this only occurs 25 % of the time it wont be a reversed diode or miss wired switch. It could be a diode going bad but you have replaced two of them, you should also change the diodes on the plumb tilt and the right coin switch to be sure . SCR-6 could be failing causing random tilts. Look it over to see if it's cracked.

I checked this resistor pack, and it seems to be fine. No cracks, and the resistance tests good. I changed the diodes, and still no luck.

#9 4 years ago

???

Pinfert

Pinside member

OP
Quoted from Pinfert:
I checked this resistor pack, and it seems to be fine. No cracks, and the resistance tests good. I changed the diodes, and still no luck.

I just checked SR20 and it reads 4.67k ohm on every pin except pin 3 where it reads 2.58kohm. could that be my problem?

#10 4 years ago

ECB

erak

Pinside member

Grimsby, ON

15y 122K 3,749 5 86

Is the playfield slam tilt or coin door contacts too close or bad diodes? And activating when bumper is hit

#11 4 years ago

???

Pinfert

Pinside member

Quoted from erak:
Is the playfield slam tilt or coin door contacts too close or bad diodes? And activating when bumper is hit

No, I've checked and they are both very far apart! I also replaced all Tilt diodes. Thanks for the idea though!

#12 4 years ago

DEC

GRUMPY

Pinside member

10y 95,050 8,703

OP
Quoted from Pinfert:
I just checked SR20 and it reads 4.67k ohm on every pin except pin 3 where it reads 2.58kohm. could that be my problem?

This is fine, if you were to remove this from the board pin #3 would read correct.

OP
Quoted from Pinfert:
I checked this resistor pack, and it seems to be fine. No cracks, and the resistance tests good. I changed the diodes, and still no luck.

Did you check SRC-6 or SR-6? SRC-6 has resistors and caps, the caps can act up causing issues that don't show up under testing. If you can't find any issues on the play field you may want to just replace SRC-6 with a resistor only pack just to be sure.

#13 4 years ago

MSF

Nokoro

Pinside+ Frequent

Perhaps replace the caps on the switches in that column or row. Bad caps can manifest problems in different ways.

Also check all switches and wiring in that column or row for a short to ground. Is there a wire touching a bracket or piece of metal somewhere that it shouldn’t? Perhaps a leg from a cap or diode got bent and is touching something? Shorts to ground can also cause weird problems. Unfortunately, it is like finding a needle in a haystack sometimes. You really have to examine everything closely.

#14 4 years ago

MSF

Nokoro

Pinside+ Frequent

I should also note that if it is only happening 25% of the time, it could be a short to ground that is only barely touching and occasionally makes contact with the bumper hit causing vibration. Like a switch that is gapped too closely, only a short. Make shore all wiring, caps, diodes, etc. on the switches have enough space so that nothing is brushing up against something else, even if barely.

2 weeks later

#15 4 years ago

???

Pinfert

Pinside member

So I finished changing out the capacitor and resistor on the upper bumper, and it still tilted. I was examining my work when I noticed that this leaf switch extends pretty far beyond the edge of the coil. I was able to reach behind there and feel that it was very close to touching the top of the coil piston. I figured what the heck and lopped off about 1/8th of an inch. Fired it up, dropped the top drop and hit the bumper about 100 times, no tilt! I took a picture after I cut a piece of the leaf switch off. Thanks everyone for the ideas, you really gave me hope that I might one day fix this!

IMG_20191229_205349 (resized).jpg

#16 4 years ago

MSF

Nokoro

Pinside+ Frequent

Congrats on getting it solved, but I’m not sure I’m following. Do you think the over extension of the leaf was creating an occasional short to ground?

#17 4 years ago

???

Pinfert

Pinside member