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(Topic ID: 334800)

Stern Meteor MPU switch matrix issue

By KW_pins

1 year ago



Topic Stats

  • 9 posts
  • 4 Pinsiders participating
  • Latest reply 1 year ago by Quench
  • No one calls this topic a favorite

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  • Meteor Stern Electronics, 1979

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#1 1 year ago
OP
 
KLP

KW_pins

Pinside member

US Howell, MI

6y 29,900 27 9

Problem: switch 37 shows closed in switch test but flashes 0 every 15 seconds or so (even with J2 & J3 unplugged so it's definitely a board problem).

What I've checked/done so far:
*Reseated all socketed chips
*Swapped PIA chips and the problem stayed the same.
*Reflowed header on J2 and insured no pins were shorted to each other or ground
*Booted on bench (including fooling the board into 7th flash) and probed J2 with logic probe but the readings are all over the place. Some pulsing, some high. Not really sure what to look for.

Any advice on how to proceed would be appreciated.

Thinking about biting the bullet and just buying a Weebly board :/ but I'd rather fix this one. I hate admitting defeat.

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#2 1 year ago
 
BIL

dothedoo

Pinside member

12y 106K 7,265

Have you tried swapping the 6810 and 5101s with known good chips?

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#3 1 year ago
OP
 
KLP

KW_pins

Pinside member

US Howell, MI

6y 29,900 27 9

Quoted from dothedoo:

Have you tried swapping the 6810 and 5101s with known good chips?

Haven't tried that. I don't have known good chips on hand.

I can boot the board on the bench. What could I check with a logic probe to tell if one of those chips is suspect?

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#4 1 year ago
 
PIP

Quench

Pinside member

8y 114K 8,023

I presume this MPU board has suffered battery corrosion. Clear high res pictures will help.

Grab your multi-meter and put it in resistance ohms mode. If it's not an auto-ranging meter set it to the 200k scale.

Perform the following with the board not powered (i.e. off).

Connect the black meter lead to ground (i.e. test point TP4) and leave it connected there. With the red meter lead, probe pins 1 to 5 and pins 8 to 15 of the J2 pin-header. They should all read in the vicinity of 56k ohms. Is this what you're seeing?

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#5 1 year ago
OP
 
KLP

KW_pins

Pinside member

US Howell, MI

6y 29,900 27 9

Quoted from Quench:

With the red meter lead, probe pins 1 to 5 and pins 8 to 15 of the J2 pin-header. They should all read in the vicinity of 56k ohms. Is this what you're seeing?

All are within 1000 of 56kΩ EXCEPT pin 12 which is way lower, around .44mΩ

There's definitely some alkaline damage. Not terrible, not great either.

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#6 1 year ago
 
???

Joydivision

Pinside+ Frequent

10y 69,550 654 11

OP
Quoted from KW_pins:

Haven't tried that. I don't have known good chips on hand.

I can boot the board on the bench. What could I check with a logic probe to tell if one of those chips is suspect?

You should replace those AMI brand U7, U8 & U13 chips regardless.

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#7 1 year ago
 
PIP

Quench

Pinside member

8y 114K 8,023

OP
Quoted from KW_pins:

All are within 1000 of 56kΩ EXCEPT pin 12 which is way lower, around .44mΩ

Well, J2 pin 12 is the switch matrix return line that switch 37 lives on.
So now you have to find where the issue on that signal is.

Some possible locations are:
Top side of the board under the J2 or J3 pin header retainers (corrosive crud).
Top side of the board under one of the four 8-bank DIP switches (corrosive crud).
Shorted Capacitor C22 or C37.
The source of the signal is pin 14 of U10 so inspect it there and follow it downstream to the above locations

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#8 1 year ago
OP
 
KLP

KW_pins

Pinside member

US Howell, MI

6y 29,900 27 9

Quench

Solved!

Traced it back from pin 14 on U10 to the 56kΩ resistor at R42 that was shorted.

Replaced it and we're back in business!

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#9 1 year ago
 
PIP

Quench

Pinside member

8y 114K 8,023

OP
Quoted from KW_pins:

Traced it back from pin 14 on U10 to the 56kΩ resistor at R42 that was shorted.

Great work!
Only seen a shorted 56kΩ resistor on the switch return lines once before and it was also a Stern MPU board.

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