Williams System 7 Display problem

(Topic ID: 237953)

Williams System 7 Display problem

By Pk98

11 days ago

Topic Stats

  • 3 posts
  • 2 Pinsiders participating
  • Latest reply 11 days ago by Pk98
  • Topic is favorited by 1 Pinsider


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#1 11 days ago

I’ve been trying to bring back a Jungle Lord after 20 years in a barn.
Power supply, cpu and driverboard have been rebuild and are working.
Next up is getting the displays to work properly.
They were showing garbage, some blank, some missing digits, some overly bright digits

On the Master display board I started by removing all the ICs and placing new component back in sockets.
The more rare UDN chips I desoldered and placed back in sockets so I could move them around to troubleshoot.
The resistors measured ok so I didn’t replace.

This gave me an improvement but still not 100% success.
The 100.000 digit on P1 and P3 display is overly bright.
P2 and the two ‘match’ digits on the credits/match display are blank.
P4 and ‘credit’ digits of credits/match are ok

If I connect P1 and P3 displays flatcables only partially so that the last 2 pins don’t make contact (100.000 digit),
then P2 display and the two ‘match’-digits come back and work as also the P1 and P3 display (minus the one digits that are not connected )

If I disconnect wire 7 from the 4J5 connector on the MDB. Strobe 3 the 100.000’s on P1/P3
Now if I let the flatcable for P3 display make full contact all is ok (minus the 100.000)
But if I do the same on the P1 display The bright 100.000 digit is back on P1
And the display is dragging P2 and Mach digits down.

I’ve swapped P1 and P4 displays and the bright digit does not follow
Swapped UDN driver chips and the problem always remains P1/P3

So I’m guessing something on the MDB is shorted and driving the P1 100.000 digit even
though the strobe 3 wire is disconnected.

Anyone have any ideas on where I should look next?

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#2 11 days ago

Do you have a logic probe? Follow the strobe 3 signal around the board, the 4069 chip is suspect but you replaced that right?

See if its behavior is different from other strobes.

Have any other system 7 games you can test the display board and mpu in to see if it's following? It could also be originating on the mpu board - check the strobe 3 signal there as well.

#3 11 days ago

I have a logic probe and a multimeter to check. I'll try to follow the stobe 3 path.

The three 4069's have been replaced.
The bright digit was also allready present before i replaced all the ic's.

Sadly this is my only sys7 so I can't try in an other machine.
But even with the strobe 3 wire from the cpu disconnected the digit lights too bright on the p1 display so this should limit the problem to the MDB, no?

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