Thursday March 28, 2024

Whirlwind Pinball Repair - Battery Corrosion / Display Repair

Battery Corrosion Repair
Both U41 and U42 PIA chips were cut off the board, the pins were then removed and through-holes cleaned up.  The traces were then sanded to remove any remaining corrosion and a mixture of 50/50 water and vinegar was then brushed over the affected areas as per usual alkaline battery corrosion cleanup.  New machine socket strips were then installed into the board and new 6821 PIA chips were also installed.

But.. this didn't fix the issue.  The Player 1 display was still missing the "a" segment.  BLAST!  Oh well, at least the remaining battery corrosion damage was cleaned up.


Further Analysis
The best way to attack non-functioning code when programming is to narrow down the problem.  So if you have a 10,000 line program, print debug statements or output variable values at 2 or 3 different places in the code to start narrowing down where the error is occuring.  Then once you have it narrowed down to a sub-section of the code, do the same thing to that sub-section until you've narrowed it down to just a few lines of code.  Electronics repair can be done in the same way..

So I wanted to narrow down where the signal to the "a" segment was getting hosed.  I consulted the Whirlwind schematics again and decided to eliminate the display board as the issue.  The signal from the MPU board enters the display board at J3 pin 19.  It then goes into U9 (4049 IC) pin 3.  With the Whirlwind in Display Test Mode, I used a logic probe on U9 pin 3.  It showed the signal was not pulsing as it should be, so the problem was further up the chain and most likely the display board was fine.

Next way to narrow down was testing the signal out of U41.  I used a logic probe on U41 pin #10 and low-and-behold no pulsing there either.  But how could that be?  I just replaced the socket & put a new 6821 PIA IC in there!  Turns out, the socket wasn't the problem.


Broken Trace
Using the continuity tester on my multimeter, I checked the connection from the U41 chip pin #10 to the SRC3 pin #2.  Imagine my surprise when the connection showed open (not connected).  I began wondering if there was an issue with the socket I had replaced at U41 or a broken trace on the board that I wasn't seeing.  I sanded the traces slightly above the battery holder and above the U41 IC and still had an open connection when testing continuity between those two points, so it seemed very likely the trace was broken somewhere under the battery holder.

As much as I hated to do it since the battery holder had already been replaced by someone, I cut it off the board to expose what was underneath.

Broken Trace
Picture: No connection between U41 and SRC3, battery holder has to go..


After removing the battery holder, there was a spot on the board that looked slightly burnt.  If you look at the picture below you can see where I then sanded directly above and below this burnt spot to test continuity and verify the burnt spot was where the open connection was occuring.


Burnt Traces


Time to repair the broken connection..

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Comments:
Whirlwind Display Problem
Posted 01/04/13 2:49PM by Anonymous Techdoser
Thanks for posting this! Just picked up a WW project and my U41 and 42 look very similar to yours. My problem is the top segments of the upper display are all stuck on rather than off. This is with a known good display board from another pin. I've cleaned up the corrosion as best I could with no change. Do you think my U41 chip is bad? I've got a logic probe and diagnostic rom on the way, but would appreciate your thoughts.

Thanks