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.
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.
Time to repair the broken connection..
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 |