Battlezone repair log

Board would work sometimes, glitch others, also intermittent math box
errors. Just generally unstable.

Replaced all the rom sockets and CPU socket with new. Also replaced the
headers pins on both the CPU and math box boards with new square pin .156
headers.

Board now runs stable, no math box errors (I didn't replace the interconnect
cable pins, but with the new larger surface area for contact they seem to be
fine.)

Board works fine on bench (with o-scope) but in the upright periscope model
cabinet no picture.

This one took me a couple hours to figure out, had to pull a spare monitor
out of storage to ensure I wasn't crazy.

The harness I have on the bench is a salvage from a trashed out cabaret cab.
It has a jumper between pins L & P on the CPU edge connector. This puts the
board into "Invert" mode for direct viewing. The analog switch at E10 was
bad (replaced with DG201).

Added a switch into my bench harness to be able to exercise this invert
circuit.

Also found that maxim IC has a DG201 pin compatible part the MAX4511. I
have a couple samples on order to see if they work in this application.

Replaced E10 (DG201)

Board z channel working only partially. Many retrace lines are visible,
adjusting the monitor brightness and contrast is not able to clear the
problem.

Used the scope to trace around the z out circuits. Had a moment of wild
goose chasing the DVY4 signal which doesn't move an appreciable amount in
self-test. Verified the same signal with a good board. As the resistor
ladder dac appeared to be all good I starting looking at the Q7,8,9
transistor chain to see if that was acting up. Q8 didn't seem to be doing
much.

Traced this back through N9 (ls02) to the shift register at P9 (LS164).
A(1), B(2) and clock(8) were all good but QE(10) & QF(11) were both dead.
Piggybacked a new chip on top and got some signal which resulted in some z
channel effect on the self-test screen.

Replaced 74LS164 & P9 and now have full z control.

Badly unstable screen, vectors jumping around all over.

Found .047uf poly cap at C59 was broken on one leg.

Replaced C59 and screen stable.

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Received on Wed Oct 23 15:19:55 2013