Re: Battlezone repair log

Some great Sherlock Holmes style investigation there well done, thanks for
the read.

On Tue, Oct 22, 2013 at 11:38 PM, David Shoemaker <davids@oz.net> wrote:

> 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 15:31:06 2013