yorkshire_spam
Active member
- Credits
- 763CR
I got the PCB set on the bench and wired into the test rig.
Watchdog is barking away and nothing much seems to be happening
:-(
I hooked up the Arduino ICT tester and the main PCB ROMs and RAMS all verify fine.
I wrote an additional Custom test for the ICT that calls the Watchdog reset - that works.
Hmmm.... got distracted by how the rom paging system works and a couple of other things.
In the end, mostly out of desperation I swapped the CPU
Game RUNS!
But has divider errors in self test.
While the PCBs are running on the bench all of a sudden - no graphics.
I check the AVG ROMS and RAMs with the ICT - All good.
So I grabbed the signature analyser and RTFM'd a bit.
Got slightly side-tracked by a fking misprint on the schematics where one of the signatures is WRONG.
The signature on sheet 13A (SP-225) for pin 12 of the LS157 @ 4A is H620, it should he H62U
That wasted some time!
SA indicates that PROM at 4B is suspect - good signatures on the inputs, bad on the outputs. So I removed it and checked it - the PROM is bad. Burned a new PROM and fitted it.
SA and test probing indicates that the vector state machine is all good and it thinks everything is a-ok - but the vectors on screen are junk.
This turned out to be a bad DAC on the X axis.
Now the board is back to running again with good AVG output, but still showing divider errors for ALL tests in the self test. (Matrix tests etc all pass)
The divider errors were 2 faulty 74.374 4L and 5M. I found these by sticking the logic analyser on them and checking input vs output when clocked and enabled - differences indicated bad ICs.
Board now runs and passes all self tests!
Time to fix the monitor!
Watchdog is barking away and nothing much seems to be happening
:-(
I hooked up the Arduino ICT tester and the main PCB ROMs and RAMS all verify fine.
I wrote an additional Custom test for the ICT that calls the Watchdog reset - that works.
Hmmm.... got distracted by how the rom paging system works and a couple of other things.
In the end, mostly out of desperation I swapped the CPU
Game RUNS!
But has divider errors in self test.
While the PCBs are running on the bench all of a sudden - no graphics.
I check the AVG ROMS and RAMs with the ICT - All good.
So I grabbed the signature analyser and RTFM'd a bit.
Got slightly side-tracked by a fking misprint on the schematics where one of the signatures is WRONG.
The signature on sheet 13A (SP-225) for pin 12 of the LS157 @ 4A is H620, it should he H62U
That wasted some time!
SA indicates that PROM at 4B is suspect - good signatures on the inputs, bad on the outputs. So I removed it and checked it - the PROM is bad. Burned a new PROM and fitted it.
SA and test probing indicates that the vector state machine is all good and it thinks everything is a-ok - but the vectors on screen are junk.
This turned out to be a bad DAC on the X axis.
Now the board is back to running again with good AVG output, but still showing divider errors for ALL tests in the self test. (Matrix tests etc all pass)
The divider errors were 2 faulty 74.374 4L and 5M. I found these by sticking the logic analyser on them and checking input vs output when clocked and enabled - differences indicated bad ICs.
Board now runs and passes all self tests!
Time to fix the monitor!