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Possible improvement on CPS1 Openkey for fixing issue

I found the openkey docs, I don't see any programmer like that on Amazon but maybe I'm looking for the wrong thing.
 
I've been messing with this a bit the past few days. I hadn't realized this before but openkey-cps1's ability to program the B-21 is dependent on the board being in RESET while its doing the programming. This is because 2 of the pins related to programming are part of the 16bit data bus on the B-21. If the board comes out of RESET before openkey has finished programming it will result in a bus conflict on those 2 pins from the main CPU/game code trying to talk to the B-21 at the same time.

How long the board is in RESET is highly dependent on the capacitor in the reset circuit on the A board, which is

Short/Dash board: CC3 (right of M51953 @ 7C)
Long board: CC21 (below M51953 @ 11D)

Both are 1uf caps (16V or above should be fine). If its failing/bad it can cause a significant reduction in how long the board is in RESET. Fast powercycles can also have this effect since the cap may not get fully discharged before power is reapplied.

So you might try testing/replace that cap and see if it helps.
 
@ack i have a cps dash board which was on battery that was working fine in my NAC, i applied openkey and now it doesnt work on my cab but works fine on HAS. Could this be related to the caps issue that you mentioned above?
 
msamiullah said:
@ack i have a cps dash board which was on battery that was working fine in my NAC, i applied openkey and now it doesnt work on my cab but works fine on HAS. Could this be related to the caps issue that you mentioned above?
Click to expand...

I suppose its possible, but honestly if it was the issue I would expect it to happen on both the NAC/HAS. If you power on the NAC, wait a bit, then do a quick power cycle does it magically work?

Your symptoms sound like what @Tailsnic Retroworks was having on his Blast City and concluded it was a power supply issue.
 
ack said:
I suppose its possible, but honestly if it was the issue I would expect it to happen on both the NAC/HAS. If you power on the NAC, wait a bit, then do a quick power cycle does it magically work?
Click to expand...
Thanks, quick power cycle didnt work. However I added a jumper cable for Reset header and now it works, looks like its a reset cap issue, will replace the cap at a later date. Could it be that older PSUs are too slow to power 5V for openkey programming to be on time ?
 
msamiullah said:
Thanks, quick power cycle didnt work. However I added a jumper cable for Reset header and now it works, looks like its a reset cap issue, will replace the cap at a later date. Could it be that older PSUs are too slow to power 5V for openkey programming to be on time ?
Click to expand...
The MCU on the openkey can operate between 1.8V to 5.5V. If the powersupply has a slow ramp up to 5V then openkey could be programming before the voltage to the B-21 is high enough for it to accept the programming.
 
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