Nintendo Punch-Out - color issue (lower screen)

Flocke28

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Hi all.. i got a Punch-Out pcb.. all works fine.. only on the lower screen the color blue is always visible.. i got a new color eprom 8F but same issue.. i measured all resistors and transsitors good (q11 and q12).. nothing in the circuit looks strange.. any ideas?

IMG_1674.gif
 
What happens if you completely remove the PROM(s)? And I assume you're using a video inverter?

DogP
 
When i remove the color prom for blue (8F) then blue is gone.. i tried to bend the output pins of the prom.. when one output pin is in the socket then blue is to much.. but when i use the oscilloscope on the bend outputs the signal is fine.. when the screen have to black the output is high.. but with one output in the socket it seems the chip enable is bleeding in the signal.. looks very similar on the oscilloscope. But there is no short between the pins.. and i tried two color proms with the same issue.. but when i use the green prom in the blue socket then the image looks fine.. may i have two damaged proms of 8F?! 🤔 i burned the pink label prom of 8F for LS153 driver..
 
Are you able to read the PROMs to verify? And also verify that your 7E and 8E PROMs are from the "pink" set as well? (confirm your files aren't labeled incorrectly) And there can be mix and match between pink and white PROMs on the board, though the top will always be from the same set and the bottom will always be from the same set.

DogP
 
Heh, no... seems the actual colors on the labels are pretty difficult to tell these days. :-/

To me, I'd suspect that PROM... without it, or with a different one, the blue isn't stuck, so it seems the circuitry is OK. IMO, I'd wait for your PROM adapter to arrive, and if the PROM checks out, troubleshoot further.

DogP
 
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