Zener diode question/Atari 7800 repair

[WicoKid]

Trying to get an Atari 7800 in working order. It fairly frequently boots to Atari 2600 games but is inconsistent. It as never booted a 7800 cartridge (black screen or other, same behavior as no cartridge inserted.) The board is in rough shape; have cleaned slot connector several times and thoroughly and still same results. Have replaced a couple of fractured resistors. Was going to socket and replace RAM first then move onto other chips. 

 

Trying to cheaper parts first and there is a broken zener diode  (CR10) listed as 1N5231 on the schematics. I have zener diodes 

BZX55C. Both are rated at 5.1 V,0.5 watts. The  1N5231 data sheet indicates Forward Voltage at IF = 200 mA 1.1 volts whereas the BZX55C indicates 

forward voltage at IF=100mA 1.0 volts. I really do not know what this diode does in the circuit but if I could use the BZX55C it would save time (long weekend plus) and money (shipping). Is this part interchangeable? Can I put 2 in parallel to reach the 200 mA at which  the original 1N5231 is rated? 

 

Does anyone know if this diode at C10 is likely to prevent booting in 7800 mode?

 

Regardless, thank you for looking/reading.

[+-^CrossBow^-]

CR10 has to do with the player 1 controller inputs to the RIOT. I wouldn't really see that as being a cause for it not starting up but would see it being a problem with controls. Same diode is next to it at CR9 and also CR7 and 8 off player 2 side if memory serves.