Problem Centipede PCB

[petercasino]

Hello. I have a Centipede PCB that plays perfectly but when I go to the test screen, it always has 4 FF in the top left corner. The manual says that after clearing the high score table, the next time you play a game and then go into the test screen again, the message will disappear. Is this likely to be an issue with the the chip at E5 as the manual suggests or corrupted data?

Thanks,
Mike

 

[yorkshire_spam]

Since the ER-2055 is @E5, my guess would be that the nvram is not playing "Nicely" as the PCB expects it to - do you find it doesn't store the top 3 scores as it should but otherwise works perfectly?

 

[petercasino]

Since the ER-2055 is @E5, my guess would be that the nvram is not playing "Nicely" as the PCB expects it to - do you find it doesn't store the top 3 scores as it should but otherwise works perfectly?

Hi, yeah, the pcb is working fine apart from that. I tried replacing the ER-2055 with no change

 

[yorkshire_spam]

Hi, yeah, the pcb is working fine apart from that. I tried replacing the ER-2055 with no change

The replacement ER-2055 - is that tested and working in another PCB? I find even NOS unused ER-2055 are often already faulty due to age.
I looked at creating little adapter PCBs for Centi, Crystal Castles and Star Wars at one time so modern parallel NVRAM could be used. Can't remember what happened to the prototype PCBs though.

If the Er-2055 IS working, but the PCB still thinks the nvram is faulty I'd start looking at the various /EA lines on the PCB (/EAADDR) and the LS32 @ A4 and work from there.

 

[DanP]

Star Wars and Crystal Castles use an x2212 battery backed ram to store settings and high scores. These are very different to the 2055s used in Centipede. I think the 2055 needs some extra wacky voltage to “program” the updates. Something like -30v which is derived from +15, I forget exactly. Check all the voltages are what they should be on the PCB and validate the new 2055 is working on another PCB if you can.

 

[yorkshire_spam]

Star Wars and Crystal Castles use an x2212 battery backed ram to store settings and high scores. These are very different to the 2055s used in Centipede. I think the 2055 needs some extra wacky voltage to “program” the updates. Something like -30v which is derived from +15, I forget exactly. Check all the voltages are what they should be on the PCB and validate the new 2055 is working on another PCB if you can.

Good shout, I'd forgotten about the voltage stuff, but now you mention it I remember the 2055 never working right on my test rig because of the missing voltage.

 

[philmurr]

I made a reproduction for the ER-2055 that didn't need the -30V (but it ended up being more expensive than the originals as I found a cheap bulk lot of them) so stopped making them.

The -30V is generated by a 555 and a couple of diodes & capacitors. Usual fault is the 555. Check the voltage on pin 14 of the ER-2055 (and try not to slip with your multimeter probes)

 

[petercasino]

Thanks for all the tips.

The voltage on pin 14 of the ER-2055 is 3.7V. I'll try replacing the 555 next.