DODGEM PCB troubleshooting

[PaulSwan]

The 5101 is a CMOS RAM often used for battery backup. 2101 is a fast TTL RAM.
The 5101 has weaker drive and much slower timing than 2101. 2101 likely has more bus loading.
Paul.

[vernimark]

Ah. I ve to verify if i have both.
Could they be the cause of the reset?

[PaulSwan]

Possibly, yes - I'd replace with the right type and see.
Paul.

[vernimark]

10 rams replaced and continues to reset

[vernimark]

I can see removing EPROM in position 46 nothing changes

[PaulSwan]

A bad ROM or bad ROM decoder. There is not much to this hardware, really. It's very simple.
Paul.

[vernimark]

EPROM inolved is #5 (position 46). Its CRC is correct (bdae09fe), anyway I burned another one and nothing changed.

So I replaced the LS155 in position 41 (on my PCB is labaled 41/LS156) but nothing changed again.

Actually even if I proceeded quite well during the night now I've no idea what to check. probably the EPROM socked but I don't know what else. TTLs I tested seem to work.

[PaulSwan]

What type of EPROM is it?
Paul.

[vernimark]

2708

[PaulSwan]

There are some editions of The Invaders that use PROMS and do not have all the three supplies implemented on the power board to be able to drive a board populated with 2708. The effect of that is that the game doesn't run properly. Therefore, check you have +12, -5 & +5V on your power supply.
Paul.
 

[vernimark]

Of course i have. In fact my invaders has proms

[vernimark]

Grounding pin 6 of chip 7400 in position 12 cars run on the screen but collision are not detected.
I suspect 2101 i replaced is not working. That signal drives 5101_2101 RW

I have several 5101but only one 2101. I used a 5101 instead of the 2101 but nothing changed.

I replaced chips 11 12 13 24

[vernimark]

OK I make a break now.
Looking at the TV "Law & Order - Special Victims Unit" all night long I replaced almost everything on the board      but nothing changed

[PaulSwan]

Possible ideas are that you have a bad ROM, missing video interrupt or stuck input. Could also be a bad power supply. ROM are RAM is the most statistically likely, however if you're sure they are good...
Paul.

[vernimark]

I verified ROM crc multiple times.
I'll update you once I'll receive new 2101