Hi, I need help with a system 6 board. I can't find the problem.

I used the Pincoder ROMs for system 346 corresponding to my board.
I tested the "blancking" and it's fine. Also test the IC13 and IC16 ram memories and they also show to be ok.
When performing the IC19 test, it indicates failure.
Keep in mind, I tried the cmos memory (IC19) on another machine and it works perfectly.
In addition, in principle I verified that there was no cut track. so that is ruled out.
Then with the oscilloscope I verified if there was no signal on Data and Address Bus that was stuck high or low.
I also verify that the control signals (CE, Reset, R/W, OD) have signal.
If someone could tell me what other things to check, since I'm missing something.

Thanks in advance.

Thanks for the answer.
I already changed with another 5101 chip (a new one), the socket is new and there is no corrosion.
The chip is fine because I already verified it on another board.

Thanks for the answer.

I'm testing it outside the game, with the driver board disconnected (only the main board).

Thanks for the answer.

You were correct, it was the protection circuit.
First I removed jumper W5 and measured the output of the integrated IC24, but it kept indicating the output high, then I checked the input and observed that it indicated a low level.
Later I checked the pullup resistor (R14).
After that I assumed that the gate would be damaged, for which I removed IC24 and to my surprise it worked fine.
I finally started following the track to 1J3 N.C. and I discovered that in the factory jumper that is below they had soldered too much and somehow over the years it ended up forming a bridge.

Thank you for giving me the clue that led me to solve the problem.

diagram (resized).jpg