You generally don't want to stick probe leads on XTAL and EXTAL pins of a cpu that is using a cyrstal setup like in this board. The crystal circuit is really sensitive and you will likely stop the oscillation by doing so.

The real story about if the clock is working is the 'E' pin on the CPU. 'E' is the external clock and you can safely probe this. Ideally you want a DMM or scope to check the frequency of the E pin. It should be right at 0.895mhz. VDC reading of 0v or 5v is an indication the cpu or the crystal is not working. The schematic i am looking at is hard to read but I think the 'E' is pin40 of the 6803 chip.

For the RAM chip put a logic probe on the /CS input at P18. When you power up the game it should go high briefly then start pulsing. If it never pulses or reads 0v or 5v always during the power on self test routine i'd check Q6(if always low or 0v), U9, and D6 (if always high but pulse at U9 P6).

U5 U6 and the 6803 must be good too. If you did any soldering work around those chips I'd be double checking it. You should be able to check U5 U6 by pulling the ROMs and PIAs out of the board. Power it up and all address/data go active so then you can check for pulsing on the output sides of U5 and U6.

Make sure the ram chip has power too at P24. Schem shows it P24 of the ram connects to V_AUX which i can't find on the drawing right away. Usually that means it is tied to the reset section... but should read 5v.

VCC of the RAM chip should be 5v. That is problem. What is the voltage on the reset pin of the CPU chip, pin 6? I coudn't location the ram chip's Vcc connection by looking at the schematic, but it is probably from the reset section.

If the CPU P40, external clock, is stuck high and the crystal is good the CPU chip itself is probably bad. Check the reset at cpu chip p6 tho first. If the CPU is stuck in reset the external clock is probably shut down.

*edit*

I found V-AUX on a 6803 schematic. Make sure the 82 ohm resistor at R27 is in spec. 5.8v is a bit much at the NVRAM and R27 drops the 12v down for the RAM.

But if P40 of the 6803 is always high, the reset is high, and you put in a new crystal the 6803 chip itself is likely bad. P40 should be pulsing when the CPU reset pin is high. Try a new known good 6803 CPU chip.