This is true and same with my lw3. If you have an fm1608 nvram (ramtron) i have noticed that the boot is flaky esp if the game was just powered on. Reseating the ram doesnt do much but leaving it and turning it on after a few mins seems to do tje trick for me.

However, i have never seen the nvram fail WHEN THE MPU IS RUNNING.

I read that maybe its something with the diodes on the mpu and how the nvram picks up voltage with the de mpu, that had the ram checksum is from the last shut down not what the ecu is expecting and halts the board. Time allows this to clear but it's not consistent.

Boot with original 6264 ram, and while gsme is on, put in batteries. The swap ram with batteries still on board.

Boot with batteries.

Then after successful nvram boot, shut down, remove batteries. Wait a few mins. Boot again.

I think just batteries in an external holder would be fine..

But i think nvram has a finite life and the pulls of chips at the time were possibly exposed to higher voltage.

OR, its a combo of old ps board 5v that are super lazy and the chips have a tighter tolerance around the 5v than the original 6264, and the pintech nvram have a wider tolerance...

Im on this thread to learn more.

Ok, another thing u can try is. If the mpu is stand alone on a test bench, Can you attach a 5v to the test loop at the upper left of the mpu? If you can, do that and see if the status leds on the mpu go into PIA. If no PIA, its booting successfully.

Then you can assess if the mpu is booting without the suspect psu board.

From the pin wiki gods.

CPU Power-On LEDs.
At power-on, the CPU board performs several self tests. While watching the LEDs (Light Emitting Diode) on the CPU board, some information can be derived from them. If all the self tests pass, the LEDs illuminate in the following order at power-on.

PIA (Peripheral Interface Adaptor) and +5 volt LED turns on immediately.
After about 1/2 second, the PIA LED turns off.
Blanking LED turns on next.
+5 volt and Blanking LEDs will stay on (until the game is turned off).

The three LEDs on the CPU board.

The LEDs when the game is booted and running; the blanking
and +5 LEDs are on.

If there is a problem with the CPU when the game is turned on, the PIA LED will usually stay on, and not turn off (and the Blanking LED will not turn on). Here is what this means:

PIA LED turns ON (and stays on), blanking LED never turns on: EPROM at location 5C and/or 5B is bad.
PIA LED turns ON, turns OFF (and stays off), blanking LED never turns on: EPROM at location 5C and/or 5B is bad (this LED sequence is very rare).
PIA LED turns ON, turns OFF, then turns ON (and stays on), and blanking LED never turns on: 6264 (28 pins) or 6116 (24 pins) RAM at location 5D is bad.

To get any more information from the LEDs, use the CPU Test EPROM (which is discussed in the section, CPU Diagnostic Test EPROM).

Bench Testing of the CPU board.
Instead of doing repair and testing of the CPU board in the game, it is much easier to test the CPU board on the workbench. The only voltage needed to run a DataEast/Sega CPU board is +5 volts and ground. A switching power supply, or an old computer power supply works great for this task. Voltage supplied must be between +4.9 and +5.1 volts DC.

Lay the CPU board on an insulted mat on the work bench. Hook up a +5 volt power supply to connector CN17, in the upper left hand corner of the CPU board. The pinouts are:
CN17 pins 1,2,3: Ground
CN17 pins 4,5,6: +5 volts
CN17 pin 7: KEY
CN17 pins 8,9: No connection

Alternatively, you can also connect +5 volts and ground to the test points on the top of the CPU board, just to the right of the battery holder. Actually this is MUCH easier than using the above connector!

Right next to the battery is connector CN17 and the ground and
+5 volt test points.

Turning the power supply on should boot the CPU board, just like it was installed in the game. Once the CPU has booted (in attract mode), you can check the lamp and switch matrix connectors for activity with a logic probe. Also check the address and data lines on the EPROMs and CPU. Here are the connectors to check:
Switch Matrix Rows (returns): CN10 (key is pin 4). Should be HIGH.
Switch Matrix Columns (drive): CN8 (key is pin 6). Should be PULSING.
Lamp Matrix Rows (returns): CN6 (key is pin 4). Should be PULSING (low).
Lamp Matrix Columns (drive): CN7 (key is pin 5). Should be PULSING.

Common Solutions to a Dead CPU.
Corroded batteries can ruin the 6808 (or 6802) CPU socket at 3D (40 pin socket), the 6264 or 2064C (28 pins) or 6116 (24 pins) CMOS RAM socket at 5D, and the EPROM sockets at 5B and 5C (28 pin sockets). This is very common. Battery corrosion must be neutralized on the printed circuit board. After the affected components are removed, scrub the afflicted area with a mixture of 50% white vinegar and 50% water. Then rinse the area with clear water, and let it fully air dry. Sand any greyed areas clean, and replace the sockets and components. Check all traces for continuity, as breaks can easily occur which are not visible.

If the game will still not boot, the most common problem is a dead 6808 (or 6802) CPU at 3D. Either CPU can be used, but the 6808 is largely unavailable (hence the 6802 is used as a replacement). Also a dead 6264 or 2064C (28 pins) or 6116 (24 pins) CMOS RAM at 5D is very common.

Blanking Circuit Theory of Operation Service Bulletin.
Sega has a nice document explaining the theory of operation for the blanking circuit in service bulletin number 75. To check this out, click here and here and here.

I have tried to reference my own nvram machines and 1 will have trouble booting if i power cycle it quickly, however, waiting 30 seconds and its fine.

My other machine behaves like normal. Not sure if that helps.

It should no long req batteries in the holder after first boot

Great news!! Good to hear you got it sorted!

Thanks barakandl, its generally fine 9/10 times i power up the machine, but when it stumbles, i just turn it off, wait a couple mins and try again and its behaved. Ill check my date codes.

Its a shame that the mpu cant be modified with a jumper so the voltage isnt an issue. The FM16W08 have that wider voltage range, but also different ic package.