Another F-14 with issues. Boot up problems

Grbgemen

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When i got my F-14, every once in awhile, i noticed it would not boot. Only happened once in awhile. Now that i have finished repairing stuck solenoids/lamps rows and cleaning the play field up, i am now stuck with a F-14 that will only boot every once in awhile.

i started with the guide on pinrepair. pulled the cpu and hooked it up to an old atx power supply. tried this first:

To "go around" the POR section of the board, you can do a simple test. After attempting to boot the CPU board, ground the /RESET line on the CPU chip (pin 40 of U15) momentarily with a test clip. If the board boots up consistently without a problem (correct flashes or "0" in the LED), then the POR section is definately at fault.

CPU did not boot. So my understanding that the POR section is fine. Well i ended up replacing all the components that the guide says anyway.


Next i wanted to check the voltages from the game power supply just to be sure they were in range. they all tested fine. i think i can rule out the game power supply as sometimes the cpu will not boot when on the bench.

I also have tried replacing the 6802 CPU chip at U15 and the ram chip at U25. I checked all six of the 6821 PIA chips and they all test fine.


The only thing i have not replaced is:

Check the 74LS244 chips at U11 and U13.
If either of these two chips is bad, the game will never boot. Check both of these chips using your DMM with the game off. Set your DMM to the "diode" setting, and put the red lead on ground (pin 10). Then put the black lead on pins 1-9 and pins 11-18. You should get a reading between .4 and .6 volts. If you get a short (zero) reading, replace that chip.

i tested each chip and all readings were fine. if these chips are bad or are going bad, will the game still boot sometimes?

this thing is driving me nuts. for example, i just got in from replacing the U25 Ram chip. The board booted on the bench. when i put in the game, i got nothing.
 
its ridiculous how much time that i have spent on this thing.

i think i am going to try this next...

The Blanking Signal.
The blanking circuit is a protection circuit. If the CPU board does not boot properly, it will shut down many functions on the board (including the score display strobes, so the display glass isn't damaged). The blanking circuit must be inactive for the CPU board to boot and function, and is shown by the blanking LED (which should always be on). The blanking circuit is reset by the display strobes. Blanking problems can also be caused by a short in any connecting logic chips.

The blanking signal is the CPU board's flag to the Driver board that the CPU has booted properly. But wait, I know you are saying, "there isn't a driver board, what are you talking about?" Actually there IS a driver board. Step back to Williams' system3 to system7 and remember the CPU and driver board were separate, linked by a 40 pin interconnector. With Williams system9 and system11, Williams combined the CPU and driver board into a single physical board, eliminating the problematic 40 pin interconnector. Hence on System11 logically the CPU and Driver boards are two separate devices, but physically they reside on the same printed circuit board (which increases reliability).

The blanking signal is easily seen on the CPU board by the blanking LED. At power on, blanking is low very momentarily. As the CPU finishes booting, blanking goes high, enabling the driver board and turning the blanking LED on. Often the blanking signal will never go high or will immediately be high right at power-on (no initial blanking low signal). If the blanking signal is always high even at first power-on, this can possibly cause a brief energizing of all the solenoids and the flipper relay. This will usually blow the game's solenoid fuse. Often this is the 555 timer chip at U43 that is bad, the Q50 transistor (2N4403), and/or capacitor C58 (1uF electrolytic).

A way to test the blanking signal is to boot the CPU board with only +5 volts and ground (no +12 volts). This will keep the reset line low, and hence the blanking signal should also be low. If blanking is high there is a problem in the blanking circuit. Check the U23 555 timer chip and Q50 2N4403 transistor - these are the guts to the blanking circuit. The signal itself can be seen at U43 pin 3.

just had the board pulled and noticed that the blanking LED comes on instantly. must have missed that section before.
 
i can't believe System 11 games were this unreliable. So many F-14 posts lately!

22 year old power supply... For me is was just a low +12v... A new cap and transistor 2N6057....

She's back up and running again for me.

-Mike
 
replaced all the components that deal with the blanking circuit. board booted. powered it down and booted again. i repeated this process a few more times. letting it stay on for about 30 secs each time. the last time i tried, the blanking LED shut off after about 10 secs.

i checked all my work and plugged the ATX psu in and tried again. booted fine. checked my work again and it quit booting.

so now i have two things left that i have not replaced. 100mfd cap at C29 and the two 74LS244 chips. i checked these two chips again with my DMM and im only getting .3 volts at pin 1 on both chips. pins 2-9 are between .4 and .6 volts like the guide says. so i assume these chips are bad???
 
update on this...

ended up sending the board to Edward Cheung from rec.games.pinball for repair. he booted it up on his bench and didnt have any problems. never once did it not boot for him. he had for an entire week and did not find any issues. he ended up sending it back and just got it today.

threw it on the bench and it booted. threw it in the game and it booted. only had one issue and that was the left ball save solenoid energized upon power up. played a few games and had zero issues.

according to the pinrepair guide...

The blanking signal is easily seen on the CPU board by the blanking LED. At power on, blanking is low very momentarily. As the CPU finishes booting, blanking goes high, enabling the driver board and turning the blanking LED on. Often the blanking signal will never go high or will immediately be high right at power-on (no initial blanking low signal). If the blanking signal is always high even at first power-on, this can possibly cause a brief energizing of all the solenoids and the flipper relay. This will usually blow the game's solenoid fuse. Often this is the 555 timer chip at U43 that is bad, the Q50 transistor (2N4403), and/or capacitor C58 (1uF electrolytic).

only problem is that i have already replaced all of those components...


guess i have one question to those who might know more about it. when it says "If the blanking signal is always high" can that be seen by looking at the LED or does he mean when using a logic probe?
 
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