Reactor pcb, crystal reads low on logic probe

gorf73

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I understand that you should not be able to get a reading with a logic probe on the crystal. I am really at a loss at this point & decided to check it anyway, it is reading low. History of the board is that it was working fine and then it started to do random weird sounds and graphics and the game would freeze. Restarting the game would clear it for a couple of minutes and it just got worse over time. I have been comparing logic probe readings against a working pcb.
The bad pcb will boot up as stated above and a lot of the chips probes similar but not all the same and then the game will freeze up and most pins will be stuck, some still do pulse. When the pcb freezes all the pulses change and I get a voltage drop for a second from 4.85 to about 4.6. I took a chance and replaced the crystal and it did not help. A few of the chips in the clock circuit have been replaced in the past by someone else before it quit working. I do not fully understand how to read all schematics or how to fully understand how all chips work, hence why I compare pcb's. Can someone please help me figure out why the crystal is low. I have determined that the funny sounds are because the adress in is wrong resulting in a bad out. Same issue in a good majority of chips I probe in the ram/ rom area of the pcb. Game had worked fine at this voltage as well and so does the working pcb. All ROMS have been verified good. I have logic probe and can get a hold of a o-scope but neither one of us really know how to use it.
 
I understand that you should not be able to get a reading with a logic probe on the crystal. I am really at a loss at this point & decided to check it anyway, it is reading low. History of the board is that it was working fine and then it started to do random weird sounds and graphics and the game would freeze. Restarting the game would clear it for a couple of minutes and it just got worse over time. I have been comparing logic probe readings against a working pcb.
The bad pcb will boot up as stated above and a lot of the chips probes similar but not all the same and then the game will freeze up and most pins will be stuck, some still do pulse. When the pcb freezes all the pulses change and I get a voltage drop for a second from 4.85 to about 4.6. I took a chance and replaced the crystal and it did not help. A few of the chips in the clock circuit have been replaced in the past by someone else before it quit working. I do not fully understand how to read all schematics or how to fully understand how all chips work, hence why I compare pcb's. Can someone please help me figure out why the crystal is low. I have determined that the funny sounds are because the adress in is wrong resulting in a bad out. Same issue in a good majority of chips I probe in the ram/ rom area of the pcb. Game had worked fine at this voltage as well and so does the working pcb. All ROMS have been verified good. I have logic probe and can get a hold of a o-scope but neither one of us really know how to use it.


Sounds like you have a power supply problem or the connectors on the harness. Anything below 4.7 and you'll probably see weird things happening.

Is it original connectors? If so, check for burnt/tarnished connectors.

Have you rebuilt the power supply?
 
Thanks for the reply. The power supply had been previously rebuilt and no burnt connectors. I originally thought power problem when it first happened. I turned up power with no change so I turned it back down to where it had been working. I do not believe it has anything to do with anything in the cabinet because my working pcb plays just fine in it. It does seem to act like a power issue though.

I also meant to mention in previous post that all the jumpers have been previously soldered on the the solder side as recommended by another post I have read on gottlieb pcb.
 
Does this happen from a cold boot (i.e. always) or just after it's been on?

I would check for cold solder joints, broken/damaged traces.
 
It happens from a cold start. The more I leave it on the quicker it seems to happen. It never works from a cold start, it tries to run with glitches and then will freeze. I have thought of the cold solders. I have looked over the board often, mainly at previous repair work. I will take a little more look at it tonight and report back. Thanks again for your input.
 
It happens from a cold start. The more I leave it on the quicker it seems to happen. It never works from a cold start, it tries to run with glitches and then will freeze. I have thought of the cold solders. I have looked over the board often, mainly at previous repair work. I will take a little more look at it tonight and report back. Thanks again for your input.

So does it work at all or does it always freeze?
 
It does not work at all. It is never playable. When you turn it on, it will try to run for about 10 seconds to 1 minute. During that time it may speak wrong do different graphic glitches or just stay on the play screen but nothing is flashing or going through attract. Every now and then it will start to go through attract. If it does that and you coin up and hit the start button, it will freeze. Other then that, it will do like I said above, try to run for about 10 seconds to 1 minute and then freeze. One of the many times today that I turned it off and on, it did try to reset itself once after freezing but it just came back up with a blue screen.
Also forgot to mention that I have tried swapping all socketed chips from my good pcb into this one and still nothing. There is a trace that I had thought was a little questionable that was previously repaired but it has continuity and it ohms at 1.0. Should I run a jumper wire or if those meter properly then they should be fine? It is a trace the runs one of the data lines.
 
Bumping this up for some more help hopefully.

I just replaced the chip at B3 which is an address latch. It seemed like the output was not what it should have been but I was wrong apparently. Right from the start of this I noticed that any chip being addressed by address lines 12-15 do not work properly. These lines do not even read the same right off of the cpu when compared to the working pcb. Don't the address lines originate from the cpu, why would they be different? I have also replaced b8 (eprom select) at the very beginning of this and the crystal. I believe I am only getting one rom chip select to pulse. Both rams chip selects are doing something but they are opposite of the working pcb. Example, Ram 5 is pulsing high and low,and ram 6 is high pulse but on the working pcb the ram 5 would be a high pulse and ram 6 a high low pulse.
 
Bumping this up again for some help.
Let me start out by saying that some of the time when I probe the board I get different readings based on where the game is when it freezes.

Today I decided to check for a clock signal all around the board to the chips that I understand the signals to go to. In comparing to my working pcb they all checked out except for my CLK signal . It goes into K13 correctly but the other signal going into k13 makes the output wrong and the input on k9 wrong. The other input comes from K12 a ls260. I followed it back quite a bit and was getting wrong signals on all the chips until I got to chip G3 through G5. G5 is correct but G3 and G4 were not. I followed back from there to what I believe is a ram at E2-3. The inputs to the ram seem fine but the data output 20 is stuck high, all other toggling. Next time I turn on the board pin 20 is toggling but 18 is not.

I have been experiencing this all around the board. Address lines don't seem to be working correctly. I get inputs on chips but the outputs will be stuck high. What am I missing? What do I need to be looking at that I am not? I say that about the address lines because everything around the cpu chip is not getting correct signals in such as the ic that controls the speech at A10. Help please
 
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