Point Blank gun issues
- Thread starter Player
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SUPERSPRINT
Active member
What are your voltages at the gun position pcb?
SUPERSPRINT said:
Erm not sure where that is. The plug that goes to the gun there is 5v. It was slightly under so I turned it up a notch. Are you talking about the pcb (I assume) in the gun?? From what I can see the gun wiring goes straight to board. Could this board you mention be in the tin box with the main board?
Cheers
John
Player2020-07-04 08:19:22
Bump 
Looking at the manual the position PCB what the guns are connected to. Can anyone tell me how the sensor works as in what should be going to the gun? I put a logic probe on TRG1 and 2 and it just said high. I thought maybe there would be a pulse, I really have no idea as guessing.
If I can't sort i'll have to sell it for scrap and that will cause me great sadness
Looking at the manual the position PCB what the guns are connected to. Can anyone tell me how the sensor works as in what should be going to the gun? I put a logic probe on TRG1 and 2 and it just said high. I thought maybe there would be a pulse, I really have no idea as guessing.
If I can't sort i'll have to sell it for scrap and that will cause me great sadness
Namco guns work by cathode ray timing, so the guns are wired up to a Position PCB inside the cage which does all the fancy bits with working out where you shot.
When you pull the trigger the screen flashes white and the gun sensor sends a signal to the position PCB when the phosphor its looking at lights up. The position pcb times how long this takes from the start of a frame using the composite sync signal, it can then work out where on the screen you're pointing since it knows how far the scanning electron beam would have travelled in that time.
If your guns not tracking it's either a problem with:
- The gun sensor not being able to clearly see the phosphor (low brightness, something obstructing the view, dirty sensor).
- The position pcb not being able to read the gun sensor.
- The position pcb not getting a good csync signal
- The position pcb not being able to talk to the game pcb.
A dodgy csync seems fairly likely to me if changing the brightness doesn't help. Get the scope out and check that the csync input pin on the position pcb is getting a good signal. You can see where that is on the diagram in this manual. https://www.gamesdatabase.org/Media/SYSTEM/Arcade//Manual/formated/Point_Blank_-_1994_-_Namco.pdf
When you pull the trigger the screen flashes white and the gun sensor sends a signal to the position PCB when the phosphor its looking at lights up. The position pcb times how long this takes from the start of a frame using the composite sync signal, it can then work out where on the screen you're pointing since it knows how far the scanning electron beam would have travelled in that time.
If your guns not tracking it's either a problem with:
- The gun sensor not being able to clearly see the phosphor (low brightness, something obstructing the view, dirty sensor).
- The position pcb not being able to read the gun sensor.
- The position pcb not getting a good csync signal
- The position pcb not being able to talk to the game pcb.
A dodgy csync seems fairly likely to me if changing the brightness doesn't help. Get the scope out and check that the csync input pin on the position pcb is getting a good signal. You can see where that is on the diagram in this manual. https://www.gamesdatabase.org/Media/SYSTEM/Arcade//Manual/formated/Point_Blank_-_1994_-_Namco.pdf
Hi all.
So I have an update for this issue. So Gunblade kindly took the chassis back that he originally repaired and fitted a different type fly back, a shot in the dark but it worked fine before the monitor went down and the repair was replacing the fly back.
So re fitted and same issue, re checked everything i checked before and nothing seemed to be wrong.
So I decided to take the guns apart. I rubbed the photodiode with my finger (machine in test) and I got a reading on the test screen. The dot was moving. Tried the second gun and not working, did the same with that and working.
What are the chances of that? So both guns do work but not like they should, the screen only pics up so far until you get to certain points.
I did some reading and it seems that screen burn can efffect it, mine does have screen burn. I also think the photodiodes are shot. They made a PCB that was amplified version which replaced my PCB because of issues but they're £50 each. I would buy them if i knew they would fix the issues, i'm thinking my tube is probably about shot too.
Going to buy some photodiode and replace whats on there as surely won't hurt.
Thanks for all the replies and a special thanks to Gunblade for services above and beyond!
Cheers
John
So I have an update for this issue. So Gunblade kindly took the chassis back that he originally repaired and fitted a different type fly back, a shot in the dark but it worked fine before the monitor went down and the repair was replacing the fly back.
So re fitted and same issue, re checked everything i checked before and nothing seemed to be wrong.
So I decided to take the guns apart. I rubbed the photodiode with my finger (machine in test) and I got a reading on the test screen. The dot was moving. Tried the second gun and not working, did the same with that and working.
What are the chances of that? So both guns do work but not like they should, the screen only pics up so far until you get to certain points.
I did some reading and it seems that screen burn can efffect it, mine does have screen burn. I also think the photodiodes are shot. They made a PCB that was amplified version which replaced my PCB because of issues but they're £50 each. I would buy them if i knew they would fix the issues, i'm thinking my tube is probably about shot too
.Going to buy some photodiode and replace whats on there as surely won't hurt.
Thanks for all the replies and a special thanks to Gunblade for services above and beyond!
Cheers
John
Bit late to be useful but I can't see any way this will be the lopt, nor will it be the screen if you can see the game playing and it doesn't look obviously way too dark.
This is 99.9% sure going to be something in either the mechanics of the gun (lens, opto position/angle) or in the gun interface h/w.
I would be either scoping out the signal back from the gun sensor PCB, or sticking a logic probe on it. Check you get a pulse on the wire leading from the sensor PCB back into the gun-cab cable when the trigger is pulled. If you do, find the other end of this wire where it hits the PCB filter board. If still good, work backwards to the PCB trace it's fed on.
This is 99.9% sure going to be something in either the mechanics of the gun (lens, opto position/angle) or in the gun interface h/w.
I would be either scoping out the signal back from the gun sensor PCB, or sticking a logic probe on it. Check you get a pulse on the wire leading from the sensor PCB back into the gun-cab cable when the trigger is pulled. If you do, find the other end of this wire where it hits the PCB filter board. If still good, work backwards to the PCB trace it's fed on.
In this diagram, you want to be measuring pin 2 or 3 of the gun assy (bottom right of pic). One will probably be constant 5V, one will flip either to 5V or GND when the trigger is pulled. Don't accidentally measure the trigger pin though. That is probably one half of the power to the photodiode.
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https://webcache.googleusercontent.com/search?q=cache:UZrhaPqJ5CwJ:https://forum.arcadeotaku.com/viewtopic.php%3Ft%3D38568+&cd=11&hl=en&ct=clnk&gl=uk
moomootown
Monkeyballer
Just thought I’d add to this - I had the exact same issue tonight - guns firing but not showing on the screen. The solution was simply the contrast and brightness - has to make them higher. At one level I got intermittent working, a tiny bit higher contrast and boom - all was good. Then I did a darker stage during play testing and they wouldn’t hit one of the corners - contrast up a touch more and now all is fine.
Always worth checking
Always worth checking