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  • Lots of questions

    Hey guys. I've just received my pandora's box DX. I plugged it in to one of my cabinets that runs Metal Slug X. I had sound and picture but the screen was flickering. I swapped it over to my lethal enforcers cabinet and it worked fine, even though it was upside down and back to front. No big deal there. I'll put some pics up of my tube and chasis that was flickering. Could it be that its's not 15KHz? Does metal slug X play on a higher resolution monitor which is the reason for the flickering? I'm making a new loom for it to eliminate the wiring as an issue but I don't want to spend to much time with that cabinet if its just never going to work. Hopefully these pictures aren't too average

    There was also an a jamma adapter connected between the loom and pcb that has what seems to be a power lead hanging off it. That lead is just floating in the cabinet doing nothing. I couldn't find any information on it. What does it do?

    And my last question is am I able to physically switch the horizontal and vertical picture on the monitor from an external switch or directly from whatever pcb I have in the cabinet. Some games have it built into them when you boot up but others dont and I have to get into the back of the cabinet to switch the wires around. 1st world problem but I would like to just be able to flick a button on the cabinet if it's not going to blow anything up

    Cheers

  • #2
    dam. Sorry guys. Don't know how I put it in the pinball section. Could I get someone to move it to the arcade section please?

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    • #3
      ..

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      • #4
        Originally posted by Arcadenewb View Post
        dam. Sorry guys. Don't know how I put it in the pinball section. Could I get someone to move it to the arcade section please?
        Done

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        • #5
          You can't switch from vertical to horizontal on a crt you need to physically rotate the screen.
          Metal Slug X is a neogeo game which all use a standard 15k screen.

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          • #6
            There are 4 wires going from the chassis neck board to the chassis. They are a seperate harness and only ever have 4 wires on every brand CRT TV, monitor I have ever seen. Two of these wires at one end of the plug when swapped invert the picture. The other two wires on the other end of the plug when swapped around turn the picture up side down. You can put a switch on these wires, (the two that effect what you want to change), that swap the wires around simply using a switch. Alternatively you can pull the pins out of the connector and mechanically swap the wires around.
            Just to clarfy, you can swap around wire 1 with wire 2 OR wire 3 with wire 4. Don't swap any other combos unless you know what you are doing. It is quite safe to do as they are designed to have this done to suit all applications.
            As for the flickering, maybe the 15Htz is what your problem is but no two board games are exactly the same frequency and you may need to adjust the tube/ chassis to suit the new source. Horizontal hold and vertical hold slight adjustments may be all that is required but sometime more adjustments are necessary. Before making multiple adjustments to the chassis via the pots take a note of how they are set in case all turns turn to shit and you need to restore what you know worked.

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            • #7
              Cheers Cursed for moving the post. Thanks for the replies. I'll finish my loom hopefully today and I'll try the horizontal and vertical hold adjustments. Those wires on the back of the monitor are what I was talking about switching Autosteve. I'll have a better look at a broken cabinet and play with the wiring on that. It sounds like I can use just normally 10amp switch mechs. One for image flip left/right and the other for up/down.

              Just had a look at a crt schematic on line. An intermediate switch mech should work not a standard mech.

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              • #8
                Hi, at the risk of stating the obvious I wouldn't be switching the deflection coils on a monitor while it was running, or locating the switches anywhere where that could inadvertently happen as the output stage would almost certainly fail. At least by having to go around and change the plug the usual precaution of first removing the power should apply.

                Once your Pandoras box is connected and set up you shouldn't need to reverse the screen just to change between games so I'm not sure if I've missed the point of that question anyway?

                If the cabinet is JAMMA wired and running NeoGeo Metal Slug X that adaptor could be to suit MVS wiring which is slightly non-JAMMA, having extra coin and audio connections. The 4 pin lead obviously has power and ground but I couldn't quite see which pin the 4th wire was connected to... In any case the Pandoras box being JAMMA, should connect to a JAMMA loom without needing the adaptor.

                Regards, John
                more from John's Retro Workshop - www.jbtech.linkpc.net

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                • #9
                  The vertical hold fixed the flickering screen. I still need to finish the new loom to get all 6 buttons working. jbtech. The flipping of the image relates to a gun cabinet I'm sorting out. I have multiple games that I switch in and out of 1 cabinet. I have to keep flipping the image to suit.

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                  • #10
                    Originally posted by Arcadenewb View Post
                    Cheers Cursed for moving the post.
                    Funnily enough I think our illustrious leader Arcade King moved it the same time I did as it is in a different sub forum to where I put it.

                    Thanks boss.

                    And you are welcome Arcadenewb

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                    • #11
                      Thanks Arcadenewb, it's a relief to hear you don't need to switch the image 'on the fly' so to speak.

                      Yours may already be like this - it's common practice to divide the four pin deflection connector into two so that either the vertical, horizontal or both sections can be reversed if required. The pin spacing is different for each so they can't be accidentally swapped.

                      Regards, John
                      more from John's Retro Workshop - www.jbtech.linkpc.net

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                      • #12
                        Something I noticed after adjusting the vertical hold. Something on the chassis has become noisy. Its not a buzzing but it definitely wasn't there before. I actually have no idea off what that vertical hold is doing. I know it stopped the picture moving but how. Is it a resistance thing? I'll be looking into that tonight. I noticed there's a Jomac sub section . Maybe I should just ask him how the adjustments actually adjust

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                        • #13
                          Hi, If the picture is unstable - tearing or jittery that irregularity could be behind this new noise, is it possible to swap the old game back in, readjust VHold if required and see if the noise has gone?

                          The vertical hold control itself is a variable resistance, adjusting it changes the free running frequency of the vertical oscillator which needs to be close enough for the vertical sync pulse, arriving from the sync separator to trigger vertical flyback. If the vertical frequency is too far off the oscillator will free run causing the picture to 'roll'.

                          There should be a small range of adjustment where the picture does synchronise and within that range the most 'stable' picture obtained.

                          Regards, John

                          more from John's Retro Workshop - www.jbtech.linkpc.net

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                          • #14
                            Originally posted by jbtech View Post
                            Hi, If the picture is unstable - tearing or jittery that irregularity could be behind this new noise, is it possible to swap the old game back in, readjust VHold if required and see if the noise has gone?

                            The vertical hold control itself is a variable resistance, adjusting it changes the free running frequency of the vertical oscillator which needs to be close enough for the vertical sync pulse, arriving from the sync separator to trigger vertical flyback. If the vertical frequency is too far off the oscillator will free run causing the picture to 'roll'.

                            There should be a small range of adjustment where the picture does synchronise and within that range the most 'stable' picture obtained.

                            Regards, John
                            So I had to google the terms you used. So the monitor has a vertical and horizontal scan. The sync signal separator is a chip that measures this scanning/pulsing??? Is that sort of right? The high pitch noise apparently is made from the flyback transformer and apparently is common in crt monitors but what I've read is that its supposed to control the horizontal movement not the vertical so I don't know why adjusting the vertical hold would affect that. I should've worked in electronics repairs for a couple of years. I'm out of my depth for the moment

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                            • #15
                              Hi, you've made a couple of good points there, I'll try to answer your new questions here.

                              Firstly, I was only answering your original question about what the vertical hold does - not implying that was the source of your new 'noise'

                              Yes, the monitor scans horizontally at about 15kHz which, when running smoothly can usually be heard as a low volume, steady high pitched whine.

                              It also scans vertically at about 60Hz, this low frequency 'hum' sound is usually not, or barely, noticeable audibly.

                              The result of the two simultaneous scans is a 'raster' - a beam which quickly traverses across the face of the tube from left to right, skips back then repeats its left to right motion. As it does this it gradually progresses downward from top to bottom. Once it reaches the bottom of scan it 'flys back' or retraces to the top again and the whole cycle continues.

                              During Horizontal and vertical retrace or flyback the beam is blanked so only the forward (left to right) and downward portions of the scan show up as an image (or background raster if there is no video to display). The flyback part is much faster than the active part of scan and this is the 'blanking' part of the video waveform.

                              The sync pulses are there to cause the monitor to 'scan' in sync with the video image being sent otherwise the image elements will not appear at the correct point on the tube and the picture will appear to drift or roll, vertically or horizontally or both. If the monitor is not synced at all and free running the image could just resemble diagonal lines running across the screen.

                              The arcade monitor uses a separate sync signal which is not combined with the picture information but in most cases (such as this one) it is composite sync - containing the horizontal and vertical sync signals on a single wire. The sync separator previously mentioned simply divides these and sends them to the horizontal and vertical oscillators respectively.

                              Arcade PCBs don't generate a broadcast quality image with exact timing signals but are close enough to be displayed on a monitor, with some adjustment if required. Because of this, changing from one game to another often requires some readjustment.

                              So, upon connecting your new PCB your initial and most obvious problem was a lack of sync, resulting in the image running one way or another or rolling vertically, possibly quite fast and just appearing as flashing or diagonal lines.

                              Adjusting the Vertical hold got the monitor running in sync but now you have noticed a new noise which apparently was not present with your previous game PCB.

                              As you correctly mentioned if there is an audible noise coming from the monitor it is more often than not coming from the horizontal flyback transformer which not only creates the horizontal deflection signal but also the high voltage output which goes to the CRT Anode.

                              Given the noise was not there before we can exclude other faults for the moment so perhaps the horizontal oscillator is syncing - but only just - and a bit of irregularity in the horizontal frequency is what you can hear. Have you tried adjusting the horizontal hold yet?

                              You should be able to turn it either way till the picture loses sync (diagonal lines) then back and find a mid point where the picture is stable, listening to your 'noise' and see if it quietens down.

                              If that does the trick, great! If you still think it's a bit noisy I'd suggest again - go back to the previous game PCB temporarily and see if the noise goes away.

                              If the monitor ever becomes constantly, excessively noisy or the picture quality is generally poor it may need servicing, but before removing any monitor chassis from a machine or ever disconnecting the High Voltage (EHT) from the tube (CRT) make sure you learn the correct procedure for safely discharging the CRT. You should find some Youtube videos which demonstrate this very important precaution.

                              Hoping this helps or at least answers some questions.

                              Regards, John.
                              more from John's Retro Workshop - www.jbtech.linkpc.net

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