What is this Interference/noise on screen

[CHRIS-F]

Hi Guys,

Any ideas where to begin with getting rid of this interference/noise or whatever it is on screen, I have asked about this problem before a few years back and I never got to the bottom of it a few members advised me to re cap the psu as a start.  I did that with low esr caps and it didn't make any difference. I gave up on repairing it, didn't really have the time, but now my kids are taking an interest in the machine and the bug has hit me again, I'd really like to get it running properly more than ever, I only have one pcb to play at the mo, but ordered another and will probably will get others once its running.

The interference or ( lines or what ever they are ) roll across the screen then they slow down and roll back the opposite direction, they are not always at a 45 degree angle either, they become almost vertical sometimes.

I intend on replacing the psu and jamma loom, but where do I go from there?

Thanks Guys :-)
Chris.

[grantspain]

put a wire link from common to earth on the power supply

[CHRIS-F]

put a wire link from common to earth on the power supply

Is it safe to wire the logic ground to earth ground? someone mentioned this to me a few years back and others have said definitely do not do it.

What are the reason for the warnings not to do it and what is the cause of the interference in the first place? why does connecting the two grounds fix the problem?

Sorry I don't mean to sound like I'm not taking the advice of experts, I'd just like to know what's causing the issue, if it's safe to connect the two, what are the implications of doing so and does it make the cabinet dangerous in any way?

Regards,
Chris.

[grantspain]

perfectly safe, been doing it since 1986 when the first switch modes started to be common cab supplies- my test rig has this mod to prevent the same issue
not 100% sure why some supplies need this and some don't, perhaps something to do with noise on the earth in the supply or maybe the way some cabs are wired

[CHRIS-F]

perfectly safe, been doing it since 1986 when the first switch modes started to be common cab supplies- my test rig has this mod to prevent the same issue

Thanks, I tried a link across the FG and GND and it seemed to work fine, at first the image was rock steady no interference at all, but after a few minutes as my son was play testing he told me the graphics kept glitching, when I took a look it looks like a similar problem I've seen before when the psu was not giving enough power, any idea why adding the link could cause this new problem?

Regards,
Chris.

[behrmr]

Looks like your power supply is a problem.  It may or may not be related.

Try removing FG from the monitor vs linking it to logic ground. 

Check any fuses in the cabinet for bad connection or weak holders.

[grantspain]

just read the +5 at the jamma connector, around 5.05-5.10 will be fine
the link will not cause any issues, you may have some bad connection onto the supply which would maybe explain the issue appearing

[CHRIS-F]

just read the +5 at the jamma connector, around 5.05-5.10 will be fine
the link will not cause any issues, you may have some bad connection onto the supply which would maybe explain the issue appearing

Thanks, I never thought to check the voltage again, but looking at the response from Behrmr above made me wonder something, I don't think my monitor has a ground, someone else posted an image from Bob Roberts site the other day and that shows Earth ground connected to the psu/isolation transformer/power block/switch and monitor, but as I'm in the UK we have a fuse in every plug, so my cable comes via a fused plug straight into the psu which has a Ground/Live/Neutral the wires then continue on to the isolation transformer which also has Ground/Live Neutral, but the output has just 240AC for the Degausing circuit and I think just two cables for the monitor about 120V AC if I remember rightly, I have my coin door/credit board etc connected to Earth ground, but I don't think there is a ground to the monitor frame, could this be the problem, since I connected the jumper wire I have continuity between the coin door/monitor frame/ Earth GND etc but I never thought to test if the monitor frame was connected to Earth Ground before adding the link. should a Hantarex MTC 9000 have a connection to Earth Ground to begin with?

[grantspain]

we never earthed monitor frames until new regs came in the early 90's, certainly not on woody cabs. I think you should try linking the earth to the frame though as it takes a few mins to do
i do not see how that psu link could cause any issues unless your psu itself is on the blink, its a tried and tested mod that has been done on switch modes since mid 80's and in general always cleared this interference issue

[CHRIS-F]

we never earthed monitor frames until new regs came in the early 90's, certainly not on woody cabs. I think you should try linking the earth to the frame though as it takes a few mins to do
i do not see how that psu link could cause any issues unless your psu itself is on the blink, its a tried and tested mod that has been done on switch modes since mid 80's and in general always cleared this interference issue

Little Update,

I tried a connection from the monitor frame to FG on the psu and I think the interference was actually worse, I noticed the voltage was a bit different at the pcb with that at the psu so I took the monitor ground back off, re installed the jump wire fro FG to GND and adjusted the voltage slightly holding the black lead on GND at the psu and testing the voltage at both the pcb and one of the 74LS174 chips vcc. what is an ideal voltage at the pcb/logic chips? I think it's was around 5.08V its a little higher at the psu around 5.2V from memory I was tired last night when I tried it, forgot to write the value down,but the good thing is the interference has gone.

Now since adjusting the voltage slightly it appears to be fine, the glitching has stopped, but after about 5 mins of playing the screen will glitch again briefly, what could be causing this issue? do I need to up the voltage slightly, not sure it's a good idea as the 12V rises too what is a safe limit for the 12V?

Could it have anything to do with the Green Mylar caps on the game board, I am only just beginning to learn electronics so not sure of the terminology are they decoupling caps, what is their purpose? they are marked as .0015k50, I did buy some a while back to replace them but have misplaced them, what would be a suitable replacement ceramic maybe? what value are they?

Thanks again for your help,
Much appreciated :-)

[grantspain]

do you not have another game board?

[CHRIS-F]

do you not have another game board?

Not Yet, but I have ordered a super pang bootleg (JAMMA) board from Italy should be here soon, it's advertised as 100% working.

what is the optimal voltage to have at the board? is it 5.0V exactly or is a little higher better? I'd like to make sure I have a decent voltage before trying the new board.

Regards,
Chris.

[grantspain]

depends on if its a boot board tbh, most boots need a bit extra on +5 as they usually have more connectors and ic's than the originals. don't exceed 5.5v at the jamma

[CHRIS-F]

do you not have another game board?

Update: Thanks for the info, my new pcb arrived Super Pang Bootleg and it works fine, the colours are much better than on the city connection pcb, my monitor has never looked so good :-) I was reluctant a few years back when someone suggested linking the FG and GND as someone else said "Never Ever Do THat!" but the way I figure if the monitor was connected to FG as it's supposed to be the FG and GND would be connected anyway.

Anyway thanks for the advice on that, I'm really happy that I have no interference now, One question though if I was to disconnect the arcade psu and install a pc with my j-pac and arcade vga would the interference return as the Isolation transformer would be powering the monitor and a separate pc psu powering the pc with no arcade psu?

Thanks,
Chris.