Arcade Monitor Interference

[CHRIS-F]

Hi Everyone,

After replacing a few caps on my City connection PCB, I made an adapter to plug it into my jamma cabinet, there was wavey lines all over the place, I then realised that there was no video GND on the pcb, so after checking the pinout for both City connection and Jamma I put a jumper wire from gnd on my adapter to the jamma video gnd, it worked but there was some interference diagonal lines, then I wired up my coin mech and credit board and the interference was gone, but it's been replaced by a different type of interference, this time its diagonal lines rolling at about a 45 degree angle first up the screen and then back down again, alternating.

Anyone know what could be causing this interference and how can I remedy it? I put a few videos up of it on youtube see links below. The third video is the interference I have now and it's not really clear because of the youtube quality but it's more noticeable than that on my monitor it's bloody annoying.

1. Before adding video GND

2. Interference after grounding.

3. Different interference after installing coin mech/credit board.

Chris.

[CHRIS-F]

Here's a couple of snapshots the first one is without the grounding, second snap show the interference after grounding, I just remembered also I had a similar interference a few weeks back when I was running mame emulator on an arcade vga card and j-pac.

[lilshawn]

youv'e knocke most of it off, so that's good. but, you might have some noise getting in to the PCB from the power supply. check your 5 volt line (at the PCB) and see where it's at...compare it to the voltage at the power supply itself. more than a .2 volt drop should be cause for concern in the wiring.) your PCB voltage for your 5 volt should be about 5.1 volts.

also measure the ripple in the power supply. set your meter to AC and measure the 5 volt rail. it should have less than 2.5 millivolts AC (DC ripple) if it's higher than that, your filter caps in your power supply are going and should be changed.

also make sure your JAMMA card edge on the PCB is clean. you can hit it with a pink rubber eraser and clean them up.

[CHRIS-F]

Thanks Shawn,

I checked the psu the other day it was about 5.27v so I turned it down to 5.0v exactly, I didn't know that it was supposed to be a little higher, I thought the TTL logic chips would be more happy with 5.0v, I will check for ripple later and check the power at the pcb, I didn't know about ripple etc, also is it normal for the psu to deviate a little? when I adjusted it it was mostly 5.0v exactly but alters slightly to 5.1v and back again every so often.

[lilshawn]

it's going to vary a little with operation. i would go a little high to 5.1...but watch it as it runs to make sure it doesn't drop lower than 5.0. if it does bump it up to 5.2. you want the lowest it will ever go to to be 5.0.

you also want to check it at the board. you are going to have some loss in the line. there should be a 5v test pad someplace to check it on.

[CHRIS-F]

I Checked the psu again last night, I turned it up a bit to 5.1v. I am only getting 4.71v at the pcb. Is a drop of 0.39v acceptable? I also set my meter to the AC 200v Range, and measured the 5v rail, it measures 10.3v. How can the ripple voltage be higher than the DC Voltage? Does it sound like the psu could be causing the interference? and does it need replacing, or the caps doing in it?

I have another problem now too, my Joysticks and buttons weren't working I checked the wiring and the GND wires on either end of the jamma connector weren't connected together, so I linked them all up to GND and now I have the coin mech working, joystick and buttons working but the interference is worse than ever, and now the graphics are glitching too with whole sections of the background disappearing, could that be because I have lowered the voltage and the board is struggling or is it likely to be an eprom problem or dirty contact or something else? I put two more videos up on youtube showing the interference and the glitching.

1. Glitching
2. Interference

Update..... I still have the interference but the glitching has stopped since I turned the power back up, I replaced all the electrolytic caps in the sound section and the 12v &5v filter caps near the edge connector (Thought it might fix the crappy sound but it didn't, it may just be a crappy speaker) Anyway after doing the caps I adjusted the 5v rail so it was about 5.08v at the board and since then the glitching has stopped.

[lilshawn]

absolutely. I would say the filter caps on the output of the power supply are done and that's where the noise is coming from.

it's fairly easy to take apart the power supply box and swap them out. Basically you want to replace all the caps near the outputs. (1 on each rail maybe 2 on some rails)

the supply still works, so you are already ahead of the game. if the supply was flaking out...or not starting up, i'd say replace it, but it seems good enough to just change the caps in it.

get that power supply sending out clean power first, then troubleshoot anything else.

[CHRIS-F]

Ah! I Finally got a chance to take my PSU off and open it up, it's a Powermaster XII. I can see 4 Caps near the output 3 similar and a smaller one, which ones should I replace? Is it good practice to change all caps like the big one near the transformer (see pictures) and C24 & C13 or just the ones near the output? Do I need to be concerned with ESR or just match capacitance, voltage and temperature. I usually find that equivalent caps nowadays are much smaller, is this ok too? I assume things get smaller as technology gets better.

Thanks again,
Chris.

[lilshawn]

Sorry bout the delay. Been out of town for the week. Don't worry about the big cap. As long as its top isn't bubbled out its likely fine. The other 4... Replace them. Same uF, same or higher voltage. Try to go with 105c temp caps. They will last a bit longer. Do them one at a time. Be sure to observe which side is positive/negative before you take it out... And replace it the same way around.

EDIT:

also, check the terminal strip where it attaches to the circuit board. they are notorious for breaking the solder and getting sketch connections there.

[CHRIS-F]

Thanks Shawn, appreciate the help, I have the psu off ready just been up the wall with the kids, hopefully i'll get a min to do it this week, would you bother replacing the other little electrolytic caps while I've got it open? can't hurt can it?

[lilshawn]

it can't hurt to do the little ones. but, they don't get as stressed as the bigger value ones do (470 1000 2200 etc). I usually don't bother with them...but if you have them, go ahead. it can only get better.

[MK3FAN]

To correctly measure the power supply's output, you need to be measuring at the chips on the board and not at the PS itself. When measuring at the PS itself, you're not getting a correct reading due to the draw on the PS from the PCB. Here is an example of how to measure voltage properly...



Something else to consider, I've seen bad/going bad isolation transfomer cause this kind of interference as well. If you are using one, I'd consider replacing it.

[CHRIS-F]

Thanks mk3fan, I will be sure to test the voltages at the chips on the board when I put the new caps in the psu, what is the optimal voltage? I think Shawn or Ed said it should be a bit over 5v?

About the isolation transformer, how do they go bad? can they be tested maybe their resistance? I assumed they could either work or not work didn't realise they could introduce interference, how would that happen a short in the windings maybe?

[lilshawn]

yes the voltage should be good right at 5.10 volts. you want to watch it for a bit to make sure it certainly doesn't dip below 5.00 volts.

i have at least 100 machines out there in the wild and have only had issues with an audible hum coming from the isolation transformer...and once where one got shorted because it got flooded and filled with water. I've never had one go "bad" on it's own. perhaps mk had some abused cabs. 

i'm saying Yes, definitely, the redonkulous amount of AC passing from the power supply is the cause here.

if there was an issue with the isolation transformer, the monitor power regulator system would have blown itself up. It does NOT like line voltage one bit.

[MK3FAN]

if there was an issue with the isolation transformer, the monitor power regulator system would have blown itself up. It does NOT like line voltage one bit.

This depends on which chassis the machine has. K7000? Yes. K7400? No.

[CHRIS-F]

The Chassis seems to be a Hantarex MTC 9000 although my model differs ever so slightly from the schematics. the guys at swallow amusements identified it as a MTC 9000, but someone at the real Bob Roberts site says it looks like a modified 9000, looks to me mostly 9000 but maybe a revision.

I'm going to do the caps in the psu this weekend see what happens :-)

[CHRIS-F]

Hi Shawn,

I haven't had a minute to myself lately, kids Eh!

I opened up the psu the caps near the output terminals are as follows.

T.M. 1000MFD 16WV
T.M. 2200MFD 6.3WV
T.M. 2200MFD 6.3WV
T.M. 470 MFD 10WV

I googled T.M. and according to the jpcon website the T.M. series is a Very low impedance and low ESR, suitable for switching Power supplys and motherboards, I assume WV means working voltage, but when I searched through mouser and digikey there are too many options :-( I would like to replace the caps with original specs or better, should I be concerned with esr etc? Is it that important or would any old ebay cap do? just wanted to check before I go putting rubbish in.

Thanks again,
Chris.

[CHRIS-F]

Shawn, Ed, Anyone? do I need to be concerned about ESR etc with the above psu caps, I want to do them asap but don't want to just put any old caps in off ebay etc if it's not going to fix the problem, how do I know what esr/hi frequency caps to get? or shouldn't I be too worried about it just good quality caps? the old caps just say t.m. series.

Regards,
Chris.

[ed12]

this is easy
as u answered your own question
when u order caps
u spec high heat/low esr
they cost a tad more,but once in u never have to look back

ed

[CHRIS-F]

Ed, I googled low esr capacitors, but now I'm even more confused what is all this ripple current? I also looked on mouser but there are around 6 different caps with different ripple current etc, do I need to be concerned or will any low esr caps do? such as the following

http://www.ebay.co.uk/itm/Panasonic-1000uF-16V-105-degrees-low-ESR-electrolytic-capacitors-5-pack-/280765602279?pt=UK_BOI_Electrical_Components_Supplies_ET&hash=item415eef19e7

Also I noticed one of the caps in my psu is different, if you look at the second psu picture down in this post the second cap along is a different colour, different size and different temperature, do you think someone has done a dodgey repair in the past? the other 3 caps are rated at 105oC the small one is only 85oC and it's also rated at 10v does that make sense? I assume the 6.3 volts are to smooth the 5v rail and the 16v for the 12v rail what is the purpose of the 10v cap?

Thanks again,
Chris.

[lilshawn]

It's common to double the working voltage. 5 volt
 rail...10 volt cap (or16) 12. Volt rail...to 25 (or32)

[CHRIS-F]

Hi Guys, I finally got a chance to replace the caps in my power supply, but it hasn't made any difference the interference is still there, (diagonal lines alternating every few seconds back and forth, they slow down then roll the opposite way ), I also now have a second problem my psu is making a humming noise like earth hum, ( I don't remember it doing that before, but it has been a few months since I last had it working) if I hold the psu case I can feel a small vibration and the noise stops but as soon as I let go again the hum comes back.

Is the PSU Knackered? would I be better off trying to find a new replacement or is it something I can rectify? Also could the interference be down to something else? to be honest, when I first got the cabinet like an idiot I twisted all the knobs, Vhold, Phase, hhold, vfreq etc. how would I go about correctly setting these back to normal?

Thanks in advance guys,
Regards,
Chris.

[CHRIS-F]

  Where has everyone gone.

Changing the caps in the PSU hasn't cured the interference and now I have a noisy PSU that seems to be vibrating causing the PSU case to make a buzzing/humming noise any suggestions? have I done something wrong?

[lilshawn]

sounds like something has now gone haywire in the switchmode transformer. i'd go ahead and just swap it with a new one now. nothing you've done wrong, just how things go sometimes.

[CHRIS-F]

Thanks Shawn, are there any bad makes to avoid or any will any ebay item such as the one below do the job?

http://www.ebay.co.uk/itm/BLACK-JAMMA-POWER-SUPPLY-FOR-ARCADE-MACHINES-CE-APPROVED-EMI-FILTER-/271258016760?pt=UK_Video_Games_Coin_Operated_MJ&hash=item3f283cdbf8

Thanks again.

[lilshawn]

you are going to want to look at your original specs on the power supply and meet or exceed the ratings when replacing supplies...

the original was 5v 12a and 12v 2a

the replacement you linked is 5v 15a and 12v 4a. you should be good to go with those specs. 

[CHRIS-F]

I've been real busy lately, haven't had any time to mess with my machine, but I just want to say thanks for the advice guys, especially Shawn and Ed :-) I can't wait to get the psu sorted. Fixing my machine is becoming just as much fun as playing on it for me Lol. So far with the help of you guys on the forum I've fixed my dads record player, his jukebox and done quite a few repairs on my machine Thanks Guys.

Chris.