Hantarex MTC 9000 Flicker

[Nipedley]

Hey everyone,

My MTC 9000 is displaying very visible flicker (by flicker I mean, as if the refresh rate were really low, and you can see the screen redrawing). It's not enough to make the machine unusable, and in certain lights the flicker becomes unnoticeable, but it is there. This particular chassis has had most of it's components replaced tracking down another issue a few years ago (and only hobby use since then). It does need a new flyback which I'm trying to source, do you think that could be part of the problem?

The motherboard in this machine also needs recapping, I'm not sure if the video source could cause flicker issues?

Thanks for any ideas!

Kind regards,
Phil

[Nipedley]

Hey guys,

So I managed to source a new flyback which I installed this morning. I also replaced a few more capacitors, there's 7 left to be replaced on the chassis that I didnt have lying around so I've just ordered those. The new flyback is fantastic and has solved other small issues I was having, however this flicker/refresh problem is still present.

I've also changed out the motherboard since then, so the video source seems not to have an effect.

Once those last capacitors are replaced I'm stumped as to what to look for next - does anybody have any suggestions? What was interesting, whilst readjusting the monitor with the new flyback, after I touched the contrast control the problem seemed to get a lot worse (though it could also have been because the machine was on longer due to making adjustments).

I've attached a video. The problem is particularly visible on the video at about 10 seconds - you can see the background of the picture seems to be lightening and darkening very quickly.



Thanks for any suggestions!

[grantspain]

check resistors r90 and r110
check pre brightness pot for correct function

[Nipedley]

Hey Grant, thanks for your suggestions.

I had the chassis out today (fruitlessly trying to fix the degauss, coil is hooked up now, new fuse and positor but nothing, I'm thinking the cab wiring must be odd and calling a day on that one!) and checked out the components you mentioned which were all fine.

Interestingly enough I just had a bit of a play and for the first 10 seconds or so, both of the monitors in the cab were acting odd, the top one was 'wobbling' left and right a few pixels quite violently and the main monitor was flickering as I pictured above, and then they both straightened out at the same time, and were looking beautiful for the rest of the time I had it on. Whatever it is causing it must be something central, perhaps AC filter? The mains wiring is all solid as I checked that out a few weeks ago.

I have noticed when the main monitor is flickering the top one does wobble, but it doesn't normally straighten itself out - normally the cab will either start off flickering or start off normal and stay that way until I turn it off.

Thanks for your suggestions

[grantspain]

sega megatech machine?

so both monitor display some odd ball conditions,have you tried a different video source as its either ac mains problem,psu interference or game board related

[mgb]

One simple thing thats always good to do (it should be done anyways) is make sure that your power supply is adjusted to the proper voltage (if adjustable).
I have worked on many machines where the voltage was about 4.7 volts or so at the game board and there would be issues such as video flickers or worse, the board would often reset.

Adjust your power supply so that you have 5.1 volts or so at the actual game board (not reading across the power supply itself). I usually test at the power pins of a chip.
also you may wanna pull and clean the legs on the socketed chips (roms,etc.) alot of grime gets in there and they often benefit from a cleaning. just be careful not to break legs.

[Nipedley]

Thanks for the suggestions guys,

I'll go through the AC wiring again and check out the PSU voltages. I've swapped the gameboard out a few times and that didn't affect this issue, so I know it isn't that. The AC filter is very rusty but I'm not sure how much of an impact that would make, I'll see if I can find a replacement regardless.

It is a megatech yeah, it's come a long way since I started on it

[mgb]

That is a cool cab. I've never actually seen one before.
I wouldn't think that some rust on the ac filter would cause issues but it wouldn't hurt to replace it as they are cheap enough.
If you have swapped game boards out but kept the same psu, it would definitely be beneficial to go through the 5v adjustment.
Also how about the video lines from the gameboard to the monitors. Check and make sure they are good with no frayed or loose wires, etc.
 Any possibility of mice? I've had one service call where a monitor was taken out by a mouse chewing on the wires  I was a little surprised I didn't find a dead mouse.