Screeching noise from Machine - appears to be OK

[Nipedley]

Hey folks. Last ever issue with this machine is this screeching noise, it started seemingly randomly while I was repairing the two chassis last year. I installed the monitor with a chassis and got a screeching noise, assuming it was the flyback so replaced the chassis with my newly repaired one and still get the same noise. Highly doubt both of them have gone - what else could cause it? Sounds sort of like the white noise you get off a tv only high amplified.. And it seems to respond to whatever is on the screen, if its dark its loud if its a white picture not so much  Possibly a flyback issue on both chassis?

It just worries me cause other than that, the machine is 100%. Preventive maintenance

[grantspain]

ay up lad,
more than likely you are bit unlucky and both chassis have a noisy vertical linearity coil,the only other thing i can think of is it could be something to do with the inverter board and how its handling the sync
when it happens if you tap the chassis gently around the lin coil and the problem goes then that will prove it
you could always try swapping your inverter boards from top to bottom
i guess it the top monitor doing this

[Nipedley]

Forgive my inexperience but coils are just about the only thing I haven't had to touch yet Where is the vertical linearity coil on an MTC9000? The plastic adjustable coil? Not sure how I'd go about replacing that.. By inverter board do you mean the sync circuit on the boards? Cause in that case the repaired monitor's sync circuit is 100% new after the last issue..

[ac3]

Hi Nipedley,
Have you tried adjusting the sync pots on the control board?.  Are you using the same control/remote board?. I've noticed on mtc9000's and other monitors before the picture can be in sync but the sync pot is almost out of range and it makes a high pitch noise and changes as the image on screen changes. So give tweaking the h and v sync pots a try.

EDIT:
If that's not it, it could be dirt/dust under the anode cap either on the cap or the tube. You should always apply some silicon greese under the cap before connecting it to the tube, maplin sell it in spy cans.

ac3.

[grantspain]

sorry i meant the bridge coil and h lin coil,in this pic



try tapping them when the problem starts, if your problem goes then replace them or put some glue in them

the inverter board is mounted on the left of the chassis where the rgb first comes in

[Nipedley]

Thanks AC3 I will give that a shot tomorrow. You wouldnt believe the sync issues I had with this board in the past (3 years worth ) so as soon as I got it to stabilise I stopped messing Could well be that.

Hey Grant Ah yes, I shall have a look at those two if the easier option doesnt work out! (And when does it? xD) Having some trouble loading up the full version of that schematic though :S Site doesnt want to work for me

Hmm the inverter board, my mtc9000 chassis is different isnt it.. do you mean the one mounted with a single chassis-mount transistor on it? that's the only one on mine that matches that description, can't remember now what part of the circuit that is to do with I know I replaced it though, in my transistor megathon repair last year that finally did the trick on the sync problem

[grantspain]

was this a playchoice 10 or megatech,i can't remember-if its a megatech forget the invertor board stuff

[ablizno]

Sorry to be of no help  but for some reason the second i read this topic, all i could think of was the movie Alien...

[Nipedley]

Hehe Megatech through and through

Alien, ablizno? I sure hope there isnt an alien in my arcade machine!

I'll check the problem diagnosis stuff out later, college for now

[Nipedley]

Right well I went out again this morning to test out a bit quickly, sadly the easy option didnt work (had no effect on the sound that I could hear, anyway) playing with either V or H sync controls. Strangely enough though, the hissy-screechy sound was pretty much nonexistant. Only a little bit, infrequent short bursts of low volume. Then when I get back from college, its back to the full on noise again Very loud, noticeable and continuous even when game is on full volume. Ai ai ai I was thinking this morning maybe something to do with Temp. but its a lovely day today and very warm and only gotten warmer, so cant think why its changed from this morning to now..

[grantspain]

what happens if you disconnect the video signal?