Ms9 vertical hold

[copados33]

While I finish to troubleshoot the other chassis I installed one of my spares for the meeting I will be hosting this weekend, installed the spare one no problem but it seems it has a vertical hold problem, I don't see any v.hold pot on these MS9 chassis, is there a way to tweak this?

Assuming there is no manual adjustment on this model, what could be causing this v-sync issue? low 15khz B+ voltage?? I have tried this same chassis on different tubes with similar results.

[copados33]

Tonight I tried to give this another go, I have been told that it might be voltage problem, what I have found so far is that if I turn the B+ counter clockwise the picture stays stable, but borders get all scrambled, I put it again on the previous position and picture starts to roll vertically again.

I don't know exactly how to measure B+, been told that I can put the + probe of the mulktimeter set to AC on one leg of the R967 ceramic resistor (the big white ones), I did that and I get a read of 130v when it should be 75-76v

I have also found that when I did the cap kit I forgot to swap one cap from the p.supply area marked C955 180uf 25v cap, swapped it for a 180uf 100v one, I will test it tomorrow and see if that does something....

[copados33]

Well, I got an stable picture now which looks like this:

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[copados33]

Ok, i have meassured B+ and adjusted it to 75.1 so I guess that should be fine, picture borders are straight now, although that didn't fix the screen from rolling, I have checked caps on vertical section and all seems to be fine, I've read here that LA7853 could be the culprit, I will try to change that and will post results here.

[grantspain]

Ok, i have meassured B+ and adjusted it to 75.1 so I guess that should be fine, although that didn't fix the screen from rolling, I have checked caps on vertical section and all seems to be fine, I've read here that LA7853 could be the culprit, I will try to change that and will post results here.

yep

[copados33]

yep

The IC finally arrived from China, installed it and this is fixed!!.

[copados33]

Celebrated too soon, it broke again, sh1t

[copados33]

Does anyone know if LA7853 may break because of high B+ voltage?? I meassured it again and it was 76,3v

[grantspain]

no but it will if its a fake part or you did not replace all the caps around it or clean off any cap leakage if it occured

[copados33]

I have heard about these fake LA7853's, but how do I know if this is one of them? besides, if its a fake... shouldn't had to fail as soon as I turned the monitor on?

[presidentsenpai]

Well, I got an stable picture now which looks like this:

DisplayCollapse view

Super scrub question, but how do you get this test screen to appear? I have a NAC with an MS9 and I was an idiot and messed with all the pots trying to fix a sync issue with my JPAC connection not knowing what I was doing. I need an visual aid to re calibrate the monitor in 15khz.

[thegreathopper]

Neo Geo MVS or Capcom CPS2 have some good test screens, run one of those games, press your test button and select hardware test and you should get a Grid like your pic.

[copados33]

If someone is still interested since this is an old post,the rolling screen problem is now fixed by replacing the small SMD ceramic filter capacitor that is located on the solder side of the pcb under LA7853 can't remember its number, it is possible to replace it with a through-hole cap and put it on the components side since the pcb allows the 2 options.