Koretek KT2914F - Vertical zoom, picture way off screen

[srarcade]

KT2914F has an issue with vertical zoomed in extending far beyond the edges of the top and bottom of the screen. Scan lines are very thick, like 4x the size they should be. Last time I powered it up was about a year ago and it was fine so not sure what happened in storage. Horizontal seems to be ok. OSD is barley legible, i was able to reduce the V-Size to lowest setting to read it from there. Would this be IC201 cap area? Thought I would check before I cap the entire chassis, it looks fairly fresh.

[grantspain]

it may need a factory reset in osd,hold the "up" key on and then power on the monitor-this will take you into factory menu

[srarcade]

Thanks, thats a neat trick. I was able to tune some things but the zoom setting is too high and not changeable. It was first at 168 then suddenly 254 after I went back tweaking some other things. I could go up  but never down. See  pic: https://drive.google.com/file/d/0B70EAdThm-yqMVFuQk55bVZGbzA/view?usp=sharing It says the monitor is running in 15k mode however.

[srarcade]

After digging, I realized something I was suspecting the whole time- there are different versions of the KT2914 that have different yokes (undocumented). Last year i had two of these monitors which I assumed the same (they both pulled from same unit), one with a solid A+ 10/10 tube so I kept that tube only and trashed the other one. I swapped chassis because the other had a minor problem. I don't believe I ever powered up this K2914F on the current tube until yesterday.

The manual does not specify yoke tolerances but this is what I have:
H: 1.2
V: 8.0
DSM-2912AL
CDY-F2914D
0D28J

Tube:
Samsung A68KVE74X02

Edit: I could not find the other chassis but I had left my notes on the tube, it said K2914F also so it was probably the same chassis yet uses an entirely different yoke winding.. I'm reading another post stating their yoke at H: 0.5 and V: 3.2. Looks like I'm up the creek until I find the correct yoke, not even sure if it will be compatible with the tube..

[grantspain]

the 2914f i have worked on all have 0.300mh horizontal inductance rating,the deflection yokes are very similar to nanao ms9-29,samwa pm1745,neotec 2725

you may have a fault on the vertical deflection circuit,it's extremely common on these chassis-loads of caps and resistors aroung the tda8172 ic crap out,tda fails as well
other common fault on these chassis is flyback but that normally manifests as a very large picture-almost like it should be a 40" screen

if you are running 31khz but the chassis  osd is showing 15khz then you may have either a corrupt ram ic or one of the mosfets is failing in the switching circuits

[srarcade]

What you describe is much like what I have going on with the large image. I'll have to test stuff around the TDA8172. I am running a PCB in 15k and its correctly detecting it so I know the mode is correct at least. I'm at a loss why my yoke is giving me a high reading. It has a small crack at the top, I've pulled it off to repair it and maybe check the windings. Who knows, maybe that will be the trick..

[grantspain]

1.2ohms horizontal and 8ohms vertical sounds good to me

when yokes go bad they either display the most strange compressed image(across which axis is faulty) or they short out the corresponding deflection circuit

[grantspain]

what is happening with your vertical size setting,is it set zero?

[srarcade]

Yea, V Size is set to 0 in the pic above. H Size seems to stretch fine but gets a little unstable as it reaches the edges.

[grantspain]

what is the b+ running at

[srarcade]

What is the best test point for B+ on this chassis? I don't see a TP and the manual doesn't specify.

Reassembled everything again, yoke checked out, found some more identifying marks on it in Korean, so it's likely original to a Kortek at least.

More pictures, this time with a 24khz EGA pcb, Virtual Fighter 2. Thought i would see if the vertical result was any better than 15khz CGA. It's about the same but colors and sharpness go way down on 24khz suddenly. Geometry is not so great either, cannot pin cushion the screen outwards enough. Seems like the HV is weak, definitely need to find the B+ to know more like you suggested. Tweaking HV setting on the factory OSD menu has no major effect.

Color Bars: (yes convergence a bit out since i removed the yoke)
https://drive.google.com/file/d/0B70EAdThm-yqRUFCQ0NkTFdwRXc/view?usp=sharing

Crosshatch:
https://drive.google.com/file/d/0B70EAdThm-yqMVJER1pZZzRVUGM/view?usp=sharing

Title Screen:
https://drive.google.com/file/d/0B70EAdThm-yqN0s5LW82M2d1RVE/view?usp=sharing

[grantspain]

according the schem b+ should be 80v,read at cathode of d110
https://na.suzohapp.com/service_center/pdf/ktxx14x_sm.pdf

[srarcade]

Thanks for the schematic I missed that file. The b+ is holding around 87v.

[grantspain]

i think you should investigate the vertical deflection circuit,loads of caps and resistors as well as the ic

[srarcade]

I found this archived thread:

http://forums.arcade-museum.com/archive/index.php/t-157123.html and it looks like user cadillacman had the same issue I am facing where he had the incorrect yoke and same problem.

I think I will first try to find the other K2914-F chassis that belongs to this yoke/tube first so I can compare components at the least, otherwise I may end up repairing that chassis instead which is in shut-down.

Ryan