happ vision pro/kotrtek horizontal collapse *FIXED* *BROKEN AGAIN*

[lilshawn]

got a happ vision pro with a Kortek chassis kt-2938. in a PGA golf cab.

monitor worked fine for several hours previous until i did a player control test (which is a darker screen) when i pressed the button to end the test and exit back to the service screen (lighter in color) the horizontal collapsed into about a 2 inch wide vertical strip. The normal monitor oscillation noise began exhibiting signs of strain. the scan at the edges of the vertical line where jagged and random in frequency. Power was promptly removed.

though not a total collapse, it seems unusual to have failed this way.

the HOT tests okay, I plan on replacing before powering it up again to be sure, but due to the strange circumstances leading to the failure, does anybody have any other suggestions off the top of their head?

[qrz]

look for a/poor solder connection(s) ( arcing/burnt ) on a return cap in Hdeflection...

although,  a month ago, had a 27" wg w/same sudden failure - and for no apparent reason.
turned out to be a yoke failure. had arced between the hcoils creating a nice carbon trace...
new yoke , end of problem.

[lilshawn]

I didn't see anything obvious, but I'll check ther caps for sure.

I just thought it was a little odd that the horrizontal would choose that exact moment to crap out. I thought mayber the inrush of current switching between the light and dark might have strained something close to failing.

I just grabbed another HOT and I'll install it and we will see what's what.

[lilshawn]

Replacing the HOT solved the initial issue of no horizontal deflection. as to why the HOT failed is still a mystery. all the caps in the horizontal output section are okay.

Just to be sure I removed all the old solder and re-flowed new in the entire section. i noticed that as I heated the old solder on the flyback pins there seemed to be nothing really sticking down on the trace pad itself. imagine if you will heating up the old solder blob and having flow up and stick to the iron but leaving a dull grey almost oxidized lead coating on the trace pad. I re-flowed, then reheated the new solder and it did not exhibit the same characteristic. Be it differences in solder manufacturing or what, I don't know if this contributed to the issue, but it certainly isn't helping things any.

please also note: fixing this problem ASAP is key. leaving a monitor in this condition for even a few moments will fry so much stuff on the board, your chances of a successful fix are dwindling by the second.

[grantspain]

strange for the horizontal deflection transistor to cause a horizontal collapse,I would have expected the monitor to go into trip rather than semi work

[qrz]

i'd think this unit has a seperate output xistor for Hdeflection . ( and pwm mosfet b+ supply for the deflection)
this allows the HV to operate indepenent of sweep .
a common thing on multisync crt monitors

[lilshawn]

still an issue, monitor died again after about a week...

it sounds like the HOT is being driven that hard... (very loud disconcerting squeal.) it still tests good...i did find somewhat of a schematic why it's an effin' excel document is beyond me.... i'll try and decipher the shortcut tags in it and see what's what in the horizontal deflection area.

http://www.casinotech.com/kortek/tech_docs/info_tech_docs/crt_schematics/kt2938_Schematic.xls


EDIT: i exported it as a PDF for ease of use:

[qrz]

hm, the output xistor is a mosfet . well, 1st time i have seen that .

so, have a look at c709/r714, d707/r715
r716 may have changed value .
 q701,3 may be leaky
check 'lytics around ic701 . Hfeedback to ic701 via q702 ....

gotta be a reason

[qrz]

i should have asked before previous post  ... lost deflection again ?  Hot (q704) is a bit different than Hdeflection out (q302)

IF u have a scope that can handle the voltage ( sencore or better ), take a look at the waveform at the cathode of d303.
it should be nice and square.  distortion may indicate excessive loading .

suggest pulling yoke (if not bonded), and inspect for evidence of damage/arcing/etc...

[lilshawn]

i took a look at the yoke without removing it (the plastic is yellowed and brittle, i fear it may disintegrate on me if i attempt to remove it.) other than the plastic, it looks great. no evidence of excessive overheating or anything like that. the enamel is still light. ohmmeter shows neither of the coils are shorted, and neither read low.

i do have a scope (Hitachi)  and a 10:1 probe. though with 5v/div and with 4 divisions thats 200v...it might be cutting it close.

i'll have a look at the components you suggested. I'll be testing/fixing this chassis some more in the coming days.  i have a few other projects on the go... chopping up a golden tee cabinet and using a 42" plasma for the display and turning a Rowe CD100E into a touchscreen jukebox.



ALSO PLEASE NOTE: the chassis i have has "q714" screened on the board instead of q704 as stated in the schematic.

[qrz]

the Horizontal windings are on the inside of the yoke. vert is on the outside
do a ring check if u have the equipment. otherwise , its pull the yoke - GENTLY and inspect

note, plasmas are power hogs , and generate IR  ( heat ) have adequate ventilation





                                                     

[lilshawn]

Ya its going on a 4"x4" pole behind what's left of the cab. There will be plenty of ventilation.

I pulled the yoke off. Didn't crunch it too much. Still in one piece. Looks alright on the inside. No signs of arc or carbon tracks. Scratch that off the list.