25" Monitor gets brighter and develops lines after 5 minutes?

[MaxAsh]

Odd situation popping up with a Hantarex Polo 25" monitor. It's hooked up to a Ultimate Mortal Kombat 3 cabinet, works great, especially when I first turn it on. Here's the strange part: after it's up and running for about 5 minutes of gameplay, the screen gradually "brightens" and develops multiple thin white horizontal (raster?) lines across the screen. If I adjust the brightness, making the image darker, the lines go away. It's darker than it should be slightly, but it gets the image closer to where it is when I first turn it on.

Problem is, the next time I turn the game on, the image is really dark until 5 or so minutes go by, and it brightens up on its own. I've been adjusting the brightness on the flyback area. I've tried a few other pots, making adjustments, but no matter what I do it seems to just auto-brighten after the first 5 minutes or so. Any idea what might cause this issue?

Thanks

[grantspain]

caps or bad solder joints on crt socket

[MaxAsh]

Caps look pretty good, but I guess I could double check them all. Would a bad cap cause some sort of build-up and push the image brighter?

If the CRT socket has bad solder joints, could I just reflow them? Never messed with the CRT socket before, only components on the board.

[grantspain]

yes its difficult to tell if a cap is bad without using a capacitance meter
imo you should be concentrating on the following
c177
c14
r235
r36

bad solder joints can be reflowed of course

[chopperthedog]

I think it's a standard rule to not do any adjustments till the monitor has been on for 20 or more minutes. When I originally did any voltage, color or convergence adjustments I left the monitors on for an hour. The 3 games I have that have old crt's I turn on and come back 15min later to play.


good day.

[Silverball84]

Had a flyback do that to me once. Try bumping the screen knob on the flyback just a little when it gets bright.

[ed12]

your screen/fous controls are going south >common<
same as wells grander....
replace hot and re-adjust
play away

ed

[MaxAsh]

So far the advice has been to do a cap kit, reflow solder joins on CRT socket, and replace HOT. Any particular item I should try first? ed12, you've given me some solid advice on other issues, if you think HOT is the definite issue, I'll look at that first. Would pulling it and testing it show abnormal readings, or would they still be "ok" readings even if it's going bad?

The temporary solution has been to wait 5-10 minutes for it to auto-brighten, readjust, play, then repeat the process the next time I turn the game on. But if something is going, I'd rather replace it than let it effect other components long-term.

[ed12]

just so we are clear on the term
hot=horz output transformer..
the screen and foucs control assm. is all part and pkg of it.
there is no real test i can come up with.
but a sure visuial chk is easy
when as u say the brightness goes up
dose the unit make retrace or just about ?
and dose it tend to fall out of foucs ?
if the answer to any of them 2 questions is yes
then replace your flyback.

ed

[MaxAsh]

just so we are clear on the term
hot=horz output transformer..
the screen and foucs control assm. is all part and pkg of it.
there is no real test i can come up with.
but a sure visuial chk is easy
when as u say the brightness goes up
dose the unit make retrace or just about ?
and dose it tend to fall out of foucs ?
if the answer to any of them 2 questions is yes
then replace your flyback.

ed

No focus issues, it simply gets slightly brighter and the added brightness causes about 15-20 horizontal thin white lines to appear. Aside from that the image is fine. If I adjust the brightness slightly darker, the lines vanish. Every time I turn it off and back on I go through the same process. Would pics help?

[ed12]

no the thin white lines
tell's me u are going into a slight retrace..
u may have a neck board  cap going south
so what i would sujest is a cap kit first..
they cost less then the hot..
the systmons i spoke about are very very noticeable..

ed

[MaxAsh]

I'll take a picture later and post it just in case. Caps would be great (and cheap and easy) compared to other options I'm sure.

[MaxAsh]

Here are some before and after pictures. The first is when the game is first turned on. The second pic shows what happens after about 5-7 minutes. As you can see, the screen is brighter and develops the lines mentioned above.

[grantspain]

the issue can be only a couple of things,

bad cap at c14
bad cap at c177
bad solder joints
bad flyback screen volts pot or flyback itself


in that order

[ed12]

ya thats light retrace
recap is in order as was told to u in the below post..
i would do that first

ed

[MaxAsh]

Great, thank you, I'll take a look asap at those and report back when done. You guys are extremely helpful, as always, thanks!

[MaxAsh]

the issue can be only a couple of things,

bad cap at c14
bad cap at c177
bad solder joints
bad flyback screen volts pot or flyback itself


in that order

Silly question - were you looking at the schematic to identify the trace and components? If so, could you tell me which one? I'm looking over the manual(s) I downloaded and I'm having trouble identifying the proper locations. One document appears to show two values for C14 for example, which I thought was odd (47uF, 16V and 4u7 250V). And I couldn't find C177. Thinking I might have the wrong service manual (it's for multiple Polo models/sizes).

[grantspain]

c177 from pin 9 of the flyback, 47uf 250
c14 on neck card , 4u7 250v

[MaxAsh]

c177 from pin 9 of the flyback, 47uf 250
c14 on neck card , 4u7 250v

Thanks grantspain

[MaxAsh]

c177 from pin 9 of the flyback, 47uf 250
c14 on neck card , 4u7 250v

Caps both appear to be newer from a previous recap. Look to be in good shape - should I recap anyway? Taking a look at the socket solder joints next, tips welcome there.

[ed12]

yes
reasons are multi..
just replace them for piece of mind..
we can move on from there..
do me a fav up-load the schematic u are using.
we can better follow along then

ed

[MaxAsh]

do me a fav up-load the schematic u are using.
we can better follow along then

ed

Reflowed the solder joints, helped some, but the issue still exists. It seems less drastic, but still apparent. I'll go for the caps next.

I think perhaps I have the wrong schematic, which is why it was difficult for me to find the trace/caps. The one I have says Hantarex Polo Star. I believe this is more of an all-in-one manual, covering multiple models in the "Polo" series. I could be wrong. I've attached just the CRT Socket schematic so you could take a look and let me know if I've got the wrong one. Thanks!

[grantspain]

that is the wrong manual for polo 1 chassis,polostar are in the main vga or multisync,easy to tell a polostar as they have a vga connector
i work on absolutely tons of these chassis across the entire polo range

the brightness issue is normally cap or solder related,you should check for bad solder joints on the crt socket and the remote board connectors

watch out for bad solder joints on the high voltage poly caps whilst you are checking the chassis

another issue which extremely common on polo 1 chassis is a resistor in the 200v line goes open circuit,this causes brightness issues
R235 270k

there is a very small chance the flyback screen volts pot is at fault but it would be obvious as it would be extremely sensitive

if i had this chassis in front of me now and decided to shotgun it i would change c177,c14 and r235 and check those solder joints i mentioned

if you can wait until tomorrow i will upload the full correct schematic for the polo 1 chassis

you should also check your b+

[MaxAsh]

Hi grantspain - I attached an image below of the chassis sticker for reference. If you do have the exact manual, a link would be great I'd appreciate it. I have about 4... and I think all are wrong so clearly I'm finding the wrong docs. I'll go ahead and order the caps. I already re-flowed the CRT socket joints, no luck there. I didn't try the remote board so I'll look at that. Not sure where the high voltage poly caps are, so any help/direction there would be great, thanks.

[grantspain]

that is a standard polo 25 monitor,you could call it a polo 1

the poly caps are polypropylene capacitors,they are box type high voltage capacitors in the deflection circuit,c172 is an example

full schematic is attached,only difference is this schem is for european model which is 230vac whereas yours is 120vac-i am not sure the exact component differences between them but it would be very few and not in the area of the chassis you need help with

[chriso]

I've just had the exact same fault on a Polo

r235 220k
r36 270r

both were open circuit but looked fine.