Discoloration keeps coming back daily at bottom right corner of the screen

For monitor related issues
User avatar
keropi
Please Continue...
Posts: 294
Joined: January 14th, 2016, 6:04 pm
Location: Greece
eBay: sainshov

Discoloration keeps coming back daily at bottom right corner of the screen

Post by keropi »

Hiya!

some weeks ago I bought a really nice EIZO tri-sync 14" monitor and I was finally able to setup correctly my 286 PC/EGA setup. But I noticed that there is a small discolored area on the bottom-right corner of the screen:

Image

Image

I know it's hard to see but it does exist on the marked area. Naturally I used my degaussing rod and the discoloration disappeared. But it seems it comes back every day and I have no idea why :wtf:
There is nothing near that could affect the monitor , here is a photo of how things are arranged on my 286 desk:

Image

There is an amiga PSU under the monitor but I haven't powered it since I got the monitor. The midi modules on the right don't have any magnets or internal PSUs, everything is under the desk on the left that is not pictured.
So what could be causing this? Any ideas? I am thinking of opening the monitor and install some extra shielding on the that corner, would that be a good idea?

TIA for any help/iput! :awe:
User avatar
NoAffinity
Posts: 386
Joined: January 8th, 2017, 3:46 pm
Location: Escondido, CA, USA
eBay: noaffinity
Initials: CSG
Contact:

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by NoAffinity »

Do you have a degaussing coil? Looks like it just needs to be degaussed.

A lot of times, those monitors had a built-in degausser you could trigger through the OSD, but even if it has one, it could still require external degaussing. You will want to move it away from all the other screens and face it north or south when external degaussing.
User avatar
nem
Needs a custom rank
Posts: 2768
Joined: August 17th, 2008, 6:59 pm
Location: Finland

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by nem »

^
keropi wrote:Naturally I used my degaussing rod and the discoloration disappeared.
My best guess is something inside has been slightly magnetized even though it shouldn't have. It can happen.

You can rule out it being something external by positioning it somewhere else for a while ;)
User avatar
NoAffinity
Posts: 386
Joined: January 8th, 2017, 3:46 pm
Location: Escondido, CA, USA
eBay: noaffinity
Initials: CSG
Contact:

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by NoAffinity »

Oh, sorry, I must've skimmed over that part. :oops:

And now that I think about it, I've got the same issue in the upper right corner of my Jaleoc lo pro. I pulled it off the wall, positioned it north-facing, degaussed it and it looked fine. I put it back on the wall, west-facing, and the discoloration is back. I then degaussed it as it sits against the wall, and it made no difference. The closest thing to it that is not in the cab is a power strip/surge protector that sits about 3' above it on the wall. Is it possible that is causing my issue?

Sorry to hijack, but maybe we'll find a common theme.
User avatar
keropi
Please Continue...
Posts: 294
Joined: January 14th, 2016, 6:04 pm
Location: Greece
eBay: sainshov

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by keropi »

No worries NoAffinity I don't mind the hi-jack :awe:
In my situation an inactive powerstrip is ~80cm away under 2 wood levels and on the left side of the screen. There is nothing near that corner externally that I can identify as the culprit. I'll move it at a different position and see what happens.

@nem
Good thinking, I will open it and see what the deal is... I don't see what could be magnetized but you never know!
User avatar
keropi
Please Continue...
Posts: 294
Joined: January 14th, 2016, 6:04 pm
Location: Greece
eBay: sainshov

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by keropi »

I did some changes and now the monitor is positioned more left... I still get the corner stuff though...

Image

the monitor is very shielded:

Image Image

I have verified that the degaussing circuit each power-on works fine but other than that I have no idea what to try next. I did not detect anything suspicious at the offending corner when I opened up the monitor :(
User avatar
cools
Armed Police Buttrider
Posts: 13457
Joined: August 17th, 2008, 4:49 pm
Location: Wales, United Kingdom
eBay: hordarian
Initials: CLS

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by cools »

Tate it and see if the discolouration goes away or moves.
Image
User avatar
Asayuki
Please Continue...
Posts: 431
Joined: August 29th, 2015, 10:16 pm
Location: Remuria, Germany

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by Asayuki »

Although a magnetized object nearby might be the issue, you do say that manually degaussing with an external coil works fine until you power it up the next day.
This indicates that the PTC of the degaussing circuit in the monitor might be aged and out of spec, so it's not doing its job properly.
My 15kHz cabinet Peplos will never power up, with any item, and I am quite proud of that.
User avatar
keropi
Please Continue...
Posts: 294
Joined: January 14th, 2016, 6:04 pm
Location: Greece
eBay: sainshov

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by keropi »

Asayuki wrote:Although a magnetized object nearby might be the issue, you do say that manually degaussing with an external coil works fine until you power it up the next day.
This indicates that the PTC of the degaussing circuit in the monitor might be aged and out of spec, so it's not doing its job properly.
this is interesting, I thought they only worked or not - not that they degrade... I can replace it easily but my issue is that I don't know it's exact model:

Image

there are no other marking whatsoever on the thermistor (I have removed it to check it) and AFAIK PTH451C is just the package description... what replacement to I order I have no idea :oops:

@cools
I will also try that - could reveal if the source is external or not :)
User avatar
Asayuki
Please Continue...
Posts: 431
Joined: August 29th, 2015, 10:16 pm
Location: Remuria, Germany

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by Asayuki »

40-93 indeed does sound like a production date code rather than the rest of the part number.
Assuming that the part really went out of spec you could measure its resistance and see how it compares to the options available in the datasheet you already found.
One other thing you can measure is the resistance of the degaussing coil itself. Looking closer at the datasheet, the last column is intended to provide an indication of which model to use based on the coil resistance.

I hope this helps.

Just for completeness, the datasheet of the part is here: http://www.paulswan.me/arcade/datasheets/PTH451C.pdf
My 15kHz cabinet Peplos will never power up, with any item, and I am quite proud of that.
User avatar
keropi
Please Continue...
Posts: 294
Joined: January 14th, 2016, 6:04 pm
Location: Greece
eBay: sainshov

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by keropi »

Thanks for the help Asayuki, great catch about the coil resistance value, I completely missed it! I'll measure the resistance and chose a part accordingly now 8-)
User avatar
cools
Armed Police Buttrider
Posts: 13457
Joined: August 17th, 2008, 4:49 pm
Location: Wales, United Kingdom
eBay: hordarian
Initials: CLS

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by cools »

Asayuki wrote:Although a magnetized object nearby might be the issue, you do say that manually degaussing with an external coil works fine until you power it up the next day.
This indicates that the PTC of the degaussing circuit in the monitor might be aged and out of spec, so it's not doing its job properly.
Could you not simply unplug the degauss coil to validate this, before worrying about swapping the part?
Image
User avatar
Asayuki
Please Continue...
Posts: 431
Joined: August 29th, 2015, 10:16 pm
Location: Remuria, Germany

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by Asayuki »

I see what you mean. That's certainly possible, yes.
Desoldering and measuring is just my preference: dead easy anyway (at least for me), and it leaves no room for doubts.
My 15kHz cabinet Peplos will never power up, with any item, and I am quite proud of that.
User avatar
keropi
Please Continue...
Posts: 294
Joined: January 14th, 2016, 6:04 pm
Location: Greece
eBay: sainshov

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by keropi »

Looks like that all my efforts to get rid of this produced no result.

When I opened the monitor and posted a pic of the thermistor I actually desoldered it as well (it's easy for me as well) and I borrowed a thermistor from a 1084S monitor just to test if anything different happens:

Image

ofcourse the 1084s thermistor looks (and must be) a "weaker" version but since both are 14" tubes I thought I'd give it a go. Didn't do anything different though. I did measure the resistance between the original thermistor pins - I don't remember the values - but one set of pins had a low resistance while the other had a really big one (center pin as common).

My next step now is to measure the coil resistance and replace the thermistor with a new suitable one from the datasheet. I will report back when all that happens... 8-)
User avatar
keropi
Please Continue...
Posts: 294
Joined: January 14th, 2016, 6:04 pm
Location: Greece
eBay: sainshov

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by keropi »

Allright I measured the coil resistance and I am getting 6 ohms. I am unsure what thermistor to get as the closest one at 220/240v is rated for 8 ohms (PTH451A180N21)
Any insight on this? :)
User avatar
Asayuki
Please Continue...
Posts: 431
Joined: August 29th, 2015, 10:16 pm
Location: Remuria, Germany

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by Asayuki »

PTH451A180N21 sounds like the best choice to me as well. 2 ohms discrepancy account for a 25% difference which will reflect in a current increase with respect to the stated figures. It might be not that important, but I would also visually inspect the coil just to be on the safe side. It's probably wrapped in a black tape, and there should be no sign of overheating on the tape. You don't want one of the windings being accidentally shorted with another.

Another thing that came to my mind, which you probably already checked is the fixation points around the tube at the four corners. If the bottom right point is way off alignment with respect to the others, that might be something to take care of before you buy the spare thermistor.

I hope this helps. Keep us posted. :)
My 15kHz cabinet Peplos will never power up, with any item, and I am quite proud of that.
User avatar
keropi
Please Continue...
Posts: 294
Joined: January 14th, 2016, 6:04 pm
Location: Greece
eBay: sainshov

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by keropi »

thanks for the help Asayuki , I will order a PTH451A180N21 if I find one - did a quick search and could find a place to order it :oops:
The fixation points are OK, the tube is held into position firmly. The coil also looked OK *but* in order to really check it I need to disassemble completely the monitor, remove everything to gain access to it... that's something I am not really keen on doing :lol:

I also checked the nearby metal pieces if one is magnetized but I could not discover anything :problem:
User avatar
Asayuki
Please Continue...
Posts: 431
Joined: August 29th, 2015, 10:16 pm
Location: Remuria, Germany

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by Asayuki »

yeah ok, I tought a quick look from the outside was easier. Not really worth it then.
My 15kHz cabinet Peplos will never power up, with any item, and I am quite proud of that.
User avatar
keropi
Please Continue...
Posts: 294
Joined: January 14th, 2016, 6:04 pm
Location: Greece
eBay: sainshov

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by keropi »

I can find cheaply the MZ73-18RM270V thermistors: http://www.dxmht.com/products/degaussin ... mistor.htm - but the datasheet states 10ohm coil resistance... it's no good right? Plus it's a Chinese manufacturer... my searches for a Murata part were fruitless. :oops:
User avatar
Asayuki
Please Continue...
Posts: 431
Joined: August 29th, 2015, 10:16 pm
Location: Remuria, Germany

Re: Discoloration keeps coming back daily at bottom right corner of the screen

Post by Asayuki »

Being it a PC monitor, where the degausser gets used at each power on, I would try and stick with a part identical to the original.
Since we can't know for sure whether the thermistor is really worn out or not, it would make little sense to add another variable in the picture.
Yet of course the part is nowhere to be found. Maybe some TV repair shop might have a couple unused ones from back in the days?

By the way, cools has suggested to simply unplug the coil. What happens the next day if you use the monitor with the coil unplugged?
My 15kHz cabinet Peplos will never power up, with any item, and I am quite proud of that.
Post Reply