LCD Monitor failure modes ?

[Adrian Brentnall]

HI Folks I have a 'no-name' LCD monitor, it used to be on this PC but was replaced by a newer 'widescreen' monitor a couple of weeks ago. Original monitor was intended to replace the ageing CRT monitor on the PC in the studio (whose screen is getting dimmer & dimmer.....!)

So - LCD monitor sat on the office floor for a week or so (waiting for round tuits), and, yesterday, made its way out to the studio. Plugged it in - powered it up - indicator leds work but no picture! Very brief flash of an image when first powered up, but nothing after - also no on-screen display.....

Took it apart, jiggled all the internal plugs / sockets (it has one logic board and another that looks as if it drives the illumination - couple of transformers and dire warnings about high voltage ) - but no joy...

Now it's probably BER (beyond economic repair) - but, ever-hopeful... I thought I'd ask here...

I'm guessing that the most likely failure is of 'whatever' illuminates the screen - but I'm guessing that this is likely to be a proprietary part rather than anything you could get a replacement for.. and, since a replacement is under ?100.... but I'm loath to chuck the thing away for the cost of a possible cheap repair.

Anybody fixed one of these and can offer suggestions ?

Thanks Adrian

[Harry Bloomfield]

It happens that Adrian Brentnall formulated :

The thing which illuminates the screen is like a miniature fluorescent tube driven by an inverter. It is supplied with around 12v, which the inverter turns into something like 1500v, to strike the lamp. You could try replacing the inverter plus tube (expensive) or try replacing just the large three legged switching transistors (Triac).

[Adrian Brentnall]

Thanks Harry A Google turned up lots of info about changing the electrolytic caps on the inverter board - which might be worth a quick look. I had it in bits yesterday, but didn't study the caps that closely.... might look again later today.

There's a trend developing here - I've got a 12v 7A linear power supply and a rather nice 50W bass amp that both need re-capping..... ...just a matter of getting the components and the box of round tuits available at the same time I should probably go through my stock of NOS components and ditch all the electrolytics - as most of them are at least 25 years old....

Thanks Adrian

[John Williamson]

To check whether it's just the backlight that's failed, shine a bright light on the screen, and you may see the display very dimly by reflected light.

[fred]

In article , Adrian Brentnall writes

The backlight sounds like a likely suspect. Usually lit by 2 or 4 miniature cold cathode tubes run off inverters. The inverter(s) start but if a tube fails to start (draw a specified current) within a second or two then the inverter will shut down to protect itself so that explains your brief flash of picture.

I had one with 4 tubes (2 top, 2 bottom) that ran off 2 inverters (2 transformers), one tube had failed and taken out an inverter with it (quite common). By dismantling the display (carefully noting arrangement for reassembly) I could get to see the tubes and see which was out or on the way out (dim, pink, or discoloured tube ends) in the brief flash of operation. Short story is that I cut it around to use just 2 tubes (1 top, 1 bottom) working off the 1 working inverter but I had to reverse engineer the inverter circuit to disable the faulty inverter and remove the link to the other inverter which wanted it to shut down in the absence of the other.

It's been working a year since the repair and the light from 2 tubes is not noticeably dimmer than the 4.

I considered doing a more complete repair but replacement tubes aren't really that cheap and fully repairing the inverter would have taken longer than I was prepared to spend. New inverters are just too pricey.

An alternative I considered was to use white LED light strips but even that looked a faff and the 2 tube solution meant I didn't need to take it any further.

HTH

[Adrian Brentnall]

Hi Fred

Thanks for that... As it happens, I do have a couple of led strips ....

Thinking back, when this screen was 'full-time' on this computer, I wasn't able to let it go into power-save mode because it wouldn't reliably come back out of it - so maybe the tubes are just worn out...

I'll see if the electrolytics look obviously 'bulged' - and if they don't then I guess I'll probably give up. Don;t really have the time to get deeply involved with a 'clever' fix.....

Thanks Adrian

[Adrian Brentnall]

As I say - there was the briefest flash of 'picture' at power-on - which could be a tube trying to light..??

Thanks Adrian

[Roger Mills]

Are you *sure* it's broken? Have you tried it with the computer to which it had used to be connected? There's an outside chance that your studio computer is trying to drive it in a mode which it doesn't recognise - or even that the computer's video card has failed. Does the old CRT still work?

[John Williamson]

From your description here and below, it could well be that the tubes have just died of old age.

[The Natural Philosopher]

We all have a monitor like this that we have asked about and subsequently scrapped.

[fred]

In article , Adrian Brentnall writes

I'd forgotten about that possibility but should have remembered as this monitor had the caps changed on it a couple of years ago. In that case the indicators were out too as the main psu just shut down.

Think you're right on the pragmatic approach, if you're not a student or in the business of fixing them then it's not worth the time on a cheap generic monitor.

[pete]

If you're willing to enter a "free software" frame of mind and value your time at zero, then it might just be worth tinkering with. However from an economic point of view almost certainly not. Years ago faulty LCD monitors used to fetch a high price on eBay (though I could never understand why - unless it was for insurance fraud), but nowadays the tenner you'd make hardly seems worth the effort.

If you don't want to just toss it, there might be an electronics enthusiast in your area who would strip it for parts.

[MuddyMike]

My thoughts entirely. Also you said the original CRT was getting dimmer & dimmer, could that be a sign of the video card in the PC dying and the replacement monitor killed it completely?

Mike (who knows nothing of the inner workings of monitors)

[Adrian Brentnall]

yes - I'm sure..... Old (increasingly dim!) CRT works with studio pc, faulty lcd screen is faulty with all 4 pc's and laptops, fault when swapped with my wife's PC which uses the same model screen....

In Python terms, 'It's a late monitor'

While I admire folks who have the nerve & the know-how to re-engineer backlighting circuits, and while I hate throwing (potentially) fixable kit away, I think I may just shell out the ?80 for another screen...

It'd make sense anyway, 'cos this PC has two screens on it (very handy for web design work) - and they're different screens from different manufacturers - with different brightness / white levels etc. It'd make sense to run two identical screens on this machine and relegate the newly space screen to studio use...

Against my principles - but there's only so much room you can set aside for 'waiting to be fixed' kit

Adrian

[Adrian Brentnall]

It's possible... I bought the monitor before we moved over here to Ireland - so it's at least 5 years old....

(fwiw the 'dim' crt out in the studio must be more than ten years old - so I guess that doesn't owe me anything either ) Adrian

[Adrian Brentnall]

Along with all the other 'come in useful one-day' kit!

Keep trying to pluck up the determination to dump the old laptop - it's a Tosh Portege 7020 (!) with docking station - ex-corporate - must have cost a small fortune when new, but came to me in bits in a carrier bag. The screen went on that about 5 years ago - but eBay yielded a complete replacement for a tenner, which, after gutting the necessary bits, went back on eBay and sold for twelve quid....

I'm no longer a 'road warrior' - so don't have much need for a laptop - but, every so often, it comes in handy to run a slideshow at an exhibition... but the 192 megs of RAM does slow it up a little - and, before anybody asks, I can't persuade it to boot from a USB stick or CD in order to install linux! Adrian

[Adrian Brentnall]

This one seems to be OK as the only working bit of I/O (the red-green power light !) responds appropriately when connected to a VGA cable

It's the inherent 'stubbornness' that's the problem - the 'I should be able to fix it' syndrome.... Probably stems from being brought up in the 'fifties. I well remember Dad sitting hammering 'reclaimed' bent nails flat before re-using them. He & Mum moved down to Cornwall with very little cash and rebuilt / extended a bungalow more or less on their own - masters of 'make do & mend'.....

How times change! Adrian

[Adrian Brentnall]

Yes - sad but true

Then there's the postage.......

Aargh! - that's me..... Even that's not as attractive a proposition as it used to be - wot wiv it all being smt and custom logik .

Not like the good old days when you could use the tin-snips to cut the PA Tray out of an old blue Pye Westminster, feed it with 1kv and get

50watts out on 2m ssb!

Progress! Adrian

[Adrian Brentnall]

- No - I'm pretty sure that the studio PC is good - the faulty monitor is faulty with three other video sources.....

As to the old CRT - you just can't get the paraffin nowadays!

About the time I bought the (now faulty) lcd screen, I Freecycled its predecessor - a lovely 21" Crt. Weighed an absolute tonne - think the youngster who came to collect it was a little surprised by the sheer weight & bulk of it. Cost me the best part of 500 quid new!

Adrian

[Mike Tomlinson]

In article , Adrian Brentnall writes

Loads.

95% of the time it is capacitors in the PSU that have become leaky.