A really loud cracking noise, akin to a 'zap', and the screen distorts

You could try this link, but it would be far cheaper to upgrade to a new or second user LED/LCD monitor
http://www.eserviceinfo.com/index.php?what=search2&searchstring=schematics+diagrams+hp+7540+crt+monitor

Open this website
manualslib.com
then choose your make and model for a manual.

There is the problem with Controller IC in CRT, Please repair it with local monitor repair shop.

Sounds like your CRT is dying. Sometimes older ones can take longer to turn on, I would suggest upgrading to an economy LCD, they're pretty cheap.

posted 2 times, please erase one, thanks.
P110.

its a tuby 4:3 monitor, useless for wide video. plays.
1600 x 1200 at 85 Hz
do not exceed this, or boom. 1920x1080 will fail.
no resolution stated by you. and matters big time on all old monitors. (old = poor resolution only)

redux for less....words...
does it fail on all PCs connected, sure
does it fails set to lowest Resolution and 60hz?
RGB BNC only proves the analog side works.
not the digital side.

The VGA needs sync
if the PC is working (is it? on other monitors set to below reso.?)
then the 2 sync lines are active
at 1600 x 1200 , max (cant exeed this, ever)

then if that is true then the OSD buttons now work
do they? this is next.

does the On screen menu button work?
if not? it's a digital failure.....
or power to that section dead. or weak.

only googling finds schematics this old.
sorry.
nobody fixes these now, for good reasons.
labor costs on it would exceed a new LCD. fast.
we call this throwing good money after bad.

I didnt know they still made cathode ray tubes. Id suggest you junk that thing and get a decent LCD screen.
It is beyond the scope of this website, and possibly your skills as an electronic technician to go through complete troubleshooting scenario.

well its not first hand ever.
its a vacuum tube CRT relic, why own such a thing>
the monitor old and weak, ask all such monitors are.

why pop for this. and end using junk like this again.
good luck with the VIRUS magnet XP,
you dont need a driver for any monitor
$30 wopping bucks, the price of freakn, potted plant.
why deal in 50lbs of glass and VACUUM??????


why walk past this deal. and walmart
https://www.walmart.com/search/?cat_id=0&facet=condition%3ARefurbished&query=computer+monitor&sort=price_low#searchProductResult

As a result of aging monitor alignments drift, giving rise a a myriad of odd symptoms. Open the monitor up (of course it's got to be off), locate the scanning coils on the neck of the tube. Right there on are disk-shaped permanent alignment magnets. The scanning coils are electromagnets that produce the raster (scanning pattern), while the low-strenght permanent magnets allow the alignment to be varied ever so finely. Chances are that this alignment has drifted. Reconnect and turn on the monitor and with something being displayed, turn the disks one-by-one, observing the effect on the screen (a large mirror in front of the monitor would help much). Note that normally the disks are secured at the factory using hot glue. You may want to warm up the glue before starting the re-adjustment to make it easier to turn the disks. I am quite certain that this will solve your problem.

- A bended color pin at the VGA connector. (If pin one is bend then there would be no red color)

- A defective VGA signal cable. If the internal wires were broken then there would be missing colors. You can check if the signal cable is good or bad by doing a continuity test using a multimeter.

- Dry joints in the CRT board such as in the CRT socket pins, video pre amp and driver IC and even at the connector pins. In fact this problem contributed about 80% of Monitor color problems. Applying fresh solder would usually solve the color problem.

- A defective IC either in the Video Pre-amp or Video Driver IC.

- Faulty components in the CRT board. It could be a shorted driver transistor or even electrolytic capacitors that the ESR reading had shot up!

- A bad CRT socket. Sometimes decayed glue could cause the internal pins rusted and thus affecting the colors. Replacing only the CRT socket would definitely solve the problem.

- A weak or a defective picture tube (CRT tube). Yes, I do came across one of the electron gun (most probably the cathode materials had used up) in the tube faulty caused a missing color in the screen. There’s no way to repair this type of problem-the only way is to replace the CRT tube.

- In the newer type of Monitor, color setting is save in the EEPROM IC . Thus, if the EEprom data is corrupted, you would also get a missing color! The only way to repair it is to reprogram the IC or use a soft jig to tune it back the color setting.



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try to change the LCD power settings ... this is a hardware assue ... but i think it will change when u change this settings