That's moisture in the neck connector and the moisture causes focus and acceleration voltages to arc every once in a while. Thoroughly dry out the connector (with a hair dryer or something). Also pay close attention to area around the flyback transformer, any discharge there can result in destruction of the transformer or surrounding parts.

Most better monitors use degauss when powered on. You can also use this feature from the menu or dedicated button. If it's doing it by itself after already powered on then something is wrong.

That’s good news if you think it could just be moisture, I can get them moved on to better homes. I’ll dry the remaining ones out a bit before trying them. It would explain why they seemed to stop doing it after being used for a while.

They’re not degaussing, it’s just a fraction of a second flicker, the degaussing is a different sound. It’s more of a slightly unnerving electrical arcing type sound than a click.

Hate to say it, but everytime I get that zap/crack sound and the display cuts out when you hear it, that is the flyback transformer. Something about the winding's break down and short or arc. I have only changed about 4 myself, and everytime I do I sweat bullets due to all the horror stories I here about the high voltage shock risks.

lowlytech wrote:

Hate to say it, but everytime I get that zap/crack sound and the display cuts out when you hear it, that is the flyback transformer. Something about the winding's break down and short or arc. I have only changed about 4 myself, and everytime I do I sweat bullets due to all the horror stories I here about the high voltage shock risks.

😒 this is what I’ve read on the internet generally but I was hopeful I wasn’t unlucky enough to have bough 9 CRT screens all with knackered flyback transformers so I was hopeful it could have been the moisture thing? The barn they were stored in is very damp - all the PCs that came out are pretty rusty (although so far I’ve saved 4, 4 definitely need motherboard repairs and the other 3 I haven’t tried yet)

did you illegally download your CRT? Cracks are not allowed here

oeuvre wrote:

did you illegally download your CRT? Cracks are not allowed here

That joke warez thin after a while.

I won’t shareware I got them from, I’m keygen it quiet

(Sorry, that was really clutching at straws)

lowlytech wrote:

Hate to say it, but everytime I get that zap/crack sound and the display cuts out when you hear it, that is the flyback transformer.

It's not always the flyback transformer itself. As Tiido correctly pointed out it can be caused by a humid/corroded CRT socket, and also by a dirty and/or incorrectly fitted anode cap, since dust is hygroscopic it can create a low resistance path from the 2nd anode to ground when moist.

Good practices from the TV repair trade dictated replacing the CRT socket (just the plastic socket, not the whole neck board) at the slightest incidence of arcing or corrosion, cleaning the vicinity of the anode cap and applying vaseline or silicone sealant to it to prevent moisture ingress, especially in humid climates. A common problem caused by leaky CRT sockets in household TVs was EEPROM data corruption due to the RF noise from the arcing messing up sensitive stuff. If you reprogrammed/replaced the EEPROM without replacing the CRT socket it would definitely come back to you corrupted again.

133MHz wrote:

lowlytech wrote:

Hate to say it, but everytime I get that zap/crack sound and the display cuts out when you hear it, that is the flyback transformer.

It's not always the flyback transformer itself. As Tiido correctly pointed out it can be caused by a humid/corroded CRT socket, and also by a dirty and/or incorrectly fitted anode cap, since dust is hygroscopic it can create a low resistance path from the 2nd anode to ground when moist.

Good practices from the TV repair trade dictated replacing the CRT socket (just the plastic socket, not the whole neck board) at the slightest incidence of arcing or corrosion, cleaning the vicinity of the anode cap and applying vaseline or silicone sealant to it to prevent moisture ingress, especially in humid climates. A common problem caused by leaky CRT sockets in household TVs was EEPROM data corruption due to the RF noise from the arcing messing up sensitive stuff. If you reprogrammed/replaced the EEPROM without replacing the CRT socket it would definitely come back to you corrupted again.

Wow, I really wish there was an old school CRT repair tech in my area. I would love to learn how to safely work on them. CRTs are actually gaining popularity due to the retro craze, but it's the one thing I don't dare teach myself how to fix. It's just too dangerous without an experienced teacher.

I started off in the hobby by being dangerous! Actually I learned to work on them and around them by recapping monitor chassis boards back in the mid 2000's. I've got a discharge wand that I had someone make up for me to assist in discharging the tubes before servicing. Plus I wear leather gloves when pulling out the chassis or tube just in case.

are these 9 CRT's all the same identical model? 3 out of the 4 flyback's I have had to change were all on apple macintosh branded monitors, so it may have been a design flaw or defect with the flybacks they used? Otherwise I hope it is maybe a moisture issue that can "self heal" for you.

So as far as I can figure out, the 7 Compaq CRT monitors (2 unbranded) went with the 4 Deskpros in the lot I bought from a barn. They’re all the same model Compaq screens. I believe these were part of a much bigger fleet of machines used by a school, and that for whatever reason these particular screens and PCs ended up in the barn. None of the desktops were working when tested (I’ve fixed one so far) so it’s a possibility that the PCs and screens were moved there because they were faulty during the time they were in use and not that they went bad while in storage... but I can’t be certain.

I’ll have to give them some more thorough testing to try and figure out if it’s moisture from being kept in a barn for years or the reason they were put in there in the first place!

As an ancient TV repair engineer ..I have worked on thousands of CRTS over the years ..
Not that I see many these days ..
but rarely had a shock of a CRT ..providing you take the neccessary precautions ..
A fying lead connected securely to ground/chassis or the graphite coating on the rear of the crt glass...and an insulated metal probe on the other end ...
you slide the probe under the rubber EHT cap /sucker on the rear of the CRT and ground the EHT tab ..
leave it grounded out for several hours ...
usually this is long enough ..but overnight if you want to certain.
you may hear a crack at first connection ...but dont worry about this ..
PLEASE make certain the monitor or TV is is NOT powered in any way before attempting this .
Once fully discharged the CRT EHT connection (this acts like a giant capacitor )..
remove the eht plug ..and ..clean the area with ISO alcohol.

You can then use this product from servisol ..to suspect areas before reassembly

Servisol Plastic Seal 60 - ebay number (6100009000)

A coat of this over the flyback transformer ..and CRT base board is also advisable.
again clean the ares fully before applying the sealant.

rgds
VS

britain4 wrote on 2018-06-21, 19:54:

I’ve got 9 Compaq CRT screens from a job lot in my shed at the moment and I have to get rid of some as I don’t have the space! […]
Show full quote

I’ve got 9 Compaq CRT screens from a job lot in my shed at the moment and I have to get rid of some as I don’t have the space!

A few of them when first turned on made a little “crack” sound from inside the screen along with the picture flickering as it made the sound

The frequency of this varies but on the worst one it did it about every 5-10 seconds at first before getting less and less frequent the longer the monitor was on. Is this something that can happen after a CRT’s been in (slightly damp) storage for a long time (probably the best part of 15 years) that’ll stop happening as they get some use or is it a sign they’re knackered?

I don’t want to start selling them only to find they’re crackling and dying for the new owner a week later but at the same time I don’t have time to thoroughly check all 9 of them for hours on end!

Funny. Last year I trash picked a 17" that had been sitting in the rain for some days. It was surprisingly clean inside and looked very unused. The former owner said it used to work and sat ~15 years before they put it onto the trash pile. I hadn't high hopes for it, but it worked after letting it dry for a few days. However, it made distinct snapping sounds like those of a high voltage DC spark flashing over, combined with a jitter of the picture. At first, it did that every one or two seconds or so, and after a minute of on time the frequency already decreased significantly. A few minutes it decreased to about 2 snaps a minute and after two hours of playing Doom the snapping was gone for good until this day. As I didn't see any visible sparks in the dark I just thought "ok, maybe there was water in the flyback".

However, last week I got donated another one with only the degauss PTC broken. I fixed that, and when turning this one on it showed exactly the same "snapping" symptoms as the one last year. This monitor was also stored in working condition ~15 years ago, but this time in a dry place. I had this thing running for like 60 minutes in total and the snapping frequency is already down to around one per 15 minutes. That doesn't make it easy to locate the source.

This behaviour can't be a coincidence. It has to be related to these things having been stored unused for a decade. I suspect something is "self-healing" when you turn these back on. I wonder if there is a hidden spark gap somewhere which would explain why I am not able to see these sparks in the dark.

Bought a 2000 Compaq MV720 off ebay that has been having this same issue. Click paired with the screen image expanding with some color distortion and dimming. Then, image contracting and color and brightness restoring entirely.

At first, the click was pretty violent and the image distortion exaggerated and it occurred frequently. As I dare not open this monitor, I had few options to troubleshoot. The only real thing I could do was move the power source from a basic power strip directly to the wall. Since doing that, the clicks are not as frightening, the image distortion not as dramatic, and it occurs maybe once shortly after the monitor is turned on.

Not sure if this is due to power source or just me turning the monitor off and on to test. Either way, I was hoping some of the folks who had posted here a couple years ago could give updates on their monitors which were experiencing this issue.

lowlytech wrote on 2018-06-22, 02:04:

Hate to say it, but everytime I get that zap/crack sound and the display cuts out when you hear it, that is the flyback transformer. Something about the winding's break down and short or arc. I have only changed about 4 myself, and everytime I do I sweat bullets due to all the horror stories I here about the high voltage shock risks.

how about a pop sound between minutes, untill you leave it on for like an hour and there is no sound, like baking 1 popcorn
image is perfectly fine, but it does that sound

would that be....humidity in the suction rubber? is there a risk of fire or is it dangerous?

My old Goldstar monitor did this when I had 386 back in the day. I just opened it and cleaned all parts from dust. It seemed to be temperature related in my case. It never caused any permanent damage.

lowlytech wrote on 2018-06-22, 02:04:

Hate to say it, but everytime I get that zap/crack sound and the display cuts out when you hear it, that is the flyback transformer. Something about the winding's break down and short or arc. I have only changed about 4 myself, and everytime I do I sweat bullets due to all the horror stories I here about the high voltage shock risks.

Is it even possible to get a flyback transformer for a crt? Because if not, I'd hate to buy a new-old stock one, especially if I need to buy a specific kind for a specific crt board.