Sony PVM briefs bright flashes

[daifuku74]

Hello everyone and happy new year! I often visit this site as a reader but it is my first post.
Probably you have a clue for troubleshooting my Sony PVM-1440QM. Overall it works all right but has like random brief flashes of brightness (say 0,4 seconds each) when using an external game system plugged into SCART.
Flashes do not seem to appear at a regular interval, nothing wrong with the audio when it flashes.
Except H and V center, stretching and basic stuff after buying the monitor, I did not make any crazy other image adjustments with the internal pots (no OSD settings menu on my model).
Just before the last setting, there was some kind of white halo on the top center at some point (maybe a stretched white line?) and I got rid of it by adujsting V.BLK.
Could a V.BLK exaggeration trigger the flashes? Or is the monitor slowly dying or needs a capkit? I hope not I just bought it second hand a few months ago and could not really appreciate it yet, barely 5 hours of playing.
Of course I can use it like it is now, but I want to be sure I'm not harming it.
Thank you everyone for your input on what would be the best to do now.

[daifuku74]

CRT gurus are you here please

[buttersoft]

I have a feeling that both those issues have come up on this forum before, though probably not for the same sets, let alone the same set you have.

On arcade monitors I've seen some brightness issues like your description to do with the pots in brightness controls getting dicky, and i've seen brightness issues on PVM's to do with resistors in the screen grids, but those are pretty vague places to start.

The white line at the top i can't remember anything about, unless the descriptions on here were about a slight lens shape to it?

Best bet might be to grab the service manual for that set and start reading and thinking, and come back with more questions.

[gray117]

V Blank / vertical blanking to remove a line or halo? Odd... odd ... maybe...

Issue only occurred only after having made service menu adjustments or was there before?
If not, try to restore previous settings. If no record try and find a reference of what default service menu settings would be and go from there. If not try mid range - ish for most settings that you know you changed. And start over.

Can't remember/doesn't matter whether it was before service menu adjustments or or not: Issue is certainly there now? Continue.

Occurs on all inputs just not scart?
Occurs for content on any other inputs?
Occurs with different systems and cables?
If yes for all, then yep, we're looking at something just with the general monitor for sure. But you never know perhaps it could be down to some small thing. Part of me almost wonders it there's something going on with the sync/ground... but that's probably wishful thinking... Appears to happen even if you lower/raise the brightness? No external thing that could interfere?

It happen pretty regularly like every x seconds? Or just like once now and again in say an hour?
Effect is like a switch or does it fade up and then back down?
Does it kind of pulse/come or go at all at any time?
Is the image stable or does it move/scroll/distort at all?
Got a video of it happening?

... Assuming there's nothing loose/obvious; I'd feel like the best bet will likely be down to something either capacitor or resistance based... it's just there's typically a lot of capacitors or resistors in a pvm (compared to like an arcade monitor) and it's going to be a pig to just blindly replace... Especially if the issue remains after all that work...

[daifuku74]

Thank you to both of you, that sheds a good light on possible solutions.

I found back a photo of the halo in the top center I referred to, before I got rid of it by adjusting V.BLK.



The brightness pot maybe has something, I didn't even think about this but that makes sense.
Let's add it to the checklist.

I don't recall of this white halo being there before my first adjustments.
I tried picture adjustment because previous owner had like 50% of the total screen used in the center
and that was way too small.

I will try to find BNC connectors to input on another source than SCART.

Brightness brief flashes happen with at least 3 of my home consoles that keep a stable image on other my other CRTs, all with different cables.

About timing, this does not seem to occur every x seconds, it is not regular.
Honestly, since this symptom I did not push test for longer than 5/10 minutes, in doubt it hurts the PVM somehow.
Effect is like a switch and very quick, I caught it on video (at the very beginning) but it is not very noticeable while filmed.
https://www.youtube.com/watch?v=XiFahxQBMIE
It adds brightness for a split second, but no other distortion or movement happens.

Maybe I could check the inside for somthing loose or a cold solder, especially on the scart side?
The monitor is off since like two weeks.
Hopefully I can open it safely and try to look for obvious stuff.

If a capkit becomes necessary, is there a place that sells the kits for each PVM?
But if even resistances need a swap, well that becomes complicated.
I could try changing V.BLK again, but I remember the pot made no real obvious effect past some point.
Maybe I went too far with it?

The reason I suspect V.BLK is because the other stuff I changed is pretty straightforwared, Horizontal strecth, vertical, nothing too error prone.
I was not feeling to good tweaking it because it's really close to the back tube coil and even with a long
plastic stick you can feel the electricity in the air

As for interference, I have my computer about 1,5m away from the PVM, a small laser printer 50cm above, and a cast iron radiator close to the monitor.
Could that be a concern?

[gray117]

As for interference, I have my computer about 1,5m away from the PVM, a small laser printer 50cm above, and a cast iron radiator close to the monitor.
Could that be a concern?

Maybe printer/radiator but doubt either enough to be doing anything. Unplug the tv and put it in the middle of the room, wait 5 min, plug it back in the middle of the room and see if any change. Easiest thing to test first. No point driving yourself nuts trying to fix/tweak something if the problem is a lump of metal or a microwave etc.

The brightness pot maybe has something, I didn't even think about this but that makes sense.

Yeah I don't know ... may be just symptomatic as to whatever is causing your brightness pulse.
At this stage, looking at your video the good news is that I think the guess at to a capacitor/resistance issue is a good bet.

If a capkit becomes necessary, is there a place that sells the kits for each PVM?

I don't know, google says try contacting savon-pat on ebay, but read on first

The bad news is that just replacing all caps/resistors is a complete bitch to replace on a pvm... and probably half having nothing to do with what you're hooking up. Arcade monitors have like 20-50 caps total. A pvm ... 100 to 200+ (?) depending on model... so service manual to target suspect is a must, areas like chroma/neck/power/rgb-in I should think, hopefully keep it within the 10-30 caps per feature range... unless you love soldering, or can see something blown/bulging.

Service manual:
https://www.manualslib.com/manual/12736 ... PVM-1440QM
(download button)

^^ Lists all components, but there's so many it'd just make me plug my OSSC into a flatscreen personally... I'm a wimp

[daifuku74]

UPDATE:
I was not too hopeful about plugging the monitor somewhere else and see if anything's better
BUT there are no more unwanted flashes when it runs somewhere else than close to the radiator.

THEN I REMEMBERED
on the radiator itself is some device to measure how much energy is used by it and
this device (I totally forgot it was there at first, sorry) somehow communicates wirelessly.
I find it a lot more potentially problematic than the radiator alone.
Here is how it looks:


I asked the company responsible for it what I can do with this device and the answer is basically nothing...
I can't move it somewhere else, I can't open it or isolate it (I thought with some EMI shielding of some kind),
because it will alter the feedback and my invoice, they say.

So I think I'll just use the PVM somewhere else, I can't think of any other place really, but here we are.
Or is there a way to isolate the PVM by sticking some shielding on its right side?
I remember having seen some kind of sheets of foam coated with metal, maybe that could help?

I couldn't think of the device at first because with other Trinitron TV there was no issue, even when standing precisely where the PVM is now.

Thank you everyone

[Bratwurst]

Or is there a way to isolate the PVM by sticking some shielding on its right side?
I remember having seen some kind of sheets of foam coated with metal, maybe that could help?

Cheapest method I can think of to test this would be a sheet of aluminum foil placed between the monitor and the radiator meter. You must ground the foil, use an small alligator clip lead or something similar. Could even twirl one corner of the foil around bare wire as a last resort.

[daifuku74]

I will try that and report!
Many thanks!