Hi oheybea and welcome to VOGONS!

Not sure what else there is to try other than to disassemble the CRT completely and look over everything carefully again, especially since you had trace damage before from leaked electrolytic capacitors. It's quite possible some traces might have degraded and broke again if you couldn't get all of the electrolyte cleaned up.

That said, it's probably best to replace all United Chemicon LXF capacitors at this point, both on the main board and the neck board. And not only those, but also look for any brown-colored Nichicon PR and PL series.. The PR series were especially bad, and always have a failure mode as you saw with your UCC LXF series - they leak from the bottom. In fact, many electrolytic caps from that era that used quaternary ammonium salts in the electrolyte were affected. IIRC, it degrades the rubber and makes the caps leak. Otherwise, UCC LXF and Nichicon PR were pretty good and durable caps, aside from that small detail.

So probably start by removing any further problematic caps and then give the boards a good wash with dish soap and water, then dry for a few days. This should get rid of any leftover electrolyte. After that, inspect the board carefully - particularly all traces. Also try pushing on most components to see if any of them had their leads corroded from the electrolyte. You could have components that look perfectly fine and appear to be in the correct spot... but pushing them may reveal if a lead has become broken.

If all of that checks out, then start the "normal" troubleshooting process for CRTs - i.e. check the HOT and vert. deflection transistor. On later Sony-made monitors (not sure if this will apply to yours or not), HOT is actually separate from HV (high-voltage) generator (i.e. has a separate transistor.)

Might also be a good idea to take some pictures and post them here for people to see. Perhaps a video too? From what you describe based on the sounds the monitor is making, it appears the degauss coil is working (loud buzz that fades) and possibly at least the main supply is running... but perhaps the HV supply/flyback isn't?

That's about all I can think of at the moment.
You don't need an oscilloscope to repair CRTs, though it can certainly make the repair easier/quicker. But multimeter and taking the time to test as many parts as possible should be able to get you to the problem eventually.

thank you for the response!

i was looking at other similar NEC monitor repair logs where it always seemed to have a step of "replace nearly every capacitor", so my next course of action was going to be to look at the main board next. indeed, all of the capacitors i've removed - UCC LXF, taicon and nichicon have leaked from the bottom. washing the board(s) with dish soap were something i did not consider.. i was using 99% isopropyl alcohol on affected areas but that also makes sense!

You could have components that look perfectly fine and appear to be in the correct spot... but pushing them may reveal if a lead has become broken

this very thing did happen with a few resistors, amazingly the ones i have checked on the PSU board are still operating in spec. certainly i can post some photos of the carnage.. though i warn it is pretty gnarly..!

From what you describe based on the sounds the monitor is making, it appears the degauss coil is working (loud buzz that fades) and possibly at least the main supply is running... but perhaps the HV supply/flyback isn't?

indeed the monitor does degauss, and i can hear some other coil trying to start and then shutting off as long as a video source is plugged in.

nevertheless, i've attached a few photos of the crusty, fishy damage:

Hello there fellow multi sync user xD.
Funnily enough I'm also in the process of repairing a NEC multisync , but the original one from 1986(mines built 1987).
And it also had instability and horizontal issues , the caps didn't appear to be leaking as far as i could tell though on mine?
Though from what I've seen online some other people had monitors that did.
I did a nearly full recap but the horizontal is still wigging out. That said I'm going to check out the cap i didn't replace on the B+ rail.
But yeah hopefully your repair goes well.

oheybea wrote on 2025-04-23, 03:22:

hi all! i'm about at my wit's end here... long story short, i have ended up with a very cheap NEC multisync XV17 CRT from 1995 t […]
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hi all!
i'm about at my wit's end here... long story short, i have ended up with a very cheap NEC multisync XV17 CRT from 1995 that has given me a whole load of trouble as i've tried to get it up and running again.

when i first got the monitor, it did indeed work as advertised... in that it would show a picture (albeit a very jumpy and unstable one). one i had built up the courage to finally open up a CRT *and* poke around, i very quickly found out at least one source of these problems. almost every single capacitor in the power supply had either leaked spectacularly, or were starting to. it was so bad that it smelled like fish as i examined some of the worst PCB trace damage i've ever seen. slowly sourcing and replacing these caps, and fixing plenty of destroyed traces got me to a state where the monitor was working much better! no side-to-side picture wobbling, no random horizontal collapse and it could display something for more than 5 minutes without the CRT shutting itself off.

...until i looked back on it, saw that it had lost all horizontal deflection, gasped and shut the monitor off and waited as i sifted through the blocky photocopied service manual i was able to find. now every time i turn it on, it makes the fading-out humming noise as expected, but it doesn't ever turn the CRT itself on at all. previously i could hear a 60 hz buzz from around the back, but now i only hear a rhythmic whining sound that starts and stops whenever the status light is green. i know the control board is still functioning as well as it did before i opened it, because disconnecting a video source changes the light to amber and the whining sound stops.

in the service manual i found, both the horizontal deflection and "no raster" issues i witnessed here effectively tell me to bin the whole power supply (a delta DPS-142AB in this case) or to check its voltages. while i do not have access to a fancy oscilloscope, my multimeter let me know that the floating -5V line was around -5.1V under load, floating +5V was around +4.65, +12V was +12.1, and the +6.3V heater voltage was solid at +6.3V as expected. before i brace myself and completely disassemble the thing to look for potentially even more leaked LXF capacitors, are there any other things i should try in the meantime? thank you to anyone who responds in advance (.^‿^.)

Periodic whining/chirping sound is a symptom of a PSU going into protection mode due to a short, check the power delivery circuit more thoroughly, there should be more power rails than you've mentioned here, in worst case it could be that something on the B+ rail (usually 80-220V DC) has shorted out.

I did a nearly full recap but the horizontal is still wigging out. That said I'm going to check out the cap i didn't replace on the B+ rail.

wow... it really is a pretty common problem. i went overboard and ordered all 40 or so capacitor values called out in the service manual 😮

Periodic whining/chirping sound is a symptom of a PSU going into protection mode due to a short, check the power delivery circuit more thoroughly, there should be more power rails than you've mentioned here, in worst case it could be that something on the B+ rail (usually 80-220V DC) has shorted out.

that would unfortunately make sense... i haven't measured the high voltage rails marked as the "K" connector on the power supply just yet, but it's something i plan on doing as soon as i can devote some quality time working on the monitor.

i'll be sure to keep you all posted - fingers crossed that giving it as much of a once-over as i can at least gets it to display an image again (sob)!

it's been about 10 days, but i am back to say that... it still doesn't work 🙁 at least... for now.

per everyone's suggestions, i decided to disassemble the whole thing and check both the video board and main board that houses the flyback transformer. even though replacing nearly 50 capacitors in total didn't get it working, i am still very glad i did because lo and behold, there were more leaky UCC LXF caps to be found, though i caught these ones just in time as they were just starting to leak from the start of their legs, and hadn't dumped everything all over the board(s) yet.

all of the "low" voltage stuff on the PSU module is operating in spec according to the service manual, and the video board / microcontroller are definitely still doing their job, as the monitor still displays an amber light with no signal (the rhythmic whining also doesn't happen unless there's an input), and my XP dell box detects it as an NEC MultiSync XV17 like expected.

the high voltage stuff on the CN-K though? a total mess. pin 1 is supposed to be around +195V, but my multimeter would jump around in the mV range and freeze up while trying to switch to V measurement, and loop back around again. that gives me an inkling it's very briefly reaching its target voltage, but giving up as soon as it gets the load from a real CRT. the other pins on the HV connector are in a similar state - reading nowhere near their target voltage and often sitting in the mV range (or jumping around in sync with the whine-and-buzz pattern).

as far as i can tell, the whine-and-buzz rhythm is coming from somewhere in the middle of the PSU, maybe from one of the transformers near that area. i did make some bodge wires on a few particularly rotten traces and reflowed nearly every single solder joint on it just in case.

i've attached a photo of the PSU board as well as the whine-and-buzz sounds i got while putting a pickup coil near the monitor, if that helps anyone on where to go next. it has been one crushing defeat after another, but considering the price i paid for it and what ridiculous ebay sellers charge for this model, i'm willing to put in the work 😜

So it would seem the PSU trips shortly after B+ goes up. It can't be a dead short if you see the meter show something but it's soon gone. That being said check the HOT first, could be the PSU doesn't detect the short and what you see is just a couple of volts dropped on the resistance of the copper trace before the overcurrent kicks in. If in doubt desolder HOT and see if the B+ comes up. On some really older stuff this is not very safe for the PSU to have B+ unloaded, I don't think this kind of PSU like on the photo would mind but if you want to be extra cautious then add a load, say a 25W 230V lightbulb. The B+ should be in spec with such load.

Another thing that might be tripping the PSU is HV being too high but that usually needs the horizontal to run for a bit on the first try (say, a second or a half). Later tries might trip faster because tube stays charged. Which is easy to test without any equipment, see if hair on your arm get attracted to the front of the glass. If not, there's no HV so that's not what is tripping the PSU.

Agree with Deunan - check for high voltage (via method he suggested... and also listen if the HV "static" comes up during power on... might have to disconnect degauss coil to hear it) and if nothing comes, then remove the HOT and see if B+ is OK.

As for the picture of the PSU above - I presume this was taken before the recap?? (since there are LXF caps in there still.)
If possible or if you already have them, picture of the bottom (solder side) would be good to have too, just so we can perhaps do some tracing of the PSU. (Usually I use these to determine the how PSU achieves regulation on the secondary side, among other things.)

Don't get discouraged by what's going on so far.
With older CRTs like this, if the tube is still good and they don't require some unobtanium IC replacement (which is rare anyways, since old CRT circuits tend to use more discreet parts), chances are you should be able to revive it and keep it going for many more years. Just keep chipping at it and keep us posted what you find based on the above suggestions by Deunan.

Deunan wrote on 2025-05-03, 23:28:

check the HOT first, could be the PSU doesn't detect the short and what you see is just a couple of volts dropped on the resistance of the copper trace before the overcurrent kicks in. If in doubt desolder HOT and see if the B+ comes up. On some really older stuff this is not very safe for the PSU to have B+ unloaded, I don't think this kind of PSU like on the photo would mind but if you want to be extra cautious then add a load, say a 25W 230V lightbulb. The B+ should be in spec with such load.

Another thing that might be tripping the PSU is HV being too high but that usually needs the horizontal to run for a bit on the first try (say, a second or a half). Later tries might trip faster because tube stays charged. Which is easy to test without any equipment, see if hair on your arm get attracted to the front of the glass. If not, there's no HV so that's not what is tripping the PSU.

a dead HOT would unfortunately explain exactly what happened right before it gave up on me, in that i had looked over after it was running the longest it ever had at once (a whole 10 minutes!) then made some clinging noises before i saw a single white vertical line and hurriedly shut the thing off. before replacing the few capacitors i could on the PSU, it would stay on for maybe 2 minutes at most before shutting the CRT itself off but leaving the microcontroller running.

i tried the arm hair test, and sure enough nothing happened. i have done that to other CRTs so i know what to expect, and this tells me for sure that no HV is getting to the CRT. i can see that the heater is coming on as it should, but that's about it.

momaka wrote on 2025-05-04, 21:04:

As for the picture of the PSU above - I presume this was taken before the recap?? (since there are LXF caps in there still.) If […]
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As for the picture of the PSU above - I presume this was taken before the recap?? (since there are LXF caps in there still.)
If possible or if you already have them, picture of the bottom (solder side) would be good to have too, just so we can perhaps do some tracing of the PSU. (Usually I use these to determine the how PSU achieves regulation on the secondary side, among other things.)

Don't get discouraged by what's going on so far.
With older CRTs like this, if the tube is still good and they don't require some unobtanium IC replacement (which is rare anyways, since old CRT circuits tend to use more discreet parts), chances are you should be able to revive it and keep it going for many more years. Just keep chipping at it and keep us posted what you find based on the above suggestions by Deunan.

oh yeah, i should have said so 😅 that photo was taken before i had done any work to the PSU whatsoever, now all of those fishy smelling UCC caps have been replaced with rubycons and nichicons. i left the two big nichicon capacitors in place as i didn't see any leaking, and they aren't the bad series mentioned earlier on this thread. i do have replacements for the 2nd largest one with the 9442 date stamp just in case, though.
i'm realizing now that i never thought to take a good flat photo of the PSU's traces before, and can certainly do that later today as i plan on tearing it all down again to get to the suspected-dead HOT. i'll still attach the closest equivalent i have for the time being in case it still ends up being useful, which was before i replaced any capacitors but after i scrubbed the bottom of the board with a toothbrush soaked in 99% isopropyl alcohol.

the tube to my eyes looks quite good, and i'm honestly surprised it doesn't have any noticeable burn in as if the built-in "Service Information" screen is to be believed, it has spent at least 48,961 hours powered on 😱
fingers crossed that it is something related to the HOT causing a lack of stable HV from the PSU.. that and hoping i can find a replacement if it is indeed blown!

as promised, here's a photo of the bottom of the PSU, some parts of it really do not look pretty after the capacitor damage... but there's continuity where it needs to be, amazingly.
i got sidetracked with other projects and didn't get to removing the largest main board which houses the flyback and HOT just yet, but i imagine i'll be able to get to it either tomorrow or wednesday.

Deunan wrote on 2025-05-03, 23:28:

That being said check the HOT first, could be the PSU doesn't detect the short and what you see is just a couple of volts dropped on the resistance of the copper trace before the overcurrent kicks in. If in doubt desolder HOT and see if the B+ comes up. On some really older stuff this is not very safe for the PSU to have B+ unloaded, I don't think this kind of PSU like on the photo would mind but if you want to be extra cautious then add a load, say a 25W 230V lightbulb. The B+ should be in spec with such load.

so i desoldered the HOT and the results are interesting to say the least... i am confident that both the HOT has died and there is still a looming PSU problem, as doing a resistance and diode test on the HOT, a 2SC5047, got me this:
in resistance mode - base to emitter ~ 23 ohm, emitter to collector ~ 3 ohm
diode check - ~0.04 V on both collector - base and emitter - base

as for the PSU, i had measured the CN-K pins on its end while the monitor was powered on with the CRT's HV CN-K connector disconnected, and the voltages were still nowhere near what the service manual called out. i can't remember the specific values for everything, but pin K1, which should be +195V, was giving me +85V at best (and this was with no load on the HV at all)

despite the setback, there is a glimmer of hope: with the CRT connected, i can hear more relays clicking in the power supply when a VGA signal is detected, and the light buzzing sound i heard from the CRT before it stopped displaying anything has returned, though there was no vertical line and the arm hair test still came back negative. before today, i would only hear the degaussing coil and the repeatedly-whining sound in the middle section of the PSU. i will say i am a bit on the fence with ordering a replacement HOT while the power supply is still providing way too little HV despite the recap, and am honestly unsure what else to check on the PSU, as i fear the voltage irregularities could potentially zap whatever replacement HOT i put into the monitor as well...

You won't get HV without HOT on most monitors, it's generated by the same pulses that drive the horizontal deflection. In fact quite a few monitors have a simplified PSU that delivers B+ and one, maybe two low voltage rails for the logic circuits, and the rest (like CRT bias voltages, aux. deflection voltages) is generated via flyback transformer.

Your HOT is dead, and your B+ is half of what it should be. I'm too lazy to trace your PSU circuitry but chances are it's a not a flyback topology but more like HF transformer with two primary windings or push-pull drive. This requires two diodes on the output and one of those might have died when the HOT shorted. Depening on the load on the transformer and how the feedback is done it might be producing half the voltage now with that diode open. So you need to test it and possibly replace it. Hopefully the winding in the transformer isn't damaged.

I would suggest fixing the PSU first. Trying a new HOT right now might kill it, and more then likely damage the PSU further. Not to mention possible damage to the the flyback transformer (which hopefully didn't get damaged). Once you get correct B+, or near it, verify it can be loaded with a bulb at least. That's one less variable and much cheaper than having to replace a bunch of parts all over again.

Deunan wrote on 2025-05-08, 10:53:

chances are it's a not a flyback topology but more like HF transformer with two primary windings or push-pull drive. This requires two diodes on the output and one of those might have died when the HOT shorted. Depening on the load on the transformer and how the feedback is done it might be producing half the voltage now with that diode open. So you need to test it and possibly replace it. Hopefully the winding in the transformer isn't damaged.

while i don't have any of the diode replacements on hand, i think you're onto something...
i had checked a diode which traced to one side of the large transformer labeled MP-130B, and it tested as expected, giving around 0.58V on a diode test with the probes facing the correct way, and then OL the other way around, plus a resistance reading of around 2 megaohms. a diode on the opposite end, which unfortunately is covered in some white epoxy obscuring its label, was giving me a lower voltage drop reading on the diode test in both directions with a resistance a tiny bit over 1 ohm, also in both directions...

both diodes were by the larger transformer - the bad one specifically was near the transformer's bottom right-hand corner, and the one that tested OK was near the top right.

i almost want to desolder every diode on the PSU to check if they're bad, but i can't. not yet anyway 😜

Well as I've said the PSU must be working first to test or repair anything else. There is really no point in doing any other stuff unless you get it going, because if it's properly broken and some unique parts are damaged (say the transformers) then the whole PCB is junk, for parts, unless you have another such monitor already to be picked apart.