Help fixing strange NEC CRT TV noise - Page 1
Forum section: electronics / repair

author: OriginalDan
author_rank: Contributor
timestamp: January 11, 2023, 07:30:56 am
content: hi I've got aNEC ST-2602 CRTfrom 1986 the last few boot ups is giving a really odd sound thats rapidly getting louder with each brief use, its not the usual 15khz whine nor is it arcing, i couldn't find any schematics for this model the only somewhat similar schematics is for 120vcm-1991a/2591abut that version appears to have a different board layout. and mine is 240vjust a warning the mp3s have 15khz whine and i had to normalize boost the volume as the phone didnt pick it up well but its quite audible in real lifenoise1.mp3 is what ive recently heard, noise2.mp3 the sound changes if i adjust the vhold dialfirst assumption is a dying cap or two on the vertical line somewhere but i took off the back cover off:album of the inside with higher res imagesjust a quick inspection the boards have majority rubycon capacitors that all appear fine,img06img07img08around the flyback transformer is dirty but nothing stands out to me,theanode cap image24looks worn but that might just be dirty, I'm not sure where'd id find a replacement anode wire and cap as the rest of my crts are much smaller 14"17" not 26"the neck board transistor legsimage17all have similar gunk on the legs, they might be worth replacing? although the 'NEC C1506 L4YS' seem rare at roughly $52AUD for 2x of themhttps://datasheetspdf.com/pdf-file/785150/NEC/2SC1506/1unsure if there's a modern equivalantso I'm kinda stumped, I'm gonna wait atleast a day before i discharge the anode and remove the chassis board for better imagesi was going to gift this to a friend who wanted it for retro consoles but it really sounds like whatever part/parts are making that noise more and more is gonna die very soon, so id hope we can find the cause for preventive maintenance before something goes pop as parts like the flyback are impossible to find nowrecalled a louis rossmann video mentioning to not straight away clean a board as it might erase clues leading to the issue so i might hold off on that for now but it certainly needs a clean, maybe some of those transistors replaced but for over $100 it doesn't seem worth it, a full recap seems excessive given they're not nonamesany suggestions?

author: inse
author_rank: Super Contributor
timestamp: January 11, 2023, 09:44:52 am
content: 1st of all: clean the chassis with either a brush and a vac or compressed air.Check the solder joints at the FBT.The noise might come from a loose ferrite core, you can carefully poke around with an isolated tool (chopstick) in the running set trying to locate the culprit.Include also the deflection coils.I have never seen a worn out anode cap, if there was an isolation problem you would have noticed discharges.Except from the noise, the set works fine?Transistors don’t emanate noise.

author: OriginalDan
author_rank: Contributor
timestamp: January 13, 2023, 03:55:43 pm
content: thanks, i left it for 2 days. no pop or anything on the discharge, hosed the mainboard down and again with demineralised water, then scrubed with 99% iso, it did have white film forming on it i assume is leftover from the tap water or factory flux but a few rounds with iso seemed to get it ( don't have after pics due to iphones being the worst thing imaginable)stupidly right at the end i forgot to plug the anode back in and booted it up to some screeching, turned off and redid the discharge on the anode plugged it in and thankfully i didn't fry myself or anything elseit's an improvement i can still slightly hear it but only with no input static, when i had a vhs playing via the composite bnc input i couldn't hear the noise anymore, when i can hear it, it's a lot more quietso hopefully for now the problems solved, poking around with a plastic tool when the noise was notible didn't seem to have any effect so I'm not sure. best wild guess is some parts near the flyback might be on their way out judging by the heat discolouration on a few components?was hoping itad be possible toRGB modbut with no OSD i don't think it's possible. the two primary ICs areUPC1365C-NECwhich has rgb output but no input, although there is a luminance input so it Might be possible for an svideo mod?the other IC isUPC1377Clooks like id grab sync from that chip if svideo was possible, i don't quite know enough yet and without schematics I'm likely to kill something lol.also i lost a fair amount of images transferring from an iphone to windows because i moved images instead of copying, cancelled after the first two and somehow lost half the images, never had that happen on any android phone T_T

author: inse
author_rank: Super Contributor
timestamp: January 13, 2023, 05:18:29 pm
content: I had this white residue also after cleaning PCBs, I assume this is undissolved ingredients from the flux and should not be an issue.