songoffall wrote on 2024-02-29, 13:30:At this point in time, I want to go through a checklist. First reason why this might be happening is the ray not being able to recover fast enough after bright and dark pixels. That points to the high voltage power capacitors.
That's what I thought about the 15" HP, but the high voltage caps on B+ were still relatively OK... though I didn't have time to check them for excessive leakage current, so still debating on that one with myself.
songoffall wrote on 2024-02-29, 13:30: I replaced the filtering cap which was definitely dead - bulging cap, melted bottom, readings at about 25% of its spec - but there are many more caps I should go through before ruling the power board out.
Ooof, that pretty bad. By the looks of it, that's the main filter cap at the input of the PSU. I'm surprised it failed, as those usually last the lifetime of the tube/PSU - even from not-so-great brands like Samyoung.
songoffall wrote on 2024-02-29, 13:30:Estimated lifespan of electrolytic caps is 10 years, and this monitor has been working without recapping for 25+ years I think. A complete recap might be in order here.
Yes, a recap is likely in order, though I wouldn't say because the capacitors are over 10 years old.
In my experience in the field, capacitor lifetime can vary A LOT.
Obviously inferior brands don't usually last anywhere as long as the known-good Japanese brands do. But even then, if someone asks me how long any capacitor will last, I always say "it depends".
And it depends on the following:
- temperature: the higher the temperature where the cap is used or was stored will work to reduce its life span. Generally, for every 10C drop in temperature, the life span doubles.
- aqueous vs. non-aqueous chemistry: while non-aqueous chemistry doesn't offer as low-ESR as aqueous chemistry (and as such is more likely to run hotter in higher-frequency circuits, thus resulting in reducing its life span) , it's also usually more stable long-term. So that's part of the reason why general purpose 85C and 105C capacitors rated for 2000 hours (what's commonly found in CRT TVs and monitors) still tend to last for so many years. Of course, the ones from less-than-great brands like Samyoung won't last as long as equivalent Japanese offerings (such as Nichicon VZ/VR, Rubycon YK/PX, Panasonic M/NHG, and United Chemicon SMG/KMG.) In that regard, this is where I really appreciate Sony CRTs - they almost exclusively use Japanese capacitors.
- age / manufacturing technology: <-- this one is a bit odd. I find that some very old but good quality caps from the 70's and 80's that are made with thicker foil (they look huge compared to modern caps) may last for quite a while. Case in point, I just cracked open my dad's Sony stereo amplifier that's made in the late 70's because it would take over 30 minutes to turn On when cold. I suspected I'd find bad caps, but so far none. Not only that, but the original 40 Y.O. Nichicon and Nippon ChemiCon caps are reading quite well in terms of ESR and capacitance. Only a few are starting to linger near the +20% mark on capacitance. However, when I checked them for leakage current (high leakage current is often why a cap will read high capacitance on a cap meter), they were 100% in spec. So it goes to show that not all old caps need replacing.
-brand: obscure "no-name" brands always seem to fail sooner than others. Then there's the less-than-great brands like Samyoung, SamWha, Teapo, OST, Jamicon, L-tec... and countless others... that tend to do OK for the useful lifetime of the device, with some exceptions here and there. And then there's the Japanese brands (mentioned above) that almost always will outlast the useful lifetime of the device, and then some more.
songoffall wrote on 2024-02-29, 13:30:I am unwilling to let the CRT go in any scenario, because there's a limited number of them left and every scrapped CRT is one less. Especially a pretty decent CRT like this one. I mean, it's no Trinitron, but it's quite good.
Totally understandable, and I feel the same way too when it comes to CRTs. Trinitron or not, I like to save them all. Actually, I myself prefer most shadow mask monitors over Trinitrons, especially these late Samsungs, as they have pretty decent picture and geometry. I'm still kicking myself in the back for not picking up that 2nd Samsung 955DF when I had the chance many years back (lady in an office was giving 2 of them away, but I only picked up one because I didn't want to deal with all of the mocking from friends and family at the time, telling me that collecting CRTs is stupid.) My favorite by far are Hitachi and NEC -tube monitors. As for Trinitron, I only like the older ones made before 99-2000 (ones with the horizontally non-flat tubes.) In terms of color balance, the last generation(s) of Trinitron leaves a lot to be desired, IMO, especially the larger 21" CRTs.
