Dark picture
Ok, this is no doubt a problem in the "Brightness: area. IF the set wasn't as old, sometimes a control on the main Board, could be adjusted, this would increase the voltage to the CRT drive, and "Brighten" the Picture. However with the set being 10 years old, the components would have aged so much, that I doubt, that it would have any effect. As it would only lift the picture by say a dB or a dB&1/2. If a Picture is VERY dark, say -3dB as I suspect yours, is, say, -3dB, that would be about 1/2 the usual brightness. I have no doubt that the components in and around this circuitry, have become faulty. It also may be that the Switchmode power supply, also may be involved, it may have failed, on that voltage "Rail" and be supplying insufficient current, to make the circuit function properly. It may even, be you CRT "Emission" may have failed somewhat and it is on the "Way out". Due to the age of the set, and the type of problem, you have. In my professional opinion, it may be time for a New unit. In my shop, a repair such as this, regardless, and especially, if it is a whole new CRT, then the cost is going to be quite high. I would recommend that you put the money, that you would spend on a repair, towards a new unit, with a long term warranty. You see, even if you "Fix" your existing problems, a 10 yo, set, is still, a 10 yo, set, and will, now, more than ever, will be prone, to break down again, according to the statistics, for units of that age, 72% of all "Repaired" items, fault again, within the next 12-18 months, usually fatally.. If you do entertain the idea of repair, you need to contact, an Hitachi, local office, and ask for a referral, to an authorised service center. you see at an "Authorised" place, they work on the brand name units all the time, they usually have original parts at hand. they are ALWAYS less expensive. They are honest.. You should then ask for a "Quote" for the repair, before proceeding with any work, this way too, you can make up your mind as to repair or replace.
I do not recommend that you DIY, if only for the type of fault, that you have, and, the prospect, of spending good money after bad, trying to narrow it down, if at first one doesn't and fix it. Also it is in a high voltage area, and considerable skill is required there. I have included a link for a user manual. Below is a thing called a service manual, I couldn't find an exact one for your unit, but, it will give you the idea of whats required to attend to matters like this, it;s what us engineers use to troubleshoot and repair. have a read...
http://www.epanorama.rackhost.net/schematicsforfree/Video/Products/Samsung%20HLN5065W.zip
Below user manual.
www.devicemanuals.com/.../Hitachi/Hitachi-50UX58K-User's-Guide-TVRVM05EZz.html -
