cam.in.head Posted March 6, 2023 Share Posted March 6, 2023 hi. this is technical advice in theory ! sort of. have we got any tv / audio / ice electronics engineers on here who would be willing to answer various little questions i have regarding my other hobby ? OR can anyone reccomend a good useable online forum .there seems to be many forums out there but i just dont know which one to join.which one would be most suitable for me. Quote Link to comment Share on other sites More sharing options...
Trooker Posted March 7, 2023 Share Posted March 7, 2023 (edited) I bashed tellies for a couple of years back in the days of the CRT when many of the problems came down to the power supplies, the line output stage or dry joints! Video recorders were also fairly electro-mechanical devices with many issues being belts, idlers, and the occasional i.c. if not the switch mode power supply. I don't claim to be able to design electronic circuits. Nowadays amongst other things I specify and install recording studios for education. No component level soldering required and I haven't used an oscilloscope in at least a decade but I may be able to help point you in the right direction. No idea about forums though, maybe join a few and see which ones have a decent vibe. It won't take you too long to sort the wheat from the chaff. Edited March 7, 2023 by Trooker 1 Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted March 7, 2023 Author Share Posted March 7, 2023 thankyou very much for your reply. im an industrial panel designer/ builder and servo motor engineer by trade and am learning the finer arts of electronics as i go along as my hobby.still got a few crt's under the bed but am now lost on a panasonic plasma power supply. the tv works perfect with another board .no issues .but if i fit this original one it will run for approx half hour (still appears perfect)then one ceramic resistor gets too hot to cope and goes oc. everything on the board looks and seems to test ok.no swolen electrolytics,solder joints good,diodes all ok.etc etc. i was going to try lifting the various fuses and adding a loop of wire so i could amp clamp them and check which circuit is drawing too much, i was hoping to find a nice friendly tv engineer who would say " ah its usually the ******* on those ". will do some more checking tonight with a watchmakers eyeglass ! Quote Link to comment Share on other sites More sharing options...
Trooker Posted March 7, 2023 Share Posted March 7, 2023 (edited) Not a scooby about plasma displays sorry. I suspect that sadly modern TVs are kinda considered throwaway as the time taken to repair rapidly makes them beyond economical repair so finding a TV guy today may be a bit like finding a navigator for a jet. Do you have the circuit diagram and oscilloscope? A half hour fault is such a pain. I’d suggest that any video circuitry has been long established and unlikely to draw much current at all. Sound the same, it’s possible the built in the audio amp may be dying but fairly unlikely. In my day you could unsolder them as they tended to be a single line dil package and had a small heat sink. Maybe get a couple of cans of freezer spray and cool down whatever is driving the plasma and see if that extends the time before the resistor overheats I have no idea what drives the display itself but imagine that there will be either transistors and a transformer to get a very high voltage to create plasma, or, possibly fast switching mosfets would do the same job but I’m very much guessing. I suspect that’s most likely to be what’s drawing the most current but equally the pre-amp stage before the main plasma amp/generator stage may be struggling if the output stage is out of kilter. Just a thought! Have fun! Edited March 7, 2023 by Trooker Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted March 7, 2023 Author Share Posted March 7, 2023 thanks for reply. tonight i have swapped many parts from one perfect board to my other one and still the fault remains. so far i have spent around 50 hours on this .its not that i dont have a working tv now.more a case of ,what is the faulty component on my old board ? obviously for a job this would be not worth it time/moneywise but for a hobby thats a different matter. i dont like to be defeated but my understanding of the full workings of a board are just out of my limitations. oh well. thanks anyway.much appreciated . 1 Quote Link to comment Share on other sites More sharing options...
Trooker Posted March 7, 2023 Share Posted March 7, 2023 Great commitment 👍 Still worth getting some freezer spray 😊 Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted March 14, 2023 Author Share Posted March 14, 2023 found it ! these power supplies use the resistor only for first switch on .then it gets bypassed .in all the time ive been testing this i never reslised that when you switch it on there should be 2 seperate relays which pull in a second apart. the second one was never pulling in and so the resistor was staying in line. relay driver transistor wasnt working. small sot23 device. swapped from other power supply and now gets 2 clicks and resistor stayscold ! fitted new one to other board and now have 2 working boards. that took a while but got there in the end . ! 3 Quote Link to comment Share on other sites More sharing options...
Trooker Posted March 14, 2023 Share Posted March 14, 2023 Well done you! Experience is often hard won. If you have an interest in the older stuff there’s a guy that runs weekly Facebook/youtube videos on restoring valve wireless sets. It seems that he’s now retired from repairs and restoring but doing guides for others to learn. https://www.radio-workshop.co.uk/membership-join/ Quote Link to comment Share on other sites More sharing options...
cam.in.head Posted March 15, 2023 Author Share Posted March 15, 2023 will have a nosy at that. thankyou. yeah if id known how the power supply was supposed to work i would have known that the resistor cannot ever get hot ! its fun learning thou regardless of the time involved with hobbies. it must be or we wouldnt do it ! 1 Quote Link to comment Share on other sites More sharing options...
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