I'm [attempting to] fix this "space age" Panasonic TV for a friend, and have gotten it mostly working except for the "touch pad" power button. This is the first set I've seen with this, the power is controlled by a touch pad, not a physical switch or button. I didn't even know they had this technology in the early 70s when this set was made, but they didn't seem to have it perfected at the time.

Most of the time, when the set is plugged in, it will turn on. When the power button is touched, the picture will dim slightly and get smaller. I assume the the set is getting a little less power. Touching the button again returns the picture to normal. If you puch it on and off enough, you can get the set to almost turn off, with a very din small picture and almost no sound, but if you push the button again to turn it on, the picture will only get a little brighter and expand slightly. If you unplug the set and plug it back in, you are back at the beginning. Once I was able to get the button to turn the set fully off and on, but then it started to do what it does now again.

I don't have a schematic for the set, and have no idea how the touch button works (I still don't understand those touch lamps :scratch2: ). There is a small circut board that I assume controls the touch button as there is a wire leading from the board to the button. There are no relays in the set, so I assume it cuts the power some other way. Could it be a bad diode or voltage regulator?

I attached a photo of the control board and the front of the set, you can see the button as the silver rectangle over the three small knobs. The set is Model TR-542.

Thanks for any help!

I don't know for sure but I have that identical tv here.I wonder if it controls an off board voltage regulator or something.Mine works fine.I tried to sell this tv at the flea market but no one wants B&W tvs anymore.

I guess if I wanted to take a shot in the dark on that set without a schematic, I would change that one electrolytic capacitor but there is a good chance it won't help. That is, if you have a used one handy to solder in.
I expect you need to search for a schematic but you may get lucky here and some expert here may have had that exact problem and write about it.
Just read about here and there, give advice where you can, and maybe you will get that reply.

Actually, the first thing I did was change that one cap on the board, and like you said, nothing happened...
I'll poke around it some more, and see if some of the voltages change when the button is touched, maybe I'll figure out how it's [not] working.

It's a shame you aren't closer.I'd love to get this set out of my way but it may not be worth shipping.Sometimes you can find a problem by comparing to a properly working one if you can't find a schematic.Or just cannibalize one to get another working. I only usually do that with junkers.Not with working sets though.I was getting ready to donate this and about 5 other 12" b/w solid state sets to Salvation Army if they'll take them.Can't even give away solid state b/w sets on freecycle around here.Listed them twice.Practically can't sell color sets unless they're modern style(plastic case table models with tube width cabinets and the speakers and buttons underneath,black or the new silver always sells better but woodgrain sells as long as it's this style)If it has speaker on the side,a display with the channel no. instead of OSD,wooden case or console it's considered old and they don't want it.Have to sell really cheap(under $20 and that's tough)Have to let turn knobs go for $10 or under.Not even worth the time fixing them.I can't throw a tv away until I try though.When HDTV takes over only tv collectors like on here will want any old tvs at all.

I would check TR87 on the switch board. It is the switching transistor that controls the regulator in the power supply. Looks like most any general purpose NPN transistors (nte123a) will work on that board. Looks like there is an oscillator (which you control with the touch pad) then a wave shaper, two stages of squaring amps, a two transistor flip flop trigger, then a switching transistor to control the main voltage regulator (TR71) through a 10 ohm resistor (R826). Looks like it would have been much cheaper and easier to just leave all that rube goldberg circuit out and use a regular switch in the primary of the power supply transformer. I tried to scan the schematic, but my obsolete hardware is refusing to cooperate today. It is in Sams 1384.
Good Luck
Bill R

At our shop we have been able to sell some of the good quality modern 27" sets that we have fixed, such as JVC's and Magnavoxes from the late 80's/early 90's, as a replacement to people who come in with sets that have fairly big problems.
We then take the old one in as a trade in to use for parts.


We were able to sell a late 1980's GE ctc-169 console to a lady who had a 1988 RCA with power supply problems. She preferred the console style. We have found though that mostly what we sell is service, that of repairing the client's set or if it's a modern one with big problems, that of providing a good reconditioned subsitute.

We really have not been able to sell TV's outright as that kind of customer usually will be looking at the wal-mart etc to buy rather than a service shop.
I did donate a lot of working 1980's sets that I got from Texas Recycles Day to the Helping Hands thrift store and most of them sold.

I think though unfortunately b/w sets are kind of disliked by the general publi c because you can get a 13" color set so cheap like $79.00 and people are too used to color these days.

I know the touch pad works by causing a change in capacitance when touched that causes an osc. frequency to change, and that change is detected and used to switch whatever gets switched. I would help out on the sams too but I don't think our library goes that recent.

I was looking at it again tonight, and now its getting worse, it will turn on and off without me even touching the switch. I'll look into those transistor problems that Bill suggested. I was thinking of just bypassing this board and adding a switch to the volume control, but I would have to find a way to take the board out of the circut, since it is now turning on and off on its own.

Thanks for the Help!

You may need the circuit board if it contains the regulator for the power supply, looks like its really time for the sams cause this is the kind of troubleshooting wit h an unusual circuit that I will really need a schematic to see what's going on. it s too easy to waste a lot of time and frustration on something like this when it's kind of cryptic as to how it really works.

You could probably just pull R826 out to disable the board, but what would be the fun and satisfaction in that? Just kidding, I looked at the schematic and wondered myself what the rational was behind that anyway. Use 7 transistors and all the extra resistors and caps just to do what one inexpensive switch would do. Maybe their thinking was along the lines of more transistors the better. Kind of like the tube counts in some vintage radios. More = better
Bill R