RCA (Thomson) F20TF10 in a coma

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  • SteveNielsen
    Retired Tech
    • Jun 2012
    • 2327
    • USA

    #101
    Re: RCA (Thomson) F20TF10 in a coma

    Thanks, that is what I've been doing, taking pics and tracing out on the computer screen, traces are too hard to see otherwise. That collector connection goes all over the place through jumpers galore.

    You'll have to bear with me though, I have a 9 year old daughter who keeps swiping my camera. Plus I can only spend limited time looking as it hurts my old arthritic neck. I'll keep you updated as I find out.

    Comment

    • SteveNielsen
      Retired Tech
      • Jun 2012
      • 2327
      • USA

      #102
      Re: RCA (Thomson) F20TF10 in a coma

      Sorry for the delay. Here are some pics of that area that are clearer I think.
      Attached Files

      Comment

      • kasfamily
        Badcaps Veteran
        • Aug 2014
        • 765
        • Russia

        #103
        Re: RCA (Thomson) F20TF10 in a coma

        I study photos. IP301 now is voltage on pins ?

        Comment

        • SteveNielsen
          Retired Tech
          • Jun 2012
          • 2327
          • USA

          #104
          Re: RCA (Thomson) F20TF10 in a coma

          Yes, IP301 still has proper voltages; 9.2v on pin 1 and 5.9v on pin 3.

          I've got some of the circuit traced out from pin 26 on the video chip but not completely. So far it goes nowhere near the flyback.

          Comment

          • Andrew F. Ali
            Badcaps Legend
            • Jan 2014
            • 2450
            • Trinidad & Tobago

            #105
            Re: RCA (Thomson) F20TF10 in a coma

            Is that bulging cap opposite the crystal and just above to Main IC??? I see Qio2 next to it but that isn't the label it should be Cxxx.

            Comment

            • kasfamily
              Badcaps Veteran
              • Aug 2014
              • 765
              • Russia

              #106
              Re: RCA (Thomson) F20TF10 in a coma

              Need actual voltage IP330, TP390 and TP391

              Comment

              • SteveNielsen
                Retired Tech
                • Jun 2012
                • 2327
                • USA

                #107
                Re: RCA (Thomson) F20TF10 in a coma

                Andrew, the cap isn't bulging, it's the lighting and shadows. It's labeled CV28 on the other side of the cap.

                Kasfamily, here are the voltages:
                IP330
                Pin 1 = 10.4v
                Pin 2 = 0v
                Pin 3 = 8.6v

                TP390
                E = 0v
                B = .5v
                C = 8.7v

                TP391
                E = -.01v
                B = .67v
                C = .03v

                When measuring TP390 I accidentally shorted B to C which turned on HV to CRT anode.
                Last edited by SteveNielsen; 10-15-2014, 06:37 PM. Reason: Corrected; I shorted Base to Collector on TP390, not Emitter.

                Comment

                • SteveNielsen
                  Retired Tech
                  • Jun 2012
                  • 2327
                  • USA

                  #108
                  Re: RCA (Thomson) F20TF10 in a coma

                  TP390 has already been tested ok out of circuit.
                  I just pulled TP931 and it tests ok as well.

                  My accidental short of B-C on TP390 turning on HV tells me something is not turning that transistor on.

                  Wish I had a schematic for this board.
                  Last edited by SteveNielsen; 10-15-2014, 08:30 PM.

                  Comment

                  • kasfamily
                    Badcaps Veteran
                    • Aug 2014
                    • 765
                    • Russia

                    #109
                    Re: RCA (Thomson) F20TF10 in a coma

                    OK!TP391 controls the supply of 9 volts on pin 26 TA1268 through TP390. Enable signal is applied to the base TP391(may be to press POWER button). If not, need photo area board from N to R and 0 to Z, with two sides. What would follow the chain of signal control base TP391

                    Comment

                    • SteveNielsen
                      Retired Tech
                      • Jun 2012
                      • 2327
                      • USA

                      #110
                      Re: RCA (Thomson) F20TF10 in a coma

                      Yes! Pwr button now functions! WIth the set off though I can still hear quiet hissing but unable to pinpoint it yet.

                      I am able to test the CRT, turned screen control up enough for dimly lit screen, shorted pins 6, 8, 11 and got fairly bright Green, Blue, Red. If the short gets' left on a pin for more than a second or so the set shuts off again. I assume that is normal in this test.

                      Comment

                      • SteveNielsen
                        Retired Tech
                        • Jun 2012
                        • 2327
                        • USA

                        #111
                        Re: RCA (Thomson) F20TF10 in a coma

                        The TV will now come on using Pwr button and will show a full screen of snow for about 1 second then shuts down. If I press a menu button after powering on the menu appers but blinks and image gets vertically squashed then TV shuts off.

                        Comment

                        • kasfamily
                          Badcaps Veteran
                          • Aug 2014
                          • 765
                          • Russia

                          #112
                          Re: RCA (Thomson) F20TF10 in a coma

                          Very good headway! Maybe will take a photo of the screen, but I not clear get all.

                          Comment

                          • SteveNielsen
                            Retired Tech
                            • Jun 2012
                            • 2327
                            • USA

                            #113
                            Re: RCA (Thomson) F20TF10 in a coma

                            Something else just went wrong, the screen is all white with retrace lines now even with screen control all the way down, turning it up it gets brighter and will shut off if turned up past a point.

                            Comment

                            • kasfamily
                              Badcaps Veteran
                              • Aug 2014
                              • 765
                              • Russia

                              #114
                              Re: RCA (Thomson) F20TF10 in a coma

                              Reported connector connected?
                              Attached Files

                              Comment

                              • SteveNielsen
                                Retired Tech
                                • Jun 2012
                                • 2327
                                • USA

                                #115
                                Re: RCA (Thomson) F20TF10 in a coma

                                It's connected ok. The white screen started after I nudged the blue elecrolytic next to the flyback transformer when the set was on. I've pulled the cap and it checks ok. I'm looking for bad solder joints, etc. in that area but see nothing out of the ordinary yet.

                                Comment

                                • Agent24
                                  I see dead caps
                                  • Oct 2007
                                  • 4913
                                  • New Zealand

                                  #116
                                  Re: RCA (Thomson) F20TF10 in a coma

                                  Originally posted by SteveNielsen
                                  It's connected ok. The white screen started after I nudged the blue elecrolytic next to the flyback transformer when the set was on. I've pulled the cap and it checks ok. I'm looking for bad solder joints, etc. in that area but see nothing out of the ordinary yet.
                                  Might pay to just resolder everything in that area just in case, sometimes they're not easy to see.

                                  I also noticed in a previous photo that capacitor is right up against a ribbon cable, perhaps it was not the capacitor being bumped but rather the capacitor bumping the wire?
                                  "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                                  -David VanHorn

                                  Comment

                                  • SteveNielsen
                                    Retired Tech
                                    • Jun 2012
                                    • 2327
                                    • USA

                                    #117
                                    Re: RCA (Thomson) F20TF10 in a coma

                                    That's a good call Agent24, in fact that cable had a bad contact at the CRT board on the same connector (BU004) that I repaired lifted pads/traces for, but it seems to have been the connector itself not quite seated and that problem is gone now. Now I'm kind of back to square one with HV but nothing on the screen, except the power button still works. I am going to touch up the soldering as you suggest.

                                    Comment

                                    • SteveNielsen
                                      Retired Tech
                                      • Jun 2012
                                      • 2327
                                      • USA

                                      #118
                                      Re: RCA (Thomson) F20TF10 in a coma

                                      Well folks, my repair of BU004 on the CRT board has failed. The stress from the stiff cable was too much for it plus I think the contact pins inside the plastic connector shell got mispositioned due to heat from soldering. I guess I could try eliminating the connector, strip back the cable and hardwire it to the board but I'm concerned that would suffer the same fate and tear the traces again unless I glued it down or provide some sort of strain relief for it.

                                      Comment

                                      • kasfamily
                                        Badcaps Veteran
                                        • Aug 2014
                                        • 765
                                        • Russia

                                        #119
                                        Re: RCA (Thomson) F20TF10 in a coma

                                        May be necessary to replace or extend the cable to the BU004. Use for this the softer and more flexible wire.

                                        Comment

                                        • SteveNielsen
                                          Retired Tech
                                          • Jun 2012
                                          • 2327
                                          • USA

                                          #120
                                          Re: RCA (Thomson) F20TF10 in a coma

                                          That's a good idea. Thanks. I'll see what I've got that's suitable.

                                          Comment

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