RCA (Thomson) F20TF10 in a coma

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  • SteveNielsen
    Retired Tech
    • Jun 2012
    • 2327
    • USA

    #121
    Re: RCA (Thomson) F20TF10 in a coma

    I elected to try repairing the connector and connections on CRT board. I epoxied the connector shell to the board and it is solid. Connections from the main board through the cable and the pins on the CRT board connector are good. I soldered thin wires to replace borken traces on the CRT board and continuity checks are all good.

    Before I reconnect everything and test again I want to ask if it is ok to leave the Gem Star 4 board disconnected? I've never used that function and I won't.

    Comment

    • kasfamily
      Badcaps Veteran
      • Aug 2014
      • 765
      • Russia

      #122
      Re: RCA (Thomson) F20TF10 in a coma

      Hi SteveNielsen, welcome back! I do not know what it Gem Star, but perhaps control processor needs information about the board and its serviceability.

      Comment

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

        #123
        Re: RCA (Thomson) F20TF10 in a coma

        No idea but this: http://www.justanswer.com/tv-repair/...el-remote.html suggests it's OK, at least for that model.
        "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
        -David VanHorn

        Comment

        • SteveNielsen
          Retired Tech
          • Jun 2012
          • 2327
          • USA

          #124
          Re: RCA (Thomson) F20TF10 in a coma

          Thanks for the link Agent. I'll try it unplugged. It uses those plastic film ribbon cables that like to come out of connectors and/or break.

          Hi Kas. Gem Star (or Gemstar) is a TV Guide service that tells you all about what's on TV channels sort of thing. I don't think it's available where I live and even if it was I'd never use it.

          Well, anyway, I got the junk all plugged back in and same story, no HV to the CRT, no low voltage turning on. It made no difference having the Gemstar unit plugged in or not. All the previously measured voltages are the same as last time:

          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

          Oh yeah, I also touched up all the solder joints in the area of the flyback.
          Last edited by SteveNielsen; 11-05-2014, 07:41 PM.

          Comment

          • kasfamily
            Badcaps Veteran
            • Aug 2014
            • 765
            • Russia

            #125
            Re: RCA (Thomson) F20TF10 in a coma

            Check the voltage at DP57 (+14VE) and again "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

              #126
              Re: RCA (Thomson) F20TF10 in a coma

              Originally posted by kasfamily
              Check the voltage at DP57 (+14VE) and again "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"
              DP57 = 12.5v but is not the same as +14VE, +14VE is 0v.

              edit: I may be measuring the wrong point for +14VE, I tested the point directly above the printing, however the point to the right has 12.5v and does trace back to DP57.

              These are the best pics I can get. In trying to trace out the paths I get lost under the printing in the n/p x 1 area.
              edit: that was tracing the emitter of TP390 though.
              Attached Files
              Last edited by SteveNielsen; 11-07-2014, 09:49 AM.

              Comment

              • kasfamily
                Badcaps Veteran
                • Aug 2014
                • 765
                • Russia

                #127
                Re: RCA (Thomson) F20TF10 in a coma

                DP63 cathode must be 14V, while the inlet and IP330 is 12V and the output level 9B. So this very little 12.5V. It is necessary to check the CP64 and Zener DP57

                Comment

                • SteveNielsen
                  Retired Tech
                  • Jun 2012
                  • 2327
                  • USA

                  #128
                  Re: RCA (Thomson) F20TF10 in a coma

                  CP64 is a 3300uF 16v and tests 3026uF, 2.8 ohms ESR.

                  DP57 tests ok. It reads as diode, Uf 807m, 32pF.
                  (I don't know what "Uf" is supposed to mean on this tester for a diode, forward voltage? In transistor testing with this tester Uf indicates base-emitter threshold voltage. I assume that it is indicating that the forward voltage is 807mv.)

                  I also checked C62 (470uF 25v) which reads 450uF, 3 ohms ESR.

                  edit: both caps are 85c
                  edit: corrected typo in line 1 to read 2.8 ohms, not .28 ohms.
                  Last edited by SteveNielsen; 11-08-2014, 10:52 AM.

                  Comment

                  • kasfamily
                    Badcaps Veteran
                    • Aug 2014
                    • 765
                    • Russia

                    #129
                    Re: RCA (Thomson) F20TF10 in a coma

                    DP57 painted as zener.UF807m can not find in the series UF800 not http://pdf1.alldatasheet.com/datashe...TE/UF806F.html. And as the voltage DP63 cathode?
                    Attached Files

                    Comment

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

                      #130
                      Re: RCA (Thomson) F20TF10 in a coma

                      Originally posted by kasfamily
                      DP57 painted as zener.UF807m can not find in the series UF800 not http://pdf1.alldatasheet.com/datashe...TE/UF806F.html. And as the voltage DP63 cathode?
                      UF807M is not the model, he says his tester shows 'Uf 807m" which is probably the forward voltage.

                      Originally posted by SteveNielsen
                      CP64 is a 3300uF 16v and tests 3026uF, 2.8 ohms ESR.

                      I also checked C62 (470uF 25v) which reads 450uF, 3 ohms ESR.

                      edit: both caps are 85c
                      edit: corrected typo in line 1 to read 2.8 ohms, not .28 ohms.
                      In a switching PSU around 3 Ohms ESR would be terrible. Here where they use general purpose capacitors it may be more acceptable, but a 3300uF should test lower.

                      Check this ESR table (http://www.jestineyong.com/esr-meter-table/):
                      Attached Files
                      Last edited by Agent24; 11-08-2014, 03:30 PM.
                      "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                      -David VanHorn

                      Comment

                      • kasfamily
                        Badcaps Veteran
                        • Aug 2014
                        • 765
                        • Russia

                        #131
                        Re: RCA (Thomson) F20TF10 in a coma

                        Thanks Agent24 for the correction, and I look very tired search diode UF807m

                        Comment

                        • SteveNielsen
                          Retired Tech
                          • Jun 2012
                          • 2327
                          • USA

                          #132
                          Re: RCA (Thomson) F20TF10 in a coma

                          I'm sorry about that Kas. Thanks very much for the effort.

                          Thanks Agent, I figured 3 ohms was pretty high for it too. The 470uF ESR is pretty high too. I have a lot of gp caps in my collection, I'll look for replacements.

                          Comment

                          • SteveNielsen
                            Retired Tech
                            • Jun 2012
                            • 2327
                            • USA

                            #133
                            Re: RCA (Thomson) F20TF10 in a coma

                            False alarm, my cheap ESR meter wasn't working right, needed new battery. The caps are ok after all.

                            Comment

                            • kasfamily
                              Badcaps Veteran
                              • Aug 2014
                              • 765
                              • Russia

                              #134
                              Re: RCA (Thomson) F20TF10 in a coma

                              I did for the ESR meter external power supply used for this charging adapter from a cell phone. Just tired of changing batteries.

                              Comment

                              • SteveNielsen
                                Retired Tech
                                • Jun 2012
                                • 2327
                                • USA

                                #135
                                Re: RCA (Thomson) F20TF10 in a coma

                                I might do something like that. It wasn't just the battery either, I was using cheap alligator clip test leads that weren't making good contact. They haven't given me much trouble like that before but I suppose it mattered more when the battery got low.

                                Comment

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

                                  #136
                                  Re: RCA (Thomson) F20TF10 in a coma

                                  It makes me think though, maybe you should check all the capacitors in the power supply.

                                  I had a fault in my own TV last week where two capacitors went open-circuit on the -23v rail resulting in a huge amount of ripple on that rail. In turn, that caused the RGB amplifiers to fail to operate correctly and the picture to vanish.
                                  "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
                                  -David VanHorn

                                  Comment

                                  • SteveNielsen
                                    Retired Tech
                                    • Jun 2012
                                    • 2327
                                    • USA

                                    #137
                                    Re: RCA (Thomson) F20TF10 in a coma

                                    I've already checked the PSU caps but am thinking of checking all the caps.

                                    I found the source of the hissing sound though, it is the transformer in the lower center of the board near the power supply. I used a modified stethoscope to find it.

                                    Comment

                                    • kasfamily
                                      Badcaps Veteran
                                      • Aug 2014
                                      • 765
                                      • Russia

                                      #138
                                      Re: RCA (Thomson) F20TF10 in a coma

                                      If the source of the noise LP02, it may be damaged by the ferrite core inductor

                                      Comment

                                      • kasfamily
                                        Badcaps Veteran
                                        • Aug 2014
                                        • 765
                                        • Russia

                                        #139
                                        Re: RCA (Thomson) F20TF10 in a coma

                                        Here is a small example of how customer to look for the noise in the power supply and also thought that the noise transformer and even delayed his wire. A faulty filter capacitor 47uF turned 400V - he was just broken one pin. While the receiver was working, was only affected by noise from the power supply.
                                        Attached Files

                                        Comment

                                        • SteveNielsen
                                          Retired Tech
                                          • Jun 2012
                                          • 2327
                                          • USA

                                          #140
                                          Re: RCA (Thomson) F20TF10 in a coma

                                          It is LP03 that hisses, the one with the yellow around the frame and copper strap. It's marked
                                          VDE (in triangle) 2114390 FEC 0105c
                                          SRV3906-010

                                          Searching on any of those numbers has no results.

                                          Comment

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