Philips FR-740 working but no audio output

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  • seve91
    Senior Member
    • Oct 2013
    • 72
    • Italy

    #1

    Philips FR-740 working but no audio output

    Hi everyone,
    i got this Philips FR-740...it powers on, i can see the front display, but no audio output at all.
    No burning components on the motherboard. Any suggestions?

    Here there is the service manual



    thanks
  • CapLeaker
    Leaking Member
    • Dec 2014
    • 8020
    • Canada

    #2
    Re: Philips FR-740 working but no audio output

    Does it power on normally, or is it some error like protect? If it powers up with no error, maybe something is stuck in the head phones jack?

    Comment

    • R_J
      Badcaps Legend
      • Jun 2012
      • 9526
      • Canada

      #3
      Re: Philips FR-740 working but no audio output

      plug in some headphones to see if there is sound from the headphone jack

      Comment

      • seve91
        Senior Member
        • Oct 2013
        • 72
        • Italy

        #4
        Re: Philips FR-740 working but no audio output

        Originally posted by CapLeaker
        Does it power on normally, or is it some error like protect? If it powers up with no error, maybe something is stuck in the head phones jack?
        Originally posted by R_J
        plug in some headphones to see if there is sound from the headphone jack
        No, it powers on normally, no errors.
        No items or other stuff inside the headphones jack.
        Inserting IN and OUT the headphones is correctly detected.
        For example with headphones connected, i cannot enable the surround mode, because it says (take out headphones first).
        If i disconnect headphones, then i can enable surround mode.
        Headphones are working good, very good and clean sound.

        Comment

        • R_J
          Badcaps Legend
          • Jun 2012
          • 9526
          • Canada

          #5
          Re: Philips FR-740 working but no audio output

          Looks like if it has audio to the headphones, there should be audio getting to the input of the stk ic's. Did you try all the outputs? meaning the sorround speakers as well.
          I guess check and make sure you have + & - 40 volts to the ic's, then I would check the solder connections on the ic's sometimes they break
          Since its not in protect I would think there is 0 volts at the + of all the speaker terminals, maybe check and make sure.
          Last edited by R_J; 09-04-2017, 09:15 PM.

          Comment

          • seve91
            Senior Member
            • Oct 2013
            • 72
            • Italy

            #6
            Re: Philips FR-740 working but no audio output

            Originally posted by R_J
            Looks like if it has audio to the headphones, there should be audio getting to the input of the stk ic's. Did you try all the outputs? meaning the sorround speakers as well.
            I guess check and make sure you have + & - 40 volts to the ic's, then I would check the solder connections on the ic's sometimes they break
            Since its not in protect I would think there is 0 volts at the + of all the speaker terminals, maybe check and make sure.

            Yes i tried all the output speaker (2 front, 2 rear, 1 center).
            +40V and -40V is present in both STK, solder connection looks perfect.

            These voltages are printed in the philips schematic:

            STK496-070 (i have STK496-090 in the pcb):
            9 = 39,5V
            3 = 40V
            8 = -39.5V
            12 = -33.6V
            1,2 = -40V
            4,5,6,7,10,11,13,14 = 0V

            STK496-270
            11 = 39,5V
            14 = -33,5V
            10 = -39,5V
            3,4,19 = -40V
            7,8,9,12,13,15,16,17,18,20 = 0V

            Measured those values, all verified. But -33.5V and +-39.5V is a little bit higher, cause voltages are 40.2V.

            Comment

            • seve91
              Senior Member
              • Oct 2013
              • 72
              • Italy

              #7
              Re: Philips FR-740 working but no audio output

              advices?

              Comment

              • seve91
                Senior Member
                • Oct 2013
                • 72
                • Italy

                #8
                Re: Philips FR-740 working but no audio output

                please any help?

                Comment

                • stj
                  Great Sage 齊天大聖
                  • Dec 2009
                  • 30944
                  • Albion

                  #9
                  Re: Philips FR-740 working but no audio output

                  any schematics around?
                  philips used to sell the service manuals so someone must have scanned one!

                  Comment

                  • seve91
                    Senior Member
                    • Oct 2013
                    • 72
                    • Italy

                    #10
                    Re: Philips FR-740 working but no audio output

                    sure, here is the link:


                    but can't figure it out what is the problem. Voltages seems to be all present. Maybe the final amplifier are broken

                    Comment

                    • stj
                      Great Sage 齊天大聖
                      • Dec 2009
                      • 30944
                      • Albion

                      #11
                      Re: Philips FR-740 working but no audio output

                      page 16,
                      make sure all 6 volume settings are centered.

                      page74 shows the audio leaving the input selector into the amp circuits through an electrolytic.(2541,2542)
                      i would scope or tap off of that to see if the audio is making it through the switching section first.
                      this is a complex bastard, but atleast the schem's are readable!

                      Comment

                      • seve91
                        Senior Member
                        • Oct 2013
                        • 72
                        • Italy

                        #12
                        Re: Philips FR-740 working but no audio output

                        Originally posted by stj
                        page 16,
                        make sure all 6 volume settings are centered.

                        page74 shows the audio leaving the input selector into the amp circuits through an electrolytic.(2541,2542)
                        i would scope or tap off of that to see if the audio is making it through the switching section first.
                        this is a complex bastard, but atleast the schem's are readable!
                        page 16, all volumes centered.
                        page 74: i have signal on both 2541 and 2542. Checked the output of the opamp (pin 1 and 7), signal is good.
                        page 75: i have signal on inputs of TDA7437, front and surround ok
                        page 76: i have signal on 2534 and 2535, no signal on 2536-2537.
                        page 79: i have signal on 2310-2316, and also 2334 if i enable surround. no signal on 2905-2913 even with surround on.

                        Comment

                        • R_J
                          Badcaps Legend
                          • Jun 2012
                          • 9526
                          • Canada

                          #13
                          Re: Philips FR-740 working but no audio output

                          On page 79, whats the voltage on Q7310 collector? Also check if the amp on/off circuit is working.

                          Comment

                          • seve91
                            Senior Member
                            • Oct 2013
                            • 72
                            • Italy

                            #14
                            Re: Philips FR-740 working but no audio output

                            ok, page 79:
                            A of 6305: 0V
                            K of 6305: 3.2V
                            C of 7309: 0.04V
                            C of 7304: -41.5V
                            C of 7310: -41.5V

                            Comment

                            • seve91
                              Senior Member
                              • Oct 2013
                              • 72
                              • Italy

                              #15
                              Re: Philips FR-740 working but no audio output

                              any help?

                              Comment

                              • R_J
                                Badcaps Legend
                                • Jun 2012
                                • 9526
                                • Canada

                                #16
                                Re: Philips FR-740 working but no audio output

                                It looks like the comand from the front panel is not turning on the amp, I think A of 6305 should be around 4.5 volts not 0
                                On page 34 the Amp lr on comand comes from ic7412, I see there are also a couple led's off that ic, dvd & Surr, is it posible to comand those led's to change from the front panel? to make sure the ic is receiving comands.
                                Last edited by R_J; 09-30-2017, 01:31 PM.

                                Comment

                                • seve91
                                  Senior Member
                                  • Oct 2013
                                  • 72
                                  • Italy

                                  #17
                                  Re: Philips FR-740 working but no audio output

                                  Originally posted by R_J
                                  It looks like the comand from the front panel is not turning on the amp, I think A of 6305 should be around 4.5 volts not 0
                                  On page 34 the Amp lr on comand comes from ic7412, I see there are also a couple led's off that ic, dvd & Surr, is it posible to comand those led's to change from the front panel? to make sure the ic is receiving comands.
                                  Yes, both leds are working DVD is on when input 6CH/DVD is selected. SURR is on when you push surround button (surround is not available in 6CH/DVD mode)

                                  Comment

                                  • R_J
                                    Badcaps Legend
                                    • Jun 2012
                                    • 9526
                                    • Canada

                                    #18
                                    Re: Philips FR-740 working but no audio output

                                    looks like ic 7412 is working, Do those other lines change like the Amp lr on (pin 6 of 7412) or mute (pin 7) Those lines could be checked on plug 1410 also
                                    Last edited by R_J; 10-06-2017, 04:19 PM.

                                    Comment

                                    • seve91
                                      Senior Member
                                      • Oct 2013
                                      • 72
                                      • Italy

                                      #19
                                      Re: Philips FR-740 working but no audio output

                                      Pin 6 always 0, pin 7 alway 4.9V

                                      Comment

                                      • R_J
                                        Badcaps Legend
                                        • Jun 2012
                                        • 9526
                                        • Canada

                                        #20
                                        Re: Philips FR-740 working but no audio output

                                        On plug 1410 pin 11 amp prot (page 34) do you have 4.4 volts? Its hard to follow where things connect in this old type pdf (can't search)
                                        Last edited by R_J; 10-06-2017, 05:33 PM.

                                        Comment

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