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Damn near started a fire in my Hot Rod Deluxe

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  • #31
    Originally posted by Oldmactech View Post
    Rebuilt the traces on the 470r resistors and the two Zener Diodes.

    R78 and R79 are now +/-48 and +/-16 in spec.

    Some symptoms remain, sone changed.

    Yellow overdrive light still lights even before standby switched.
    Stuck on drive channel, master and drive pots now function not previously. No channel switching.
    Normal volume now no longer functions. .
    No reverb.

    Guitar sounds good if you like the drive channel. Input one is louder than input two.

    Going back to the schematic to look for clues.
    Well, you're getting close. I think you may have issues with not only U3 (4560D), which controls the channel switching, but also U2 which drives the Reverb tank and amplifies the return form the tank, and if it's bad, U1 probably is also, since you've had issues with the bipolar 16V supplies. There's a very good Test Point chart on the schematic to aid in troubleshooting the channel switching (U3A & U3B). On U1 and U2, their outputs at pins 1 & 7 should be at/near 0VDC, when good. Of course, a broken lead in the reverb tank will also be a cause for no Reverb....a very common problem, and simple fix, as long as the tiny reverb xfmrs DCR readings are nominal (about 78 ohms on the input, 220 ohms on the output of the two xfmrs that connect to the RCA connectors).

    If your three IC's are all good, then the clues will be found in the Test Point chart for the switch settings using both the front panel buttons as well as the foot switch, if you have one.
    Logic is an organized way of going wrong with confidence

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    • #32
      No footswitch......dammit.

      Comment


      • #33
        Originally posted by Oldmactech View Post
        No footswitch......dammit.
        No matter......those can be tracked down used, and simple to repair.
        Logic is an organized way of going wrong with confidence

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        • #34
          Measured the iCs

          Pin 1 Pin 7

          U1 15.69 15.69
          U2 -17.1 -17.1
          U3 -8.6 -8.3

          These are VDC.

          I measured several of the test points still trying to make sense of the readings.

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          • #35
            replace IC1, IC2, IC3

            Originally posted by Oldmactech View Post
            Measured the iCs

            Pin 1 Pin 7

            U1 15.69 15.69
            U2 -17.1 -17.1
            U3 -8.6 -8.3

            These are VDC.

            I measured several of the test points still trying to make sense of the readings.
            IC 1 & IC2 (T072) are both bad....replace. IC3.....Pin 1 is TP33, and Pin 7 is TP36. Neither of your readings are correct as shown on the Footswitch TP chart on the schematic, so that IC also is bad...replace with 4560D. TL072 will NOT work for U3.

            NJM4560_E[1].pdf
            Hot_Rod_Deluxe_Schematic.pdf
            Logic is an organized way of going wrong with confidence

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            • #36
              IC 1 & IC2 (T072) are both bad...
              I think you are right, but considering all the trouble the OP has had with his 15v rails, we need to verify that those ICs are indeed getting proper power at the corner pins.

              And when it comes down to troubleshooting the channel switching, PLEASE use the TP guide next to the switching circuit.
              Education is what you're left with after you have forgotten what you have learned.

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              • #37
                Thanks. I’m looking on Digikey for ICs. Lots of choices,I need to be careful to order the thru hole versions.

                I’m not up on the lingo -OP is Original Poster?

                Explain what the TP Guide is?

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                • #38
                  Yes, OP is Original Poster. TP is test point.
                  "Yeah, well, you know, that's just, like, your opinion, man."

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                  • #39
                    Ok, yes I am using the TP guide that is companion to the schematic. I took several readings today and several are not reading what I would expect. I only had a few mins today but will post some later tonite or tomorrow.

                    Thanks.

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                    • #40
                      The ICs in your Fender are what we call DIP - dual inline package - mostly plastic, though some are ceramic. Doesn't matter for you. Your ICs sit on the circuit board with their legs extending through the holes in the board, soldered on the other side. This is referred to as "through-hole" mounting to contrast "surface mount"..Surface mount or SM, are the tiny parts soldered right on top of the board.

                      Other alphabets like SOIC are surface mounts. If it doesn't say DIP, it isn't going to fit. DIP ICs come in various number of legs, depending upon type. DIP-8 means same thing as plain old DIP if it is an 8 legged part.
                      Education is what you're left with after you have forgotten what you have learned.

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                      • #41
                        Thanks for the explanation. TP testing tomorrow, may have to order some parts.

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                        • #42
                          Did TP testing and the results are more than confusing. Almost nothing reads in spec. (And I put a new battery in my old DMM)

                          Test point

                          TP Read Expected Read

                          2 0 100mv
                          3 1.82 1.72v
                          4 -1.9 13mv
                          5 Wandered 252mv
                          6 1.72 1.72
                          7 .3 .33
                          8 220v 850mv
                          9 1.92 1.72v
                          10 .5 500mv
                          11 223v 13.3V
                          12 1.87v 1.72v
                          13 10.74 1.2v
                          14 15.4 66mv
                          15 15.7 66mv
                          16 39 39vac
                          17 35.3 1.2vac
                          18 2.2 1.14vac
                          19 0 870mv
                          20 -18.65 11.6v
                          21 -18-65
                          22 13.56
                          23 -.33 744mv


                          24-30 or so were inaccessible due to mounting on the daughter board housing the tubes. Still mounted in the chassis.

                          Testing was done following the procedure on the schematic. Pots at 1/2, reverb off (CCV) etc.

                          I have ordered replacement ICs for all three. Of note, components R4, r3, R11, R16, R22 all make an audible pop and or scratch when probed.

                          TP 19 Tp20 and Tp 21 - 0, 18.68 and 18.65 are pins 1,3,7.


                          Tp 32 -.49
                          Tp33 -.49
                          Tp34 -14.8
                          Tp35 .5
                          TP36 1.0

                          U2 pins 2,3, 5,6,7.

                          Anyone? Thanks very much.
                          Last edited by Oldmactech; 03-11-2020, 09:46 PM.

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                          • #43
                            Originally posted by Enzo View Post
                            And when it comes down to troubleshooting the channel switching, PLEASE use the TP guide next to the switching circuit.
                            Originally posted by Oldmactech View Post
                            Ok, yes I am using the TP guide that is companion to the schematic. I took several readings today and several are not reading what I would expect.
                            I think you misunderstood Enzo and are referring to the TP layout drawing.

                            On the schematic itself, in the lower left area, there are notes on what voltage you should see on TP's 31-36 under various switch conditions. Those are the ones you need to check for now. Some you can't do without the footswitch, but most you can.
                            "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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                            • #44
                              We were just dealing with you getting your +/- 16V Power Supply stable, then dealing with your Channel Switching NOT working. There is a chart on the left side of the schematic under the heading "Footswitch Operation", which gives you TP31 thru TP36 with specific Footswitch or panel switch settings. That's for sorting out the problems with the Channel Switching operation, which isn't yet working.

                              You had already measured the voltages on U1, U2 & U3. U1 & U2 were latched up, and need to be replaced. And what you had for U3 wasn't anywhere in the ballpark for TP33 (U3 Pin 7) & TP36 (U3 Pin 1). That IC also needs to be changed JRC 4560D. As your amp is, apart from the amp switching and the Reverb not working, functional, so I wouldn't waste time trying to wander thru all of the schematic's Test Points....that WILL drive you nuts, and, we're beyond that.
                              Logic is an organized way of going wrong with confidence

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                              • #45
                                Thanks. Indeed, will drive one nuts. Interesting how Fender puts the test points upside down on the chart.

                                Can’t do anything until the ICs get here, ought to be fun de-soldering all 8 points on them.

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