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Blues deluxe..same ole' problem

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  • Blues deluxe..same ole' problem

    Hi all!

    Well it seems these blues deluxe's have a lot of problems. It started with the channels switching on their own. I had it repaired under warranty(about 10 years ago) and was told at first they cleaned the "relays", then a few weeks later I had to take it back with the same problem and they said they replaced the "relays". This worked for maybe a month or two, the problems started again, then eventually the amp just stopped working all together. The amp powers on, all the tubes light up, but I have no sound at all from either input, or channel. If I plug into the power amp in on the effects loop, I do get some sound, and if i strum hard I get a loud distortion sound. I've done some reading about it on here and other forums, and I saw what was mostly suggested;

    TN94-7: For Blues Deluxes serial numbers prior to T-36620, replace R85 & R86 (330 ohm 5 watt) with two 470 ohm 5 watt Wire Wound Footed resistors (Fender P/N 041256). They specifically require "footed" resistors (the ones with the little bumps on one side) that will keep the body about 1/8" away from the pc board.

    TN95-5: Check for value of R71 in channel switching circuit. Early amps have a 10K ohm 1/4 watt. If it is, it should be changed to a 100k ohms 1/4 watt.

    I opened up the back of the amp and saw one of the 470ohm resistors had de-soldered itself. So I checked to make sure the resistor was still good, it was, and I re-soldered it. This however didn't change anything.

    I'm unsure what these "relays" are that they replaced. Is it R71? I'm adding a picture here, is this what I need to check? I measured the ohms of it while on board and it is reading 6.24k Could this possibly be causing my problems?

    http://img31.imageshack.us/img31/6417/p10e.jpg

    This hasn't worked for me in about 10 years, I would love to have it back, so any help would really be appreciated!

    Thank you,
    Joe
    Last edited by lobes; 12-28-2009, 02:02 PM.

  • #2
    R71 is a resistor and not a relay.From the picture your problem is obviously in the area of that 470 ohm resistor.It didnt "de-solder itself" something shorted and burned up that part of the PCB causing enough heat to melt the solder and probably the traces on the PCB.

    Comment


    • #3
      The burn is even worse on the other side. I assumed it was just careless soldering by the guy that "fixed" it. Any idea where I should go from here? Is there anything that I can do?

      Comment


      • #4
        Originally posted by lobes View Post
        The burn is even worse on the other side. I assumed it was just careless soldering by the guy that "fixed" it. Any idea where I should go from here? Is there anything that I can do?
        First, get the right schematic and take some measurements. Be advised that LETHAL voltages are involved and if you have no electronics background you should probably find a reputable shop. That area seems to be your rectifier diodes for your main B+ supply. I would start by pulling the tubes and finding out if the the supply is present and correct. You are seeing the heaters light up which come from a different tap on the transformer. Check the rectifier diodes and resolder everything in that area. If the board is severely carbonized you may have to dremmel it out and replace the traces with jumper wires. My guess is that you have a power supply problem caused by a short elsewhere in the unit. Possibly bad output tubes, but it could be a lot of things. Make sure that your speaker load is good.

        Comment


        • #5
          Blues Deluxe

          The 470 ohm 5 watt resistors (both of them) are used in conjunction with CR22 & CR23 (16 volt zener diodes).
          This is how the +16 & -16 volt supply is developed.
          This is mainly used to power the opamp IC's.
          CR22 & 23 look like they got a bit toasty.
          The 470 ohm/ 5 watt resistor that is standing up is R86.
          Check that you have -46Vdc on one end of the resistor (R86) & -16 Vdc on the other.
          The 470/ 5 watt resistor (R85) next to it should read the same, only with a positive 46Vdc on one end & +16Vdc on the other.
          Get some voltage readings & we will take it from there.
          Attached Files

          Comment


          • #6
            Thank you guys

            Ok, I checked the voltage on the two 470ohm resistors. One of them measures 46v on one side, 16v the other. The other measured -46v on one side, and -66v on the other. Is the resistor bad? Thanks again for the help so far!

            Comment


            • #7
              470 ohm 5 watt resistor

              Sounds to me like it is not connected on the zener diode side.
              Reflow the resistor solder joints.
              If the solder pad is that bad, run a wire to the diode.
              Use your meter on diode check & check each zener diode.
              They should read above 0.650.

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              • #8
                Cr22 is reading 0.600 and cr23 is 0.002. So does this mean I need to reflow the 470ohm resistor solder joints? Or the cr23 solder joints?

                Comment


                • #9
                  CR23

                  .002 on CR23 is not acceptable.
                  It is shorted.
                  Remember I said it looked like it got toasty?
                  The part number is: IN5353B.
                  Now this explains the severe heat on R86.
                  What took out the diode?
                  Either it just decided to fail, or it was caused to fail.
                  Once you remove the diode, check resistance across where the diode was. (from the anode pad to ground.(non striped end of diode. The other end (cathode) is already at ground)
                  This may tell if the -16Vdc rail is being loaded down.
                  If it is, you will want to remove C44 from circuit.
                  Then measure the same point again.
                  If it is a high value (<2K ohms?) then the circuit is probably o/k.
                  Roughly compare it to the cathode of CR22.
                  If the value is low (>100 ohms?) something is amiss on the -16Vdc rail.
                  Happy Hunting

                  Comment


                  • #10
                    You've been a ton of help, thank you!

                    I guess I will hunt this part down. I wonder if radio shack sells it..After I find, and install it, I will update this. I will be one happy guy if this gets my amp working again after 10+ years of it sitting collecting dust. Thanks again!

                    Joe

                    Comment


                    • #11
                      Zener Diode

                      IN5353B is a 16 volt/ 5 watt zener diode.
                      I do not think Radio Shack is going to have them.
                      A quick look showed 5 & 12 volt.
                      Try Newark Electronics, Mouser Electronics, Allied Electronics or MCM.
                      I like to search Find Chips
                      FindChips.com Search
                      I typed in Find Ships one day.
                      Cool site if your a pirate.

                      Comment


                      • #12
                        Thanks Jazz P Bass!

                        Is this what I need?
                        1N5353BRLG ON Semiconductor Zener Diodes

                        Also, should I replace my 10k(measured 6.24k on mine) r71 with a 100k r71?

                        Just out of curiosity, do you believe replacing the bad cr23 is going to fix this thing finally? Or is this just a step by step process, eliminating one thing at a time? I'm afraid of getting prematurely excited

                        Comment


                        • #13
                          I repaired one of these for exactly this problem a few years ago.

                          The problem turned out to be..........................

                          Some of the wave solder residue that sticks to the bottom of the board had become conductive and was intermittently shorting out the channel switching.

                          Step 1: Clean all that crap off the board. All of it, thoroughly.

                          Step 2: Touch up EVERY SINGLE solder joint on that amp. Takes 45 mins or so but you'll be glad you did.

                          You have at least one problem you know about: Crappy soldering. #2 fixes that. Given the symptom you've described, I'd recommend #1 anyway and see if that works. You can test it by watching the values at your channel switching switch contacts change with a VOM as you manipulate the switch. If you dont get the right values every single time, but sometimes it just doesn't seem to work or gives weird values, try #1.

                          Every pcb/wave soldered amp I own gets treatment 2 soon after I buy it. I've found they just are not road worthy/reliable without doing that. I recommend it to everyone who brings me an amp to fix as well. If I just fix one thing, its likely I'll see the amp again soon for a different issue caused by the same global problem: Crappy solder joints. Its easy to do once you've got the amp apart, just do it and save yourself time and heartache down the road.

                          While you are in there, address any cheap component issues. Fender reissues for example use craptastic under-rated resistors in the power supply. Replace them all with better, or it *WILL* fail, its just a matter of when, and it will probably be right in the middle of an important gig. If they skimped on anything, power section resistors and screen grid resistors are the most common but look for other things, replace them with good quality sturdy components. Again, its easy and fast to do once you have the thing apart, so just do it while you're in there.

                          Comment


                          • #14
                            16 Volt Zener

                            Yes that is the correct diode.
                            R71 should be 100K. Here is the link for the 100K resistor:
                            30BJ250-100K Xicon Carbon Composition Resistors
                            As to the amp working or not, you need to take some resistance readings where the diode was, as posted above.
                            If the -16 Vdc rail is loaded down you need to find out why.

                            Comment


                            • #15
                              wizard333-thank you for the advice. I'll be honest though, this amp just isn't worth all that effort to me. I'm not great with soldering or electronics really, but if there is something like replacing a resistor or diode that might fix this, I am more than willing to do it. If what you suggested need to be done I'd definitley take it to a tech, but I also don't want to waste money on this. So like I said, I am hoping for a rather easy, cheap fix. But I do appreciate your advice, thank you!


                              Jazz P Bass-I'm sorry to say that I don't quite understand how to take resistance readings where the diode was. So I'm going to order the parts and I will reply back to let you know what happens when I install them. Thank you again for all your help!

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