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Commodore PET 2001 flyback dead transformer.

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    Commodore PET 2001 flyback dead transformer.

    Dear All,
    I am not a technician and I hope that I have found the right English translation for the part that is dead in my PET 2001.
    Some photos to be sure.
    Can somebody help me to find a spare part?
    Thank you very much
    Attached Files

    #2
    Your English is perfect!

    I have not had much luck in finding one for you either. I will have another look - there are alternative part numbers that can be used. EDIT: Sorry, not getting any hits at the moment.

    What part number is written on the VDU PCB (Printed Circuit Board) that the transformer came out of? It should be something like 320032, 320033 etc. There were three (3) monitors made for this machine over time...

    Just out of interest - how have you determined that it is this component that is faulty? It may not be.

    Dave
    Last edited by daver2; August 27, 2021, 12:37 AM.

    Comment


      #3
      Hello,
      the computer is not with me, at home of a friend that helps me.
      He sent me the attached pictures, are they with the required P/N? They are different than the ones you wrote in your email...
      Flavio
      Attached Files

      Comment


        #4
        Hello Dave, do I have any hope?

        Comment


          #5
          I did have a look, but didn’t find anything.

          The CDU-B79-CMD 9 is the 2001N 321445 monitor.

          I’ll have another look shortly for you.

          Dave

          Comment


            #6
            In the 1970's and later, it became popular to build the EHT rectifier into the body of the line output transformer. It simplified the insulation requirements. In small monochrome TV's or VDU's there is usually just the one EHT rectifier in series with the EHT lead. More often than not, when the transformer fails, it is not the actual transformer windings shorting or going open circuit, is is the EHT rectifier shorting out. This loads the transformer's internal EHT winding during scan time with the capacitance of the CRT bulb, and the transformer appears defective. You can check this by trying to measure any resistance on the EHT winding connection and the EHT cable, it pays to use a VTVM, not a DVM for the test. Still it is always worth adding the new rectifier as a test.

            In any case, often, all that needs to be done to effect a repair, is to cut the EHT cable in the middle of its length and insert another rectifier, these are easy to get on ebay. For a 12" monochrome monitor usually a 15 to 20kV rated part is fine. It needs multiple layers of insulation over the join, usually 12 to layers of heat shrink sleeve is enough, or you can use a section of acrylic tube about 10mm or 1/2 inch internal diameter and about 3 inches long and fill it with non-acid cure silicone rubber over the added rectifier and solder joins.

            These sorts of rectifiers work:

            https://www.ebay.com/itm/35361866049...Cclp%3A2334524

            The best EHT rectifiers in the world are made by VMI (Voltage multipliers inc)


            https://www.ebay.com/itm/19372494502...gAAOSwl4Fflsv3
            Last edited by Hugo Holden; September 13, 2021, 01:27 PM.

            Comment


              #7
              FWIW, the PET prototype and a few of the very early production units used flyback transformers taken from Zenith portable televisions.
              During development they used parts from a Zenith TV for the wooden prototype and later bought a bunch of these TVs retail for parts to use in the pilot production run.
              Unfortunately I don't know what specific model was used and of course the PCB layout changed, so one of those probably wouldn't fit in the footprint anyway, even if it's electrically compatible.

              Also, FWIW, I've never seen one of the flyback transformers fail. Usually it's just a bad solder connection on the board.
              I've seen tubes wear out, resistors burn out, deflection drivers and voltage regulators fail, but never seen a bad flyback.

              Comment


                #8
                Originally posted by daver2 View Post
                I did have a look, but didn’t find anything.

                The CDU-B79-CMD 9 is the 2001N 321445 monitor.

                I’ll have another look shortly for you.

                Dave
                Hello... a bit of luck...?

                Comment


                  #9
                  As Hutch mentioned its uncommon for them to go. How are you certain yours is dead. There has been a ton of bad info going around the internet and youtube videos on how flybacks fail left and right, but this is far from true. When it comes to crt troubleshooting, I never suspect the flyback.. I would suspect the crt itself first.

                  Now i only own two PET's. Both 2001-8 models but those flybacks dont look anything like the flybacks in my systems. The ones i have look very siilar to the flybacks in the ADM 3/A terminal. the ones attached in the photos look almost identical to the ones found in the Apple monitor II model A2M2010.
                  Last edited by VERAULT; December 13, 2021, 05:56 AM.

                  Comment


                    #10
                    For what is worth, I can add that also in my limited experience of about a dozen 9" 2001/2001N monitor repairs I've never seen a bad flyback. It would be interesting to know how it was tested.
                    In other CRT monitor repairs I've found one bad flyback in a DEC VT-340 and on a couple of arcade vector monitors.
                    Commodore issued different versions of the 9" monitors (at least 4 that I have seen) and they have different flyback transformer models (probably only pinout varies on a few of them).

                    Frank IZ8DWF

                    Comment


                      #11
                      From post #2...

                      >>> Just out of interest - how have you determined that it is this component that is faulty? It may not be.

                      The question still stands...

                      How have you (or your friend) determined that the LOPT is faulty?

                      Dave

                      Comment


                        #12
                        You can do a "Ringing Test" on the Flyback Transformer and make the correct decision on it's state.

                        Here is a link to that type testing. https://drive.google.com/file/d/0B8j...ZvttaJ1QzuRmZQ

                        If you don't have the equipment, find a local HAM Operator's Club in your area, and ask for a Technician that can help you.
                        Lot's of older HAM Operators are still around.


                        What is a "Gimmick?"

                        https://www.vcfed.org/forum/forum/ge...or-replacement
                        If you need a short-term solution, you might want to consider using a Gimmick.

                        A short tutorial here. https://www.youtube.com/watch?v=v1wWL6TGWOE

                        https://www.vcfed.org/forum/forum/ge...n-track/page15

                        1. Got a schematic? A "gimmick" is usually just a couple of piece of hookup wire (solid core), not connected to one another, but twisted together. They form a very small value capacitor, whose value can be varied by adjusting the number of twists. Gimmicks are/were used by hams as part of the neutralizing circuit in an RF power amplifier, usually connected between plate and grid to inject a small amount of negative feedback. Gimmicks were also used in old receiver designs where you wanted to lightly couple a local oscillator into a mixer stage.


                        http://www.zimmers.net/ might be of help with a Schematic similar to this one:
                        http://www.zimmers.net/anonftp/pub/c...01N/321445.gif


                        Larry -- KA0DMJ
                        Last edited by ldkraemer; December 14, 2021, 06:15 AM.

                        Comment


                          #13
                          Originally posted by daver2 View Post
                          From post #2...

                          >>> Just out of interest - how have you determined that it is this component that is faulty? It may not be.

                          The question still stands...

                          How have you (or your friend) determined that the LOPT is faulty?

                          Dave
                          Hello. I have asked and he sent me the attached two photos.
                          I completely do not know what they are and what they are used for... I hope you are much more skilled than me!

                          He wrote me that the "yellow" tool reports the FT is NOK, while the white one reports it is OK.
                          He also wrote that the yellow can reach much higher voltages while the white one can only test with some [mA].
                          My friend idea is that there is a loss of insulation internally, so not repairable.

                          Attached Files

                          Comment


                            #14
                            The EHT on all of the three (3) monitor boards for the Commodore PET 2001 machines only (!) operates at some 10 or 11 kV - so not sure why your friend has a reading of 24.5 kV. Is that what your friend is testing it with? If so, he may have damaged them by testing them...

                            Either that, or they are breaking down because they were never designed to operate at that Voltage. Is your friend testing them (erroneously) as though they are a TV CRT perhaps?

                            If your friend is referring to internal insulation breakdown - at what voltage is it breaking down at? If the answer is 24.5 kV - then there is nothing wrong with the transformer...

                            Dave

                            Comment


                              #15
                              The 24.5 kV on the box of the tool. In the photo the tool is off. I confirm that my friend told me that the tested voltage is around 10 kV.

                              Comment

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