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PDP11/20 restoring

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    #16
    I'm working on the H720F power supply at the moment. I was quite surprised to see two 1 Amp 1N4001 rectifier diodes are fused with a 5 Amp fuse. So the load on the 8V could go up to 5 Amp without tripping the fuse. In the meanwhile the diodes will short circuit and there is no fuse in front of these diodes. This will fry a few PCB tracks.
    8V power.jpg

    And again fried connectors...
    Fried H720 connectors.jpg

    I've seen this in several dec machines. Pulling the full 5V current on just one tiny contact... And if there is a short circuit, traces will be blown away instead of a proper fuse... Since I have to make a new power harness I will add some wires to bypass the connectors. But I'm surprised to see these kind of problems over and over again...

    Guess the +5V in my 8/M for example... Made a bypass on that one too...
    03.jpg 04.jpg

    Regards, Roland
    WTB: Case for Altair 8800 ...... Rolands Github projects

    Comment


      #17
      Originally posted by Roland Huisman View Post
      .. I've seen this in several dec machines. Pulling the full 5V current on just one tiny contact... And if there is a short circuit, traces will be blown away instead of a proper fuse... Since I have to make a new power harness I will add some wires to bypass the connectors. But I'm surprised to see these kind of problems over and over again...
      Us DEC field service techs have seen dumpsters full of burnt DEC switching power supplies. Not just the connectors, but good sized charred black holes where PCB material used to be. ex: H744's had a number of ECO's in ongoing attempts to improve the design and reduce the number of scrapped power supplies.
      WTB: DEC PDP8-E rack header panels
      FPP8-A, TM8-E, H851, PC04

      Comment


        #18
        Originally posted by ftcnet View Post
        Us DEC field service techs have seen dumpsters full of burnt DEC switching power supplies. Not just the connectors, but good sized charred black holes where PCB material used to be. ex: H744's had a number of ECO's in ongoing attempts to improve the design and reduce the number of scrapped power supplies.
        I spent some time repairing H744, H7440 and H7441 supplies. The four H744 had their bridge rectifier blown. One of them in very spectacular way in that the metal top with the heatsink was gone (wonder where it ended up?). All the H744 had one burnt off AC inlet connector-termninal. It acted as a fuse... The H7440 and H7441 had switch transistor casualties. In the H7441 even most components in the driver stage and the free-wheel rectifier were fried while the H7440 only had a bad output cap aside from the main switch transistor.



        www.datormuseum.se

        Comment


          #19
          So I'm clearly not the only one with DEC power issues

          Originally posted by pbarton View Post
          Regarding "Another thing which got my attention are these capacitor boards. Does anyone have pictures and/or a model name of them?"
          That is a G8000 +8V Filter Network.
          That makes sense! while studying other documentations I found that G8000 more often. It seems that I need
          one if I want to use a M7800 serial card on a DD11-A SPC backplane in combination with a 720 power supply.

          G8000 position.jpg

          In the meanwhile I found the little schematic of the G8000 and combined with the little picture
          I think it should look a bit like this sketch...

          G8000 trial.jpg

          Does anyone have a picture of the G8000 front and back so I can copy the texts as well?
          Thanks in advance!
          WTB: Case for Altair 8800 ...... Rolands Github projects

          Comment


            #20
            Originally posted by Roland Huisman View Post
            Does anyone have a picture of the G8000 front and back so I can copy the texts as well?
            Thanks in advance!
            I have photos of the G8000A (lacks the diode, I think) here:
            http://svn.so-much-stuff.com/svn/tru...EC/Gxxx/G8000/

            Vince

            Comment


              #21
              Originally posted by vrs42 View Post
              I have photos of the G8000A (lacks the diode, I think)
              Hi Vince,

              Thanks a lot! Google didn't show that card on your site. And I didn't expect 16 bit related stuff on your site Your pcb has also the diode. I have updated my PCB and ordered a few. I refused to add the 'FLIP CHIP' text mirrored on the back of the PCB...

              G8000 render final front.jpg

              And tonight I have finished my brand new power harness. I used an old 9 slot backplane to keep the right distance between the boards. The GND and +5 are made double so the full current does not have to go trough one single pin any more... So soon I can check my power and also if I have the right voltages on the boards before I power it up with them in the backplane off course.

              IMG_20210408_191936.jpg IMG_20210408_215904.jpg Nieuwe kabelboom.jpg

              Regards, Roland
              WTB: Case for Altair 8800 ...... Rolands Github projects

              Comment


                #22
                Tested the power supply and power harness. I made one mistake, I swapped the -15 and -25 on the H720 connector. So I corrected that and the band new cable was ready to use in the machine itself.

                The front panel had a rough time once... A resistor broken, and four bulbs were replaced by LED's. When they removed these four bulbs they damaged the pcb vias at this place. You need to be very careful to remove these bulbs. And to use LEDs they removed the pre-heat resistors. Since 25% of the bulbs were broken I decided to replace all of the bulbs with new bulbs. Removed the LEDs and replaced the pre heat resistors.
                01 front.jpg 02 front.jpg 03 front .jpg 04 front.jpg

                There were several modifications on the backplane. One of them was even a relay to switch a ssyn signal. There were some other modifications done to the backplane. Most of them were for the two SPC slots. I've brought everything back to original, added the wiring for the G8000 boards.
                05 backplane.jpg 06 backplane.jpg

                I've made a drawing for the fan panel but in the meanwhile I've decided to test with a temporary solution
                08 fans.jpg

                Top cover is ready, when all covers are done I will paint them black as the rest of the cabinet.
                07 top cover.jpg

                First test learned that bit 6,7 and 8 were always on and bit 9 always off. I fixed that with replacing two 7474, one 7420 and one 7430 on the M725 board.
                09 PDP11-20 first power on.jpg

                Loading an address works, examine addresses is behaving weird while depositing is counting up the addresses in a good way. Still a lot to do... A little demo from what it is actually doing now...



                To be continued...
                WTB: Case for Altair 8800 ...... Rolands Github projects

                Comment


                  #23
                  Some people are missing the XX2247 key, but I have the opposite problem.
                  I'm missing the XX2247 lock itself and all parts with it. I've been searching on the
                  internet for pictures of the lock construction. It seems that it is the same construction
                  as from the PDP8/L. So I can copy that construction.

                  The biggest problem is getting the lock itself. It would be great if someone could actually
                  sell me such a lock. But I'm afraid that most people would not let go of their parts...

                  So I've been looking for a tubular lock on Ebay. Most locks have one or two slots to pull back
                  the key in a certain position. But DEC had three positions off-power-lock. I think I have to live
                  with that problem. But I was wondering, are these locks also available on the XX2247 spec?
                  Or am I forced to use just a different key?

                  Lock.jpg

                  Regards, Roland
                  WTB: Case for Altair 8800 ...... Rolands Github projects

                  Comment


                    #24
                    Does anyone know where I can find the KM11 overlay for the PDP11/20?

                    Thanks, Roland
                    WTB: Case for Altair 8800 ...... Rolands Github projects

                    Comment


                      #25
                      The RICM has most of a PDP-11/15 system. I believe that we have all of the boards to make a processor. We don't have the backplanes for the KA11. Any leads would be appreciated.
                      Member of the Rhode Island Computer Museum
                      http://www.ricomputermuseum.org

                      Comment


                        #26
                        I don't have the original KA11 overlay but here's a picture of the overlay from Guy Sotomayor's replica. His overlays match the originals that I have (11/35, 11/45, RK11-D) so I'm confident this will also match the original. Guy's boards use LEDs and machined light baffles, so the physical dimensions of the display board are slightly different from the original but functionality and signals are the same. 1120_overlay.jpg
                        Jack
                        www.computerarium.org

                        Comment


                          #27
                          Hi Jack,

                          Thanks a lot! It seems he still has them on his website. If these fit on the
                          original KM11 than it might be a good idea to order a set of these overlays...
                          I only have a set for the 11/05 and the RK11D. The paper protection foil is still on the
                          RK11D and I have no idea how to get it off without damaging it... The glue is hardened...

                          Originally posted by m_thompson View Post
                          The RICM has most of a PDP-11/15 system. I believe that we have all of the boards to make a processor. We don't have the backplanes for the KA11. Any leads would be appreciated.
                          Well, I wonder if there is any wiring list for the 11/20 backplane like there is for the PDP8/L. I haven't found in yet.
                          When you have a wiring list you should be able to make your own backplane from three unibus backplanes.

                          If anyone knows where to find the wiring list then please let me know. Sometimes it is
                          hard to find a signal on the backplane... So I could use it too...

                          Regards, Roland






                          Last edited by Roland Huisman; April 16, 2021, 11:12 PM.
                          WTB: Case for Altair 8800 ...... Rolands Github projects

                          Comment


                            #28
                            Unfortunately, Guy's overlays don't quite line up with the lamps on the original KM11 but you could certainly use one as a basis for a replica to fit the original. Given your talents, it should take you about 5 minutes to scale one up and print it on a transparent sheet. :>)

                            Not sure why the uploader chose to invert my image, but so be it.
                            KM11_twice.jpg
                            Jack
                            www.computerarium.org

                            Comment


                              #29
                              Hi Jack, too bad... Then I will print your layout on a transparent sheet. Good enough for me...
                              WTB: Case for Altair 8800 ...... Rolands Github projects

                              Comment


                                #30
                                I've been given an original lock for the machine. But it had some issues. Two of the rollers were cracked at multiple places.

                                12 lock broken.jpg

                                So I made a negative silicone mould in vacuum to prevent air bubbles in the copy.
                                Then I filled that with a two component casting resin.

                                13 Making a mould.jpg

                                Next is to drill the hole for the screw and you are ready to go.

                                14 copies.jpg

                                Now the lock is complete and working again. I made a few spares as well.

                                14 lock fixed.jpg

                                In the meanwhile I painted the covers. The fan panel is made by a watercutter at the moment.


                                10 covers black.jpg

                                All baby steps to get the least original PDP11/20 in the world

                                Regards, Roland
                                Attached Files
                                WTB: Case for Altair 8800 ...... Rolands Github projects

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