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Video issue with Apple II Europlus.I need help please.

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    Video issue with Apple II Europlus.I need help please.

    Hello all.

    Yesterday i got my one and only Apple II Europlus with motherboard (820-0001-07).



    I buy it as faulty. Today was the day to start up my effort to repair it. First it has exploded one Rifa inside the power supply that i replace it. I did the same with the second one that was inside. I measure the voltages and all was ok. Every IC is in socket so, i take out every ic one by one i clean the legs and i put them back. I find some that was faulty. That was: A2/74LS00, B6/74LS257, B7/74LS257, B8/74LS174, D13/74LS161 and D14/74LS161. I test every ram IC 4116 and all are in working order.

    After all the above i decide to switch it on. What i got is that:





    What unusual i saw in this machine is one card that looks like hand made. This card connect with one other card that is behind the keyboard. Both card pugged with IDT plugs to A5/SPCL Rom socket, c9/ram socket and A7/keyboard socket. That's mean that original SPCL Rom it is not present. I don't know what this card do and i don't know also if that mod card is responsible for the video issue.

    Here are some photos:








    Thank you and sorry for my poor English and that i upload photos with imageshack. I dint find solution with forum uploader



    You do not have permission to view this gallery.
    This gallery has 1 photos.

    #2
    Hi,

    It is really surprising how many IC's were faulty. How did you determine they were, where you using an IC tester to do it ? I would be suspicious that a number of those IC's would still be ok.

    Back to your question though:

    The video monitor image shows that the H scan oscillator in the monitor is out of lock with the incoming H sync pulses. This means the H hold control in the monitor is likely out of adjustment. You can see from the display there are a number of wide bars, repeating and tilted downwards to the right, this is a typical pattern for the H scan osc in the monitor being out of lock.

    There can be other reasons why the H lock goes off. One could be that the H sync pulse has gone missing or abnormal, or is at the wrong frequency.

    So firstly try to adjust the video monitor's H hold control. If it does not come into H lock, it would be good to look with the scope at the video signals & sync pulses feeding the monitor. I'm guessing that this computer has a composite video output with syncs & video combined.
    Last edited by Hugo Holden; May 13, 2021, 05:18 PM.

    Comment


      #3
      Hello and thank you for your help.

      About the IC's, i tested them with ic tester. The true is that two of them (74LS161) had almost broken leg that why i replace them. But the 2X 74LS257 and the 74LS174 was faulty. The 74LS00 that i wrote that was faulty it was my mistake because it is in working order.

      Now about the video output i tried to adjust the tv monitor with no luck, but i have to say that some times with no reason and not with something that i do i get fully square output on the screen but not static, everything flashes. Then with no reason again the screen goes back to the screen that you saw in my first post. Here is a photo of the square screen output.




      I decide to give a try with other Tv, a modern one. I take from the start a square output but again with every symbol flashing.





      I leave the machine turn on and did some other work. When i get back after 20 minutes i saw the same square screen, but this time static. Nothing was flashing and i had way much clean output. Even after serval reboots i had the same result. Here is the photo.





      To be honest i don't now what to check next. I never had an Apple II before and i am not well know of electronics. Recently i got an oscilloscope and if we can use it to repair that beauty i wait your commands. I will try to find schematics for (820-0001-07) motherboard.

      Thank you!

      Comment


        #4
        Well now the monitor is in horizontal lock, and you can see the abnormal display.

        I am unfamiliar with the Apple computer, so I will leave it to others to explain why the display data is abnormal.

        Comment


          #5
          Nice. Thank you for your help so far!

          Comment


            #6
            I double check every ram again. I found one faulty. I am sure that before it was in working order... anyway. I replace it and i saw the boot screen . The cursor is flashing and the keyboard works but not very good.

            The only problem is that i have vertical lines in the screen. Any suggestion please?

            Comment


              #7
              As I said I am unfamiliar with this computer, but I can say that vertical lines like that suggest that one bit (possibly more) of the video RAM is stuck, or a defect in RAM control. So probably a faulty video RAM chip remains.

              If you know the addresses of the video ram, you can write to it, and if the hardware indicates which RAM looks after the addresses you can then work out which of the RAM IC's is not working.

              I did this once for a Matrox video card in a SOL-20, to find defective video RAM. The method is described in about page 3 to 8 of this article, it should be possible to do a similar thing with your computer:

              http://worldphaco.com/uploads/MATROX_ALT256.pdf
              Last edited by Hugo Holden; May 14, 2021, 03:53 PM. Reason: typo

              Comment


                #8
                I check every single ram and all of them is in working order. I am gonna see the solder side for a cold joint. What I am afraid is that the original character Rom is missing and his job do the hand made card. I thing it is a custom character rom card for two languages. English and Greek. If EPROMs in this card lost some of the data from the years, it is a reason for this behavior? And if yes, what can I do now?

                Thank you.

                Comment


                  #9
                  I wish I could help more, but I have not owned or repaired one of these computers before, but there will be people on this forum who have and surely be able to help you.

                  Comment


                    #10
                    One thing you could check for, with a scope or logic probe, is to fill the screen as much as possible with some symbol or letter or pattern and then look at the output pins of the video RAM chips to see if it is stuck high or low. Even though the RAM IC itself might be ok, it might not be receiving the correct control signals, or one other explanation could be something like a faulty tristate buffer IC on the RAM's output, that buffers it to the bus, or a physical short on a line somewhere. I guess it could be faulty character ROM, but that is probably less likely with the regular vertical lines appearing, which looks more like a problem associated with the video RAM circuits.

                    It would help to have the schematic, the manufacturers circuit description and a scope to test the important points in the video RAM's circuit.
                    Last edited by Hugo Holden; May 16, 2021, 02:21 PM.

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