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  • Apple A2M6021X Monitor Repair.

    Fix this a few weeks back and been meaning to write up a quick repair log.
    This is the 240 volt version of Apple's colour composite monitor which is NTSC 50htz. This monitor will only work with Apple IIe Platinum's with the NTSC International motherboards which have a specially clock to NTSC 50htz. The American ones are 60htz so these are special to our region. My 240 volt Apple IIc also works in colour with this monitor. It will not work with the PAL adapter.

    I bought the monitor from Ebay knowing it was faulty with the hope to get it going considering how hard these monitors are getting to find now I thought I'd take the punt.
    The seller tried selling it for $300 BIN! $300 for a faulty monitor? tell him he's dreaming! Naturally after a few weeks it went up for auction and I got it for $120 bucks and thanks to @furballx and @WOKA it made the trip up north into my greasy hands.

    On first turning it on it made a ear piercing scream...ok not good I immediately thought shit bad Flyback Pulling the monitor apart to my horror there was a wire hanging down off the neck board (focus) and I could see straight away somebody had tried a gunshot repair. All caps had been replaced and a bunch of resistors and diodes too.
    Don't you hate when you buy something listed as "oh it just stopped working" only to find out it's been messed with.....shame that wasn't in the listing. What makes matters worse is there is no information or schematics available for this monitor anywhere!

    Taking the back off I turned the monitor on and managed to pinpoint the squeal which was coming from the little transformer which is part of the switch mode power supply. The switch mode supply's the B+ which should be sitting around 115 volts however it was only around 75. After talking to @Jomac he suggest there could be a short in the EHT. Without any way of testing the EHT I removed it to see if the B+ would jump back up to where it should be.

    Sadly it didn't but I more confidant that the flyback was ok. I decided to focus my attention on the switch mode section where a number of resistors had been replaced.
    Click image for larger version

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    Pulling the back off two problems already, the convergence rings have been misaligned and the bigger issue is who ever reassembled the chassis fed the two wires under the shroud. One of the wires insulation was stripped back and touching the shroud grounding it.
    Turning it on again I pinpointed the squeal was indeed coming from the switch mode transformer.
    Click image for larger version

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    Doing some measuring with the multi meter the two diode circled in red were shorted. Seeing as the monitor had been fiddled with I started pulling up the resistors which had been changed. Pulling up the 27 ohm resistor @R504 circled in black the diodes read correctly. Without a schematic it all I could do guesstimate the value based on other schematics I found using the STR40090 regulator. all I know for sure is it should be in the Kohm range not ohm!
    Click image for larger version

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    All I had was a pair of 22Kohm 2 watt resistors tied them in series to make 44k. We now have a nice 115v on the B+
    EDIT: @R504 has since been confirmed to indeed be 27 ohm. I haven't changed mine back and is still running strong.
    Click image for larger version

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    Suicide test setup!
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    No squeal and now I have something on the screen even if it is vertical collapse.
    This was caused from the service switch being set in the middle position.
    Click image for larger version

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    I found out about the 3 way service switch on an Apple forum. For normal operation this switch needs to be set to the left position(opposite to in pic), you'll get the vertical collapse in the center.

    At this point if I turn up the high voltage on the EHT I can see scan lines however no picture from my Apple IIe, all horizontal, vertical and sync adjustments work however nothing from the front panel does, brightness, contrast colour etc.
    I believe this is the original problem the monitor had before the previous owner decided to take the gunshot approach.
    The monitor uses a single video NTSC chroma processor chip TA7644BP. Probing around the IC with a scope I wasn't getting anything from the outputs.
    Click image for larger version

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    Ordered a chip from Ebay and popped it in.
    Click image for larger version

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    Realigned the convergence rings and fired her up.
    Click image for larger version

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    Success.
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    Some fine tuning.
    Click image for larger version

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    Oh and this is what the picture looks like with the service switch to the right....

    Click image for larger version

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    A few reassembly pics
    Click image for larger version

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    And done. Monitor has been working flawlessly and the picture is magnificent.
    Big thanks to the AA Member who's sending me up a smokey A2M6021x monitor so I can get the correct values on the resistors. I'll update the thread when I find out.
    Lastly I'm really surprised on the lack of information out there. A lot of people seem more interested in whacking LCD's in these cases than fixing them.

    CRT's rule!
    Last edited by Arcade King; 31st August 2019, 10:21 AM.

  • #2
    Originally posted by Arcade King View Post
    Fix this a few weeks back and been meaning to write up a quick repair log.
    This is the 240 volt version of Apple's colour composite monitor which is NTSC 50htz. This monitor will only work with Apple IIe Platinum's with the NTSC International motherboards which have a specially clock to NTSC 50htz. The American ones are 60htz so these are special to our region. My 240 volt Apple IIc also works in colour with this monitor. It will not work with the PAL adapter.

    I bought the monitor from Ebay knowing it was faulty with the hope to get it going considering how hard these monitors are getting to find now I thought I'd take the punt.
    The seller tried selling it for $300 BIN! $300 for a faulty monitor? tell him he's dreaming! Naturally after a few weeks it went up for auction and I got it for $120 bucks and thanks to @furballx and @WOKA it made the trip up north into my greasy hands.

    On first turning it on it made a ear piercing scream...ok not good I immediately thought shit bad Flyback Pulling the monitor apart to my horror there was a wire hanging down off the neck board (focus) and I could see straight away somebody had tried a gunshot repair. All caps had been replaced and a bunch of resistors and diodes too.
    Don't you hate when you buy something listed as "oh it just stopped working" only to find out it's been messed with.....shame that wasn't in the listing. What makes matters worse is there is no information or schematics available for this monitor anywhere!

    Taking the back off I turned the monitor on and managed to pinpoint the squeal which was coming from the little transformer which is part of the switch mode power supply. The switch mode supply's the B+ which should be sitting around 115 volts however it was only around 75. After talking to @Jomac he suggest there could be a short in the EHT. Without any way of testing the EHT I removed it to see if the B+ would jump back up to where it should be.

    Sadly it didn't but I more confidant that the flyback was ok. I decided to focus my attention on the switch mode section where a number of resistors had been replaced.
    https://www.aussiearcade.com/attachm...hmentid=144449

    Pulling the back off two problems already, the convergence rings have been misaligned and the bigger issue is who ever reassembled the chassis fed the two wires under the shroud. One of the wires insulation was stripped back and touching the shroud grounding it.
    Turning it on again I pinpointed the squeal was indeed coming from the switch mode transformer.
    https://www.aussiearcade.com/attachm...hmentid=144456
    Doing some measuring with the multi meter the two diode circled in red were shorted. Seeing as the monitor had been fiddled with I started pulling up the resistors which had been changed. Pulling up the 27 ohm resistor @R504 circled in black the diodes read correctly. Without a schematic it all I could do guesstimate the value based on other schematics I found using the STR40090 regulator. all I know for sure is it should be in the Kohm range not ohm!
    https://www.aussiearcade.com/attachm...hmentid=144457
    All I had was a pair of 22Kohm 2 watt resistors tied them in series to make 44k. We now have a nice 115v on the B+
    https://www.aussiearcade.com/attachm...hmentid=144458
    Suicide test setup!
    https://www.aussiearcade.com/attachm...hmentid=144461
    No squeal and now I have something on the screen even if it is vertical collapse.
    https://www.aussiearcade.com/attachm...hmentid=144462
    I found out about the 3 way service switch on an Apple forum. For normal operation this switch needs to be set to the left position(opposite to in pic), you'll get the vertical collapse in the center.

    At this point if I turn up the high voltage on the EHT I can see scan lines however no picture from my Apple IIe, all horizontal, vertical and sync adjustments work however nothing from the front panel does, brightness, contrast colour etc.
    I believe this is the original problem the monitor had before the previous owner decided to take the gunshot approach.
    The monitor uses a single video NTSC chroma processor chip TA7644BP. Probing around the IC with a scope I wasn't getting anything from the outputs.
    https://www.aussiearcade.com/attachm...hmentid=144466https://www.aussiearcade.com/attachm...hmentid=144467
    Ordered a chip from Ebay and popped it in.
    https://www.aussiearcade.com/attachm...hmentid=144468
    Realigned the convergence rings and fired her up.
    https://www.aussiearcade.com/attachm...hmentid=144469
    Success.
    https://www.aussiearcade.com/attachm...hmentid=144470https://www.aussiearcade.com/attachm...hmentid=144471
    Some fine tuning.
    https://www.aussiearcade.com/attachm...hmentid=144477
    Oh and this is what the picture looks like with the service switch to the right....

    https://www.aussiearcade.com/attachm...hmentid=144472https://www.aussiearcade.com/attachm...hmentid=144473https://www.aussiearcade.com/attachm...hmentid=144474https://www.aussiearcade.com/attachm...hmentid=144475
    A few reassembly pics
    https://www.aussiearcade.com/attachm...hmentid=144476
    And done. Monitor has been working flawlessly and the picture is magnificent.
    Big thanks to the AA Member who's sending me up a smokey A2M6021x monitor so I can get the correct values on the resistors. I'll update the thread when I find out.
    Lastly I'm really surprised on the lack of information out there. A lot of people seem more interested in whacking LCD's in these cases than fixing them.

    CRT's rule!
    test

    Comment


    • #3
      Excellent repair. It's a shame the original owner made it harder than it needed to be!

      Do you know if the centre position of the service switch does anything? Also do you have a pic of where you measured B+ from.

      I know your getting another monitor but if you want any resistor values let me know and I'll check them on my screen.

      Cheers

      Comment


      • #4
        The service switch in the center position gives you the vertical collapse. Theres a pic above. The test point for the B+ is in front of the little yellow transformer, you'll see 2 test points ones a ground the other is b+.
        When I can get in front of the PC I'll circle them for you.
        Thanks for the offer on checking the resistor.

        Sent from my HTC 10 using Aussie Arcade mobile app
        Last edited by Arcade King; 22nd March 2019, 04:06 AM.

        Comment


        • #5
          vehicle collapse … that must be one dangerous switch : You mentioned the switch was 3 way... or does the centre and right positions both give you vertical collapse?

          I have another one of these screens that has a high pitched squeal when powered up but no picture... might be a good time to have a look.

          Cheers

          Comment


          • #6
            Yeah stupid phone auto correct.
            Click image for larger version

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            SW800 Center position

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            Right
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            and left is normal (switch pointing towards edge of chassis)
            Click image for larger version

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            B+

            Comment


            • #7
              I just got the same monitor with a similar problem. Buzzes when turned on, thought it was the fly-back as well but it could still very well be.

              The original value of the resistor is supposed to be 27k, not 27ohms that it was replaced with. I'll check again to confirm.

              Power transistor ( D1651 ) , I believe it's the HOT right near the flyback conducts both ways between C & E so it's definitely toast.

              I removed the fly-back and the HOT from the monitor chassis and the monitor still buzzes. Measuring around 125VDC at the B+ test point.

              Any ideas. At this stage I think it's safe to say I need a new fly-back and power transistor.

              Comment


              • #8
                The switch mode will squeal without a load, it did the same thing for me when I pulled the flyback out to isolate the switch mode.
                Hopefully your EHT is ok. I'd check the circuitry around the HOT and look for any bad resistors and caps then replace the D1651 and anything around the sub h-sync.
                The EHT produces several other voltages 8, 12 which can be checked on pins 3 (12) and pin 33(8) on the TA7644BP and around 24 volts on the KA2131 Pin 9, make sure to adjust your B+ down if these voltages are too high. Obviously you cant really test the high voltage of the EHT but a good sign will be static on the screen and the good old crack when you discharge.
                Thanks for conformation on the 27k resistors. I had a feeling who ever gun shot the chassis mixed up the kohms with ohms. The 44k is working fine so I'll leave it be until I have to pull it apart again for what ever reason.

                Comment


                • #9
                  Thanks for the great info!

                  I ordered a couple D1651s in case I miss something first try and will definitely get in there and check the components around the flyback and HOT. I've read some posts that people who have worked on these have not come across a dead EHT yet or have rarely come across one, usually it's the HOT that goes bad.

                  This monitor is such a pain to work on but is a testament to how well they are built, I just hope I can put it back together again with all the correct screws

                  Where is the B+ adjustment on the chassis ?

                  Comment


                  • #10
                    Click image for larger version

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                    B+ circled in black H-sync sub Red

                    I've been wanting one of these for years so worth the effort to fix Shame there is little information out there.
                    They had an Apple IIe Platinum set up in my primary school library I use to spend time on it typing basic programs.
                    I just need a mouse and mouse card to complete mine.

                    Comment


                    • #11
                      There's hardly anything out there. Hope I can get this working without too much trouble as I have a IIe enhanced which has the the same motherboard as the Platinum and needs a monitor that can handle NTSC.

                      PAL encoder/colour cards are also very rare so I'll need to get this working.

                      I'll confirm the value of the resistor and take a photo of it when I get home.. but I'm pretty sure it measured 27k.

                      Comment


                      • #12
                        I stand corrected.
                        It is indeed 27 ohms.

                        Click image for larger version

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                        Comment


                        • #13
                          Originally posted by palindrome View Post
                          I stand corrected.
                          It is indeed 27 ohms.

                          https://www.aussiearcade.com/attachm...hmentid=145222
                          Hmmm well that makes me feel like a git. Here I thought the resistors had been changed however it looks exactly the same as yours so I wonder what was pulling down those diodes...I know for certain my B+ wasn't right until I changed that resistor...
                          I'll have to pull the monitor apart and put the resistor back in to confirm.

                          Comment


                          • #14
                            Something else in that circuit must be out of wack and your new value worked around it somehow.

                            Wish there was schematic for this.

                            Comment


                            • #15
                              Click image for larger version

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                              Can you please check the values of the circled resistors. I still believe they have been changed.

                              Comment

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