Black screen on MK2 reloaded, but same chips in another MK2 work fine

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Don't Panic. Please wash hands.

    Hello,


    I have two MK2s. One I have had for some years and works great! Another I just received, but unfortunately I have not had it working successfully - it always outputs a black screen.


    I believe the chips are all OK, because they work together in the other, original MK2 - I tried the same power supply.


    The factory memory test passes. The onboard LED stays on solid. The USB console works fine, and I tried reinitializing memory from flash, and also uploading a new kernal to test. I verified both have the same, latest firmware.


    I tried 2x6526, 2x6526A, 8500 CPU and 6510, and 2x8565R2 VIC IIs, and 6581R4/8580 (I also tried with no SID installed at all). All chips work in the original MK2.


    I also tried using my U2P cartridge. It also displays a black screen. However if I press the middle button, I am able to access the U2P menu and navigate it with the keyboard. So I think the video output path may be OK.


    Please is there anything else I can try, or maybe I have a faulty system? I inspected the ZIF sockets and they all seem fine and make secure contact.


    Thanks,

    Each and every board passes a single-unit-test here before it's packed, and the partial operation you describe supports that "a lot" is already working.


    The most common problem is contact in the ZIF sockets. These aren't magic, but very crude: They just push against the IC pins from two sides, and it's just two metal lips. The slightest bending of pins may cause contact problems. To get around that, you can insert the chips, close the ZIF socket (lever down) and then move the chips sideways in the sockets. This does require quite some force, as 40 pins need to be moved while being squeezed by spring contacts. However, it scratches away any oxide layer and secures contact.


    I take it you're using the same PSU to test the two boards?


    Jens

    Thanks for the fast response and advice! Unfortunately no luck here. I tried the "scrape" procedure - translating each chip left to right a few times with the ZIF socket closed. I also tried a different PSU (I tried my lab bench supply, set for 12V with a current limit at 2A - the black screen MK2 draws about 400mA running, the working one draws almost 500mA). I also tried my dead test cartridge - still a black screen. Finally, I tried all my chips in my Backbit Chiptester Pro - thinking maybe there's some slight tolerance difference that causes one board to not to work with the same chips. The Chiptester says all the chips are fine. Getting a bit desperate here I suppose. :-)


    Are there any other things I can try? I do have a scope so I could take a look at address/databus activity? if this were an original C64 I feel like the symptoms are similar to some kind of PLA issue... If not I guess I'll just put it down to bad luck for me, something happened in shipping I guess. Ah well it can happen!

    If this is a new unit we've shipped, there's of course warranty - and it's meant for cases exactly like this.


    However, since we'll be on holidays these coming two weeks (last working/shipping day is tomorrow), your parcel should not arrive any sooner than July 17th here.


    Jens

    Thanks so much! Really appreciate the help and support. Please let me know if there's any further action I should take here for a replacement? Also very happy to do some more diagnosis if that would be helpful for you.

    To make diagnosis easier for us, it's always helpful to know what heppened to the board, no matter how small the incident may have been. What may look insignificant to you may give us a major hint and save us hours of diagnosis.


    One common error is that people try to operate the board on the black bubble bag that the board comes in. They don't realize that the black material is conductive, so the board either doesn't work at all, or you're getting artefacts on screen.


    There's of course always "things that are also connected" - if a monitor solution has it's own power supply, this might cause trouble. If you are comparing to the other board, make sure to have the exact same parts used, the same accessories connected.


    A closer look into the expansion port may reveal bent pins. You've described using diagnosis carts. With all the DIY-stiff out there that looks nice, but does not come with chamfered edges, it's very well possible that inserting one of those DIY-carts has damaged the 44-pin cartridge slot.


    And there's of course the obvious: Any screws that fell into the computer, conductive parts that you may have installed it on, dings on the edge of the board - this may all affect proper operation.


    Jens

    Thanks. The two carts I used were a U2P, and a Commodore dead test cart (hard to know if it's genuine but it is pretty old/well used). The MK2R was outputting a black screen though before I used the carts (I did the full chip swap first). I only used the S-Video port to test via a generic Amazon S-Video to HDMI converter (I use this adaptor extensively for many things and have never had an issue). The board was tested while it was sitting in the lower half of a C64C case.