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Thread: Mindset repair

  1. #41
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    Yes I have two of those units with the fader. One I plugged in developed a bad smoking habit and tagged out, but the other is fairly new and seems to power up okay. My read of the video production system manual suggested that you should test out the machine without anything connected, which implied to me it didn't matter. In the event I did hook up the 'good' slider and per the instructions had the slider all the way down towards the bottom of the unit. But nothing changed with video, etc.

  2. #42
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    >>> My read of the video production system manual suggested that you should test out the machine without anything connected, which implied to me it didn't matter.

    Agreed now I have re-read the manual.

    Dave

  3. #43
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    Just been looking at the pictures of the main PCB.

    That's interesting if you have one crystal and two 8042 micro controllers. I wonder if one is connected to the crystal and this one (in turn) feeds the oscillator to the other one?

    It would be much easier to find a schematic...

    I further note in this image http://bitsavers.org/pdf/mindset/pictures/pcb/06.JPG that the capacitor you refer to has one end lifted up and a bit of insulating tape preventing it from making contact with the PCB. I wonder why?

    Dave

  4. #44
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    Nice catch on that photo Dave! I was very tempted to desolder one end and see what happened.. but I wanted to investigate more before resorting to surgery. Perhaps on that particular board the cap just failed and they pulled it?

    With regard to the keyboard 8042, pin 2 of that IC, U17 is connected to pin 3 of U18, a 74LS367. Pin 3 of IC U17 is connected to pin 5 of U18. I'm going to probe around the two 8042s a bit and see if I can establish any links between them.

    One note - by way of accident, when I was buggering around with my logic probe with the system plugged in but not powered on, if I slipped with my probe and accidentally contacted two pins on the sound 8042 together, it would suddenly start the machine, sometimes with the activity LEDs lit, regardless of the power switch. I'm not sure I agree with Al that the sound chip has no bearing on the rest of the system.

  5. #45
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    Interestingly - if you look closely at this pic of what appears to be another Mindset on Old-Computers - it also has a piece of tape blocking that cap off at one end.

  6. #46
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    Yeah, there's definitely something going on here. I just checked 8bitguy's video on the Mindset, because it has some high res shots of the area - and again, that cap is disconnected.

    mindset - cap.jpg

    It's hard to tell for sure but it almost looks like they have it soldered to one of the VIAs near that IC??

    Here's the segment where it appears on 8bitguy.

  7. #47
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    If you look at the two pictures (cpu_b.jpg and cpu_t.jpg) here http://bitsavers.org/pdf/mindset/pictures/pcb/ you will see that the green wire snakes through the via to pin 3 of the nearest 8042 to the crystal. I wonder if there is a fault in the PCB and the machines seem to work OK - except when they age?

    Probably clutching at straws???

    Dave

  8. #48
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    Interesting. Well, let's give it a try, shall we?

  9. #49
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    Actually.. I think I see why this is happening. Looking closely at photos.. it appears the track from the cap to pin 3 is missing? Maybe the first batch of boards was erroneous?

  10. #50
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    Okay,

    So I decided to switch to the other Mindset and play around some with that. First of all, its horizontal sync seems to be better than the first one. Instead of getting wavy blue screens like in my photos, I get solid.

    The rest of the behavior is the same.. no clock at the sound chip, no activity on half the RAM.

    One interesting thing though.. if I hammer some keys like Sys Config in the first 10 seconds of posting... all activity on the RAM that has activity ceases. I think I am causing the machine to crash or something. I've done this a bunch of times and confirmed if I leave it alone the activity continues indefinitely.

    I think I will start trying to document the circuit. Unfortunately custom chips like the video controllers are basically black holes.. but maybe I can spot something else that might be causing difficulty. It's unfortunate Mindset's owners never saw fit to release schematics etc as the company sank.

    My fear is, that if it's the custom chips.. basically all Mindsets are doomed to die.

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