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Thread: My first Rev 0!

  1. #1
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    Default My first Rev 0!

    After years of lusting after this revision, I finally have it right here in my shop!

    IMG_4668 (1).jpg

    IMG_4669 (1).jpg

    IMG_4670.jpg

    IMG_4672.jpg

    Basically right now it powers up to a solid white screen, a screen full of solid bars, or a screen full of Gs. The machine doesn't respond to Reset or CTRL-Reset. I have tested the ROMs in another Apple II and they work fine, so I guess it's going to be a hunt around the board for whichever IC(s) is/are causing problems.

    I tested the power supply and voltages, etc seemed good.. but every now and again when I power on, I get a steady ticking noise inside. I also am avoiding using the actual power switch on the PSU, because it makes a nasty crackle sound every time you switch it to ON, just like on my Rev 02.

    Anyway, got some work ahead of me, but as far as I can tell this is a very nice, clean, all original machine.

  2. #2
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    Default

    Congratulations !!!!

    For the power switch, they are still available. You just drill out the rivets and then replace them when you are done.

    Check your keyboard (remove it and use a continuity tester). The switches might just need cleaning. An eye dropper full of 93% ISP to flood the switches and a few hundred presses each and they tent to come back to life. Sometimes I remove the screw from the bottom of the switch so that when I flush it with ISP the junk has a place to flood out. Then I put the screw back in when I’m done with each switch. A time consuming process but switches are rare but not unobtainable but saving switches is the right thing to do when you can. Also I tend to remove the key caps when I do all this to protect them, especially the raised power indicator.

    Cheers,
    Corey

  3. #3
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    Thanks Corey.

    I did try a working keyboard but got little change. I have done the ISP trick to great success and have a bag of A2S1 keyboards for parts to fall back on if need be.

    Gonna keep following the service guide and test ICs involved in the reset and ROMs. I'm thinking this should be fairly simple.

  4. #4
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    Default

    Wow- nice! It's even a 16K... That's very early and not upgraded. Unusual...

  5. #5
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    Yeah I am a bit surprised there wasn't more interest in it when it was on ebay. It appears to be entirely original from stem to stern, and seems to have been well kept. There's scarcely any dust on the motherboard or components.

    And it came with its bag, original first Rev Apple paddles, a Heuristics 20a card with microphone, and an A2M2010 green screen, which regrettably was not packed really at all and suffered what I hope is just cosmetic damage.

    I got it for $2900 after watching it with a BIN of $4999 initially that kept falling. Don't know why it didn't sell.

    Seems like A2S1 prices are generally kind of slipping a bit lately.

  6. #6
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    Okay so I went through replacing each chip one by one.. but have not really gotten too far. Basically I get a solid mess of screen garbage but nothing otherwise. The keyboard reset function seems to work, I'm assuming things like the crystal/timing are working because we wouldn't have stable video otherwise.

    I tried swapping in an Applesoft ROM set, hoping to have an easier visual on what is going on.. but right now it's just solid pages of nothing, no sign the computer is doing anything.

    Gonna have to probe this one.

  7. #7
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    You want a bit of help with this one?

    Let me get my schematics out...

    Dave

  8. #8
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    This is a good reference - and contains the schematics for a Rev. 0 (as well as later models) https://mirrors.apple2.org.za/Apple%...escription.pdf.

    My initial suggestion is (as usual) an oscilloscope to make sure that the low voltage supply rails are correct and within specification (+/- 5V and +/- 12V) and that the clocks are all present and correct. See figure C-2 for the schematic and table 3-1 on page 32 for a good description of some of the key clock signals.

    I would also look at pins 2, 4, 6, 40 and 7 of the 6502 CPU.

    Pin 2 is RDY and should be mostly high (never permanently low).

    Pin 4 is /IRQ and should be mostly high (never permanently low).

    Pin 6 is /NMI and should be mostly high (never permanently low).

    Pin 40 is /RES (reset) and should be permanently high.

    Pin 7 is SYNC and should be pulsing. One pulse for each instruction fetched from memory.

    That will do for starters!

    Every machine that has a 6502 CPU you should proceed as above.

    Dave
    Last edited by daver2; October 4th, 2019 at 01:56 AM.

  9. #9

    Default

    My rev.7 had similar problems, it was an intermittent clock to the 6502. I think you should start checking reset action, clocks and address buffer operations. The problem in my case turned out to be oxidized pins on a chip. SInce almost everything is socketed on those motherboard, it's a very likely problem.
    Though I haven't removed any other chip than the problematic one, since I hate doing unnecessary things
    The power supply switch arcing can be avoided by spraying some contact cleaner inside the switch and operating (unplugged) the switch a few times. Mine is not arcing anymore.
    However I'm sure you know it, those PSU really need to be serviced (RIFAs inside!) before plugging them in.

    Frank IZ8DWF

  10. #10
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    Default

    Thanks guys.

    Dave! Good to hear from you again! Yes I have sort of embarked on what you suggested. For the time being I have replaced the original PSU with a known good, and from what I can see so far the power rails on the board look good.

    I am kind of thinking sockets also, maybe a break somewhere as I am not seeing any evidence of corrosion anywhere in the least. As I manhandle the board removing and reinstalling chips, I sometimes will get a random screen of characters that are changing.

    I'm really hoping I didn't accidentally destroy the keyboard.. while reconnecting it I inadvertently had the connector down too far, so that pin 1 and 16 were not connected to anything. I think I got lucky as it looks like the -12v would have just gotten connected to an NC pin. 5v would have gotten connected to strobe and ground would not have been connected.

    I will dig into this more after work with the scope and see what I can see. I was hoping to cheat my way to a quick win. You know what they say about cheaters..

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