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  • Posts

    • Thank you @techknight for your reply.   The first photo was just to show what the board looked like when I got it.  As part of repair, I cleaned up the area and added all of the missing components including R11.  I don't believe NMI button is stuck because if I press it before the screen comes on, it goes to death chime straight away.  So I know the button functions and it registers when I press it.  However I will check the NMI traces again as you suggested.   I checked all traces from four Bank A RAM slots to RP6,7,8 and UL11,13,16,17 (74F573) yesterday using the schematic and they are all good so it doesn't look to be trace issues with SIMM slots.  (BTW I found a mistake in the Bomarc IIfx schematic, SIMM slot data out pin should be 47, not 44.  I found a couple more as well, which I can't recall right now)   So it looks like POST passes and it goes to RAM check and I thought it maybe failing there but with all SIMM slot traces looking good, that is not the case.   From various places I read that RAM check is the last check Mac does before showing the happy Mac screen.  If RAM SIMM traces are all good, why would it fail?  Could something between RAM SIMM and the memory controller be failing?
        I am also going to hook up another Mac and see if I can use the diagnostic mode to get some more info.  Never used a diagnostic mode before but hopefully I will figure out how to use it.   I added two more photos.  One showing after cleaning up the damaged area and another showing after missing components added in (R11, D2, D3, R18)   Thanks.
    • The insane clickbait-y title is a bit much. Otherwise, Nice pair you got goin on there.
    • Yea, that takes some dedication. I would have hot-air gunned it. 
    • I dont know what a York is, but the adjustment I was speaking about is physically on the PCB that plugs into the back of the CRT, known as the CRT neck board. this control is called H-STAT, or otherwise known as Horizontal Static Convergence. it adjusts the potential to ground one of the grids in the CRT which affects horizontal convergence alignment. When I saw one of your pictures after you put the new board in, I knew right away that adjustment needed tweaked. 
    • There have been a number of discussions, in detail, on this very point.   Basically, the early PPC750's which have pins to support external L2 cache are all pin compatible.  They may require different voltages, or configurations on some signal pins (PLL configuration pins, e.g.) but the balls are in teh same place.   The PPC740 is different, because it does not have the capability of supporting an L2 cache, so those pins are not present and all the pins are rearranged.   The 750CX adds a 256K on-board L2 cache, and so again, the external connections to control the L2 cache are omitted so the pinout changes.   However, the 750CX is also not compatible with the 740 pin arrangement, although it seems like it could have been.   Perhaps they're in different size packages, I don't remember.   They are enough years apart, the process technology for the die could have changed and so the package size may be different as well.   The 750FX and 750GX are compatible with each other, but are a  change from the 750CX for some reason.   So, for example, if you have a PPC750 with external L2 cache support and want to replace it with a later model that moved the L2 cache on chip, it will not be an easy task because the pin/ball arrangement changed.