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Roninfourseven

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  1. Roninfourseven

    Mac Classic - Assistance needed

    Sadly no luck as yet, I will keep at it though.
  2. Roninfourseven

    Mac Classic - Assistance needed

    So I have a socket fitted for the68K now (Checked for shorts and continuity BTW), and the CPU doesn't overheat like an air cooled car in death valley anymore! Voltages at the power connector seem fine and I have -5v where I expect it too. But right now I have nothing on screen at all, no bong or checkerboard so it seems deader than ever On a positive note I am seeing 5v at the /halt and /reset pins on the CPU, which means it isn't stuck in reset and it hasn't halted. I guess I need to break out the scope and look at the address and data lines over the board and see what's going on. I have the schematics, but was wondering if anybody could point me at a description of all the chips and their functions. thanks again to @dochilli for the spare if slightly melted logic board, I at least have a supply of spare parts now. TIA
  3. Roninfourseven

    Mac Classic - Assistance needed

    I'll let you know once I get time to work on it! Maybe this weekend all being well.
  4. Roninfourseven

    Mac Classic - Assistance needed

    @dochilli Thanks so much, your 'care package' arrived today, it shows how bad the Maxell bomb can be!! My board luckily didn't have that, but clearly there is other stuff wrong. I have the old CPU off my board and a socket to install in it's place, plus a spare CPU (One from an Atari STE, one on the board you sent) to work with, plus I have my microscope properly set up now, so I can get to work on the next phase. The ROM on board will be a great help to as I'm pretty sure mine is toast. Fingers crossed I can get it back up to speed and then onto the next thing, my beeping Amstrad ALT386!!
  5. Roninfourseven

    Mac Classic - Assistance needed

    See my reply to techknight, they were only missing for testing.
  6. Roninfourseven

    Mac Classic - Assistance needed

    I'm not that dumb! They aren't missing, just not fitted in that picture as I was testing for shorts. It looked like C5 and C9 positive sides were connected to GND, however looking at the circuit in that section, that is correct. They are connected to a -5v regulator, so the negative side of the cap is connected to -5v and the positive side is actually connected to GND. Electronically correct, but when you're testing for shorts it does give what looks like a short. Getting schematics helped massively in understanding why it wasn't actually a short. Both caps are reinstalled and I'm in the process of fitting a PLCC socket for the CPU.
  7. Roninfourseven

    Mac Classic - Assistance needed

    That is amazing thanks so much!!
  8. Roninfourseven

    Mac Classic - Assistance needed

    That is amazing, thank you so much. I will PM my address over, and am waiting parts for the next repair anyway, and won't be able to look at it this weekend, so things are going slowly anyway. I just realised that by Maxel bomb you mean battery leakage!! Luckily I don't have that problem, but spare parts are most welcome, thanks.
  9. Roninfourseven

    Mac Classic - Assistance needed

    That would be incredibly kind, though I am in the UK so I'm not sure how we could work it? I would of course be happy to cover the postage, would you want anything for the board?
  10. Roninfourseven

    Mac Classic - Assistance needed

    On a positive note, I've confirmed that the 27C400 is a match pin for pin for the TC534200 mask ROM indicated on the schematic, and I have 2 27C400 EPROMS and ad they write/red fine in my TL866 with adapter.
  11. Roninfourseven

    Mac Classic - Assistance needed

    Ok, so I've pulled the CPU and with power on, nothing else get's hot, so maybe CPU and ROM are dead. Checking the voltages on the power connector (Now re-soldered), I get what I expect, 5v, 12v and -12v. Wondering if the CPU and ROM had some sort of pact to die together!! I certainly can't read the ROM for sure,even with my new 27C400 adaptor for the TL866. I can certainly write 27C400 EPROMS and read them back, though the original ROM is a mask rom from what I can tell, so that may be part of the problem. Voltages across the RAM seem good too and I can't find any shorts at the power plug, so that all looks fine. Ordered an SMT PLCC socket so I can pull the chip again easily if I need to. I also checked the GND and power pins in the CPU area and they are all fine with no shorts, and the CPU, had it been fitted, would have been getting 5v at both VCC locations. Nothing else around the connection array seems to have a short either. I guess we'll see what's what when I can get the CPU back in.
  12. Roninfourseven

    Mac Classic - Assistance needed

    So I have a couple of 27C400's and they program fine with an image I located on the web for a Classic, and I also have a 27C400 ROM emulator which can hold multiple images, and no different. I measured the 5v and 12v rails at the floppy port and it was fine. I also removed and refitted the power socket and found a lot of cap gunge underneath, so that was cleaned up. What was disturbing though is that after refitting the socket (Oriented correctly BTW) when I powered on the CPU was getting very hot quite quickly, so I switched off in a hurry. The socket is off again and having picked through the schematics I now have the pinout so I need to check over the power rails for potential problems like shorts. Other chips were cool. It's a bloody frustrating little machine, and for everything to be SMT bar the ROM, not going to be easy to troubleshoot. I need to try and run it under a load and double check the PSU outputs, but I'm really concerned that it's dead properly now.
  13. Roninfourseven

    Mac Classic - Assistance needed

    @dochilli funnily enough I have just done that and will try it out later I'm using a 27C400, which is 512K, so I presume that will be suitable? The image wrote no problems, though I don't know if it needs to be byteswapped or not, but the ROMs I have are erasable so not an issue if they need to be. Might explain why I see the same with or without the ROM installed. Also got new optocouplers, so I may well replace that because I can.
  14. Roninfourseven

    Mac Classic - Assistance needed

    Yes, afraid it isn't great due to the sync with the camera,but you can see the difference, especially when zoomed in. I'm really hoping it isn't the onboard RAM. I am also posting on the forum I moderate on, got some good suggestions just come in over here: https://www.exxoshost.co.uk/forum/viewtopic.php?f=18&t=3187&sid=f46145394e7703f29ea86e33807b48e1#top so I will look into those too. Hopefully my other parts will be in soon too and I can get the optocoupler replaced as well.
  15. Roninfourseven

    Mac Classic - Assistance needed

    Thanks for your reply! The problem I have is that some of the RAM (8chips) are soldered onto the logic board. I probably should have mentioned that I have tried with the RAM daughterboard removed and I don't get the checkerboard, just fine horizontal lines. I can rework the RAM if required, I just want to be damn sure it's that before breaking out the hot air gun and buying chips. Based on the RAM chips I think it is 1024KB of onboard RAM. I think I'd better break out the logic analyser and scope, see what the RAM and address/data lines are doing too. I just need to figure out a way to get it easily accessible as the power lead from the analog board is short, so getting to where I need is hard, even with the logic board out of the machine.
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