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Everything posted by gkmaia

  1. WOW spot on! A block of the LS257 failed open, exactly where the bus signal was stuck high. Replaced it and booted just fine!
  2. Yes, that is weird. I removed U12F and 11F as I am getting D9 in the data bus stuck high when compared to a working board. As they were the buffers between processor and memory I thought they could be stuck open. But they are both fine. Also the ROM ICs use the data array but I tested them on another working board. Problem is this schematic is quite incomplete... the other weird thing is that Sim 1 bank A and sim 3 bank B use the same buffer. Same for sim 2 and 4. This means this type of fault should be on the sim card, not on the main board. So... confu
  3. I got this error 00000003 00040000 By looking at Troubleshooting_Your_Macintosh_1992 : The RAM test failed while testing bank B, after passing the chunk tested for code $0002. The Z field indicates which bits failed as in code $0002. Also the second line shows what bits may have failed. But not sure how read 00040000 and what clue it makes. I was initially running 4x256kb of RAM I am sure works. Also tried to eliminate bank B by switching the resistor from 35 to 36 and using 2x1MB. Still the same issue.
  4. I am really stuck with this one. I am 100% positive the 8DIP IC pointed with the red arrow is faulty. As I swap it from another working PSU gets the PSU going again. The Ic has only a "177" marking. I suspected it was an op amp but it was a guess. Not sure what this little board does. I tried the common single and dual channel op amps and also a OP177 a precision single channel op amp... no success. Anyone have any idea of what IC could this one be?
  5. Anyone out there with some experience with a SE psu? I suspect the ic in the photo is a 8dip optocoupler. one of my SE has it faulty. Would you guys know the specs for this ic?
  6. I've made a few plots from a working SE power supply while fixing another. As I could not find a decent schematics I am uploading what I did as it could be useful to other people.
  7. Cool, thanks. that makes sense. I've made a little clip on my 3 printer to hold them safe so that wont be a problem. One interesting thing is on the conners the platter does not fit perfectly to the motor spindle. It has a bit of play. And with that in mind I did an experiment by swapping 2 PCBs, each with it is own calibration, in the same platter assembly to check how the radial calibration would react. And they both run perfectly. That tells me either there is a cosmic coincidence these platters had the exact same physical alignment or the tolerances for radial align
  8. What is the reason why the heads should not touch each other?
  9. Changing the ID worked!!! Thanks! Transferred a bunch of data and the DIY cable did pretty good.
  10. Thanks for all the answers! I will change the IDs and see what happens.
  11. I got an LCII with a hard drive inside. As I wanted a second hard drive I decided to make an adaptor to connect my other SCSI drive to it's rear SCSI port. If I start with the external HD connected it boots from the external Hd and the internal is not visible. If I start with the internal HD and later connect the external HD the external does not mount. Anything I should do such as setting the external as slave? Or come pinout on my adapter that I am missing?
  12. Are onboard RAM words tested on Classic II P.O.S.T? If they are not is there a software that tests all onboard RAM words? Compatible with Mac OS7.
  13. I do not have any goo on the head bumpers. But lots of white goo at the seal edges. The plate filter was soaked in good as well. Is there any drawback in terms of alignment if I remove the plates? Would be good to take them out and clean the whole assembly and look under the plates. What would you use to clean a plate? IPA alchool?
  14. I think I got the answer for my question. But I guess will be valuable to share. I have two connor 40mb drives. One 34 pin from my portable. One 50 pin from my LC. I swapped the logic board between the portable 34 pin case and the LC 50pin case. Turns out that my 34pin logic board + my adapator + 50pin case works perfectly on my LC. Would you recommend opening the faulty case? is there anything that can be fixed in there? Or that is pretty much a lost cause?
  15. Have anyone ever successfully disassembled the Portable LCD display? I mean remove the panel from the PCB and contacts? If so, could you share your results?
  16. That is such a valuable post. I am trying to restore my Portable and my hard drive stoped working, maybe you guys can give me some light. All started when I tried to format the drive to install a clean system. While running the HD SC Setup I did clean the partitions, create new ones and when I initialised it failed to format. I toke the drive off, build a 34 pin to 50pin adapter and got it running on my LCII. Got Lido running. Lido could find it in the bus. I could then work the partitions out and then when going to initialise (format) it failed formatting. Tried this process seve
  17. Yes, you are right. But was also good to get to know the board better. Really did not need to do that but I find fun putting a board apart like that. In the end was the TDA4605.
  18. I am going over a classic II board and my one has this blue bodge wire. Looking at some photos at the web I see quite a few boards with similar bodge. Do anyone know what is the purpose of that? Is it a factory fix or DIY upgrades? Looking at bomarc's schematics I see the connection. Can anyone help clarify? Also, do anyone know if pin 23 of U10 is connected also to that through hole eight near it?
  19. I have a few of these HD drives out of SEs, Classics, LCs... and they all seem to be perfect in terms of logic. I've attached some scans I did on a good working MFD 75W 01G and that may be useful to other people trying to pin point issues with this drive. From what I can see all my non working drives send the correct signals to the heads, main motor spins speed seems to be correct as the step motor is triggered at the correct frequency. That all leads to conclude the logic circuitry is working perfectly and the issue is head alignment or something to do with heads
  20. I got a fried resistor on my classic. I imagine that is a thermistor but not sure. From the schematics I would say it is a 20ohm at room temperature. But unsure of the watts. Can any one give me a light on that one. Another question. If I replace the resistor with an ordinary 5w 5ohm resistor just for the sake of testing the board. Will that be fine? just for testing... If that is a thermistor at 20ohms it provide almost no resistance and is there just a safety device to cut current in case of a surge. is that correct?
  21. I ordered some TDAs. At this stage as it is impossible to trace where the problem is so removed every semiconductor on the board and will get them tested on a curve tracer. If none of the fail I will mode to inductors, then ceramics, then resistors. I will put it completely apart till I find what is wrong there.
  22. Dp3 and Dp4 signal diodes are fine on mine. Reverse biased up to 100vdc and no leak. CNY17 is also good. I think my culprit is the signal out of IP1 pin 5. Any other ideas?
  23. They are there but do not align. If I adjust the POT I cannot get them all balanced. Find the +12 has a bit of a ripple. I did test Dp11, Dp5, Dp7, Dp4, Dp8, Dp12, Dp2 on a good curve tracer and they are good. The feedback Mosfet seems ok under basic testing. Haven't got it to the curve tracer. Only weird behaviour I found on the RP6. It is leaking at around 70v when reverse biased. Not sure if that is a problem as that wind does the 5v rail. Also none of the signal ones leak reversed and they all share the same peak voltage. At pin 5 of IP1 I a
  24. I have replaced some leaky capacitors on the analog and digital board of this mac. I did check some of the key voltages on the switching power supply block that seems to be inline with that Bomarc schematic. One test I did was to disconnect the +5 and +/-12 lines from the analog board and feed the digital board with clean power from my HP power supply. Computer worked just fine. Definitively something wrong with my analog board. One thing that I noticed was the positive end of the main bridge rectifier has a massive positive sine. As if the CP1 coupling cap
  25. Is it possible to duplicate the Mac OS system 6 OS disk using the Mac Plus itself to do it? Will DiskCopy 4.2 be able to do it?
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