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doctormistral

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  1. doctormistral

    Help to recover a classic mac (LB)

    After some work i got this behaviour when turning on the mac: Quick checkerboard -> Sad Mac with stripes --(after a while)-> Vertical patterns. Any suggestion about the cause or about what to check? 20200709_211825.mp4
  2. doctormistral

    Mac Classic Logic Board Versions

    Hi all, what are the differences between 820-0390-A and 820-0390-B models of Mac Classic Logic Board? Are they interchangeable? Thanks
  3. doctormistral

    Help to recover a classic mac (LB)

    Any other suggestions? Would it be worth buying an inexpensive logical analyzer to check what is going on on the board?
  4. doctormistral

    Help to recover a classic mac (LB)

    Hi marcelv, yes, I removed the battery holder at least twice to check the board, no problems. Recently I've also checked frequencies of CPU 7.8Mhz and 32.768 on RTC crystal and they are there.....
  5. doctormistral

    Help to recover a classic mac (LB)

    Hi @marcelv, yes, I removed the battery holder at least twice to check the board, no problems. Recently I've also checked frequencies of CPU 7.8Mhz and 32.768 on RTC crystal and they are there.....
  6. doctormistral

    Help to recover a classic mac (LB)

    I've just replaced 2 x 74LS245, 1 x 74LS174 and 2 x 74LS257 but unfortunately there has been no change..... so sad Screen with RAM board installed Screen without RAM board installed
  7. doctormistral

    boot from SCSI2SD v5.5 on Mac classic

    I made my Mac Classic working with SCSI2SD V5.1. The most important thing to check everything is compatible is to start with a bootable disk with System in the partition 0. I suggest you to use already made images from here, better use the 7.5.5 image. I used dd command to copy image to the board, no need to connect power supply to the board. Once connected the board to the SCSI cable the mac boot at first attempt. If you need to inspect scsi drives with HD SC setup you have to get the fixed one because the original is locked to Apple signed disks. Hope this helps
  8. Normally connecting a Mac Classic (working) logic board to only its Molex connector (so no ram card, no floppy, no disk), it starts with sound and showing the floppy with question mark on the screen. Now, I'd like to know which components of LB are (not) participating in this phase in order to concentrate on them (or exclude them) in my tests to understand why it does not start. Thanks for suggestions.
  9. doctormistral

    scsi2sd issues/continued from savagetaylors blog comments

    Hi, I successfully used SCS2SD 5.1 with a Mac Classic. Starting using the image provide in http://www.savagetaylor.com/wp-content/uploads/68k_Macintosh/Bootdisks/OS_755_2GB.zip and copying it with dd command (available for mac and win) it booted at first attempt! And no need to plug the card to the 5V. The only cases where i got the Disk? icon was when, by mistake, I tried to boot from a not-bootable partition 0 (zero) so use the link above with OS 755 (works also with 6.08). Also the Mac Classic is not listed in the compatibility list but however it works.
  10. doctormistral

    Help to recover a classic mac (LB)

    Hi all! I'm from Italy and I'm trying to recover a mac classic logical board that I've previously recovered after a Max bomb in 2012. After a full recap and a lot of cleaning the mac has come back to life but after a while a put it in a box and kept it until 2017. Than i did a check and it was not working anymore but i decided to kept it in the box because no time to dedicate to it. In these days of lockdown I decided to fix it but it appears much harder than expected! Latest Symptoms: chessboard video (sometimes messed), regardless (with or without) ram extension board and (with or without) ROM. no startup audio, until a week ago sometimes connecting the floppy cable and moving it in the connector (like to simulate a bad contact) the mac booted, now only switch the screen from chessboard to standard desktop - but not boots, nor floppy icon with "?". Tests done: The problem is likely in the LB because putting it in another Classic perfectly working I get the same problem: no sound + chessboard. Recapped again the LB Voltages are OK +-12V / 5V (regulated from trimmer in the AB) Various washes with various products. After one of which I made the situation worse moving sympthoms from 3 -> 3.1 Rom is OK because boots in the other working Classic Unsoldered (hot air desolder) + board cleanup + re-soldered various chips: CPU, RTC, SOUND, VIA, 2x 74F257A -> no change. Checked a lot of PCB lines especially DATA and ADDRESSES between ROM/CPU/VIA using the known schematic -> No problems The reset signal to CPU correctly rise high after voltage is stable. Seems that the RTC is doing nothing: I'm using a multimeter and can't find any frequency in the crystal pins nor in the pins 2, 12,13 of RTC chip. I checked this in the working mac and even here can't find and frequency in the pins 2, 12,13 of RTC but there is some confuse/variable frequency in the crystal (may be my multimeter is not enough sensitive). I'm running out of ideas and starting to think there is something deeply wrong in this board!! I'm new in this group but I've read a lot of posts, suggestions, even discovered the existence of schematics and many more ... but I'm stuck... Find attached some pics of the LB. Thanks a lot for any suggestion...
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