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  1. Measured everything 100% and no issues found. Looks like VSYNC/VBLANK is generated by Sonora chip while RGB comes from RAMDAC. Since the machine chimes (reads rom/executes code) should be no reason for no video and all traces/discrete parts are good there. It should display error hex code and sad mac. Behavior does not change with RAMDAC removed hence I assume it is dead. With VRAM removed chime is distorted like on the working board. As for apple RAMDAC - CLUT/DAC they call it part impossible to find without another board... so I guess I will have a pause for a while looking for t
  2. Quite a pickle... these retro boards usually take me max few days but this one is stubborn. If I had more parts progress would be much faster but I am reluctant in exposing the only other working board to damage so not touching proprietary chips I cannot source. These 20yrs old chips probably don't take re-flowing well, seen moist accumulating and then when heated doing damage and not all look fresh! I finished measuring abt. 90% of everything for 32bit data, 32bit addresses and other vital signals to ROM, RAM and VRAM. Some go directly from CPU to transceivers while ot
  3. Reading this other ROM boot process reaches P_mBootBeep Plays boot sound, pokes VBLANK interrupt as CRT seems to be wanting to turn on and then it should initialize ram contents? Without ram chips on board it plays boot sound but no video and no chime of death. With ram soldered in, it plays boot sound and then chime of death. I wonder aren't we back to ram?
  4. Progress has been made! It now chimes, unfortunately just to a second later play chime of death but there is no video.
  5. btw. just replaced the MCU hoping it would be semi-dead - no change. Working out QFP without stencil is refreshing 25% of LA wiring. bad thing without socketed option is that I am unable to flip the board.
  6. in fact just a generic Motorola MCU but with specific programming so true, only another board semi-dead or dead for another reason. Good to know usually they suffer from failing quartz crystal which is easy to fix.
  7. I equipped myself with 102 channel LA from 00s so... now just to learn the hw, sw, and wire it up all together. This one is a funny ride! All caps were replaced at start of this fun, clock chip measured etc. Visual inspection under microscope did not show any damage. Perhaps I have to do this hard way with probing between MCU & Sonora & Ram & Rom alltogether. 64x3 + other singals IPLx3 FCx3 DSACKx2 etc. Good for winter Does this board packs more than just 2 layers? I replaced all F245 & ALS241 chips with the ones from the working board - no change - good
  8. This one worked out well. Replaced 99% of caps and re-soldered wires going to the base and the image is on. It will not power on without source attached though. On the board the main IC is a proprietary one but also other parts/drivers are long obsolete. Best path is to get a similar/same board as a donor. EHT still has got "wining" sound even though I soldered centre rod under pressure but image is acceptable.
  9. Indeed timing could be an issue indeed. Full of hope I switched LS245 with F245D to discover nothing improved Managed to get my hands on a working board and do some measurements. BERR behaviour is different, working board does not have continuous BERR assertion. So there is some kind of an issue here related to bus/BERR. De-soldered SCSI chip, no change. I also rechecked FC0-2 and was wrong before. It starts with 1 1 1 which is CPU address space and switch to supervisor program space flipping with supervisor data space continuously. All signals go via Sonora which is a
  10. With ROM removed there's no life on the bus at all. De-soldered ram chips again. With or without ram chips behavior does not change. Soldered in another set of 8 chips with 70ns better than 80ns originals. I also found disassembly of mac plus rom. Not the same machine as LCIII but I would expect logic in what ROMs do should be similar. https://www.bigmessowires.com/rom-adapter/plus-rom-listing.asm My attention goes back to RAM/Timing/bus as chime is before any query for a boot device. Check for test software, run test, test ram, initialize ram contents. In the meantime
  11. n-th day of battle. still loosing though. Replaced all F245 with new LS245 bus transceivers, replaced all ram chips. Switched ROM chips to good known ones, measured activity on CE and OE pins, still no progress, no dong, no image. There is activity on data & address lines but a pain without LA and just 2 channel scope. It would help very much to understand what is it waiting for... graphics chip, scsi chip in what sequence they are queried. FC0 0 1 FC1 1 0 FC2 0 0 It is switching between User Data Space & User Program Space I
  12. Found it here: http://rtellason.com/manuals/Apple M1212 Monitor Schematic.pdf Not greatest scan but with good magnification somehow works. Most non obvious parts like ICs or EHT appear unobtainable from regular sources, same as for apple ASICs.
  13. Yup, was thinking about that too, assumed such level of sophistication was not present but that may be wrong. Found old schematics so soldered in EHT back and measured voltages. Can't find any datasheet about LSC1178B but it gets RGB/sync signals in and outputs RGB + drives HOT so it may well be. PS output TP1 should be 84V is 110V, TP2 should be 17V is 20V, TP3 should be 8.4V is 10V. One reason I could think of is that it is running without load since this is after transformer so nothing to pump voltages up on all rails.
  14. Machine is macintosh LC III and MMU is mentioned . The Macintosh LC III hardware, however, always operates in 32-bit mode. The memory management unit (MMU) inside the 68030 works with Sonora’s memory controller to map 24-bit addresses to their 32-bit equivalent. What is kind of getting my attention is no flipping of DSACK1 to low, it stays high all the time. It should switch port to 32 bit mode if I read manual correctly. I am fighting also with a dead CRT M1212 but was counting on at least chime of death. It started completely dead but with fixed reset circ
  15. Hard to tell if EHT is shorted with just regular multimeter. Any way to check for EHT startup safely? Checked HOT transistor and it is good no short and tested after de-soldering. When I turn the monitor on I hear de-gaussing loop working but no image, not even background (white) despite playing with brightness and contrast. When I disconnected HV cap also no "HV click" to a discharge probe. Perhaps in circuit measurement of B+ presence and other 84/100V voltages would help to narrow possible issue? M1212 is not the same board layout as the other one with l
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