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Hello everyone!


I introduce myself, my name is Rodrigo. I live in Argentina, so I apologize if my English is bad.

First, I apologize for asking for help without having helped before. I've been reading this forum since 2017, but I've only just had time to get back to work on the Mac during quarantine.


In 2017 I had the joy of finding a forgotten Macintosh Plus (Apple is not very common in my country) in an old warehouse. He had suffered a lot, he had the rear battery door with the battery burst and a lot of dirt. When turned on, the dreaded SadMac appeared with a code that I did not find in the repair manuals. Since poor Mac needed a shower, I started to take it apart. I washed its plastic parts, and removed all the corrosion that was possible (leaving marks on the analog board that do not affect its operation). But, due to my clumsiness, I made a mistake in testing. I forgot to connect the CRT ground wire, to which the Mac responded with sparks inside the Electron Gun and smoke coming from the analog board. I turned it off quickly but the damage was already done. I proceeded to plug the cable into the corner of the CRT, and turned it on again. But the Macintosh now only managed to show a small line to the center of the screen. I noticed that it was the same width as the SadMac logo. With the error code noted above, I started to see its possible causes. Which led me to the HIGH ROM. I got the file to flash an Eprom in a forum, and upon posting it, the Mac booted up, but showing only the top of the screen and a horizontal line in the middle. In the repair books, it specifies R3 and Q1 as causing this problem. But having analyzed them off the circuit, I concluded that they were fine. I do not remember when it happened, but the central line shifted higher, since there is now only an image in the upper third, no longer coinciding with the other cases raised in the books. I have replaced: R3; R2; CR2; C5, Q7, Q4 (The 2n4401 for a BC337) but everything remains the same. I also got a full identical CRT, but it displays the same way. Unfortunately I don't have an oscilloscope, nor the possibility of getting a replacement MPSU51 or MPSU01. I've started parsing two equivalents for these, but I'm not entirely sure. TIP117 for MPSU51 and TIP112 for MPSU01.




Data that may be useful:

-Analog board: 820-0082-E 1986
-FlyBack: 157-0042C
-Input Voltage: 110 (Non international version)


Hope someone can help me.


A very big greeting to all.

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In the previous days I had been analyzing the schematic of the vertical circuit, in classicmac.pdf




After discarding transistors Q1, Q2, and Q4 and having checked most of the resistors and diodes in the circuit, I suspected the LM324 op amp, but did not want to desolder it for no reason. But thanks to MacTech68 answer in Macrumors forum, I decided to try replacing it.

Yesterday I was able to go to the electronic store that is near my home (which fortunately is enabled to work during quarantine) and I got the integrated ST brand for about $ 0.35. I also bought a 2N4401 transistor to replace the BC337 that I had used 3 years ago. After desoldering the LM324 and inserting the new chip, and leaving Q4 "original", I made a final check of the diodes and resistors. Everything was correct. I turned on the Mac and huge was my joy to see the SadMac logo again.




To conclude with the vertical deflection problem, its cause turned out to be the LM324.




Please don't be a fool like me, if disarms your Macintosh, connect first the CRT ground wire to not forget it.

But in turn, I would like to add information about what happened next.
As I said earlier, upon turning on the Mac and seeing that the deflection problem was fixed, I started with the next part of the repair, the SadMac. The code that appeared was 0F0003 which appears in the repair manuals as Illegal Instruction.
Considering the problem with the ROM I removed the Logic Board, and started to remember my previous work.
Regarding the above, I must correct an error. The ROM that I replaced 3 years ago was the LO ROM. And it wasn't with a UV Eprom 27C128, it was with a 27C512. The 27C128 and 27C256 are not Pin-to-Pin compatible. I leave a small comparison that I made between the different Eprom.



I think it is possible to use Eprom 27C128 and 27C256, but it is work for another day.

Using my Eprom reader, I read the information stored in the Eprom that I put in a few years ago, and I was struck to see a lot of blank parts. I took advantage and made a backup copy of ROM HIGH and proceeded to find the one ROM to split it up.
My Macintosh had the two chips that correspond to V3 (342-0342-B as ROM LO and 342-0341-C as ROM HIGH).
Digging around a bit, I found the already split files in two places.
One, at Nightfallcrew.com and another here in which someone had separated the ROM with a small program in C made by itself. I compared both pairs of files and they were identical. But, something caught my attention. The content of my ROM HIGH is totally different! But the name of the Chip agrees with the V3 version! I am willing to upload the file as long as it does not violate any forum rule, as I am not sure if this violates any Apple copyright (In Argentina copyright is not properly regulated / controlled)
In the end, I burned the same Eprom 27C512 again after deleting it with UV, with the files obtained from Nightfallcrew. After inserting it into the Logic Board, and reassembling everything, the Macintosh was able to recover after 30 years dead.




The next thing to do is find a way to burn System 6 to a floppy disk.
Hope this can help someone else revive their Macintosh Plus, 512k or 128k. If anyone needs help with this, please feel free to ask again.

Good luck to everyone. 



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