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My Macintosh II Restoration

jmacz

Well-known member
Yet another Macintosh II restoration thread :)

Picked up a Macintosh II from a forum member a few weeks back. It had been sitting for a decade and in order to preserve it, most of the caps had been removed as well as the batteries. So it was project from the beginning. The case was a bit yellow but physically it looked to be in decent shape.

TL;DR - Before getting into the details, here she is as of this afternoon. Looking sharp. Currently plays its boot chime and shows the blinking disk icon, which is a good sign for the repairs thus far. I am in the process of getting another ZuluSCSI for it.

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Inspection

First step was to inspect the motherboard. The previous owner mentioned there was some damage near the power switch and sure enough there was an obvious broken trace there. Scanning the board, there was the usual green funk from capacitor goo on chips near where the capacitors were. Almost every capacitor had leaked at some point. The rest of the chips on the motherboard seemed to be in good shape with bright shiny legs. Multiple traces near each capacitor location had some evidence of corrosion so I had to scrape off the corrosion and some of the solder mask to be sure.

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There was corrosion in each of the blue circles but no trace damage. And there was trace damage in each of the red circles - continuity was broken in those spots.

Trace Repair

I scraped off the corrosion, resealed it with some clear coat, and for the broken traces, routed around the damage with new wiring.

Capacitor Replacement

The board is a revision B board. 14 of the capacitor locations had both through holes for axial capacitors or pads for surface mounted caps. I'm actually not sure how these revision B boards were shipped from the factory, with surface mounted capacitors or with axial capacitors. On this particular motherboard, the pads were clean (didn't look used) and the through holes were clearly used and had remnants of the legs from the capacitors that had been cut off. Four of the axial capacitors remained on the board. I purchased 16V 47uF and 16V 10uF tantalum caps for the 14 locations with pads. The four remaining axial capacitors I cut off and replaced with fresh axial capacitors.

Batteries

I read that the Macintosh II requires two batteries to even start. Looking at the Guide to the Macintosh Family Hardware, the soft power signal is sent using power from these batteries. This differs from the IIci / IIcx which use the trickle power from the PSU. Rather than going with a full size battery, I decided to try two CR2032 batteries instead. I purchased some CR2032 battery mounts. The picture was with temporary wires on them as I wanted to ensure it would work first. It did work.

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First Boot Attempt

With the capacitors on the board, I made a first attempt to boot up the Macintosh II. Failed. Nothing happened when pressing the power button. I thought perhaps the CR2032s weren't going to work. I looked up the pinout for the PSU to motherboard connector:

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Pin 15 should be the signal from the motherboard when the power button is pressed. I used a multimeter to test pin 15 and I was getting voltage when the power button was pressed. So it looked like the CR2032s were fine and something was wrong with the power supply. I opened up the power supply:

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I poked around with my multimeter, tried simulating the soft power signal, I got nothing. I could have debugged some more but it wasn't worth it because I was planning to do another ATX power supply conversion so I decided to move on with that.

Power Supply Conversion

I took the specs on the Astec power supply and found a donor ATX power supply on Amazon. I settled on a Coolmax I-400 400W power supply. The only spec that was off was the -12V which only had 0.8A vs the 1.0A on the stock power supply. Having done this conversion on my IIci and Quadra 700 before and had no issues with even 0.6A, I decided to go for it. Here's the donor PSU:

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I had heatshrinked the wires I didn't need but later soldered them off the board for cleanness. Next step was to remove the old power supply but save the power ports.

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In order to save the passthrough power for the monitor, I had to save the Omron relay and so soldered it off the old power supply:

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I could have purchased a new one but this one was working fine. Next step was to drill four new holes into the PSU enclosure to mount the new power supply.

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and with the new standoffs mounted:

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After that, it was handling the wiring. Here's a table:
  • Pin 1 Mac (+12V) - Pin 10 Yellow on the ATX connector.
  • Pin 2-6 Mac (+5V) - Pin 4, 6, 19, 20 Red + one Red on the secondary 4pin plug on the ATX connector.
  • Pin 7-12 Mac (GND) - Pin 3, 5, 7, 13, 15, 16 Black on the ATX connector.
  • Pin 14 Mac (-12V) - Pin 12 Blue on the ATX connector.
  • Pin 15 Mac (/PFW) - Send to the base of a 2N2222 transistor with a 10K ohm resistor in between.
  • Emitter on 2N2222 Transistor - Pin 17 Black on the ATX connector.
  • Collector on 2N2222 Transistor - Pin 14 Green on the ATX connector (PS_ON), followed by a 1K ohm resistor, followed by Pin 9 Purple on the ATX connector (+5VSB).
  • Also took a 3.3V line off the ATX power supply to drive the Macintosh II PSU's LED.
Finished wiring is here:

IMG_4581.JPG

Also added a Noctua fan while I was in there. Reassembled the power supply and then powered it up. Good light on the PSU and I hear the boot chime as well as I see the blinking question mark disk icon. Yes!

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Here's the motherboard and PSU back inside the case:

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So next step is to wait for my new ZuluSCSI and get an operating system loaded. Oh, and for the ZuluSCSI, I made a custom drive slot cover (3d printed) with a slot for the drive activity LED. The LED holder I also 3d printed using clear PETG. Just needs to get painted now before installing:

IMG_4586.JPG

So far so good. Next step is the OS and hopefully I don't run into any issues. Oh and I still have to inspect and probably repair the 800K floppy drive.
 

jmacz

Well-known member
Well, it's booting... only problem is that it only boots via the external SCSI port (zulu plugged in). It will not boot from the internal SCSI port even though the ZuluSCSI is getting power and is actually generating logs saying everything went fine on its end. Given it does boot from the external SCSI port, I'm hoping the SCSI subsystem is fine. Might be something wrong with a trace on the internal port. Will need to dig into that next weekend.
 

joshc

Well-known member
Great job so far, looks really tidy. Nice work. :)

Yeah I would double check all traces between the external port, internal port and the SCSI chip/circuit.
 

Chuckdubuque

Active member
You may need to send power to the ZuluSCSI through the floppy-style power socket on the board. IIRC some Macs do not provide enough power on the internal bus. Unless you ordered it presoldered, you will need to solder a Berg socket onto the board where marked (next to the SCSI connector).
 

jmacz

Well-known member
You may need to send power to the ZuluSCSI through the floppy-style power socket on the board. IIRC some Macs do not provide enough power on the internal bus. Unless you ordered it presoldered, you will need to solder a Berg socket onto the board where marked (next to the SCSI connector).

Yeah I was considering that. I already soldered a berg style floppy connector onto the zulu. But I currently only have a berg to male connector and I need a berg to female, and I have unbelievably zero adapters on me right now. I have one coming in the mail.

That said I had discounted the power because the external one is also getting power via scsi and thought it would be the same. But I will try.
 

Phipli

Well-known member
Already did! That’s where I got the PSU pinouts from. :cool:

Looking for a reasonably priced physical copy. I see some at $40.
Good luck :)

I only have a first edition, which only covers up to the Mac II and SE sadly, but its still a lovely and useful book.
 

jmacz

Well-known member
You may need to send power to the ZuluSCSI through the floppy-style power socket on the board. IIRC some Macs do not provide enough power on the internal bus. Unless you ordered it presoldered, you will need to solder a Berg socket onto the board where marked (next to the SCSI connector).

The additional power to the ZuluSCSI did not help.

But I did find the issue. Something was wrong with the 50pin SCSI ribbon cable I was using. I could have sworn that cable was good but I guess not. I had ordered a longer 50pin SCSI cable and it arrived today... used that one and it's finding the ZuluSCSI just fine now, even without the additional power.

So the Macintosh II is working fine now. Just need to put together my custom drive slot cover with LED as well as clean up and check the floppy drive, and then will be finished.
 

nekonoko

Member
So next step is to wait for my new ZuluSCSI and get an operating system loaded. Oh, and for the ZuluSCSI, I made a custom drive slot cover (3d printed) with a slot for the drive activity LED. The LED holder I also 3d printed using clear PETG.
Would you happen to know if that LED holder would fit a Quadra 700? I have the lightpipe for the power LED but not the HD activity light, and would love to do something similar for that.
 

Phipli

Well-known member
Would you happen to know if that LED holder would fit a Quadra 700? I have the lightpipe for the power LED but not the HD activity light, and would love to do something similar for that.
The Q700 one will be sort of 'L' shaped I imagine, like the IIcx / IIci. They look like this...
 

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jmacz

Well-known member
The one I made for the Macintosh II is my own custom size based on the drive slot cover I made, so definitely won't fit the Quadra 700. From what I saw, the IIci and Quadra 700 look to be different. Unfortunately I have not modeled the one for the Quadra.
 

jmacz

Well-known member
Well, that's odd.. took out the floppy drive and found it's a F75W (ie. FDHD). But this Macintosh II doesn't have the upgraded SWIM chip nor does it have the upgrade ROM either to be able to use it. I got a second 800K floppy drive from the original owner so I'll use that. But not quite sure why an FDHD floppy drive was installed.

I decided to clean the FDHD drive anyway and as I was doing so, noticed that a component was blown on the board. Interestingly, it's the same Q4 component someone asked about recently on this forum (which was blown). Will need to figure out what that component is and replace it to salvage this FDHD drive (hopefully that's all that's wrong with it). But will go with the spare 800K drive for this Macintosh II.
 

ObeyDaleks

Well-known member
Really nice job! I especially like your ATX psu conversion. I’m tempted to do one myself (even though there’s nothing wrong with my Mac II psu). Did you follow some diagram for the soft power circuit? These things are hard to find and the last conversion I did (PM8500), the resistor values on all the diagrams I found online were completely wrong.
 

Phipli

Well-known member
the resistor values on all the diagrams I found online were completely wrong.
How so? In lots of circuit resistor values are highly flexible - if you're just comparing two circuits it might not matter if a pull up is 10k or 100k.
 

jmacz

Well-known member
Really nice job! I especially like your ATX psu conversion. I’m tempted to do one myself (even though there’s nothing wrong with my Mac II psu). Did you follow some diagram for the soft power circuit? These things are hard to find and the last conversion I did (PM8500), the resistor values on all the diagrams I found online were completely wrong.

Thanks.

I referenced the Guide to the Macintosh Family Hardware to confirm the specs/pinouts on the power supply connector and then saw that the soft power signal is coming from the two motherboard batteries to pin 15 on the PSU connector. Then just needed to invert that signal for the ATX power supply.

I just used the same inverter circuit that others have used in the past: https://bylenga.ddns.net/index.php?page=Centris_ATX.php

Link to GMFH: https://archive.org/details/Guide_to_the_Macintosh_Family_Hardware_Second_Edition/page/n1/mode/2up
 

ObeyDaleks

Well-known member
How so? In lots of circuit resistor values are highly flexible - if you're just comparing two circuits it might not matter if a pull up is 10k or 100k.

Not entirely. I attached the “most circulated” diagram for PM8500. The thread itself no longer exists.

The 47k pull-down resistor in the diagram) introduces too high of a voltage drop, resulting in low input signal and therefore the PSU is always on. Lower values like 10k resulted in momentary high signal, then low again, so the PSU would turn on, then off again after 1 second or so. Using 1k pull-down resistor would and up having the PSU always off. So I ended up using a trim pot to tune the proper resistance and then measuring it for a proper pull-down resistor value. It was 5.9k ohm.

Edit: Just to explain a bit further, the hex inverters rely on a signal on the input pin being in a specific range. If the input voltage is too high or too low, the output (in this case PS-ON) will not switch properly. So the pull-down resistor on the input (and the resulting voltage drop) plays a role.
 

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