128K Analog Recap photos and WTB:128K Motherboard

David Cook

Well-known member
I recently purchased my first Macintosh 128K. Unfortunately, the motherboard is actually a 512Ke. So, TLDR... direct message me if you have a working original 128K motherboard you are willing to sell to me.

Things started out well, as the Macintosh arrived safely and indeed is the original "Macintosh" badge, rather than "Macintosh 128K". I was surprised by the size of the original mouse's thumbscrews.

Massive-thumb-screws-and-square-connector.jpg

I recognize that each vintage machine comes with the potential for missing or mismatched parts. It has a history with previous owners. However, it can sometimes be disappointing.

I knew someone had opened this Mac before, as two of the three large silver screws were missing from the case. Once inside, I noticed that four of the smaller M2.9 screws were missing, including the one that grounds the analog board to the chassis. I have ordered near-enough replacements from McMaster. If they fit, I'll post the part numbers.

Compact-Mac-screws.jpg

Next, I noticed the metal shield beneath the motherboard is missing, along with the cardboard shield on the analog board. This is irritating. Who closes up the case and then sees leftover parts and thinks "meh?".

I have purchased a spare metal shield on eBay. For now, I've fashioned a temporary cardboard shield from thick paper. I just want to ensure that the conductive shielding on the inside of the case doesn't make contact with the analog board.

1728525114933.jpeg

Although the battery holder is fairly clean, the inside of the case tells a story of a disaster. I guess this is why the motherboard was changed out.

Spill-and-scratches-inside-case.jpg

Surprisingly, the analog board is clean. Maybe it came from another Mac but from the correct time period? I believe that is a date code of 1984-39th week. Also noteworthy in this photograph, an axial capacitor shows sign of leakage. In his recap video, @JDW was right to warn people to replace the axials as well.

Chip-date-and-axial-corrosion.jpg

Inspecting the analog board, someone already replaced C3. They left the leads a little long and didn't clean off the flux.

C3-Soldering.jpg

Someone replaced the X-class capacitor C38, but not the other RIFAs? (I have now done so)

C38-Replacement-X-Capacitor.jpg

Looking underneath that capacitor, does the soldering on the right side look suspicious to you?

C38-Questionable-soldering2.jpg

The pad is missing! (Repaired by scraping the mask off the nearby trace and looping wire from the trace to the component lead.)

C38-Missing-Pad.jpg

C2 is missing the top of its label. Yet, it appears to be factory. Maybe part of the label covered the relief slits on the top so they removed it at Apple?

C2-Missing-top-of-label.jpg

Ha. I also have the factory bodge resistor.

Factory-resistor-bodge.jpg

C1 is a film capacitor. Huh. So, they started with film capacitors and got cheap with later builds?

C1-Original-film.jpg

When I first took the Mac apart, I noticed the floppy drive cable was disconnected. After recapping and reassembly, I discovered why the drive had been left disconnected: it makes noise repeatedly. I will need to take it apart and lubricate it. I suspect that (or a broken switch) is the cause.

For all my complaining, the Macintosh works. It's just that I wanted a 128K to be able to run and test my own applications for compatibility.

I guess I can burn old ROMs. Maybe there is a way to configure the resistors to only indicate 128K or memory?

If you have a spare original 128K board you'd be willing to sell to me, please let me know.

- David
 

falen5

Well-known member
So someone was in there before you - so what

its still a piece of history

dont look at what you didnt get , look at what you have
 

joshc

Well-known member
I believe fairly on, they went through a couple revisions of analog board. I believe the earliest ones have a red battery holder, and I think the colour of the capacitors is also another indicator of earlier analog boards, and a smaller flyback transformer. Analog board swaps as well as logicboard swaps were not uncommon due to the amount of problems exhibited in the analog boards when these machines were in frequent use.
 

bibilit

Well-known member
The original Macintosh had a mouse with a big connector and thumbscrews (so this is correct) the PLus had the thinner/samll one.
 

Byrd

Well-known member
Most 128Ks were upgraded either by official or unofficial means as stock they weren’t very usable. Most that are in the wild will have something going on and yours certainly has had the least possible repairs just to keep it running. I’m looking forward to fixing my 128K soon with a third party 1MB and SCSI upgrade but reckon I’ll just keep it all intact there really isn’t much you can do with a stock unit.
 

David Cook

Well-known member
I believe the earliest ones have a red battery holder,

Really? That's cool. Does anyone have a picture?

Analog board swaps

I'm not surprised. Mine does not look heavily used. The original connector solder joints are perfect, which is very different than my 512K and Mac Plus analog boards.

The Macintosh serial number indicates this is from week 35, but the date code on the chip on the analog board is later. So, probably a swap. I don't mind that because it is still roughly period correct.

The original Macintosh had a mouse with a big connector

Good to know. Okay, this mouse stays with this Mac.

Most 128Ks were upgraded either by official or unofficial means as stock they weren’t very usable.

I agree. The Mac should always have started out at 512K. : )

I suppose I wanted the original board more for the 'matching set' than functionality. Given enough time, I'm sure I'll find one.

- David
 

nathall

Well-known member
~25 years ago I got a truckload of old Macs from the University of Washington. All the 128ks had 1MB RAM mods or straight Plus logic boards. None of them were original. I haven’t seen one in original condition in person since the 80s.
 

bibilit

Well-known member
I believe the earliest ones have a red battery holder,

I have seen red battery holders in late AB units also, probably several suppliers for a same part. The early AB boards had a small top metal stiffener serving as a cooling device also, and the cardboard shield was brown instead of white IIRC
 

David Cook

Well-known member
This one is one of the first 100 Macs

Wow! Do you own that Mac?

~25 years ago I got a truckload of old Macs from the University of Washington. All the 128ks had 1MB RAM mods or straight Plus logic boards.

I just went through all of the eBay auctions for Macintosh 128K computers. Nearly all of them do not show the motherboard. Those that do, all but one is actually a 512K or better. The one Mac that has a genuine pre-512K board wants $2600 (including shipping). Some of the other auctions include 800K drives, hinting at being upgraded.

A couple of interesting lessons in this experience:
1. Most original 128K computers were upgraded for practical reasons.
2. If the motherboard isn't shown in an auction, assume it is not original (see 1).
 

David Cook

Well-known member
@JDW was kind enough to alert me to a switch by Kay Koba that will enable my motherboard to behave like it has 128K of RAM when I want to test software on it.



I will burn some original ROMs. However, I also picked up a ROM-inator as well.

- David
 

Joopmac

Well-known member
Interesting topic. Is there a list of bodge wires/modifications for the 128-Plus analog boards? I have some with a resistor at the backside, some with a resistor on a transistor.. Love to know what is the function
 

David Cook

Well-known member
Earlier in my post, I quickly hacked up a paper insulator. When I had more time, I properly traced the insulator from a Macintosh SE onto a piece of thick paper and cut it out.

Recreating-insulator-shield.jpg

Here is the insulator shield in place on the Macintosh 128/512 analog board. Unfortunately, the paper is not thick enough / tough enough. Two solder points poked through (see red circle below). The original stock is about 0.5 mm thick. So, if I really care, I'm going to need to find thicker paper or maybe plastic sheet.

Homemade-insulator-shield-in-place.jpg

The second issue is that although I made the holes for the plastic rivets (example in purple circle above), the 128/512 analog board does not have holes to receive the rivets. Uggg.

I had already ordered "91020A118 Push-In Rivets with Click-Lock Shank for 0.12"-0.16" Material Thickness, 0.122" Hole Size, Black, Packs of 100" from McMaster-Carr. Based on the Macintosh SE analog board, these seem like perfect replacements.

Push-in-plastic-rivets.jpg

- David
 

Dave928

New member
my 128k has all the 128k internals, but has a 512k back case. i figure it got swapped with an actual 512k at a dealer while in for service.

i bought it around 1990 and added Plus ROMs and a MacRescue daughterboard with 6 MB (4MB RAM like a Plus, 2MB RAM Disk).
 

David Cook

Well-known member
direct message me if you have a working original 128K motherboard you are willing to sell to me.

I have since obtained an original 128K motherboard. See this post:

 
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