Original Macintosh RAM downgrade?

[PowerMac G4 MDD]

I have a Macintosh, and everything about it is original except for the upgraded RAM. Does anyone know where I can find 128k of RAM for this Mac? Better if Apple-branded but it doesn't have to be if the Apple-branded one is too much money. It was upgraded to 512k, but IDK if that is two 256k or 4 128k... can someone tell me? If it's 4 128k then can I just remove all but one of the RAM modules?

 

[DeltaMac]

The memory slots would mean that your original Mac has been upgraded at some point, by replacing the logic board with a Mac Plus logic board - part of the Mac Plus upgrade kit.
The upgrade also means that the floppy drive is not original, nor the back cover - all part of the upgrade kit.

The original Mac had no upgradeable memory slots.
Removing all but one stick does not make it an original configuration - if that's what you are asking about.

 

[PowerMac G4 MDD]

The memory slots would mean that your original Mac has been upgraded at some point, by replacing the logic board with a Mac Plus logic board - part of the Mac Plus upgrade kit.
The upgrade also means that the floppy drive is not original, nor the back cover - all part of the upgrade kit.

The original Mac had no upgradeable memory slots.
Removing all but one stick does not make it an original configuration - if that's what you are asking about.

Everything else is original; the board is as well. Are you sure about this?

 

[MacTech68]

If it was upgraded with an Apple kit, then yes, it's original (original 512K logic board, floppy and rear case).

If it was upgraded by a third party, then it may be an original 128K motherboard with the 4164 chips de-soldered an replaced with 41256 chips and an additional circuit added (one IC and a couple of passive components). These mods vary in how they were done. Sockets may have been used for the RAM ICs, a small PCB for the additional circuit may have been used, or neither.

As standard, there are no RAM sockets on a 128K or a 512K logic board. Some of the early 128K boards had 4164 ICs that had a little white Apple logo stamped on them, but these ICs by themselves would be pretty rare find.

Until you open it up, it's hard to say what it is, since boards and rear cases could have been swapped from ANYTHING over the last 30 years.

You could make it run "like" a 128K by modifying the memory addressing, but leaving the 41256 chips in place, and replacing the ROMs and floppy drive. It depends on whether your goal is to restore it to as near to factory 128K condtiion, or to simply (from a software standpoint), make it run "like" a 128K.

 

[tdiaz]

If the back has a 25 pin connector on it .. it's not even a 512. It's not even original, other than the front bezel. That would mean someone had "upgraded" it with a Mac Plus kit, or whatever parts over the years. That you're saying anything about removable RAM would mean Plus, and nothing else. Everything else Apple offered back then was soldered in place.

If the board has silk screening to indicate 128K or 512K, it's a 512K upgrade. If the floppy drive is all of about an inch thick inside the bracket, then it's been changed to an 800K, and the board is likely a 512Ke, or Plus.

Original is in the eye of the beholder. But without pictures of at least the back side, no one can be sure what you're describing.

 

[PowerMac G4 MDD]

I never replied back to this thread... oops. Okay, I actually found a dead 128k mobo for sale, whose RAM chips have those stamped Apple logos on them. I wonder if I should get it for the parts; however, there's no way of knowing if the chips work.

Anyway, the original owner said that the RAM chips were professionally upgraded (as in soldered on), meaning that it wasn't a simple swap of the mobo over to a Plus one, or something of that sort. If there is some way I can physically disable the extra RAM (and make the Mac report back that it has the original RAM, I'd like to do so. I don't mean to do this in a hoax-y way, BTW - the Mac is otherwise original. I'd just like to "break" the added RAM without removing it.

 

[havokalien]

Ram downgrades are possible pretty easily usually as the chip size will make no difference once the removal of the hardware that does the upgrade is removed.

 

[PowerMac G4 MDD]

Ram downgrades are possible pretty easily usually as the chip size will make no difference once the removal of the hardware that does the upgrade is removed.

Are there any known instructions on this or possibly a quick text tutorial? I'd like to just remove the added hardware or disable it somehow.

 

[havokalien]

No as all upgrades were third party. It will depend on the differences company to company. Most replaced ram chips (again non issue) then some had wierd wired risers that could be de soldered or cut off and good to go, or there was a clip on deal. You wont know until you look.

 

[MacTech68]

@havokalien is correct, there's really no way of knowing.

I'm still wondering if your rear case is a 128K 512K (or 512Ke) or a Plus. A pic would be more than helpful.

Anyway, the original owner said that the RAM chips were professionally upgraded (as in soldered on), meaning that it wasn't a simple swap of the mobo over to a Plus one, or something of that sort. If there is some way I can physically disable the extra RAM (and make the Mac report back that it has the original RAM, I'd like to do so. I don't mean to do this in a hoax-y way, BTW - the Mac is otherwise original. I'd just like to "break" the added RAM without removing it.

If I'm reading this part of your post correctly, I gather this refers to your original board. In which case, it probably has a 74F253 added for the extra address. You'd still need to remove that and reconnect two adjacent pads together. This depends on the original owner's memory being accurate.

Of course, doing that means that you don't have the original RAM as soldered to the board in the factory. Instead you'll have slightly newer industry standard RAM with an extra address. The extra address will be essentially 'disabled'.

If you're prepared to 'stump-up' the money for the 128K motherboard (picture would assist) - you really need to confirm what rear case you have - or you'll be stuck. Also, maybe the bad 128k board might be something easy to repair BUT BE WARNED that's wishful thinking.

 

[havokalien]

bad mac 128 boards are normally just bad ram chips. Its very common. I know people that have a service to replace them and all goes back to operation after just that repair.

 

[PowerMac G4 MDD]

bad mac 128 boards are normally just bad ram chips. Its very common. I know people that have a service to replace them and all goes back to operation after just that repair.

I guess that wouldn't help me, then.
[doublepost=1463168770][/doublepost]

bad mac 128 boards are normally just bad ram chips. Its very common. I know people that have a service to replace them and all goes back to operation after just that repair.

Everything is original, including the case, mobo, and floppy drive. The original board was professionally upgraded to take the newer RAM.

 

[havokalien]

then a picture may help us tell you if its easily made to go back to 128 or look on the internet for the differences in pictures.

 

[PowerMac G4 MDD]

Okay, here are pics. Looks like non-Apple-stamped chips and this odd risen card, which seems to not be present on unmodified boards.

 

[havokalien]

remove the riser board and you should be right back at 128k.

 

[PowerMac G4 MDD]

You mean that odd little bit that's slightly raised? But the RAM chips aren't Apple-logo marked; they're marked with the NEC brand. You sure those haven't been changed out?

 

[havokalien]

it doesnt matter if they were changed out. did you read the other posts? third party upgrade ram defaults to lower size ram once that riser is removed because the extra address line is then shut off.

 

[PowerMac G4 MDD]

it doesnt matter if they were changed out. did you read the other posts? third party upgrade ram defaults to lower size ram once that riser is removed because the extra address line is then shut off.

Sorry, I missed that. I guess I'll go ahead and try desoldering it! (BTW, what are those "adjacent pads" that need to be reconnecting?)

 

[MacTech68]

BTW, what are those "adjacent pads" that need to be reconnecting?

Where that small circuit board is, there is a row of seven holes it's soldered into. Once you've removed it, jumper the first two holes together - from the underside is easier. The two to jumper are marked and circled in the pic below:

 

[PowerMac G4 MDD]

So just a blob of solder connecting from one hole to the other? Sounds good.

 

[MacTech68]

So just a blob of solder connecting from one hole to the other? Sounds good.

Yup. That's it. If you look closely on the underside of the board you should even see where the track between them was cut.

 

[havokalien]

Just remeber going back to 128 is going to have some downsides. Lots more floppy access as not as much available memory. Its why most were upgraded straight away.

 

[PowerMac G4 MDD]

Just remeber going back to 128 is going to have some downsides. Lots more floppy access as not as much available memory. Its why most were upgraded straight away.

I could always reverse the process I do, but I am more interested in getting this thing as original as possible.