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RAM Chip Replacement Services Needed

D

dondi

Experienced Member
Joined
Nov 10, 2017
Messages
165
Location
Los Angeles
I have a Mac 128K Logic Board out of a Drexel Mac that shows a Sad Mac error Code of 04009. I opened it up and someone has done a strange job of replacing some RAM.

I have another 128K board that has original Apple RAM chips in it so I need that swapped onto the Drexel board.

Can anyone help with that service? I am in Los Angeles but willing to ship the boards.

Thanks,

Don
 
Can I get pictures of the weird job? I'm semi decent with a hot air station atm... perhaps I can help if its not too terrible. Don't wanna deal with lifted traces, that requires a more delicate hand and experience. The board is just 2 layer if I remem right, I may be wrong. Anyone know if its multilayer?
 
Here are some pictures of the Drexel Mac board showing the RAM. Someone piggybacked three of the chips.

The error code is saying the two 4264 chips are bad (I think). The donor board has all original Apple 4264 chips. That board does not work in the Mac so I don't know if the RAM chips are good or not.
 

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Oh wow that is a pretty bad soldering job. Wouldn't be surprised if a couple of those are cold joints. I could fix it I believe, willing to give it a shot. I do have a few spare 4164s (around 15), that I have been saving to populate a AST Sixpack Plus that I can use to diagnose. Looks like its going to need a bit of work, hopefully under those blobs of solder the pads are still good. At a minimum I can clean it up and install a few sockets on those chips that were soldered badly, and a few bodge wires if needed.

Micron ram was good in the day, but somehow they don't age well. Does not surprise me that its bad. The spares I have are farchild if I recall correctly. I can reuse the apple ram if you want.

As for testing the ram, I have a CoCo2 that i modifed years ago , put sockets on all the ram. Should be able to test it.
 
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Thank you for the reply and data.

I ordered some MCM6665AP20 chips (same as on the board now without the Apple logo). They are due in next week and I may try to swap the two Micron chips myself. If I am not successful I will contact you.

I assume the board is just two sided and not multi-layered?

Thanks,

Don
 
I wouldn't 'assume' it is two layer. I may be able to see what I think are power layers in there.

Can you post a photograph of the rear of the board please.

The tell-tale sign will be the decoupling capacitors (the little two-pin glass beads). Are there any PCB tracks leading to/from these devices on the reverse side of the PCB?

If not, this will be a four layer board (at least).

Dave
 
Thanks for the data.

So I guess the question is can I just unsolder the existing chips and resolder new chips from top and bottom? Or do I need professional help here?

Don
 
You can do what the previous rework has done and piggy back working part on top of the bad.
Desoldering DIPs off a board can be difficult for the ... uninitiated.
 
dondi said:
So I guess thequestion is can I just unsolder the existing chips and resolder new chips from top and bottom? Or do I need professional help here?
Click to expand...
Depends on how experienced you are with desoldering and what equipment you have to work with. It's a job I do about 8 hours per day, 5 days per week (and have about 48 years of soldering experience). Not being a killjoy, but it you don't have the experience and/or don't have the equipment and materials necessary (a good desoldering station, low temp solder and a dependable flux), things can go wrong really quickly, especially if you're doing multiple replacements.
 
Since the board is more important than the easy to replace chips, I'd use some side cutting pliers to cut each pin on the chip near the body and remove the IC body first. Then desolder each pin - much less heat to the board. Good solder wick and some flux to clean up the holes and then install new chips. I'd use SuperWick and not the eBay stuff.
 
DeltaDon said:
Since the board is more important than the easy to replace chips, I'd use some side cutting pliers to cut each pin on the chip near the body and remove the IC body first. Then desolder each pin - much less heat to the board. Good solder wick and some flux to clean up the holes and then install new chips. I'd use SuperWick and not the eBay stuff.
Click to expand...
Agreed, but not just any type of side cutters would be dependable...I'd suggest something like flush-cutters and cut close to the body of the IC and avoid cutting deep enough to possibly cut the board or traces.
 
I always used a low speed / low torque rotary tool I own and composite cutting discs that are 1 cm. You can pick up the low speed dremels online, they are meant for polishing jewelry and doing polishing on engine heads, valves whatnot. Its so weak you can easily stop it with your finger if you wanted.
 
I bought a pair of the Hakko CHP-170 cutters and easily snipped the old RAM chips off and piggyback soldered the replacement chips on. Pretty easy and best part is the Mac came to life and works great!

Thanks for all the suggestions.

Don
 
Good work! Glad to hear it worked out well for you. =)

Welcome to the Computer Necromancer Club!
 
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