128K: bad RAM repair

[Byrd]

Hi all,

I've a stock, un-upgraded 128K which is coming up with 040001 Sad Mac error immediately at startup (and slight graphic corruption).

From the following link, I believe this refers to a failed memory test "mod3 test", data bit 0, location F5:

http://support.apple.com/kb/TA46376

... and that's about as far as my know-how goes Can anyone please tell me how I can now identify the faulty chip? In addition, the only other old Mac board I have is from 512K - any chance I can cannibalise a chip from this board?

Thanks a lot

JB

 

[applefreak]

first try

remove the logic board

remove the ramchips and reseat them in the same position

reassemble > test

second try

remove the logic board

remove the ramchips and reseat them in the opposite position

(first one (F5) > last, last one > first )

reassemble > test

 

[tomlee59]

The suggestion by applefreak to move chips around is an excellent one. The power-on diagnostic routines are not comprehensive, so a "memory error" indication might actually be due to, say, a decoder failure. If the problem does not move with the chip, the memory chip is probably ok. If the problem does move around with the chip, you can feel confident that the chip is indeed bad.

Are all the memory chips socketed in your Mac? If not, then the advice above will be impractical to implement.

 

[Mac128]

LOL exactly, if it's an unupgraded 128K the RAM chips are highly unlikely to be socketed. Tom, can a 256 chip be mixed with a 64? I would think it would function like a 64 without the additional decoding?

 

[Byrd]

Hi all,

thank you for your suggestions - I have since identified the particular "faulty" RAM chip at location F5. Unfortunately, the RAM is not socketed (then again, the same goes for the 512K board I have). I recognise I've little to lose, so I do intend to remove the F5 RAM chip to diagnose the fault - would it be better off to use a solder sucker to attempt to remove the entire chip cleanly, or snip the chip off at the legs and solder the new chip on top?

I can post pics if useful, however the RAM chip is identified as:

128K: 8432; Apple symbol MT 4264

512K: NEC 8428P6734; D41256C-15

I was planning to post this in Conquests, but the 128K was found last week while driving around for work doing house calls (medical), just like the last 128K I found (about ten years ago, a "Macintosh 128K" with carry bag). The one I found is a bonafide "Macintosh" with Imagewriter I printer, and the white plastic case with all original disks, cassette tape and power cables for other countries! Most amusingly, someone cut all the cords off - anything that gets chucked around my way attracts those who sell the cords for scrap metal value :lol: Exterior and interior it shows next to no signs of use, hardly any dust, perhaps sitting covered in a garage for years after the Sad Mac error cropped up. Made for a nice day in a busy week.

JB

 

[jsarchibald]

Byrd, you would have loved the 128K board that sold on eBay mid week then. It went for around $35, and also had an Xcalibur accelerator card. I was going to bid but forgot all about it.

 

[Byrd]

Heh yeah I saw that 128K board, bidded but no luck! Regarding the Xcalibur board ... I couldn't find a thing online for that, I assumed it was more a RAM upgrade than accelerator - what made you think it was the latter?

As noted, I do have the one good working 128K but hoping to get both going - as keepers, and as a backup for parts in future. The 128K I found years ago is my favourite Mac - and quite amazing that both work (to an extent!) 26 years later!

JB

 

[applefreak]

the photo of the ramchips is one of my 128k macintosh's

it was a mac with 'problems'

i removed the soldered chips and replaced them by sockets

the 'new' ramchips cames out 'the stock' of a dealer who stopped selling macintosh ...

its always good to have some (or a lot) spare parts

his 'stock' moved to ..... my place

generally a dealer is not the place to find working old computers

 

[Byrd]

applefreak, I tend to agree - the best working Macs are those you find for zero cost Second-hand Mac dealers - not that there are many in Australia - charge like a wounded bull and have such a know-it-all attitude I can't be bothered with them.

Pretty impressive soldering job on the 128K RAM sockets, I have to say - thank you for posting the pic. Jaycar (sort of like a Radio Shack/Frys) sell sockets which I'm looking into.

http://www.jaycar.com.au/productView.asp?ID=PI6499&keywords=pcb+socket&form=KEYWORD

My manual soldering skills are up to scratch, but as it's a 4-layer PCB I'm a little wary desoldering the module, but appreciate it'll look a lot better than snipping the legs and soldering something on top.

JB

 

[applefreak]

i don't have the appropriated tools to do such good soldering

but i know where to go,

a friend of me has a electro-shop, and that is the place to be

he has the equipment ... and i make time

 

[jsarchibald]

The board looked alot like the Levco unit I had installed. From memory, it did look like just a RAM upgrade, you could well be right. I was so tempted to buy it, as it was the original Mac board too!

 

[H3NRY]

Having done a couple hundred 128K upgrades, the soldering is not extremely difficult. Cut the legs off the bad chip with a small nose wire cutter, then heat each pin from below and pull it out with needle nose pliers. The corner pins which connect to the power and ground planes inside the board will require a lot more heat than the rest since they are well heat-sinked. Then use a solder sucker or braid to clean the holes. Unless you replace ALL the RAM with sockets, don't socket the replacement chip, because the added capacitance of the socket will make that one chip slightly slower than the rest. One source of 4264 type chips is an Apple //e 80-column RAM card - usually cheap and plentiful. The earlier ones have socketed chips. The 256K chip will also work as a 64K. Good luck.

 

[Byrd]

Hi all,

H3NRY thanks for your advice - today I desoldered a 64K chip and put in place a 256K chip from the spare 512K board I have here, using solder sucker and lots of cursing

Fired it up: usual beep, then Sad Mac error code now reads 040080

... indicating a faulty RAM chip at F12.

... little to lose, back I go!

JB

 

[tomlee59]

First, carefully double-check your repair. Use plenty of light and a magnifying glass, as well as an ohmmeter as necessary.

Also, what is pin 1 of the DRAMs connected to (I haven't looked at my 128K schematic and I don't remember the answer off the top of my head)? If it's floating, I recommended grounding it. The 4164s don't use it, but it's the higher-order address line for the 41256, and shouldn't be left floating.

And as I mentioned earlier, the memory self-test is very crude. It's not able to distinguish between a true memory failure and one that's due to other causes. Since it is very rare for multiple DRAMs to die spontaneously, you should suspect something else if, say, one more memory chip replacement doesn't fix your problem.

Good luck!

 

[Byrd]

Thanks for the tips, tomlee - like yourself I was suspecting something additional than the RAM to be at fault. Having tested the first chip, I wasn't confident that replacing another would result in a great deal of success.

However, I have some good news, having replaced a second chip - it's working! Once the board was in, it fired up straight away off the boot floppy stuck in the drive, to System 1.1g. It booted so fast by the time the CRT had warmed up it was almost at the desktop!



Picture 1: alive, perhaps after 20 years of no use

Picture 2: Circled RAM chips replaced with those from donor 512K motherboard

My very rough guide to removing RAM chips off 128K/512K motherboard:

- Using a solder sucker and iron (@ 350 deg C), remove as much solder as you can from the underside pads of the RAM chip. By the time you are done most pads should have a hole going through to the other side of the board.

- Gently, slightly bend the legs back to the centre of the hole (they are usually angled slightly diagonally, making it harder to pull the chip out if you don't do this)

- Holding the RAM chip firmly with some clamping pliers, heat the pads on the underside of the board using a mini butane torch (mine is a cheap DealExtreme torch/soldering iron, it was set to +++ full). Run the torch slowly up and down the pads, pulling the chip firmly as you do - it's tricky, but if hot enough it should slide out slowly and cleanly. It's daunting, but the hotter the flame better, I found - even if it did cause some slight cosmetic damage to the board itself.

- Once RAM chip is removed, clean up pads/holes again with solder sucker

- Replacement RAM chip should slide straight in, solder in.

JB

 

[techknight]

I just use a heatgun. heat underneith the board, and pull em streight out.

if the braid wont remove the solder, those cheapie radio shack solder suckers, do exactly that, SUCK.....

but i use a tiny 1/64th drill bit thats in a pack of dremel bits, and make holes through any solder that hasnt been removed. CAREFULL.... but it works for me.

 

[Mac128]

having replaced a second chip - it's working!

Interesting. All my Macs have returned an error code which indicated more than one chip at fault. But Tom Lee is correct, it's hardly a comprehensive diagnostic. However, I have found more often than not, that if one RAM chip has failed due to bit-rot (a symptom that seems exacerbated by extended periods of disuse), that it is usually not alone. Perhaps RAM is not unlike the human brain, if it sits idle for long periods of time, it begins to lose its ability to store and recall memories.

 

[Byrd]

I think this repair is interesting because I've never had such precise diagnostic error codes displayed on any computer I've repaired before - for a mid-80's computer to tell me exactly what is at fault is highly impressive. Even though from what others have posted, I appreciate that it usually doesn't work this way But old Apple designers would be pleased to note it did for me, many years later. In addition, having two chips fail is seemingly quite rare as well (although if a stick of RAM you'd just chuck it and move on), so I'm quite chuffed at the repair and how well it worked out, just following the Sad Mac codes.

Having fired it up - my suspicions about it not being used in recent times were wrong! Would you believe it was only decommissioned in 2000 - apparently having been used by a wealthy stock investor to keep tabs of his dividends, bills and letters. The (original) MacWrite disk is jammed hard in the floppy drive, so much so I can't even eject it using the sliding mechanism - the grease must have dried up to a solid. The good thing is the floppy drive (and disc) work fine, so I'll be extra careful freeing up the mechanism to bring it back to life again.

One other question - where is the Shut Down command for System 1.1?

JB

 

[jsarchibald]

I don't think there is one. I use a System 2.0 disk in my Mac Plus, and there is no menu option, you just have to flick the switch.