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Memory troubleshooting on a 128K
Posted by: hideehoo on 2018-01-16 20:17:22
Finally getting around to fixing the 128K.  It chimes on startup, but then immediately goes to Sad Mac.



Looks like a 0200?0 code, so I'm guessing memory in either F9, F10, F11, or F12 according to https://udcf.gla.ac.uk/~gwm1h/Error_Codes/Sad_Mac_Codes.html

Any further hits given the video corruption?  Does the piggyback RAM trick work on these to aid in troubleshooting before desoldering and replacing the chips?  How about the possibility it's one of the supporting 74xx logic chips, hence the odd error code.  The board looks original (no past work that I can tell), but it has a mix of both Apple and Motorola RAM chips on it.
Posted by: bibilit on 2018-01-17 00:14:30
You have got more than one ram bad.

Yes, piggybacking works.

Strange, the odd Ram has also the Apple logo on it.
Posted by: AlpineRaven on 2018-01-17 04:58:16
Yep I had Macintosh 128k did the same thing above - it was one of 3 memory chips that had gone bad. I replaced whole 16 of them of the same.

I replaced to Samsung KM4164B-15 16PIN 64K 150NS DRAM

Works now! It wasnt video that was bad - it was the memory.

Cheers

AP
Posted by: hideehoo on 2018-01-17 23:45:25
Thanks folks, new (used) memory is in the mail.
Posted by: bibilit on 2018-01-17 23:56:44
used ?

removing those ram chips are a P... in the A.., i won't go the used path in your place.
Posted by: AlpineRaven on 2018-01-18 00:38:49
I second that I wouldn’t get used memory either. I got mine as new old stock.

Cheers

AP
Posted by: PB145B on 2018-01-18 00:45:35
removing those ram chips are a P... in the A..
I agree! I had to remove a RAM chip like that on a Compaq Portable a while back and what I did was cut the legs off of the chip (being extremely careful not to damage the PCB) and then remove the legs one by one and clean the solder out of the holes. I know it sounds violent but if you’re careful it can be done. Probably not the correct way to do it but it was all I could do with the equipment that I have.
Posted by: hideehoo on 2018-01-18 20:25:37
I agree! I had to remove a RAM chip like that on a Compaq Portable a while back and what I did was cut the legs off of the chip (being extremely careful not to damage the PCB) and then remove the legs one by one and clean the solder out of the holes. I know it sounds violent but if you’re careful it can be done. Probably not the correct way to do it but it was all I could do with the equipment that I have.
Picked up a chinese desoldering station a few years back.

http://www.memotronics.com/vacuum-desoldering-rework-station-digital-temperature-controlled-dual-lcd-new/




Best money I ever spent on this hobby.  Make jobs like this infinitely easier than using a hand pump or braid.
Posted by: PB145B on 2018-01-18 22:50:12
2 hours ago, hideehoo said:

Picked up a chinese desoldering station a few years back.

http://www.memotronics.com/vacuum-desoldering-rework-station-digital-temperature-controlled-dual-lcd-new/

I definitely got to get one of these!
Posted by: chu-oh on 2018-01-19 00:49:32
I definitely got to get one of these!
I've got the combo soldering/desoldering station version of this. It makes recapping/removing components a dream. 

Can't recommend enough. 
Posted by: techknight on 2018-01-20 05:59:24
I picked up the Hakko FR300 and it seems to do good with what I use it for. 

I had to pick up the drill set though because when those tips clog up... well... yea..... 
Posted by: hideehoo on 2018-02-17 14:15:41
Fixed!  Got my $2 for 10 KM4164 memory from China and had at it.  Piggy backing on F9 cleared the 0200?0 error, but then I got a 041101 (Mod3 test).  Piggybacking could clear that one, but when I actually replaced the chips, it cleared.  Ended up replacing four chips in total, all the Apple branded MT4264 ones.
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