Need help with Macintosh 128k

[kingsapo]

Hello all! So a few months ago, I got a buncha old Macs from my uncle: a Macintosh 128k, a Macintosh (can't remember which model, it looks very similar to the 128k), and a Macintosh SE. The last two machines run fine, however the 128k is giving me some problems. Whenever I turn it on, it gives me this checkerboard pattern thing, and never does the boot-up chime.

I have already done some research on this problem. Some people said this is a problem with the resistors on the logic board, and that I should wash (one person even said to put in a dishwasher) the logic board. I didn't know if this applied to me, as they were referring to a SE/30.

Then, someone said to swap out the logic board with a similar computer that works. So I swapped the logic boards of the 128k and the second computer from the list (not the SE). At first I thought it worked, as I heard the boot-up chime, but then I saw nothing on the monitor. I thought it was just the logic board being incompatible with the CRT monitor or whatever, so I swapped the logic boards back. The thing is, when I turned it on this time, I also got no video, whereas I used to get that checkerboard pattern. I also got no boot-up chime. Now I'm kinda nervous that I may have done something to damage the CRT. Then again, I know those CRTs use a lot of electricity, so I'm not sure if I need to leave it plugged in for a while to let electricity get in or something.

I'm a huge Apple fan, and would love to see this thing working again, so if anyone can offer any advice, it would be much appreciated!

 

[Comeagain?]

Sorry, tapatalk problem.


Sent from my iPad using Tapatalk

 

[0megman]

Analog to digial board cable

Check the connection where the analog board connects to the logic board. This area is prone to cold solder joints and sometimes requires the solder joints on the logic board to be reformed by heating with a solder iron. There is a white plastic connector there and a bunch of PINs that stick out of the logic motherboard on the bottom is the place you resolder

Try that

Also just press down on the ROM chips to make sure they have a good seat

 

[kingsapo]

Thanks 0megman. I'll definitely give that a try tomorrow and post how it goes.

 

[Mordecai3855]

Hey if you are at all interested I'd love to buy the 128 from you and restore it
Let me know my email is:
Malefic@Rogers.com

 

[kingsapo]

Mordecai3855, thanks for the offer, but I'm really not interested in selling it.

0megman, I tried your advice, and those connectors you talked about appear to be fine. I have posted some pictures to confirm that you and I are talking about the same thing, so please do tell me if I was thinking about something else! All the memory chips appear to be ok as well. I guess the only good news is the fact that I didn't break the CRT, because when I turned it on after doing service on it, I didn't get any video from it, but when I left it running for about an hour, it showed that checkerboard pattern again. I guess the CRT needs to let electricity get back into it before it works again or something.

So back to the actual problem at hand - the checkerboard screen. I found out that this 128k also has that MacSnap upgrade card thing, which upgrades the RAM to 2MB. I thought this may be causing trouble, and thought about removing it. Then I realized that the card that houses all the extra RAM takes up a RAM slot, so if I were to remove it the computer would have less than 128k of RAM, and probably wouldn't work right. It also has that MacSnap SCSI upgrade card. That card is missing a pin, but I'm not sure if that would be causing trouble. Other than that, the only real lead I have is to wash it, which I'm not entirely sure that I can do without wrecking it, and to replace the capacitors, though I don't know if leaky capacitors would even affect this model. As usual, any help would be great!

EDIT: Woops! Almost forgot to add the links to those pictures of the connectors like I said I would. Also, I checked the connector on the analog board end, and they appeared the same (I didn't take pictures because it was difficult to get a camera in there with the CRT in the way):

http://www.flickr.com/photos/65362025@N03/5950560291/
http://www.flickr.com/photos/65362025@N03/5950559881/

 

[0megman]

Yes, that is the connection I was talking about

The symptom you describe, "works after a while" is intermittent connections that heat up and then work
might as well do the re-solder thing

Hmm, MacSnap. Yes, those can be troublesome since they were user upgrades

Those sometimes had traces cut and wires added to get the memory upgrade

I would pull the MacSnap and replace the mem chip to bring the unit back to original 128k

I have a 512k board that I pull mem chips off of and have had good success with getting 128k boards up again.

Post a picture of the motherboard

 

[kingsapo]

Alright, so I haven't gotten around to re-soldering that connector we were talking about, but I did try taking off that MacSnap thing, and that didn't help. Weird thing is, the MacSnap upgrade goes over the existing memory, so all the original memory was already there. Then, I tried removing the MacSnap SCSI upgrade card, which was this card that sat between the two ROM chips and the logic board, and allowed for a SCSI connection. I really thought that would work, since now there's nothing in between the logic board and the ROM chips, but it didn't help.

Taking these two components off didn't make the computer usable again, but it did change the appearance of the screen I was getting on startup. Before, I was getting a solid checkerboard pattern, whereas now it's this weird array of black and white bars. You'll see what I mean in the links to the images.

Before Removing MacSnap Upgrade Cards:
http://www.flickr.com/photos/65362025@N03/5955325024/

After Removing MacSnap Upgrade Cards:
http://www.flickr.com/photos/65362025@N03/5954766017/

Also, since you asked, here's a pic of the logic board:
http://www.flickr.com/photos/65362025@N03/5955340710/

Thanks for all the help so far!