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Mac 512K - Single Dot Display

N

ngtwolf

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Hi All,

So a while back I was given a non-working Mac 512k that had a sticker on it that said 'Bad CRT' (the person who had it also got it that way with other equipment and wasn't interested in doing anything with it). Plugging it in gives a single dot in the display, but it does make other boot sounds and some sort of mac Ding, like it might actually be doing something. I don't really know anything about Macs since I went straight from 8 bit machines to Atari ST to PC's and everything I have with built-in CRT's, the CRT was the part that always worked on them (vs having to fix other parts). Does this seem like it is a bad CRT or something else? It's missing a keyboard/mouse, but don't want to pursue finding those if the CRT is bad. Attaching picture.

20181008_023705.jpg

(sorry it uploaded sideways.. but not important for reference)

I'm going to open it up to check it out inside but, any thoughts?

Thanks!
 
You have no horizontal or vertical deflection. Check to see that the yoke connector is plugged in and the connector and socket are not burned up. It's a known failure point.
 
NeXT said:
You have no horizontal or vertical deflection. Check to see that the yoke connector is plugged in and the connector and socket are not burned up. It's a known failure point.
Click to expand...

Great, I'll check it out once I figure out how to get it opened. Hah! I got the 5 screws off (well, the two handle ones were already missing) but it just doesn't want to open for whatever reason.. Anyway, at least this will give me something to look at once I do.

Thanks for the info!
 
Okay, looks like that's it. Is there a recommended fix? I mean, I can obviously put it back on ghetto style, but should I just be swapping these connectors (and if so, anyone know what these connectors are?).

IMG_20181114_180502.jpgIMG_20181114_180454.jpg
 
Al Kossow said:
PCB connector pn Molex 15-31-1046
plug 19-09-1046
Click to expand...

Great, found them on mouser (about the cheapest i could find these connectors.. so much for my bulk ordering from china..haha). Appreciate the guidance! I'll update when those come in (ordered cheapest shipping option). In the meantime I can clean up some concerns inside and check the various solder joints.
 
Haven't updated for a while so here's where i'm at. Right before thanksgiving the connections came, so I swapped them out and also reflowed all the solder connections on it and tested, and it worked. Floppy drive might not work, but at least i got a display. I tried it a few times and all was good. Closed it back up (without back case), tested again.. good. Realized I missed a couple of the case screws behind the motherboard so discharged the screen (i'm paranoid - it did spark where-as the other times it didn't because it was mostly sitting for a bit between handling), put in missing screws, and reassembled again. This time however, I got a single long horizontal line. Double checked all the solder joints and also made sure there was continuity from the solder joints to the CRT and they're all good. No idea what to test now, it's like something went, but if it's not the solder connections, i'm not sure what it would be next. I did follow through the mac service manual out there testing the voltages (5 / 12 on the floppy connection, it was a little low so I did a minor adjustment for that) and a few other basic things, but no progress. Googling around I saw mention of it possibly being capacitors and there has always been a weird smell inside the mac, but I kinda just attributed it to being old and i saw some oxidation and rust in a few (non critical) spots. I don't notice any capacitors look out of the ordinary. I did replace the Rifa's earlier in the process as those looked kinda bad, but that was before this new issue. Anyway, maybe others who have seen this have some idea where to look? Not sure at what point I should just call the time/date on it and move on. :)

IMG_20181201_233619.jpg

Thanks!
 
The CRT has vertical collapse, it's most likely going to be a faulty component in the vertical section of the analog board. You'll need a schematic and a multimeter and ESR meter at minimum to start testing components. Capacitors are going to be the number one culprit, just because they look fine doesn't mean they are fine. Old caps tend to start to leak electrically, which can cause all matters of havoc.
 
GiGaBiTe said:
Capacitors are going to be the number one culprit, just because they look fine doesn't mean they are fine.
Click to expand...
Seconded. I had a Mac Classic with exact same symptom as shown in photo above; leaking capacitors was the fault.
 
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