68kMLA Classic Interface
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| Display issue on Plus | |
| Posted by: petteri on 2022-02-03 11:28:16 I have a Plus with a strange display issue. I checked the typical soldering issues but no luck. There is a bright and blurry glowy area in the very bottom of the screen. I looks like the whole image has fallen down and out of focus. My wife told me the computer smelt bad as well. Any ideas where to start trouble shooting? | |
| Posted by: petteri on 2022-02-03 20:46:08 This is how the screen looks like now. | |
| Posted by: desertrout on 2022-02-04 20:02:51 Thanks for sharing the image! I assume this was working well until now? Has the analog board been recapped? I personally don't know enough about the vertical sweep circuit to be sure, but usually if there's a component failure it collapses toward the middle as thin white line... afaik. This is something different. The smell would suggest a failing flyback transformer... is the smell new as well? Sorry I don't have any specific suggestions at this point... I'm surprised someone else hasn't chimed in yet! | |
| Posted by: petteri on 2022-02-05 02:02:49 First this screen had typical flickering like they do with bad solders. I re-soldered bunch the typical analog board points. After that it worked ok for a moment. I moved the mac around a bit but then it started to flicker again and the picture went down. At the same time my wife said it started to smell bad. Unplugged right away. I don't see any burnt components though. | |
| Posted by: Johnnya101 on 2022-02-05 03:14:12 That looks kind of similar to what happens when a tube gets hit and loses vacuum, but I've never seen one turned on like that. Is the tube good? See any obvious cracks by the neck area? You say it worked okay for a minute, as in showed a desktop or flashing disk icon? | |
| Posted by: petteri on 2022-02-05 04:09:55 Yea, it did pass the mem check and I got the disk icon. So I assume the power supply side of the analog board is ok. I don' see any cracks or such on the tube. Edit: I think something shorted on the analog board. I had the case in place while I was testing but I forgot the white cardboard covering the analog board. As I moved the mac I pushed from the side. Is the metallic looking layer inside the case conductive? | |
| Posted by: Johnnya101 on 2022-02-05 04:30:02 Looked up some older threads with similar ish problem. Help with dead Mac PlusI have had this Mac Plus for years with intent to repair it. When I acquired it, it would boot and work but the screen would get very blurry. Tapping the side of the computer would sometimes correct it for a few seconds. I'm good at soldering but never really worked on high voltage stuff, so...
68kmla.org
MacColby/128k Screen IssueMy current project from the Colby estate is to revive a MacColby (1st pic). When I first turned it on, I actually got a loud bong, and the usual floppy question mark, so I was elated (2nd pic). It took me a while to de-stuck the two floppy drives, and I could get everything going in record time...
68kmla.org
I'd start looking at those and see if any of those issues could cause yours. The second one has your same issue. | |
| Posted by: LaPorta on 2022-02-05 05:57:08 Yes, the metallic coating is conductive, and yes, it is possible to short things that way. Don't ask how I know... | |
Posted by: petteri on 2022-02-05 07:09:58Yes, the metallic coating is conductive, and yes, it is possible to short things that way. Don't ask how I know...Alright, I might need a new analog board then... | |
Posted by: desertrout on 2022-02-05 10:25:22Alright, I might need a new analog board then...Unless you want to dive in a see what the cause is. The nice thing about these analog boards is that they're almost always repairable with readily-available parts (aside from the flyback and one pesky SCR). A bad smell at the time of the short could suggest a blown capacitor, so look for opened tops or cracks on caps, check resistors (especially R2 and R3)... perhaps you blew a transistor in the vertical sweep circuit (I assume yours is an international board so Q1 and Q4?) Many have found this book helpful during a process like this: https://vintageapple.org/macbooks/pdf/Macintosh_Repair_&_Upgrade_Secrets_1990.pdf But a short could have done all sorts of interesting things, so a new board may be the fastest route to a working machine. Personally I enjoy trying to solve the issue, it's part of the hobby for me. But I appreciate you may just want the machine back in working order sooner than later. 🙂 | |
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