68kMLA Classic Interface

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Dead Mac Plus?
Posted by: HAL2001 on 2016-02-03 16:46:10 Today I saw a dead Mac Plus ED. It shows no picture and it just boings repeatedly. Any ideas? Thanks.
Posted by: Elfen on 2016-02-03 17:32:13 Analog board not producing the proper voltage (under-voltage). It may have other issues with the analog board, and maybe a stuck disk in the drive.
Posted by: uniserver on 2016-02-03 21:04:05 analog board needs a service buddy.
Posted by: unity on 2016-02-03 21:22:11 Could be as simple as bad solder joints at connectors, logic board and analog/video. A very, very common issue with the Plus and older models. Or component failure. I never fire one up without checking solder joints first since they can melt connectors, etc if bad. Plus they are very quick/easy to fix since only the bucket and shields have to come off. If those end up being fine, dig deeper. Oh, and never assume they "look fine". They cracks can be tony, reflow of solder a must. Here are some pics I made a while ago to help people.
Posted by: HAL2001 on 2016-02-03 23:01:48 Thanks. I read on this board somewhere that a plus never ever needs recapping. Is that true?
Posted by: CC_333 on 2016-02-04 07:22:18 Yes and no. The logic board only has through-hole axial electrolytics and uses few, if any SMD components, so there's virtually no chance of cap related damage occurring. In other words, the logic board is virtually indestructible. The analog board, on the other hand, is chock full of caps, many of which have begun to leak, making this a very weak point. Exacerbating this problem is the fact that it is prone to overheating (causing all sorts of heat-related damage), and was full of problems even when these machines were still relatively new. Therefore, recapping the analog board (and examining/replacing any other components that may have suffered heat-related damage) is a must if you want the Plus to work reliably. I hope this clears things up a bit 🙂 c
Posted by: unity on 2016-02-04 09:08:07 HAL2001, I have yet to meet a Plus that needed an analog board re-cap but I am sure ones exist. With the caps used they typically will dry rot out making failure hard to detect. I have never seen one myself or an example of one with leaking caps like is really common on the Classics. Caps evolved a lot over the years, sometimes for the worse.
Posted by: uniserver on 2016-02-04 10:12:48 i have not met a PLUS 128K 512k Analog board that has not NEEDED caps... Those dam things are leaking and you might not even be able to tell as they are dribbling at the base. With the se... i have worked on a few that have not been leaking. just like APPLE II SMPS power supplies... same way... i have not met one yet that was not at least dribbling at the base of the output stage caps of the SMPS.
Posted by: uniserver on 2016-02-04 10:21:47 nobody can say exactly what the problem is at this stage... because it could even be burnt up flyback... or rectifier... but after you change all the caps... and inspect the virt deflection connection for cookedness. and you can clearly see fried solder joints on the back of the ab as they have a black ring and have been cooking and are carbon tracked up from the thermal expansion/contraction movement... that is why they need to be vacuum desoldered... then flux + wick cleaned then re-soldered and not just " touched up " could still be the rectifier and flyback... considering your problem. but maybe there is some life still left in those... hard to say... you can always adjust the 5v pot , its the one in the middle of the AB, if that if its trimmed up too high .. you will get a process where the computer comes on and then shuts off, that pot does require adjustment usually after a re-cap.
Posted by: Elfen on 2016-02-04 17:37:33 They cracks can be tony, reflow of solder a must. Here are some pics I made a while ago to help people. Never reflow the solder. They will just begin to crack and break after a few months time. The best thing to do is to desolder the jacks, clean then up, and put fresh solder and flux to them. It will hold much better and last for a much longer time.
Posted by: unity on 2016-02-04 20:41:11 Never reflow the solder. They will just begin to crack and break after a few months time. The best thing to do is to desolder the jacks, clean then up, and put fresh solder and flux to them. It will hold much better and last for a much longer time. Well I will do what has been proven to work by thousands of people. Never an issue and its fast.
Posted by: HAL2001 on 2016-02-05 10:47:52 Thanks everybody!
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