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Macintosh Plus boot problem - Maybe a cracked solder?

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Hello! :)

As this is my first post here, let me say that I'm very delighted to have found such a wonderful community of people who still cares about our beloved, ancient Macs. I think it's a really helpful place, it has already saved me quite a lot of time!


Next, I'll move on to the problem that's puzzling me.

I recently bought a "working" (so it was said) Macintosh Plus with 4 mb of RAM, dated 1987. The system came in a somewhat disappointing shape, but I managed to clean it up to a good looking state.

I borrowed a keyboard, a mouse and a startup disk from a friend of mine who also has got a Mac Plus and I tried to power it on (I should note that it's an american 110V build, which I plugged in to the power outlet via a 220V -> 110V power adaptor).

I noticed immediately that something wasn't quite right - the screen buzzed and the Mac refused to boot, so I slapped gently on the side and it came up with the nice happy Mac; so I thought that there could be some loose connection somewhere.


I went on using it for about 15 minutes, enough to check that everything was working (I was trying to connect with the external HD drive) when suddenly the screen went black with a trembling spark in the middle and a very strange noise, like a "blip blip" that kept going on.

I immediately unplugged the power cord and let it rest for some minutes before plugging it back in - this time to see the screen completely black, and the very annoying "blip blip" sound coming from inside the machine.


I did some research on this forum, and there seems to be a few options about what might be happening here:

- blown up diode: the main suspect here seems to be the CR20 diode, which I read fails quite often in the american version of the plus

- dead capacitors somewhere, possibly in the power supply?

- cracked solders


I tend to see the last one as the more likely, since I read in this topic that another user seems to have had the same problem and fixed it with reflowing some loose connections. But I'm not quite sure yet, so I thought it would be wiser to hear your opinion on this matter.

It may help to know that the "blip blip" noise is not coming from the floppy drive, but is clearly an electrical sound coming from somewhere deep inside the case.

I still haven't opened the Mac (I don't have the right torx 15 screwdriver yet) so I don't know the status of the board, I'm trying to come up with a diagnosis to know where to look and what to pay attention to.


As an attachment to this post I uploaded a recording of the "blip" noise so that you can have a better idea of what's actually happening here.


Thanks in advance for all the help!

Cheers :)


Sherry Haibara

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Yep, the slap worked the first time but after that it no longer boots at all.

I'm gonna look for a cheap soldering tool to open it up and see what I can do!

Speaking of soldering, do you suggest any particular precaution to take? I'm kind of worried of the CRT and the high voltage capacitors on the analog board, though I've read that apparently leaving it unplugged for a few days should suffice to discharge it completely.



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Read through this:




Will probably answer any questions you have, including CRT discharge.


Hello unity,

thanks! I was just reading that topic to see if I could get some insight about my problem too.

I'll definitely try to open it up and have a look at the joints. I'll update this topic with the results of my finding; thanks for the help!

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OK, I'm having some real trouble opening up the machine.

I removed all the five screws (two on the bottom, two under the handle and one behind the battery cover) but it still refuses to open. It seems like something is still holding the back case in place.

If it can help, there's a strange "lock" attached to the bottom left of the machine (as shown in the attached photo) that seems to be glued with the case, but I don't see how that should prevent the case from opening.

Any suggestion?

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The lock won't prevent the case from being opened.


Put back the screws, but not all the way down and lift the unit (above some soft material... a bed or similar) screen down, the case will probably pop.


Alternatively, while holding the case above the floor, push with your fingers on the ports of the logic board.


Macintosh casings are hard to get in.

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thanks! I finally managed to open it. It seems like the front frame may be a little damaged and the back is not fitting anymore in the correct way, as I noticed from the beginning that, when the Mac is closed, the bottom right corner of the machine is a little "open", in a non-symmetrical way if you look at the bottom left corner.


Anyway, since I managed to open it, I decided to put on a little experiment and try swapping the logic board with another Macintosh Plus ED (european version) that I know working for sure.

The results: the ED with the swapped logic board booted up just fine!

So I think we can definitely rule out the logic board, there must be something wrong with the analog board.


I tried to have a look at the top of the board, being careful not to touch the CRT to prevent accidental damage to the tube (and avoid getting a potential shock, though the computer has been unplugged for over 10 days now). From this quick look the capacitors seems to be still in nice shape and they don't seem bulged; there's something that resembles white glue around some of them, but it doesn't seem like any of them is leaking (though a better examination is necessary).

When I've got enough time I'll try to take the protective cover off the analog board and reflow the power connector that goes to the logic board and see if it gets better.


Thanks for the help guys!

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My Macintosh 512Ke did exactly the same thing. The Plus uses the same Analog Board, so it's relevant here too.


  • No Video / Loss of Video on Display
  • "Flup", "Whup" or "Blip" noise from inside machine


First of all, I think you'll find that the noise is from the Floppy Drive, as it attempts to start up over and over again. Listen closely to the drive from the opening on the front of the machine.


It sounds like you have a solder joint issue. In the case of my machine, the problem was simply the result of cracked solder joints on the Flyback Transformer. Like yourself, I left the machine turned off for a while. Then I discharged the CRT - the Flyback Transformer is the part of the CRT assembly that still packs a punch even after it's been shut off for a while, so discharging the CRT is strongly advised. Then I reflowed the following 10 solder joints:






You'll recognise them at a glance since they're located near the top of the board and are the only solder joints on the back of the Analog Board to be arranged in this manner.


Once that was done, the machine booted right up and ran stable. I've had to perform the same repair to my other 512Ke and two Macintosh Plus Analog Boards since then.


Your board could still require additional work, and this may not necessarily be the fix, but I would look closely at it since there's a good chance it could be.




~ Mic.

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Just had the chance to listen to the attached MP3. Definitely not the Floppy Drive, but similar to the sound my 512Ke was making with the Floppy Drive disconnected.


Mine is a 220v version of the Analog Board, so the component layout is a little different and the solder joints on the Flyback may be a little different. However, considering the symptoms, I wouldn't rule out the solder joints on the Flyback as a possibility.

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It seems like the front frame may be a little damaged and the back is not fitting anymore in the correct way, as I noticed from the beginning that, when the Mac is closed, the bottom right corner of the machine is a little "open", in a non-symmetrical way if you look at the bottom left corner.


Quite possible that the vinyl sleeve is not inserted properly and gets caught by the rear bucket. The sleeve needs to be pushed into the little plastic thingies that hold the analogue board.

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Hi all,

I finally decided to order a soldering tool so that I can try fixing it.

The first thing I want to check is the flyback transformer and the analog board joints in general, as iMac660 suggested they could very well be the culprit here.

I have a question regarding the soldering procedure, though: I wonder if it's necessary to remove the analog board from the chassis in order to work on it? If I need to remove the analog board from the chassis, how should I proceed? I don't know if it's possible and/or practical to make the Mac sit on its side without the rear case on, so I'm looking for some advice here.


Thanks for all the help!

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You should be able to do it without removing the analog board

I did my mac plus today (resolderd the flyback, yoke and lb pwer connectors aswell as replacing two cracked filter caps) without removing it


Was nice to turn it on for the first time in the 5 - 6 years I have had it and not have to slap it on the side to get video ;)

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