Macintosh Plus rebooting non stop

[danda]

Hello everyone,

I have a Macintosh Plus that I got a couple of years ago. When I first got it I had a problem where I would turn it on, it would come on, get as far as the flashing question mark icon on a floppy disk, but after a fraction of a second on that screen it would reboot. It would continue doing this until it was manually switched off. After about a day, the problem went away, and I never thought much about it.

I had not used it for quite some time (a few months), but when I turned it on again today I found that this problem had returned.

Does anyone know what is wrong and how to fix it?

Thanks,

Andrew

 

[bigmessowires]

Hmm, I've never heard of that symptom. Sounds like a logic board problem, or maybe a 5V supply voltage that's out of spec.

Have you taken a close look at the logic board?

 

[Ike]

Check the voltages on the external floppy connector.

Also, try to gently slap the left side of the mac when you are sitting in front of it, tiny broken solder joints in the connector going to the logic board might cause that issue I believe. A re-solder/re-flow of any connections in the area of the power connector and switch are a good idea, but beware of the filter caps as they can contain high voltages.

Now my plus once did the same thing, and after I fiddled around a bit with the things above, it never did it again.

 

[trag]

That symptom is often a sign of a low 5V supply. As others wrote, check the 5V supply first. If it's down below about 4.95 or 4.9, see if you can adjust it back up. If not, you'll probably need to rebuild the analog board (replace some caps and rectifiers).

 

[danda]

Hi everyone,

I think that the Macintosh Plus has some loose solder connections somewhere because I managed to get it to boot for a few minutes when I slapped the left hand side. After a few minutes it went back to the non stop rebooting problem. I have ordered a Torx screwdriver from here: http://www.ebay.com/itm/231115554403 , but it will be a few days until I can begin to work on it as postage to the UK takes some time.

Also, I decided to check all my other Macintosh computers and unfortunately it seems that my other Macintosh Plus has developed a similar fault. It turns on and works for a while, but has two faint bands of horazontal lines which move up and down the screen. After a couple of minutes the Macintosh will reboot, and then instantly reboot again. It does not show any picture on the screen, probably because there is not enough time between reboots (less than a second). It will continue rebooting constantly until it is switched off. I switched it of after about 30 seconds as I did not want to damage it. I tried slapping the side, but this did not seem to make any difference.

Does anyone know what could be wrong with this Macintosh?

Thanks

 

[bibilit]

Hi,

Very common problem on a Plus.

Yoke J1 is often faulty but easy repair, also look for C1 capacitor on Analog Board.

Everything needed here:

www.ccadams.org/se/classicmac2.pdf

 

[danda]

Hi bibilit,

Thanks for the info. Just to clarify, which Plus are you talking about. Is it the first one (which reboots as soon as it reaches the flashing question mark on a floppy disk), or the second one (which comes on, works but has two bands of horizontal lines moving up and down, then after a while restarts and keeps instantly restarting)? Or (hopefully) are you talking about both of them?

Thanks

 

[bibilit]

Hi,

Maybe both, the file is pretty well done and really interesting.

Let us know.

 

[danda]

Let us know.

I will do. Now I just have to wait for that Torx screwdriver to arrive!

 

[danda]

A quick update: the Torx screwdriver arrived today, so now I just have to find some time to take the Macs to my friend who is better at soldering than me.

 

[danda]

OK, time for an update.

The good news is that all of these Macs (And another) are now working again. The two Macs mentioned in this thread had a surprisingly simple problem. All I had to do was unplug J4 and plug it back in again. The other one needed re soldering on J1.

Thanks everyone for the great support and patience. It is great to have these Macs working again.

 

[unity]

Odds are if unplugging and plugging in worked, there is a bad solder point. I have worked on more than few compact Macs and recently worked on five more. Before I even power then up they come apart and every single solder point that involves a connector is reflowed with a bit of new solder. Including at the logic board. The computer can work okay with a cracked solder point, but that point can heat up. I have a couple connectors that are burnt and melted. They only way they got that bad was pro-longed use.

So be careful when checking them. I use a high powered LED and move it around the points and angles to see cracks. Even then they are not always visible which is why I reflow them all then check all the others for caps and such.

 

[bibilit]

Goods news.

 

[Sebastian]

Odds are if unplugging and plugging in worked, there is a bad solder point. I have worked on more than few compact Macs and recently worked on five more. Before I even power then up they come apart and every single solder point that involves a connector is reflowed with a bit of new solder. Including at the logic board. The computer can work okay with a cracked solder point, but that point can heat up. I have a couple connectors that are burnt and melted. They only way they got that bad was pro-longed use.
So be careful when checking them. I use a high powered LED and move it around the points and angles to see cracks. Even then they are not always visible which is why I reflow them all then check all the others for caps and such.

Bad solder or just a bad connection in the plug.