Mac Plus turns off after short time

[Timbo]

Hi everyone,

Long time lurker but very short time poster!

I have looked through the forums but haven't seen a question same as mine yet (if there is I am sorry and I will delete this post).

There are 7 Mac Plus's at home I have been hoarding away (hate that word). The other day I got motivated to pull them out and have a play.

First one tripped the house circuit safety switch after about 3 minutes.

Turning the next 6 on achieved the same result, some after 30 sec and others after 2 or 3 minutes. Grr

Pulling these guys apart revealed no apparent capacitor problems wrt bulging or leaking caps on the logic or analog boards.

Where do I start?

I see C1 mentioned but seeing as all 7 have the same problem (all previously working a couple years ago) there must be a known cause?

The screens were bright and clear when they were running.

Any suggestions would be appreciated.

Thanks

 

[Macdrone]

High current draw like that sounds like a bad analog issue. But for all to have the same problem that is strange. I have three pluses and the power connector to analog board will draw and sometimes crack the so.der and has to be resoldered. The C1 is common but with a bright clear screen I would pull the plastic cover on the analog and look at the power connector back sides. As for all of them doing it try the units in different plugs as once the breaker was tripped it can take hours before its not easily trip able by any real load, especially if you don't have ground fault plugs with the resets.

I hope this info made sense and helps you.

 

[RickNel]

If the same problem occurs with 7 different machines, I would be looking at the house current circuit. Do you have heaters or other high-load items (like washingmachines, stoves) running on the same power circuit? Maybe the circuit-breaker itself is getting a little old and over-sensitive?

 

[krye]

I've never seen a classic trip a breaker. Since all the machines tripped, I'd say the outlet was suspect. Did you try somewhere else in the house?

I have all these Macs plugged in only 2 outlets and nothing ever trips:

 

[onlyonemac]

Try taking a couple of the Pluses to a friend's house and try them there. If the problem goes away, then it's probably your circuit, not the innocent Plus.

Also, can you relate the turning off of the Pluses to any particular event (like a disk being ejected/formated)? Sometimes things like a disk ejecting and continous drive activity raise the Mac's power consumption significantly.

 

[CC_333]

I have all these Macs plugged in only 2 outlets and nothing ever trips:

That's quite an impressive display!

Unfortunately, I don't have anything else to add, except that it seems that if there were something wrong with the Pluses, they would be doing other odd things, and they would probably trip the breaker instantly.

 

[James1095]

What sort of circuit is this on? Unless it is overloaded with other devices, I doubt that over-current is tripping it. Is the breaker a GFCI (RCD in Europe) or AFCI? Both of those are somewhat notorious for nuisance trips, especially older generations. It's not uncommon for the noise suppression capacitors to leak enough current to ground to trip a GFCI. Try isolating the ground pin on the power cord and see if the problem remains. There's a good chance nothing at all is wrong with your Mac.

 

[Timbo]

Thanks for all the replies so far.

It's the RCD in the house that they are tripping- no heaters operating.

I took one of the Mac's out to my parents place yesterday and got the same results after a couple minutes- had booted up and was justing sitting there doing nothing.

Plugging in other known good Macs to the same power outlets don't give any trips.

I will have another play today and see what I can find.

Isolating the ground pin? Will have a look.

Thanks

 

[onlyonemac]

DO NOT ISOLATE THE GROUND PIN!!!

It is there for your safety. If the Mac is causing earth leakage through the ground pin, then isolating said ground will cause the leakage to flow THROUGH YOU not safely to the ground.

Also, I believe that pin is used in the CRT system somewhere???

 

[Brett B.]

DO NOT ISOLATE THE GROUND PIN!!!

Do you know what you're talking about? I am convinced that you do not. Isolating the ground will do nothing to YOU assuming you don't fawking touch live wires and/or circuitry inside the computer, which you would not be doing anyway.

Just to clear up YOUR misconceptions, the CRT ground lug is used when discharging the tube itself. http://apple.doit.wisc.edu/servicesource/ss/safety/safety.html#Discharge

OP - That is certainly an odd situation you have going on there. So you have ruled out the house wiring by testing it at your parents house.

Just to be clear, only one of the Pluses trips your RCD correct? Not all of them? The other six just lose video but stay powered on? I think you should pick one and carefully test the analog board. Touch up all of the solder joints if you want.

 

[James1095]

Relax, the ground/earth connection is a secondary safety system, intended to protect the user in case of a fault condition such as an internal short between a live wire and exposed metal parts. Obviously I'm not advocating permanently disconnecting the ground pin and leaving it that way, but isolating it temporarily is a perfectly valid troubleshooting method. In North America, many houses built prior to the 1960s don't have any grounding at all and it's not uncommon (though not advisable) to use adapters on grounded plugs that go into a 2-prong socket. You are supposed to ground these adapters but nobody ever does. Unless a fault in the equipment exists, there should never be measurable current flowing through the ground lead, that's what neutral is for. In fact, ground and neutral tie together in the panel and come from the same place.

A GFCI/RCD works by monitoring the current flowing through the live and neutral leads, and tripping if there is a difference of more than a few mA. The assumption being that any current passing through live that is not also passing through neutral is leaking to ground, possibly via one's body.

A lot of equipment has capacitors connected between live and ground and sometimes neutral to ground to shunt electrical noise before it gets out through the power entrance. Some of this stuff (such as old Macs) were designed before GFCI/RCD breakers became commonplace, and some GFCIs are more sensitive than others. The result is precisely the sort of nuisance trips you're experiencing. You may be able to replace the suppression capacitors with some of lower capacitance, or just disconnect them entirely, accepting that you may get a bit of interference on the radio, TV, or other RF devices around the house.

 

[RickNel]

James 1095 said:

You may be able to replace the suppression capacitors with some of lower capacitance, or just disconnect them entirely

Lower value filter caps sounds like a good thing to try. Not sure I'd recommend disconnecting entirely, though. Might you not get some electrical noise propagating inside the Mac, maybe affecting the CRT?

Typically a too-large filter capacitance will trip a fuse or external circuit-breaker when the extra inrush current fills up the capacitor as it is first switched on. OP's symptoms take up to 3 minutes to trip them - suggests something cumulative, like heat buildup and/or ESR buildup in caps on the analog board. Weird that others haven't reported the same thing with Plus or other Compacts. Also defies probability that 7 machines would exhibit the same problem simultaneously.

Rick

 

[James1095]

This is different. The filter capacitor you are referring to is the DC filter capacitor used to smooth the pulsating DC coming from the rectifier. A discharged capacitor has a very low impedance and acts much like a short circuit until it charges up, something that can take long enough to blow a fuse or trip a breaker in extreme cases. This is rarely an issue with small switchmode power supplies, but the very large filter capacitors used in 50/60Hz linear power supplies common in large audio amplifiers and such often have something to limit the inrush current.

The capacitors I'm referring to are small film capacitors used in the noise filter. They are there to block high frequency noise from the switching regulator and digital circuits from getting out of the computer and radiating from the power wiring which can potentially interfere with other devices. These capacitors are small enough to appear as a very high impedance to the 50-60Hz line frequency, while still shunting high frequency noise, but there is still *some* leakage current, sometimes enough to trip an excessively sensitive GFCI. It's not uncommon for a GFCI/RCD to take a bit of time to trip when the ground leakage is only just barely enough to trigger the thing.

 

[Timbo]

Thanks for all the replies!

I was hoping for some success to report but nothing so far- I ordered a bunch of new caps for the analog board last Monday night and thought they would have arrived by now. No such luck.

I took one of the analog boards though and reflowed the solder on a lot of the connections, especially around where the power connecters, power switch and flyback tranny are.

Result is the computer boots and stays on for about 5 minutes then trips the RCD.

I would play more tonight but the family gets annoyed when the Mac takes their youtube, TV and internet with it...

Hopefully my replacement caps will arrive next week and will get some results (I wasn't able to order the lot though).

To answer an earlier question- all the Mac Plus's give the same result.

Oh, and for RickNel- there is a Mac Plus on eBay (Australia) with the same description at the moment.

Thanks guys.

 

[RickNel]

Timbo said:

Oh, and for RickNel- there is a Mac Plus on eBay (Australia) with the same description at the moment.

Thanks - I saw that. So it is very likely caps failure in the analog board, combined with modern circuit-breakers.

Seller asking $70, no accessories - would cost me $100 including freight, for a possible wreck.

Same seller failed to sell a SE for that price a few weeks back. Need to get real.

The latest auction price for a non-working Plus on eBay here was $17. I might give $25 for a local purchase, freight free.

Rick

 

[oldmacs]

I had two Macintosh Pluses that did this.

One I sold, but I still have one.

Mine would sit there on a white screen then trip, after about a minute. I then sold one and kept the one that looked better. However when I got it back out about a year later, it turned on with garbled image, If I thumped the side it would boot up. However it would then trip after about 5 minutes.

In my case I attribute it to the Flyback transformer slowly falling off the analogue board due to bad solder. However I am scared senseless of opening ANYTHING with a CRT in it!

 

[James1095]

I really doubt it has anything at all to do with the flyback transformer, that is on the secondary side of the power supply. Look for film capacitors between live and ground near the input power connector.

No need to fear the CRT. The zap from that feels like a strong static electricity shock on a dry winter day. It doesn't feel good and should not be handled carelessly, but it's very unlikely to kill you. Also unless you remove the anode connection from the tube, all of the HV circuit is well insulated and fairly safe to handle. More dangerous is the electrolytic bulk filter capacitor in the power supply, these are charged to "only" 160 or 330V but pack a LOT more energy than the capacitance in a CRT. Either way unplug the thing and let it sit for a few minutes, most everything will discharge itself. For extra caution, take a cliplead and touch it across the capacitors you want to discharge.

 

[oldmacs]

Would the Capacitor really trip a circuit breaker though?

When I taled to some vintage Mac people about a year ago, they said that it was probably tripping from arching as the transformer slowly pulled away from the board.....

My Plus hasn't been turned on since about 2011 ish so would it be fine?

 

[Timbo]

However I am scared senseless of opening ANYTHING with a CRT in it!

I was at first but haven't had any troubles. Common sense helps and I normally leave it turned off for a while anyway.

Got my first lot of new caps in the mail yesterday (but not all).

Have soldered in about a dozen but waiting for my new C1 and C33/36 (filter caps?).

Hopefully another couple days then I can power up a Mac Plus and see if it will work (for more than a few minutes).