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Released by Apple on January 16, 1986, the Macintosh Plus is an upgrade to the original Macintosh and the Macintosh 512K.

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Macintosh Plus Trouble shooting.

I have had trouble with this machine a lot but i need a little help.

I noticed some broken solder mask and broken traces but i know those traces are not important because they go to the battery compartment. But i need to know why wont it start. When i turn it on it makes a Hi voltage sound. Like a Click-THUMP sound and then nothing happens. Sometimes it does it over and over again or just once.

When i power it off after the sound/s then power it on again the sound does not happen and there is no sign of life!

SYMPTOMS: A HI Voltage Click-thump sound , no startup BONG, No video or sound , and a black screen.

Also can someone give me the list of capacitors on the analog board?

Update (09/16/2019)

Block Image

These are some broken traces

NOTE: not my image!

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Are you sure they are broken and not the over-cover just isn't scratched. Did you check the continuity? Can you post your board so we can so how it looks do both sides and as detailed as you can.

par

I can get another computer for the same price as it would cost to fix this one and also that would give me a machine to test the analog and logic board on.

par

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You’ll need to search out the service manual out on the web to help you troubleshoot.

The biggest problem will be finding parts for this system. Most parts houses have long since disposed of what they had.

A high pitch whine is a failing flyback transformer. In addition most cases the electrolytic capacitors have rotted out in the power supply as well.

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Would it be best to just buy a whole new analog board? I can't complain because it was working when I got it early this year. But for 40$ I could not help but know this would happen...

par

How much are you going to spend on this system?

Sure getting a new analog board might get you going if it's in good shape. But remember the caps will likely need replacing if it hasn't been done already.

par

@danj The problem is the keyboard and mouse for these pre-ADB Macs is worth more then the system.

par

I got the keyboard with it too no mouse what shame.

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It’s a common issue for these to have bad solder joints due to their age. This isn’t difficult to repair, but you really should go over the entire board and refresh all of the joints to keep the rest of them from failing as well. J4 on Pin 1 is notorious for this problem, so that would mean in theory all of the original solder should be considered suspect and redone.

HOWEVER, you need to take precautions with these Compact Macs as they use CRTs. These are the ~15k volt ones since they are B&W (and have a bleeder resistor), but you need to know how to safely discharge it. The best way is a proper CRT discharge tool like the Apple CRT tool (076-0381) or a rubber handle flathead screwdriver with thick jumper leads on a grounding point to discharge it. DO NOT trust the bleeder resistor in any of these M68k Macs since it’s probably long since burned out. Keep one hand behind your back as well just in case, so the charge doesn’t go to your heart and kill you. It shouldn’t even be trusted in the PPC Macs, but you at least know it probably works.

As far as the capacitors go, this site has a list. The 128/512/Plus use the same analog board, with the only difference being the motherboard and case markings. If the capacitors fix nothing, you will need a flyback transformer which is harder to find then a replacement board that is sold cheap but needs work or is recapped by the seller (which WILL cost more).

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I have discharged the CRT and also I may not be able to afford a new board. I just put it together after looking closely at the analog board. I seem to only have 2 broken traces...

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@Bobby Gunnels These are not good first time collectors macs for this exact reason. They are expensive to repair and always seem to need work.

What you may be able to do is use appropriate gauge wire and rework the board. It may not work, but it's better then wasting the machine.

par

I am going to do a quick test and see if I left the brightness control down and see if I even get anything on the screen. I also am going to try to use alligator clips to jump one of the broken important traces. I will record the result and also try to leave it on a lot longer. May I also say this is a smoke test.

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Bobby Gunnels sera éternellement reconnaissant.
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