Apple II clone power supply repair

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Joined: Sep 11 2009
Posts: 26

I have replaced some of the capacitors on a power supply that I have that has come out of an Apple II clone (MICRO II) but I want to test it before I reconnect it to the board. The problem is that the +12v was actually putting out (if I remember correctly) over 15 volts. All of the other power leads are in range. I understand that the power supply will not stay powered up unless it is connected to the board or is fooled. What I need is for someone to explain to me what resistors do I need and how to wire those resistors up to fool the power supply so that I can take readings. Thanks

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Offline
Joined: Sep 11 2009
Posts: 26
Re: Apple II clone power supply repair

Does anyone know if it will be a problem replacing a 3300uF 10V capacitor with a 3900uF 10V?

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Joined: Sep 11 2009
Posts: 26
Re: Apple II clone power supply repair

I went ahead and replaced the capacitor. The power supply produces 12 volts on the + 12v lead but jumps up to over 16 volts once connected to the board. What will cause this to happen?

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Joined: Sep 11 2009
Posts: 26
Re: Apple II clone power supply repair

OK, so now I have replaced every capacitor and still, the power supply voltage on the +12 lead wants to jump up to 16.7 volts while all the other leads remain in range once the supply is reconnected to the board.

Simon27's picture
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Joined: Jul 7 2005
Posts: 73
Re: Apple II clone power supply repair

Could there be something on the board causing a short on the 12V?

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Joined: Mar 1 2012
Posts: 9
Re: Apple II clone power supply repair

A short on the board will not lead to a higher voltage of the powersupply. I would say the problem has to be on the powersupply itself. Hopefully it is not a shortage in one of the transformers in the powersupply, that may definately push up the voltage!

Use lightbulps of the proper Watt to test the powersupply at the regular current level. Do not test this on the motherboard, or you may blow up your RAM and other components.

I replaced the powersupply of my clone by a regular ATX powersupply: that works, but it does not fit in the regular case though. However, dumped the regular case 30 years ago and replaced it with a metal case with a fan, which solved many problems. Now I use a PC case and a AT keyboard converter.

Good luck with your repair!

Peter

speedyG's picture
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Joined: Nov 16 2011
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Re: Apple II clone power supply repair

the problem itself is the capacitor, because without load it collects up the power to the limit of the capacitor i.e. 3300µF/16 Volt loads up to 16 Volt. So to get proper measurement at the 12 Volt line there must be some load ( for example a 15 volt 1 Ampere motor from a toy ) that uses the power and requests the regulator to operate correct. With the load you should then measure again and find out the correct value. If later connected to the mainboard the value should not drift then to much from that measured value, because at the mainboard there are devices that give load to the supply.

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Joined: Sep 11 2009
Posts: 26
Re: Apple II clone power supply repair

Update..... I replaced the PSU board with an updated one from one of the electronics sites. It only uses half of the space of the original in the case and seems to stay cool.