Apple II Power Supply Repair Help

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Apple II Power Supply Repair Help

I just picked up a II+ locally that is in pretty good physical shape. It appears from the property stickers that it belonged to NC State University at some point, and the label says A2S1, despite have a IIplus case cover.

Anyway the board is a clean Rev4 with many upgrades- looks like lower case, a Videx card, Applicard, and a Saturn 64/128k RAM card.

No power, though. It did turn on *once* then died. I opened up the PSU and the fuse is blown. I know it happens for a reason, so what is the easiest way to test the bridge rectifier, and if bad, what is the replacement part?

I found another thread where someone said the DB1 is the #1 reason for blown fuse.

-Pete

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Re: Apple II Power Supply Repair Help

Also, forgot to mention. It's an Astec Model AA11040...

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Re: Apple II Power Supply Repair Help

First of all... here you will find most schematics of the Apple (Astec) Powersupplies.

ftp://bitsavers.informatik.uni-stuttgart.de/pdf/apple/power_supply/Astec_Power_Supplies_Aug82.pdf

Secondly, I suggest to exchange ALL Elektrolyt Condensators and for sure the Protection Capacitor C1 (Polyester Capacitor type X3 0.1uF 400V) as this could blowup after more then 30years while the Elektrolyt Condensators are typically dehydrated after such a long time. After that I believe your power supply will work again.

Such dehydrated capacitors will lead into a higher current or shortage and I believe that's the reason while the fuse is blown. Maybe the Bridge Rectifier is defect while I don't believe so.

Hope this fix your issue... and I hope you are familiar in electronics and how to handle a solder iron...

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Re: Apple II Power Supply Repair Help

Yes, thanks - I am familiar with soldering and know the very basics of electronics. I have tested the bridge rectifier with diode test, and it seems to be OK. The caps look OK, no leaking or swelling. Should I check them all for short?

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Re: Apple II Power Supply Repair Help

You can do this

using an LCR Meter but anyway I do prefer to exchange such old capacitors as they are probably dehydrated. In most cases this will lead into follow on problems then, maybe not yet but sometimes later. When I get an old machine I always start to exchange caps after a short Power on test to prevent damages on other electronic components because of old caps.

I've just done this on an old C64 and Amiga 500 and I also exchanged the caps inside the external power supplies. Some days ago (here far to late) I exchanged all caps at an old Computermonitor after the Protection Cap blows. I thought it works well so why should I do exchanging caps? This was a wrong assumption.. but that's my experience.

I can't promise that this will solve your problem... but it's a good starting point.

Have a nice weekend

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Re: Apple II Power Supply Repair Help

With an unknown machine and a blown fuse, I usually just change the fuse to see if someone did something stupid. Since you don't know if the machine suddenly stopped working or it stopped working when they plugged in a bad card. I know there is a crowbar circuit in the supply but I think there are still ways to blow the fuse. I don't put the rivets back in until I confirm the fuse doesn't blow again.

If the fuse blows again, then I start looking for something wrong with the supply or machine.

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Re: Apple II Power Supply Repair Help

I swapped the power supply with another machine and after finding bad RAM and some chips not plugged all the way in, it is back working.

Are those fuses available at a local store like Lowes/Home Depot? Radio Shack is gone from here... they are all Sprint cell phone stores.

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Re: Apple II Power Supply Repair Help

If memory serves correctly, I haven't changed one in a while, they are the fuses with actual wires attached to them. I don't think that's a home depot thing. You can change it to fuse clips, then use a home depot fuse.

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Re: Apple II Power Supply Repair Help

The fuse in my PSU is in a holder. I replaced it, and it blew immediately. I went through and tested the bridge rectifier again, and it is indeed shorted- I have continuity between the AC leads which should not be there. I will order one and see how it goes. Smile

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Re: Apple II Power Supply Repair Help

I have the guts from my Apple //e Platinum power supply that the line filter cap went bad(not needed). No wires on it but if you want it its yours for the cost of shipping

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Re: Apple II Power Supply Repair Help

Thats very kind of you. Thanks.

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Re: Apple II Power Supply Repair Help

The new bridge rectifier fixed it right up. Thanks everyone.

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