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Apple IIe dead PSU


shoestring
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Hi All.

 

I've just received a dead Apple IIe computer recently and I'm looking for some help from someone who has some experience with these power supplies.

 

I have the Astec AA11042C 240v version which is completely dead. Fuse tested fine.

 

So far I've replaced all the electrolytic caps including the two filter caps which can fail spectacularly and spill brown goo everywhere. The electrolytics

on the high voltage and output side were either out of spec or bulging. I also replaced the bridge rectifier which looked cooked but otherwise tested OK with the diode test on my DMM.

 

To be honest I don't know much about switching power supplies but as I understand it the astec needs to be under some load before you can can measure any voltages from the connector which connects to the Apple IIe logic board. I'm measuring around 240v across the AC inputs of the bridge rectifier but I am not sure what to look at next, any ideas ?

 

Unfortunately I can't use the IIe as a load, there is a short between 5v and gnd somewhere on the logic board and I'm pretty sure the the DRAMs are fried. The 12v lines look fine. I'll have to remove those DRAMs and test them later once I track down the short, luckily I have 4 brand new 4464s on hand.

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I think I may have found the culprit.

 

The transformer T3 has a broken winding one one of the coils. It barely looks repairable

even though the break is visible at one of the pins.

 

Anybody know where I can find a suitable replacement ?

 

Edit.

 

Repaired the broken winding on T3

 

Apple iie now powers up, beeps twice and green power light is on.

Edited by shoestring
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Addressed a couple of issues with the keyboard.

 

Some keys seem to print multiple times before the key bottoms out, so that made typing difficult and frustrating.Some keys were stubborn and wouldn't respond without some effort.

 

Here's my fix in case it hasn't been covered in much detail.

 

Take the machine apart and remove the keyboard, de-solder all pads to remove the PCB from the back of all keyswitches. It's a lot of work and you need some skill to do this properly but it's well worth it. Clean the opposite side of the PCB free of dust accumulated over the years, there was a lot of dust under the keyswitches in my case. Dust can attract moisture which may cause oxidation and also may conduct, it's your computer's worst enemy.

 

Solder the keyswitches back to the PCB and put the keyboard back together. Get some isopropyl alcohol and pull the keycaps off the troublesome keys, pour drops of alcohol down each side of the keyswitch and work the key up and down, side to side. This cleans the contacts inside of the switch free of dirt and other gunk. Work the key until the problem disappears, some keys take more work than others.

 

You should now have a fully functional keyboard.

 

What an interesting project this has been so far.

 

I hope this helps someone out.

 

 

 

 

 

 

 

 

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Good luck with the keyboard. I found I had to replace keys that had problems and ones with broken pegs were impossible to fix.

Power supply. I need to replace the caps on my IIGS board and probably should do my original IIe and IIe clone as well.

I listen to the open apple podcast regularly and they recommend this site for power supplies: https://www.ultimateapple2.com/catalogzen155a/index.php?main_page=down_for_maintenance

however, the site is down for maintenance right now, but this could be what you need. otherwise, you could look on ebay.

 

http://a2central.com/7000/ultimate-micro-finalizes-release-of-new-universal-power-suppy/

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I investigated that link earlier for alternatives but had already committed to repairing the original power supply and wanted to keep the system as original as possible. I had already spent about $30 on capacitors and other parts, replacing those was necessary but the actual problem was with the smaller transformer ( PWN control isolator ) which failed due to a short somewhere, perhaps one of capacitors.

 

It's definitely worth considering changing those caps before your power supply suffers the same fate, if you're still using it. My original fuse in the primary was still good because the failure was obviously in the secondary,low voltage output section, so don't rely on the fuse.

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As for the low resistance ( 4.5 ohms ) between +5v and ground mentioned in my initial post, it turned out to be a non issue at all.

 

The 4.5 ohms was coming from the small keyboard lamp. It's connected directly to 5v and you will measure some resistance there because of it.

 

Just simply remove the keyboard ribbon connector and expansion cards from the PCB first before you trouble shoot the 5v line.

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