Apple II Plus - Lockup/Freeze

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Joined: Oct 9 2019 - 10:05
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Apple II Plus - Lockup/Freeze

Hi,

I have an Apple II Plus that is giving me some problems. When I boot to a prompt and run some basic instructions, everything seems fine until a few minutes pass (idle or in use) the computer freezes. I still might have a flashing cursor, but keystrokes are ignored. If I switch off the power and turn it right back on, I'm ususally greeted with a screen of white horizontal lines. If I leave the Apple off for a few minutes, it will usually work (no white bars.) I've also tested this with the floppy drive and booted up various games and apps. I get the same results. Everything works great until it just freezes up suddenly. I did find a few threads on this forum that featured some code to check the RAM but unfortunately every attempt to input this has ended with a lockup. I feel like this wouldn't be a RAM issue since turning it off and back on should clear the RAM and it should work and fail in the same way. Instead I get the video issue. Since giving the Apple some time to sit results in it booting up and working (for a few minutes) I feel like it must be something overheating. I don't think it's a video (chip?) issue because it's not like the video scrambles suddenly while in use. I've cleaned the board, I haven't buttoned up the case in quite a while, and I've removed all the expansion cards. Sorry if this is all stuff that's been gone over and over. Any help would be appreciated. I'd love this machine and I don't want to let it go!

 

 

 

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Last seen: 8 hours 14 min ago
Joined: Jul 5 2018 - 09:44
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First thing to do is meter

First thing to do is meter the power supply.  That's the most common point of failure in these.  Next make sure all the chips are firmly seated.  Sometimes contact can be intermittent and that can be affected by heat.  Next if you suspect heat issues feel the chips and see if one is getting very hot.  If so it may indicate a problem.

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Last seen: 3 weeks 4 days ago
Joined: Oct 9 2019 - 10:05
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Thanks! I'll give these a

I tested the power supply. The 12v rail fluctuates between 14v and 10v. Powering it on, especially with the shell off of the PSU, it makes a clicking sound. My first impulse is to replace the capacitors but the clicking sound is not that. Anyone know what that might be and is it related to having bad caps? I don't see any leaks but a few of them feel lose. Thanks!

 

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Last seen: 8 hours 14 min ago
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Are you testing the power

Are you testing the power supply unplugged from the motherboard or testing the voltages with it hooked up?  Sometimes the voltages will not be that stable on an unloaded power supply.  4V seems like a pretty big swing, but the going over 12V seems worse than dropping to 10.  I've seen the 12V on Apple II supplies drop below 12V, especially during disk activity as the Disk ][ draws quite a bit of current.  As for caps, I probably wouldn't just go in there and start replacing them, except for the RIFA caps which are prone to failure in a very messy and stinky way.  The electrolytics I would generally only change if they show any signs of leakage or bulging.

 

Anyway, the power supply isn't the only thing that can cause instability, it's just the first thing to check.  I'd recommend downloading the PDF of one of the books on repairing Apples.  You can find them on sites like bombjack, Asimov and archive.com  If you can't find them I can probably dig up URLs, but they should be easy enough to find.

 

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