Odd Apple IIe power supply issue...

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Odd Apple IIe power supply issue...

Hi everyone. I have an Astec AA11040B power supply on an Apple IIe. When I turn off the power supply, the +12v and +5v lines can take over a minute to drop to zero volts. (However, the -12v and -5v lines drop to 0v almost immediately after the supply is turned off.) The result is that I will turn off the computer, wait a 5-10 seconds to turn it back on and the previous session will still be on the screen. Just with a lot of garbled characters and nothing will really work... I often have to wait 2-3 mins before I can restart properly again. 

 

I opened up the supply and replaced the RIFA cap because it was bulging, but it didn't fix the issue. I wanted to check if anyone has seen this or has any advice on where to focus before I jump in and start de-soldering caps.

 

Thanks!

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What happens when you plug

What happens when you plug off the power cord?

 

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Hi RalfK. Same behavior when

Hi RalfK. Same behavior when using the off switch or pulling the plug from the supply. Slow steady drop to 0v. 

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The positive voltage rails

The positive voltage rails usually have large capacitors. The negative rails are barely used and thus only smaller capacitors are used. I don't think the issue you describe is a power-supply issue. There is no need for the supply rails to drop all the way to 0V, just to make a reset work.

Does a normal system reset (keyboard) work as expected?

If so, then I'd look into the reset logic instead. Even if the 5V rail had only dropped slightly, once it rises back to 5V, a processor reset signal needs to be generated about 200ms (reset pulse). This should trigger a reliable system reset.

To me it seems the reset logic in your machine does not properly detect a slight voltage drop - and that's causing the issue.

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MacFly wrote:If so, then I'd
MacFly wrote:

If so, then I'd look into the reset logic instead.

 The problem has more to do with the RAM retention. This will prevent a cold boot.

Although it's hard to fathom why the 5V supply doesn't drop faster with all that load, the RAM can sometimes hold its charge much longer.

 

BTW, the ROMX boards solve this issue 100%. And the //e and //c versions are coming out very soon!

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Thanks for the feedback

Thanks for the feedback MacFly! I'll start digging in to that. Was not looking forwarding to replacing caps. The supply seems fine otherwise, and voltages are steady. 

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Thanks jeffmazur! Those ROMX

Thanks jeffmazur! Those ROMX boards are really cool. I'll keep my eyes out for the new //e version. :)

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jeffmazur wrote:MacFly wrote
jeffmazur wrote:
MacFly wrote:

If so, then I'd look into the reset logic instead.

 The problem has more to do with the RAM retention. This will prevent a cold boot.

Although it's hard to fathom why the 5V supply doesn't drop faster with all that load, the RAM can sometimes hold its charge much longer.

 

BTW, the ROMX boards solve this issue 100%. And the //e and //c versions are coming out very soon!

 Some 4164 RAM chips do have internal capacitance that prevents short term clearing on power-down.

I have this issue with my IIc+ and one of my IIes.

The RAM operates 100% reliably otherwise - just short power-downs are not enough to cause 100% RAM clearing and this makes cold-starts after a short power down unreliable.  The issue is solved by powering up while holding down the Open-Apple key, or by doing an Open-Apple-Control-Reset combination.  

This seems to force a wipe of the RAM on powerup allowing for a smooth boot.

Interestingly, the more use these machines get the fewer the instances of powerup glitches due to RAM not clearing.  

 

You can replace all the RAM chips with new 4164s (or even 41256s with the extra address pin lifted) and that usually corrects the problem as well.

 

 

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Thank you baldrick, this is

Thank you baldrick, this is great info! I shall send a turnip immediately! ;)

I didn't know about the open-apple power up. That trick works perfectly, and I get a good reboot every time.

Good to know it's not a more serious issue with the board or power supply. Thanks everyone who responded! 

 

 

 

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Hi again baldrick. You were

Hi again baldrick. You were 100% right about the memory chips. The RAM chips on my motherboard are Motorola MCM6665AP20's. I swapped the motherboard chips with the OKI MSM3764-20 RAM chips on my IIe 80COL/64K board. I get clean boots every time now, no need to hold down the open-apple key. The Motorola memory in the 64K board works fine and doesn't cause the reboot issue there. Super happy to have fixed this. Thank you!!

 

I found a bunch of useful info on these RAM chips on the following site: http://www.minuszerodegrees.net/memory/4164.htm

 

 

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