PC/AT "power good" problems

dwight dkelvey at hotmail.com
Sun May 29 09:30:18 CDT 2016

Power to a load tester is not the same as power in a system.
It is likely that one of the other voltages, other than 5V is
being loaded down with a shorted tantalum capacitor in
the system.
I doubt there is a problem with the supply.

From: cctalk <cctalk-bounces at classiccmp.org> on behalf of Richard Cini <rich.cini at verizon.net>
Sent: Sunday, May 29, 2016 4:16:15 AM
To: CCTalk
Subject: Re: PC/AT "power good" problems

Chuck –

        My wording was probably less than precise, but “never comes out of reset” means that it never POSTs. Nothing on the screen. No cursor. No boot message. No BASIC. Keyboard does reset though (I see the three LEDs blink on, then off). I watched for a good 5 minutes before giving up. It’s been a long time since I worked with this machine but I’m pretty sure there is a sign-on banner or something.

        For comparison, I pulled my old original PC (64k/256k mobo) with expansion unit and 10mb HD and it took an excruciatingly long time to boot, but it did have a blinking underline cursor on the screen while it thought about booting.


Rich Cini

On 5/28/16, 10:30 PM, "cctalk on behalf of Chuck Guzis" <cctalk-bounces at classiccmp.org on behalf of cclist at sydex.com> wrote:

>On 05/28/2016 07:17 PM, Chuck Guzis wrote:
>> Bear in mind that the PC AT BIOS during POST goes through some
>> rather arcane protected-mode memory tests, using the CMOS "why did I
>> get here" byte when coming out of reset.
>...which reminds me--check the status of the "programmed reset" line
>coming from the keyboard controller.

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