[sebhc] H89 Power-up problems.

Barry Watzman Watzman at neo.rr.com
Sun Jul 9 07:00:46 CDT 2006

The problem is not the line voltage; 117 is a [VERY] nominal.  The computer
should work all the way from about 100 volts to about 130 volts, but all of
your other voltages seem off by WAY too much.  Definitely could be a power
supply problem.  Check everything, even the wiring of the transformer.

-----Original Message-----
From: sebhc-bounces at sebhc.org [mailto:sebhc-bounces at sebhc.org] On Behalf Of
Mark Garlanger
Sent: Sunday, July 09, 2006 2:14 AM
To: sebhc at sebhc.org
Subject: Re: [sebhc] H89 Power-up problems.

On 7/9/06, Lee Hart <leeahart at earthlink.net> wrote:

> These symptoms both point to problems on the TLB. I'd check the supply
> voltages. The TLB needs +8v, +16v, and -16v to work. It has onboard
> regulators to convert these to +5v, -5v, +12v, and -12v.

The values on my DMM are +7.3V +17.6V and -18.1V...
Most likely the +7.3V is the source of my problems. Based on the
schematics, it appears that the keyboard encoder uses Vcc2 (one of the
5V supplies).

I measured the one you sent me and see just over 9V on that same line.

But then I checked the wall voltage: 117V!!! what it should be 120V?
Well there is alot of computer equipment in this room... Tested my idea by
I turning on the laser printer... down to 115V with dips down to 112V.
Turned off all no essential lights/monitors/systems... and it's up to 118V.

I guess this H89 is more sensitive to low voltage, but low voltage seems to
be the problem. I'll need to either move some of this equipment out of
this room or figure out a way to get a dedicated circuit or two directly
the service panel.

With the laser printer on I was able to see problem with the terminal
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