In article <3F2B19E2.4772E3C@ntlworld.com>, Dr. David Kirkby <drkirkby@ntlworld.com> wrote:
>
> Here's a picture of the front of the RS/6000 7025 F50
> http://www.medphys.ucl.ac.uk/~davek/rs6k.jpg
> you should be able to see the display in the top right, and may just
> see the 6 LEDs to the left of the display.
>
> Here's a close up of that display
> http://www.medphys.ucl.ac.uk/~davek/rs6k-leds.jpg
> where you should see 3 rows of LEDs on a PCB - three yellow and three
> green. The picture is taken with a flash, so you can't see what LEDs
> are on, buy the top and bottom green ones are on, with the machine up
> and running.

That's interesting! I'd never noticed these. I looked through the F50
service guide PDF file, and it's singularly unrevealing except to say that
it is part of the 'operator display' (LCD) assembly. That's it.

I'm going out on a limb, but since I don't see any documentation on it, and
the fact that it's ordinarily hidden... makes me think it isn't designed
for end users.

Most likely it's designed for service personnel or engineers that had to
debug the F50. Some PC motherboards has LEDs on the board to make it easier
to differentiate between a power failure and video adapter failure, or
blinks them in certain patterns to give out different error codes which
becomes more useful in case of video failure. Conceivably, can see the same
kind of use with a broken LCD display or video failure of some kind.

Maybe the LEDs are used during the F50's BIST (built-in self tests; IBM
term for what PC makers call the POST -- power-on self tests) or maybe the
other LEDs comes on after the BIST detects a serious hardware failure?

With six LEDs, you have the capability to represent up to 64 different
error codes (2^6, whereas an on LED represents 1, off LED represents 0,
hence two bit values per position).

Just theorizing due to lack of further information.

-Dan

Dan Foster wrote:
> > see the 6 LEDs to the left of the display.
> > Here's a close up of that display
> > http://www.medphys.ucl.ac.uk/~davek/rs6k-leds.jpg

> That's interesting! I'd never noticed these. I looked through the F50
> service guide PDF file, and it's singularly unrevealing except to say that
> it is part of the 'operator display' (LCD) assembly. That's it.
>
> I'm going out on a limb, but since I don't see any documentation on it, and
> the fact that it's ordinarily hidden... makes me think it isn't designed
> for end users.
>
> Most likely it's designed for service personnel or engineers that had to
> debug the F50.

> Maybe the LEDs are used during the F50's BIST (built-in self tests; IBM
> term for what PC makers call the POST -- power-on self tests) or maybe the
> other LEDs comes on after the BIST detects a serious hardware failure?
>
> With six LEDs, you have the capability to represent up to 64 different
> error codes (2^6, whereas an on LED represents 1, off LED represents 0,
> hence two bit values per position).

In fact, they can do better than that, as at least one flashes at
about 1 Hz under some circumstances, so that could I guess increase
the number of error codes to 2^12, or 4096.

I can understand they are designed for service personnel, but it would
be nice to know myself, as I'm going to be the only one servicing it -
I don't have a contract with IBM for my home computer.

If anyone does know, please let me know.
--
Dr. David Kirkby,
Senior Research Fellow,
Department of Medical Physics,
University College London,
11-20 Capper St, London, WC1E 6JA.
Tel: 020 7679 6408 Fax: 020 7679 6269
Internal telephone: ext 46408
e-mail davek@medphys.ucl.ac.uk