| This PC that I aquired had a problem sometimes with the VDU-start-up,
| BIOS-start-up ...
| Sometimes the display wouldn't "start"; one of the many Mercer models.
| Sometimes this could be 'fixed' by powering the display ON/OFF, after
| the PC had started booting. Which can be problematic when you want
| to select at boot-time.
| The display has got some strange action, in that it takes a second for
| its power light to show on or off. As if it's got a PSU which takes
| time to stabilise/re-discharge.
| Also when it's started from cold, it clicks [sound] and flashes its
| power light, for some time, before it starts properly. It seems to
| need to warm up.
| The similar smart-ass PSU-control, where the 'on/off' button is
| not hardwired, but is just a 'request/suggestion' signal, is
| problematic.
| So with the CPU-Bios & the VDU & the ON/OFF-PSU forming a trio
| of inter-related 'agents', there's lots of scope for
| problems/confusion.
| Ie. compare to the old-days when the CPU-Bios, VDU, PSU+switch
| all were more independant.
| I've been away for a week [the 3V cell still measures 3V] and when I
| tried to boot, it started its VDU clicking/pumping. When the VDU
| didn't display after 5 minutes of continual 'pumping' I tried activating
| the on/off
| PC switch and observed the delayed action of the PSU fan.
| My previous understanding was that the VDU needed to warm up,
| before receiving display signals.
| Later on & offing of the VDU and PC, showed the PSU fan to be dead.
| Then when I plugged the PSU [the double-row (I think 20 pin) type]
| to another MOBO which works with the
| non-double-row power-connector, that MOBO failed to show 'power'.
| Since the PSU gets a signal [other than the on/off switch] I
| apparently can't just assume the the PSU is defective.
| Q - how do I test the PSU ?

Arno wrote:-

> Don't do this yourself, unless you have extensive experience
> testing and repairing electronics. It may be risky, since you
> can find up to a potential 450V inside that PSU.

Thanks, I expect to be able to measure at the outputs of the
sealed box. Can someone provide insight or a pointer to the
possibly complex interaction of the: 1. PSU, 2. MOBO. 3. VDU ?

In the original PC design the PSU was hardwired for on/off,
and the VDU's inputs controlled only the display.

Now I see that VDU's LED of my 2nd box has a 3rd state:
which showed 'something wrong' when I floppy-disk-booted
between Linux and oberon.

With the new capabilities, there are potential complexities;
like the 'race effect' where the time-out occurs before the
boot-selection is shown on the not-yet-warned-up-VDU.

Obviously, there's a possibility of subtle faults where, instead
of just hardwiring the on/off from the PSU to the MOBO, you
- toggle a signal to the MOBO, which
- at some later time, depending on conditions determined by
the MOBO,
- sends a signal back to the PSU; which happens to power the
MOBO, which is controlling it [the PSU] !

Thanks for any input,

== Chris Glur.