I'm still in TROUBLES

From: Douglas Little <dmlittle_at_compuserve.com>
Date: Fri, 24 Oct 1997 14:38:33 -0400

> As Jo Even Skarstein told me i fitted
> the inductor (L102) resistor (100 Ohms)
> betwin pin 14 of U20 and pin 110 of
> SDMA, and it still do NOT work with the
> Afterburner !!!!

In my experience, it should not be necessary to fit any
kind of clock patch in order to make the AB/Nemesis
combination actually boot up. The clock patch is only
there to sort out DMA signal problems.

In fact, the relatively low resistance of the inductor and
the resistor in series can STOP the machine from
booting completely because the DMA clock must be
present before the machine can fire up. A weak DMA
signal will result in a black screen.

Apart from this, it is only necessary to fit the inductor
modification on Nemesis revision #1 cards because
the buffer is different. The more recent boards (the one
you have there) does not need any kind of clock patch
to work on AB/Nem.

There are several causes for black screens on the AB
with or without Nemesis (more frequently with Nemesis).

1) The Nemesis is booting at 20MHz or 24MHz instead
of 16MHz. This will certainly cause a black screen. Try
to ground the thin white & black wires to lock the board
in the 'off' position to make sure the machine is working
properly before doing anything else. You may get a
very pleasant surprise. Some machines boot with the
IKBD/MIDI switching pins in a high state, and this can
annoy Afterburners. There are several things you can
do about this, but it's best to make sure it's really the
cause before you try to fix it.

2) Missing clock. If one of the oscillators is missing or
loose, the machine may not boot up properly. This is
less likely if you don't have problems at 16MHz as the
Falcon couldn't boot at all without both clocks fitted. It
is not well known but Nemesis needs 2 clocks fitted
to work at all. The reason is connected with the point
given above.

3) Weakened DMA signal caused by an inappropriate
clock patch. Remove any clock patches until you get
the thing booting up as far as the Atari logo or Desktop.

4) Fault on clock signal tracks leading to expansion
port. If a track is accidentally cut or if the buffer is not
properly wired to the correct locations, the expansion
port will not get a clock signal and your machine will
not boot. The 68030 would not have this problem as
it does not need the expansion port to boot. The AB
certainly does need it. Check the buffer wiring and the
contact points on the motherboard.

5) Make sure you have at least one SIMM fitted on
your AB in rear slot. Most newer cards require RAM
to boot up.

6) Check the ground connections between the outer
ground rail and the 'e' points on the Nemesis card.
It should only be necessary to connect 3 of these up
but forget them and you could have problems.

I think that should give you something to think about,
particularly point #1 which is probably the cause.

> So I really don't Know what is the pro-bleme, and
> hope that my AB bord is not definaltely broken !!!

I doubt it. They are not as easy to damage as you
might think. I've never seen one die even when they
were fitted wrongly or stopped working. It's almost
always the Falcon or the fitting or excessive clock
speeds that lead to difficulty (unless the card is bad
from the very beginning - and some are).

> Thanks for help, but it seem that i need
> some more !!!!!!

Check the above points and see how you get on.

It's hard to accelerate the AB reliably, but I have
performed several 40MHz upgrades now and all
of them have worked properly without exception.
The only one I had difficulty with was my own and
that was the first one I ever did.

Good luck,

Received on fr. okt. 24 1997 - 22:08:00 CEST

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