Re: Klunky IIGS - no docs - where do I start?

[dempson@atlantis.actrix.gen.nz (David Empson)]

In article <4cj960$5mm@yama.mcc.ac.uk>,
Duncan Entwisle <duncane@jumper.mcc.ac.uk> wrote:
> 
> Ok, brought up the control panel - selected display - it states it is 
> running the monitor output at 60Hz not 50Hz, even though it was produced 
> in the Republic of Ireland. Thre appears to be a cluster of three 
> capacitors near the right hand side of the composite socket, and a gap 
> for three to its left - presumably this has something to do with setting 
> the rate?

No - you set the video scan frequency by using the
Control-Option-Reset menu.  Items 2 and 3 on this menu are used to set
the scan rate to 50 Hz or 60 Hz.  They also cause all other Control
Panel settings to be restored to their defaults.

> I thought the IIGS ran an RGB monitor at 15.blah wotsits like the Amiga, 
> BBC, and CGA rather than the 32.blah wotsits of VGA - in which case its a 
> matter of pins surely (anyone got a pin out of that port?)

15.75 kHz (or thereabout) compared to 30 kHz or higher for VGA.

Pins?  Definitely not.  It is a matter of the frequency of the scan
lines being output to the monitor.  The IIgs is outputting about 15750
lines per second, whereas current monitors expect at least 30000
lines, and cannot lock onto a slower signal.

> I presume, given the range of colours, that it needs to be analogue RGB.

Yes.

> Finally, I get a bank faliure error in the memory - 02 E0 02 00. I think 
> this manifests itself as a " on the character display - if its only
> two bits in the display memory, is it likely to have any real effect
> (I can put up with a minor abberation in the display)

This error (from the IIgs self-test) means that bit 1 has failed in at
least one location somewhere in bank E0, which is the first bank of
"slow" RAM.  It contains the video displays, and is also used by the
firmware for buffers, memory allocation tracking, parts of the
operating system, data storage, etc.  The leftover parts can be used by
programs (via the Memory Manager) if most other memory has been used up.

It is likely that this test includes writing to video memory, but you
should certainly not assume that the only fault is in the video area.

In particular, the " character has more than one bit set (it is 22
hex), and the test didn't indicate that bit 5 also failed.  I suspect
that the " character is there are part of the self-test, which stopped
suddenly when it found a fault.

If you are getting a RAM fault in bank E0, you will have to replace at
least one of the four "slow" RAM chips.  According to the circuit
diagram, bit 1 of bank E0 would be contained within the chip labelled
UM4, which is the rightmost of the four "standard RAM" chips (at the
front of the motherboard, just under the edge of the power supply).
You will have to remove the front plastic "ledge", which is done via
three clips on the bottom the case.

If you want to replace this chip yourself, I strongly suggest you do
it by cutting off the pins of the old chip (next to the plastic part
of the chip), then soldering a new chip (or socket) onto the pins.  Do
not attempt to desolder the pins from the motherboard, as it is a
four-layer board, and you could damage it quite easily.

Better still, get a professional repair job, or replace the
motherboard.  Alltech Electronics in the USA does board swaps for the
IIgs.

> will it of checked the rest of memory or halted immediately

The self-test probably starts with bank E0, then progresses to bank E1
(the second slow bank), before going on to banks 0 and 1 (the fast
banks), so you might have more than one fault.

> Is there any way to get the Apple to perform the other later tests,
> so that I can check the rest of the hardware out?

No.  If the RAM is faulty, it is possible that the other tests will
produce meaningless results anyway.

-- 
David Empson
dempson@actrix.gen.nz
Snail mail: P.O. Box 27-103, Wellington, New Zealand