emulatorII-list

Hi,
A large email is posted for list member information and comment - happy to
take further dialogue offline at rob@....

We do have the EII debug EPROM, but not the VDU terminal thats needed to
work it  - its on the list to procure !! I am not surprised the service
centres turned you down in the UK, its a long haul to getting this EII
sorted as all sorts of chips could have been damaged. I hope the follwoing
helps - but we aren't as good as a service centre..

Provided the EII was working well before the CDROM was plugging in over
RS232, the most likely cause of the problem is incorrect wiring of the
connection between the EII and CDROM or possibly the CDROM drive pushed an
unusual voltage down the wire to the EII. Seems like something big happened
for the PSU to fail, and the EII to die big time.

Swapping out parts is a last resort, as there are so many... Some
diagnostics should be attempted first to narrow down the problem.

The RS422 connector goes to some interface electronics before reaching the
Z80 processor. IC132 and IC107 are in the direct line of fire of any wrong
voltages on the RS422 connection. If these fail it should not prevent a
firmware boot from the onboard Boot ROM. A dead Z80, or dead Boot EPROM will
cause no LCD display.

Does the LCD backlight come on at power on, even though no characters are
dispalyed ? If there is no backlight either the LCD has faded away (very
common problem) or the inverter is bust. Check the inverter is pushing out
100VAC to the LCD (see schematics for pin out). Maybe it got caught in a
power spike. If thats okay, an LCD swap is a reasonable next step - if just
to be absolutely sure there is a working LCD with a backlight !

The LCD will tell us how far we have got in the boot process - if at all.
Given there is some attempt to read the disks the display should say "Boot
in Progess" - if its doesnt then the Z80 or Boot ROM is dead. The Scanner
Boot ROM seems okay as it puts all the lights on. The lights do NOT stay on
when booting an OK EII.

The EII uses a Z80A at 4MHz, so a Zilog Z80A or Z80B (6MHz) will do. They
cost UK pounds 2 from Farnell (www.farnell.com)

LCD's cost just UK pounds 12.37 from  www.review-displays.co.uk (cool huh -
not the E-mu US Dollars 120!!)
Email Gill Graham [GillGraham@...] for details.

Ideally you also need a 14pin LCD cable to replace the old one, as it gets
messed about when you desolder. These are available from Farnell part number
139567. Farnell deliver free in the UK.

You can disconnect the bottom drive, but it makes no difference. The EII
will look for a diskette in lower if it can't find one in upper.

Reseat all chips and check all power connectors and interface connections.
Especially the power connector to the main PSU, its famous for working
loose - some guys remove the molexs and solder the wires on directly.

Hope this helps a bit !
Rob