HP 9845 C with 280 option startup failure
tequilizer at gmx.net
Sat Nov 12 17:14:54 CST 2005
I tried to pull those monitor signals high, however the effect is the
same. Guess I have to look closer at the memory defects. One way to go
is to use a dedicated test rom or one of the exerciser cartridges. The
test rom was used by the service personnel only, and therefore will be
hard to find. However I recently acquired a system 45B/C exercise
cartridge. The tape contains a couple of memory checks among other tests
and supports autostart.
Since I assume you've got a running system, can you tell me whether the
system tries to launch the autost program from a 9845 tape before,
during or after the power-on memory test (in case the "auto st" key is
latched, a tape is inserted and the system is being switched on)? If the
program is read from tape _after_ the power-on test has been completed,
I'll have to find another way.
> In the 98780, there is one video timing chain, physically located on the
> text (alpha) PCB. It's the traditional chain of counters, decoded by AND
> gates, used to control JK's to provide various timingt signals (you need
> the schematics, OK :-))
> Many of the signals are passed across the monitor backplane to the
> procesor (graphics) PCB, but there is no complete timing chain on that
> PCB. The only board that provides syncs to the analogue section is the
> text PCB, and from what I rmember, tbere are no control inputs to that
> timing chain depending on whether it's in text or graphics mode.
> I was under the impression that the 98770 (colour) and 98780 (enhanced
> mono) were pretty similar to the user apart from the obvious difference.
More information about the cctech