HP 9845 C with 280 option startup failure

[Tequi Lizer]

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.

--Ansgar
> Yes. 
>
> 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.
>
> -tony
>
>
>