HP 9845 C with 280 option startup failure

[Tequi Lizer]

>   
>> Internally your machine should be completely identical to mine, except 
>> one or two ROMs which are special for the color monitor, even the RAM 
>> expansion probably is the same (98407A).
>>     
>
> In which case, start pestering Dave Colver for the schematics :-). 
>
>   
There is another difference, the 9845C were shipped with colored 
functions keys ;-)
I already tried to contact Dave, maybe he's currently on vacation...
>> What I'm really interested in: The model 200 versions have a new power 
>> supply unit, no voltage check points any more, but a 4 LED indicator 
>> (and twice the number of electrolytic capacitors inside). Those LEDs
>>     
>
> Yep, I traced out schematics of the PSU too.
>
> Be warned this is _by far_ the most complciated supply you're likely to 
> meet. it's on 5PCBs, there are 17 chips on the control board (counting 
> the chopper transsitor modules for the secondary-side regulators). And 4 
> maine chopper transistors.
>
> A rough breakdown of what is on each board : 
>
> PSU mainboard (09845-66520)
> ---------------------------
> Mains rectifier
> Startup transformer/rectifiers 
> 2 main chopper transformers
>
> +5, +/-12V output (09845-66517)
> -------------------------------
> Output filters (and energy storage inductors for the LV switching 
> regulators) for the logic supply outputs
>
> +/- 22V output (09845-66519)
> ----------------------------
> Output filters, etc, for the tape drive and printer power supplies
> Chopper driver transistors
> Crobar for the printer supply (this is the only crowbar in the unit!)
>
> Chopper (09845-66518)
> ----------------------
> 4 indentcial chopper circuits with transformer-coupled drive (drivers for 
> that are on the -66519 PCB). Wired as 2 totem poles across the 400V 
> rectified mains to drive the 2 main chopper transformers
>
> PSU Control (09845-66534)
> -------------------------
> Startup/cotnrol supply regulators
> Output rectifiers
> Chopper control for the 2 main choppers
> Switching regulator control and choppers (PIC6xxx series devices) for the 
> +12V, +7.5V and -12V supplies
> Overvoltage and overcurrent shutdown
> Init/PowerOK circuit
>
>
> The PIC6xxx chips are basically a darlington pair chopper transistor, the 
> flywheel diode and a few resistors in one can. I think I managed to find 
> data for them on the web somwehre.
>
>  
>   
Thanks, I'm glad my PSU is still working. I've had enough trouble with 
the 9845A PSU, which is only as half as complex, although the functional 
modules are the same.

>> flash in a special pattern sequence during power-up, and then stay all 
>> on (I actually don't know whether this indicates success or failure). 
>>     
>
> The LEDs monitor 4 supply lines in the unit : 
> 1) +Vdrv (+ve supply to the chopper driver from the startup supply)
> 2) +5V sense (main +5V output)
> 3) VPrtSense (Printer supply)
> 4) -8V (-ve supply for the control circuit)
>
> All should be on if the supply is working ccorrectly.
>
>
>   
>> The power supply unit in the monitor has a similar LED indicator, after 
>> finishing power-up, only the rightmost LED is on, which indicates 
>> success (at least that's what the manual says). How is it in your system?
>>     
>
> The mono monitor doesn't have its own mains supply, it runs off assorted 
> voltages from the CPU box supply. Of coruse it does generate the HV for 
> the CRT from the flyback transformer as usual.
>
>
>   
That's interesting, so even the fast mono graphics monitor is powered by 
the mainframe PSU. By the way, do you have an idea how to build a 
home-brew startup fixure? I guess the only signals which are really 
important are the NP and the NL signals. The first resets the address 
registers of the alpha circuit and grabs the fist word from the crt 
buffer in block 1, the other probably initiates another PPU bus 
arbitration for grabbing one complete line of text from the crt buffer 
in block 1. Maybe in absence of a crt the alpha circuit makes some kind 
of continuous bus capture and the whole system hangs. And maybe the 
mainframe can run even without crt when NP and NL are both pulled up to 
logical 1. Two resistors would then be enough.

Another probably important signal is the HALT-signal, from which the PPU 
knows it's the PPU and not the LPU, and which is generated by the alpha 
circuit but probably triggered by the NP signal.


-Ansgar