HP 9845 C with 280 option startup failure
ard at p850ug1.demon.co.uk
Thu Oct 27 20:10:28 CDT 2005
> > I haev no idea what the Option 290 is either. In fact I don't even know
> > what I have -- I know it's a 9845B with the high-speed language
> > processor, 2 tape drives, intenral printer, 1 256K word RAM board (and
> > the usual 2 RO</RAM boards), and a 98780 enhanced mono monitor.
> Then you probably got what is called "option 270" with something like a
> total of 318 kbytes plus 512 kbytes memory extension. If you're
No, that's overdoing the memory. I have 32K words (64K bytes) on the
language processor ROM/RAM board. 16K words (32K bytes) on the periperal
processor ROM/RAM board. And another 256K word (512K byte) RAM card.
> interested, I think you can check in one of the 9845 specification
> brochures from www.hpmuseum.org.
Well, it's not that important.
> 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 :-).
> 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)
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!)
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
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
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.
> 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.
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