19 Mar
2005
19 Mar
'05
7:24 p.m.
Yipppeeee! The 9915B now works. My remaining worry is that I do not
Excellent...
know why! After removing things to allow me to check
them in isolation
and then putting them back, I started providing power to the different
parts of the PSU. First the +12V supply worked, then the -5V and -12V
supplies worked, then the +6V, and finally the +5V. Every time I expected
the fuse to blow, but it didn't. So now the whole thing works fine.
I _hate_ faults like that. There almost certainly is something wrong, and
it'll come back at the wrong moment. However, it's difficult, if not
impossible, to find a fault that's not there at the time, so all you can
do is wait...
The 9915A still does not work, but I have found that C45 (the thin tall
390uF capacitor connected to pin 4 of transformer T2 via diode CR12) is
shorted. That removes power to the V+ supply taking out the +6V and
the +5V supplies.
RIght. And doubtless really loads T2, either triggering the current limit
circuit, or at the very least pulling other supplies down.
Now all I need is a replacement for C45 and I am in business.
HP really loved to use silly value capacitors in their PSUs for no good
reasons as dar as I can see. The tolerance on an electrolytic is
typically something like +/-20%, or even +50%/-20%. Which makes me wonder
why I have a PSU board with an assortment of 5600uF and 6000uF caps on
it. As another example, the 9845 PSU contains som 810uF caps -- 820uF is
a prefered value. Hmmm...
I, therefore, wouldn't worry too much about getting an exact replacement
for C45. I would think a 470uF would be fine.
Many many thanks Tony.
BTW the first time I looked at the 9915 motherboard I freaked out,
because the PSU is all over the place. In some cases analog components
At least HP did provide some links to disconnect the 3 main PSU outputs
from the rest of the machine..
Incidetnally, the 9915 PSU is by no means the most complex HP computer
supply I've seen. That honour goes to the 9845.....
are located right next to the digital logic. But with
Tony's help and
his schematics, I managed to map my way around the board. Now when I
If anyone else needs them, they're now on a CD-ROM with many other
reverse-enginnered HP calculator scheamtics. You get it from Dave Colver
(secretary+hpcc.org), IIRC it costs \pounds 15.00, and I think he can
take Paypal (unlike me, he deosn't mind new ideas :-)).
Here's a list of what you get :
chargers/eramco_pp Portable Plus car charger (Eramco)
chargers/hp82028
chargers/hp82054 Car charger
chargers/hp82055 Woodstock car charger
desktops/hp110 `Portable'
desktops/hp86b desktop computer, external video monitor
desktops/hp87 HP87 and HP87XM desktop computers
desktops/hp9100b First generation RPN desktop
desktops/hp9810 Second generation RPN desktop
desktops/hp9815 RPN desktop calculator
desktops/hp9825 First HPL desktop (also covers 9831 BASIC desktop)
desktops/hp9830 First BASIC desktop
desktops/hp9915 Industrial control computer (based on HP85)
desktops/integral Portable unix machine
handhelds/classic/hp35 First handheld scientific
handhelds/classic/hp45 Second handheld scientific
handhelds/classic/hp55 Scientific with timer
handhelds/classic/hp65 First handheld programmable
handhelds/classic/hp67 Handheld programmable
handhelds/classic/hp70 Simple financial handheld
handhelds/classic/hp80 Financial handheld
handhelds/hp48sxKeyboard HP48SX keyboard matrix
handhelds/printing_classic/hp46 Printing 45
handhelds/printing_classic/hp81 Printing 80 (with many more functions)
handhelds/spice/hp32e Non-continuous memory Spice (other 3xE are similar)
handhelds/spice/hp33c Continuous memory Spice (other 3xC are similar)
handhelds/sting/hp10a Printing adding machine
handhelds/sting/hp19c Programming printing calculator
handhelds/topcat/hp91 Printing scientific calculator
handhelds/topcat/hp92 Printing financial calculator
handhelds/topcat/hp95c Never-released printing programmable calculator
handhelds/topcat/hp97sio I/O module part of HP97S
handhelds/voyager/hp16c Programmer's calculator
handhelds/woodstock/hp21 Scientific calculator
handhelds/woodstock/hp22 Financial calculator
handhelds/woodstock/hp25 Programmable calculator
handhelds/woodstock/hp25c Continuous memory programmable calculator
handhelds/woodstock/hp27 Financial and scientific calculator
handhelds/woodstock/hp29c Continuous memory programmable calculator
peripherals/hhp_eprom EPROM box for HP41
peripherals/hp2671g HPIB Thermal printer
peripherals/hp7440hpib HPIB ColourPro plotter
peripherals/hp7470opt003 HPIL Plotter
peripherals/hp7475 HPIB Plotter
peripherals/hp82104 Card reader for HP41
peripherals/hp82143 Dedicated thermal printer for HP41
peripherals/hp82162 HPIL thermal printer
peripherals/hp82168 HPIL modem
peripherals/hp82440a IR thermal printer
peripherals/hp82440b IR thermal printer
peripherals/hp82985 Portable Plus video interface
peripherals/hp9114a HPIL disk drivc
peripherals/hp9114b HPIL disk drive
peripherals/hp98034 HPIB interface for HP9825
peripherals/hp98035 Real time clock module for HP9825
peripherals/hp98036 RS232 interface for HP9825
peripherals/hp9866 Thermal printer for 9800-series
peripherals/hp9877 External tape drive for HP9825
peripherals/hp9878 Expansion chassis for HP9825
peripherals/rsu Eramco MLDL unit for HP41
peripherals/rsu2 Eramco MLDL for HP41 (card reader case)
peripherals/wand75d Wand for the HP75D
-tony