HP-29c malfunction symptoms
Message #1 Posted by Xavier A. (Brazil) on 12 Feb 2009, 4:09 p.m.
Hello everybody,
Last time I posted in this previous thread, everything were OK with my HP-29c: After changing the conventionnal battery pack for a new NiMH one, I could make some calculations, even type a little routine in PRGM mode and make it run: I was satisfied, thanks to this Forum (I didn't thank Dick, but I think to do it another way one day, true), and those who took some time to answer me very friendly.
Well, I let two days ago the NiMH pack during a whole night in the Hp and, I was surprised the day after to find one more time the display:
000000000000
Bad news! could say Katie, as she said here (I'm really very impressed with her knowledge). Well, perhaps not so, since I could modify this display by pressing some keys or moving the switch ON/OFF a lot of times.
Here are some examples NOT IN SPECIFIC ORDER (unless for the beginning) of what I succeed to display:
1234567890AB (just a duodecimal grid)
0 last digit (0) very very bright
0 0 both digits (0) very bright
Er.........-
81.8-0000000
- -
-0- - then blank
-0-000000000 then blank
- -.
. .........
999999999999
..6111111100 with dots after each digit, unless the last one
000000000006
Error0000000 with a display full of zeros (unable to represent here) at half intensity
Error....... then blank
290000000000 a secret code of this HP? fuzzy & intermittent display and then blank
f and hexadecimal countdown (f, e, d ,c, etc.) at a frequence surely < 0.7 s (appr.), and then blank
(another time, the HP displayed
999999999999 , then began an HEX countdown which could have reached
99977886fb99 if I didn't stop it two hours later)
This time, I finally obtained:
Error
0
0...........
0.
0.00
0.00........ (fuzzy dots) and then blank; or
0.00........ (fuzzy dots) but stay on; at this point, pressing the '1' key, I obtained:
98.. ..23.1. or
97.. ..23.1. or
0.00 . (last dot was fuzzy)
AND FINALLY
0.00
After that, I was (and I am usually) able to do some calculations:
sum, division, etc.
Log, sqr, etc.
Angle calc., etc.
Stack is working. First registers as well, indirect as well (I only checked R15 and R29). Operations on registers are OK as well.
At this stage, I still have two permanent problems:
1/ when I am typing some number keys, (4, 5, 6 most of the time), the HP sometime displays wrong signs (h, or a, or another number, 4 for 6 for example);
2/ It is impossible to program more than 10 instructions: at this time, the HP displays
000000000000 and stays frozen. The only way to 'debug' it is to put away the battery pack half an hour, or so, and begin again all the process.
I think it is not a RAM or ROM or ACT problem,
I think it is a dirty cicuitry problem, with this solution:
Quote:
Re: Have to agree with Katie on this...
Message #9 Posted by Geoff Quickfall on 6 Dec 2008, 10:46 p.m.,
in response to message #8 by Stan McFarland
Hi Stan,
I think it sounds like the battery rivet. To answer your first post:
1. remove the case back
2. remove the top circuit board (this will allow access to the
power tracings from the rivets.)
3. with one probe on the rivet work backwards from the rivet to
identify the problem
4. reverse the board and test the second rivet and trace.
5. IF the problem is found clean the board (vinegar rinse
followed by water rinse followed by alcohol and then a thorough
drying. (I use a shoe box with a hair dryer on COLD setting)
6. apply silver conducting paint.
On the second point,
1. clean the rivet with a fiberglass brush; fine wire brush; or
sand paper.
2. If blue residue exist clean with vinegar.
3. rinse with 90% alcohol.
4. just stick a little solder flux on the rivet,
5. then apply the solder iron and heat until the existing solder
flows, add some if required.
6. clean rivet with alcohol to remove acidic flux.
There is enough spring action in the battery to force the contact between the rivet and battery terminal. I doubt the rivet is worn flush with the circuit board, if I interpret your question correctly. If it is then try filing some of the circuit board back to expose more of the rivet edge to the battery. OR, build up the rivet with solder.
Hope this helps, Geoff
If so, thank you Geoff.
IDEAS AND COMMENTS ARE WELCOME. (sorry to have been so heavy).
Regards,
Xavier
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