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HP41C - 16 registers missing
11-09-2019, 02:46 PM
Post: #1
HP41C - 16 registers missing
Dear all,

We just bought a used hp41c.

Without any module, after SIZE000, in prgm we see "00 reg 47".

We can play with REG/PGM sizes within the 47 regs.

If we add a memory module, It seems nothing change. After SIZE000, in prgm we still see "00 REG 47".

But, after a "hole" of 16 nonexistant registers, we access the memory modules depending or the physical port they are plugged in :
in port 1, we have REG(SIZE + 16) to REG(SIZE + 16 + 64)
in port 2, we have REG(SIZE + 80) to REG(SIZE + 80 + 64)
and so on ...
With REG00 to REG(SIZE - 1) still available.

And we have "nonexistant" if we try SIZE(more than 47), even with memory module(s) plugged in.

What may be the reason ? Memory chip failure ? Address line issue ?
Workaround ? Chip accessible to replace ?

Thank you very much for your help
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11-09-2019, 07:49 PM
Post: #2
RE: HP41C - 16 registers missing
Each RAM chip on the HP-41 supplies 16 registers, sounds like one of them is not working. I am not sure if they correspond one-to-one with physical ICs, or if multiple were 'mounted' into the same IC, and whether that changed over time, I never bothered to check.
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11-09-2019, 10:48 PM
Post: #3
RE: HP41C - 16 registers missing
Some things to try:

1. Have you tried the RAM module in all 4 slots?

2. Do you know that the slots work properly (e.g with a ROM module)? It's possible the connectors inside are dirty or damaged from a battery spill.

3. Can you test the RAM module on another 41C?

4. Try CAREFULLY cleaning the 'inside' contact side of the 'fingers' in the open side of the RAM module, perhaps they are dirty from age and/or a battery spill in an old 41 where it was stored. If you have it, clean the contacts with DeOxit RED; if not, try Isopropyl Alcohol.

Good luck, and please update this thread if/when you find the solution.

--Bob Prosperi
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11-09-2019, 11:28 PM
Post: #4
RE: HP41C - 16 registers missing
(11-09-2019 07:49 PM)hth Wrote:  Each RAM chip on the HP-41 supplies 16 registers, sounds like one of them is not working.
Yep that sure look like it! ... or a solder join has broken.
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11-09-2019, 11:40 PM
Post: #5
RE: HP41C - 16 registers missing
Oops, a closer reading (47 vs 63) reveals the problem is mainframe RAM, not module RAM. Sorry for the incorrect advice. Those tips are useful, but for a different problem.

--Bob Prosperi
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11-10-2019, 12:51 AM
Post: #6
RE: HP41C - 16 registers missing
If it is a fullnut the simplest way to fix it is to swap out the motherboard. You might put an item wanted in the classifieds. Anyone who has made a 41CL may have a spare. I used my spare to fix another 41 but someone may have one.
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11-10-2019, 09:04 AM
Post: #7
RE: HP41C - 16 registers missing
Hello everybody and thank you

Unfortunately, I realy seems to be a dead RAM chip.
The point is now to get a replacement chip or a main board. Why not upgrading to CV or CX !

I start looking for one, and will publish news.

Thanks
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11-10-2019, 04:21 PM
Post: #8
RE: HP41C - 16 registers missing
(11-10-2019 09:04 AM)bricator Wrote:  The point is now to get a replacement chip or a main board. Why not upgrading to CV or CX !

Or a CL... Not cheap but well worth the layout.

There are only 10 types of people in this world. Those who understand binary and those who don't.
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