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Early (earliest?) HP-41C find.
07-27-2018, 09:50 PM (This post was last modified: 07-30-2018 06:45 AM by Diego Diaz.)
Post: #1
Early (earliest?) HP-41C find.
A few days ago I get another HP-41C with a couple of modules.

Nothing unusual as I'm always looking for module shells/connectors for the Clonix & NoV's projects.

Upon a first inspection it was clear that this HP-41C has a pre-production s/n 1916A00066.

Previous documented earliest s/n from Richard Nelson is 1916A00078 here

The bottom cover has some cosmetic differences from the early production units:

No golden ball contacts. A couple of slots instead of holes for those balls.

The back label is made of painted aluminium instead of vinyl.

Also the colour of the cover is a bit more clear than the production units and the "U" frame between the upper and lower shells is dark grey instead of dark brown.

However the most "interesting" part was inside.

The CPU board was populated with ROM versions D, D, D. Chips 1LA315, 316 and 317. The last one was the unkown.

Earliest production run carries ver. D, D, E. Chips 1LA315, 316 and 322; soon replaced by 333 for bug #1 correction.

All the known bugs are present of course, and since such 1LA317 ROM2 (ver. D) was never on the wild, it's reasonable to imagine that some other(s) undocumented bugs are also present in this unit.

I'll be back home in a few days and will extract the ROM contents; in case someone is interested in fiddling with this pre-production ROM version, I'll gladly share the image so it can be used in some emulator... Just for the sake of curiosity. ;-)

Best from Caribbean.

Diego.

"Do not suppose, check it twice."
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07-28-2018, 01:15 AM
Post: #2
RE: Early (earliest?) HP-41C find.
Hi Diego,

this is good news:-)
Would you consider taking some pics of your early bird, and share them here?

Cheers

-- Ray
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07-28-2018, 03:21 AM
Post: #3
RE: Early (earliest?) HP-41C find.
Hi Raymond,

Here they are...

   
   
   
   

I've also noticed cosmetic differences in the screw wells; they're full circles not "truncated" at the top, like the production units.

Pretty curious finding indeed... :-)

Cheers

Diego

"Do not suppose, check it twice."
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07-28-2018, 03:31 AM
Post: #4
RE: Early (earliest?) HP-41C find.
Hi Diego,

that was fast:-)

Many thanks for the pics.
Seems the early plan for the AC adapter contacts was with curved feather sliders instead of the gold balls.

Cheers

-- Ray
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07-28-2018, 12:54 PM
Post: #5
RE: Early (earliest?) HP-41C find.
Thanks for sharing this find and these pics Diego!

Where did you find this machine?

Were you aware it was a very early machine, or were you just very, very lucky?

--Bob Prosperi
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07-28-2018, 05:03 PM
Post: #6
RE: Early (earliest?) HP-41C find.
Hi Bob,

I was looking for "cheap" modules (Memory, Math, Stat... ) to recycle into Clonix/NoV's.

A couple of modules and working 41C below $100 seemed a good deal. Would keep the modules, througout cleaning the 41C inside out, may be replacing the I/O Flex, and sell it back to get some return. That was my thought.

I saw the s/n an know it was an early unit, but can't figure out it might be the *earliest* unit out there. And of course had no idea that it has an unreleased OS inside... In short, yes, I,ve been very, very lucky. ;-)

Enjoy your weekend!

Diego.

"Do not suppose, check it twice."
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07-28-2018, 05:34 PM
Post: #7
RE: Early (earliest?) HP-41C find.
(07-27-2018 09:50 PM)Diego Diaz Wrote:  A few days ago I get another HP-41C with a couple of modules.
(omissis)
Upon a first inspection it was clear that this HP-41C has a pre-production s/n 1916A00066.
(omissis)
No golden ball contacts. A couple of slots instead of holes for those balls.
(omissis)

Hi Diego....lucky guy Smile
for what were the slots designed for.... another system for external power connection?
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07-28-2018, 07:07 PM
Post: #8
RE: Early (earliest?) HP-41C find.
Hi Aurelio,

As Raymond pointed out (and that's also my guess) this prototype was designed to provide power contacts thru some sort of "curved blades" or " feather sliders". I'm affraid we may never know for sure... Undecided

Cheers.

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07-28-2018, 09:00 PM (This post was last modified: 07-28-2018 09:00 PM by aurelio.)
Post: #9
RE: Early (earliest?) HP-41C find.
(07-28-2018 07:07 PM)Diego Diaz Wrote:  Hi Aurelio,

As Raymond pointed out (and that's also my guess) this prototype was designed to provide power contacts thru some sort of "curved blades" or " feather sliders". I'm affraid we may never know for sure... Undecided

Cheers.
thank-you Diego and sorry Raymond......I've missed your replay....
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07-29-2018, 07:46 PM
Post: #10
RE: Early (earliest?) HP-41C find.
I have a lot of curiosity in that pre-production ROM image!

What a great find!
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07-31-2018, 06:28 PM
Post: #11
RE: Early (earliest?) HP-41C find.
Hi all,

I've managed to extract the .ROM images from pages #0, #1 & #2. (Ver. D, D, D)

You can use V41 emulator (release 7B) available elsewhere to test and play with them.

Please PM me with your e-mail if you're interested in these .ROM files.

Since earliest 41C OS release was D, D, E; main interest will be in comparing "D" ROM2 with its "E" counterpart, and see what changes HP made in its first production batch.

Obviously, M-code expertise (which I don't have) will be required for this task. Therefore M-coders help will be much appreciated in documenting these changes.

Best wishes.

Diego.

"Do not suppose, check it twice."
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08-01-2018, 11:07 AM
Post: #12
RE: Early (earliest?) HP-41C find.
Thanks for the DDD ROMs Diego. I’ve been able to run them in V41.

Comparing the "D" ROM2 with the "E" version I’ve found two code differences:
  • The ROM "D" doesn’t include the PATCH5 which is included in ROM "E". From the VASM listing: PATCH5 - POST-RELEASE FIX TO DEL NNN TO MAKE IT WORK WHEN LINE#=000
  • There is a significant difference in the PKIO20 part of PKIOAS - PACK I/O BUFFER AREA & KEY ASSIGNMENT AREA AT BOTTOM OF PROGRAM MEMORY.
However my M-code expertise is limited and I can’t go further in the change details
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08-01-2018, 11:58 AM
Post: #13
RE: Early (earliest?) HP-41C find.
Hi Diego

Can you please post a picture from the bachside from the CPU Board.

Many thanks
Patrik
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08-01-2018, 05:43 PM (This post was last modified: 08-01-2018 05:44 PM by hth.)
Post: #14
RE: Early (earliest?) HP-41C find.
This was a great find of archeology!

Like Didier pointed out, PATCH5 was added to correct the DEL function with 000. The D ROM obviously has this bug.

The packing of I/O area was changed and the old code looks wrong. There are two cases here, either the buffer has been marked unused (nibble 13 equal to 0), or it is to stay (same nibble non-zero, but not 15). In the delete case, the buffer is removed correctly as far as I can see, but the keep variant treats the buffer as being one register longer than the size indicates. This means it will move one register too many and probably cause issues as it will lose synchronization with the buffer headers.

The code in E version is greatly simplified and does it right.

Or perhaps more likely, the copy code is actually correct and the removal code is wrong! It could be that HP initially intended the buffer size to be minus one, which would make some sense as a zero buffer makes no sense at all. A zero would then mean that the buffer is one register long. Changing the meaning of the length caused another bug later on in that the HP-41 will get into an infinite loop with a zero length buffer! This was worked around in the ROM0 rev H (and CX ROMs), allowing backarrow-ON to break such lockup loop at power on.

At least the D ROM is not consistent here and has a bug. I think that when they fixed it, the code became so much simpler by just using the size "as is", that they went for it. Limiting the max buffer size to 255 instead of 256 is a small price to pay for much simpler code, but as mentioned it resulted in other consequences later on, which they maybe did not think about at that time. This is my educated guess.
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08-01-2018, 05:50 PM
Post: #15
RE: Early (earliest?) HP-41C find.
This also explains why there is an area of NOPs here in the E and later ROMs. Simplifying the code saved 14 words, but they needed to keep the locations of the following entry point labels which probably had been decided "fixed" before this problem was found and corrected.

Håkan
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08-01-2018, 06:20 PM
Post: #16
RE: Early (earliest?) HP-41C find.
Hi Didier, Patrik, all...

Thanks for the preliminary M-code research Didier. Hopefully we'll soon have more feedback on this, as several users are checking the NUT2-D.ROM file.

This is the bottom side of the CPU board Patrik.

   

Apart from the obvious tracing errors:

- Q2 is connected to PWO thru a piece of wire.

- C10 is connected to Vbat with a thick wire jumper soldered to a scratched part of the trace.

You can also see that there is no Q3. The one that makes DATA go LOW qith every Phi2 pulse.

It would be interesting to find out (sould it be possible) the reasons why HP included this on its first production batch.

The Service Manual estates that Q3 (and associated resistors R4 & R5) should be removed when ROM IC's are replaced with 120K ROM 1LG9-0001. I can't see why Q3 is depending on ROM IC's since Q3 only deals with DATA line and ROM IC's are not connected to DATA whatsoever. (?)

The PCB seems to be from 1978 52nd week.

CPU IC is (obviously) of the first generation 1LA5-0001.

Power supply is 1826-0566 in ceramic package. (MIL specs?)

I'm using the early 41C board schematics as refference to draw this one's. Will post it once it's finished.

Best wishes.

Diego.

"Do not suppose, check it twice."
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08-01-2018, 06:27 PM (This post was last modified: 08-01-2018 06:27 PM by Diego Diaz.)
Post: #17
RE: Early (earliest?) HP-41C find.
Hi Håkan,

Your reply enters while typing my previous post.

Thanks a lot for the insight about D>E versions mods. :-)

Cheers

"Do not suppose, check it twice."
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08-02-2018, 04:10 AM
Post: #18
RE: Early (earliest?) HP-41C find.
Thanks Diego

Your CPU Board looks like a prototype.

I have a very early one with production no. H-1914

Patrik
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08-07-2018, 12:16 AM
Post: #19
RE: Early (earliest?) HP-41C find.
Yes, my earliest production unit is also a three transistor with CPU board H-1914.

It comes into an HP-41C s/n 1941Axxxxx and D, D, E, OS version.

Tall keys, golden ball AC contacs and *shiny* faceplate (instead of the matte one) with grey frame line (instead of silver).

   

Hope you can see in the picture.

Cheers!

Diego.

"Do not suppose, check it twice."
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09-06-2018, 07:07 PM (This post was last modified: 01-03-2019 03:26 PM by CY-CL.)
Post: #20
RE: Early (earliest?) HP-41C find.
Known Prototype's:

1916 A 00066
1916 A 00078


Known Eearly Production HP-41C

1926 A 00137
1926 A 00148
1926 A 00199
1926 A 00248
1926 A 00250
1926 A 00255


Do you know other 1916 or 1926 ????

Thanks
Patrik
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