Strange HP-41 Display Problem

[Mike]

I have an HP-41CV with a very strange problem. I cannot display A, B, or C in the Alpha register beyond the 6th character.

The characters (A,B,C) are saved, they just cannot be displayed beyond the 6th character. All other characters and even shift
A,B,C work everywhere.

For instance, if I type the following: XXYYZZAABBCCDDEE

AABBCC do not show up until the last C pushes A into the first 6 character positions. As I continue to enter characters,
eventually, AABBCC show up in the first 6 positions.

I thought it was a bad alpha register. But it seems strange that it would only dislike A,B,C and everything else is fine. Wierd!

Anyone have a clue what the problem is?

[Steve (Australia)]

OK, you didn't get a response last time so, even though I havn't seen a similar problem, I'll see if we can work through some things...

Firstly, do you have an XFunctions module?

If so, try a program like this:

01*LBL "TD"

02 .255

03 CF 28

04 FIX 0

05*LBL 01

06 CLA

07 1 E3

08 +

09 ARCL X

10 ATOX

11 RDN

12 1 E3

13 -

14 "+______-"  (Append 6 spaces then a -)

15 XTOA

16 "+-"        (Append a -)

17 AVIEW

18 PSE

19 ISG X

20 GTO 01

21 END

This will display all characters in the 2nd last position of the display, with a dash on each side. The ascii code will be shown on the left of the display.

Does it only affect A, B, and C? or are other characters affected?

I expect at least one other character to show up as a blank :-)

[Mike]

The program gave me DATA ERROR so I modified the program to do what you asked and found that the only characters that did not print in 7 and on were.

CHRs for 64 (@), 65 (A), 66 (B), 67 (C)

So, there was one other that did not print (besides space which was expected).

This is truely strange. In every way, the calculator works except that it cannot display these 4 characters after the 6th digit position.

Even entering XTOA by typing

XEQ ALPHA

shows: XEQ XTO

The 'A' is not displayed in the alpha register when even entering commands, but it is recorded internally because the instruction works properly.

[Steve (Australia)]

A data error? Where? Mine doesn't.

And I hope 32 also showed up as blank :-)

That's a VERY weird problem.

As a last resort I'd suggest opening up the calculator and looking for bad conections, but frankly, I don't see how bad connections could cause this.

The display of the HP41 is (from memory) controlled in 2 halves. Your problem is consistent with this in that only (and exactly) one half is affected.

The data in the alpha register is actually held in registers similar to the X, Y, Z, T, L registers, so it looks like they're OK and the problem is indeed a diaplay one.

It also affects operations other than the alpha register, since entering commands XEQ "XTOA" are affected, and (I assume) also program listings displayed on the screen, but not the printer (they should print OK).

[Mike]

> And I hope 32 also showed up as blank :-)

That's why I said "(except space which was expected)"

> That's a VERY weird problem.

> and (I assume) also program listings
> displayed on the screen, but not the printer
> (they should print OK).

I'll try printing. I suspect the problem is related to the connection between the PCB and the keyboard. I had a little problem, not that I think about it, making a good positive connection. Maybe that is where the problem lies.

Thanks

[Mike]

I'm beginning to think this is limited to the ability to display A, B, C only and affects nothing else. I'm going to try a different PCB connector tonight and see if that is the problem.

Thanks

[Steve (Australia)]

I thought it would.

When you have the unit open, also look closely at the connections between the main board and the display section.

Given that the display is probably like the rest of the HP41 and bitwise serial, AND considering there is no repeating pattern of missing characters, I'd suspect a faulty character generator ROM (If the HP41 actually had one!)

Good luck. Anything may work :-)