|Re: 41CV Processor/Memory Problem|
Message #3 Posted by Vieira, Luiz C. (Brazil) on 23 June 2005, 10:15 p.m.,
in response to message #2 by Howard Owen
I consider that you have a full-nut HP41CV from now on. Is that valid?
The HP41CV main memory is divided in five blocks of (64x7) bytes, or 64 registers each. There is always a 1-register low counting, as you can see in the maximum 00 REG 319 (320 = 64 X 5). This is because of the permanent 3-byte .END., and you can check this by setting SIZE  and adding at least four [ENTER^] instructions (or any other 1-byte) prior to read PACKING and TRY AGAIN.
Now that you mention that you do not have troubles when executing [SIZE] 256 till [SIZE] 319, I'd guess your HP41CV has a problem with one (or some) of the lower-addressed RAM chip (maybe uper-addressed, I'm not sure right now). Have you noticed if you also have strange contents in the upper numbered registers? I mean, after executing [SIZE] 319, what do you have with 254 [RCL][IND]X, 255 [RCL][IND]X, 256 [RCL][IND]X... Chances are you'll get weird results, though.
If you have an available 41CV (fullnut) to donate parts, you could try replacing some of the RAM chips. I have an halfnut HP41CV that ony reads 64 registers, and anytime I load a program on it (keystrokes, card reader, etc.) it has bytes being changed after the first execution. I succeeded building its mainboard in an HP41C fullnut case, so I have one of each: full- and half-nut 41C, CV and CX, altough the HP41C halfnut is, in fact, a deffective HP41CV. Because the RAM, ROM and display driver are all located in the hybrid board in the LCD assembly, there are no chances to try repairing it... (sob!)
I hope you succeed. Let us know if you need guidance.