Strange 41CX failure

[John Ioannidis]

I have a 41CX in my collection with the following strange behavior:
If I'm in program mode and I try to input a number or EEX, I get MEMORY LOST! The decimal point works. Obviously something is wrong, but what? I know I can't fix it, and it's not really affecting me (it's a spare that I use in the kitchen, covered in clear wrap), but I'm curious!

The memory loss happens ONLY when I'm trying to input an actual number, not any kind of numeric entry. It's not the pressing of the individual keys that causes the problem. I can key in RTN, BEEP, CF _ _, etc., and I can key in GTO 01, XEC 23, STO 45, RCL 67, SF 89, and they are accepted. I can even switch to ALPHA mode and enter numeric characters. I can enter a lone decimal point, but as soon as I type a number or EEX, I get MEMORY LOST.

It also doesn't matter what SIZE I have (000, 318, or anything in between). It doesn't matter if the program is packed or whether in an unpacked program i'm trying to insert where nulls exist. It also doesn't matter which partition (between a global label and an END) I'm in.

Any guesses (or points to which part of the firmware may be dead)?

[Randy]

It's most likely: 1) A fullnut 2) and it has a bad rom. The memory SIZE command doesn't affect it because SIZE is using ram (or in 41 speak that would be D/S).

There is a chance it's just creepy crawlies on the logic board causing problems. It doesn't take much to make a 41 go crazy. You can remove and wash/scrub both sides with isopropyl alcohol, dry well (don't rush it) and reassemble.

If that doesn't do it, you'll need to isolate which rom is defective and replace. The service rom is the easiest way to diagnose at that level. There are several different rom versions which usually means its easier to just replace the entire logic board :(

[John Ioannidis]

It's a halfnut, actually. Round corners.

[Vieira, Luiz C. (Brazil)]

Hi, John; allow me to join you and Randy in this quest!

In this case, the only way to make sure it is a faulty ROM is replacing the entire LCD assembly. As you probably know, it contains the RAM, ROM and display driver in one hybrid assembly (the R2D2 IC -RAM/ROM Display Driver- found all early Voyagers is a PQPF solution for this arrangement) and if the nut processor in the mainboard is O.K., it will work fine with a new LCD assembly. I have once removed it and I have the pictures. Not a hard task, just 10 soldering points to unsolder, but they need to be completely cleanned prior to remove the LCD assembly from the mainboard.

Let me know if you'd like having these pictures.

Cheers and success!

Luiz (Brazil)

Edited: 18 Apr 2006, 1:09 a.m.

[Klaus]

Do you have any key assignments (that might survive the "memory lost")?

[John Ioannidis]

Key assignments don't survive a memory loss!