HP 41CV Weirdness - Sort of Long


I want to start out my story by stating that I know, from reading the various postings on this forum, and from reading the HP literature, that the 82106A memory modules from a 41C do not work in the 41CV. It already has 320 registers (00-319) of memory, etc.

However, today I had an unusual problem with my 41CV. It suddenly went from having 320 registers to having only 192; and it lost several programs in the process. It also exhibited other weird behavior (showing all "@" signs across its display, ON switch becoming non-functional, USER toggle stuck "ON", etc. etc.) which resulted in me doing several complete resets, losing all my programs, and eventually removing the back from the calculator. I cleaned all the contacts, etc. which I could get to, but could find nothing visibly wrong (it was, in fact, already one of the cleanest calculators I have ever opened). However, it still only had 192 registers of memory upon reassembly.

On a hunch, or in the interest of stupid experimentation, I inserted two 82106A memory modules into ports 1 and 3 of the calculator. It immediately began showing 320 memory registers. If I remove the 821067A modules, the calculator will retain 320 memory registers until either A) the power is shut off, or B) the SIZE command is used, whereupon it reverts to 192 memory registers. Reinserting the two 82106A modules will re-establish 320 memory registers.

Does anyone have a logical (or even illogical) explanation for this bizarre behavior? Thanks.

Take care.



Isn't there any faulty memory chip? I don't know how to test them - can you get some spare ones and try to replace? Just a crazy idea...

Best regards and good luck!



It sounds like you have a bad memory chip. The machine checks it memory size when powered on. If you pull out a module while it is on, it will not know it until you cycle power (or possibly perform some operation that repartions memory). Clean the CPU board very well with 91%+ isopropyl alcohol and a stiff brush. A lot of times solder flux or invisible crud on the board will cause problems like this.


It definitely sounds like your U10 (possibly U11 too) D/S IC are faulty. Service manual says:

4. Execute [SIZE] 191. If TRY AGAIN -> U9 is bad.
5. Execute [SIZE] 255. If TRY AGAIN -> U10 is bad.

If you have a service module 5061-7221 (unlikely since they are rare) it will test all of the D/S ICs. Alternatively you can use Clonix with the test module image, available from Diego.


Edited: 28 Apr 2004, 11:57 p.m.



I've heard my name here... ;-)

Well, I'm still on holidays in Seville, will be back next Wed. Just wanted to advance a point regarding the Service modules emulation: as some of you already know these modules were not fully emulated by the previous Clonix-41's code version, but such limitations no longer exist. Now both service modules are fully functional, including the Card Reader test features. Two .HEX files, to load Clonix's EPROM with, will be posted at my site and at the other site... one file emulates the 41196 while the other is for the 5061-7221.

The unavoidable counterpart is that Service modules emulation will RUN all the time so the power consumption is somewhat high... (you may want to power your 41 from AC adapter, instead of batteries, while running your tests)

Best whishes from Seville.


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