Help with 41CV - memory problem ?

[timw]

Hi,
I am repairing a 41CV (fullnut, s/n 2202S40037) for a workmate and would appreciate some help. I refurbished the card reader, fixed the battery contacts and repaired the screw posts - cosmetically it is excellent. I put it back together and it appears to work ok performing simple calculations. STO and RCL work and the values are preserved when powered off.

I then entered a 4 line program and when executed the 41CV locks up and has to be powered off to regain control. Executing GTO .. results in a lockup with 'PACKING' showing on the display. I can read pre-programmed cards but they also lock up the 41CV. I am guessing this is indicating a problem with the memory IC's.

The IC's are as follows :

ILB738, ILB739, ILB740 - ROMS ?

ILA701

ILE701, ILE702, ILE703, ILE704, ILE705 - memory ?

I have removed the abovementioned chips but do not have another 41CV to test them in.

Any advice on how to proceed will be appreciated as I would like to surprise my friend by returning his 41CV to full health.

Regards, tim.

[Raymond Del Tondo]

Hi Tim,

On 1st look it sounds like there are no program Registers assigned.
Just XEQ SIZE , and fill the prompt with a Value, like 050 .
The above number tells the HP-41 to assign 50 of the available registers as Data Storage Registers, and to use the remaining memory as program storage.
Please also consult the Manual for more details.

HTH

Ray

[Geoff Quickfall]

The CV from a memory lost state should assign program registers automatically.

XEQ SIZE 000
switch to prgm mode

and record the number of program registers available and let us know if you see 319.

that would indicate that all RAMs are functional.

Let us know what you see.

Geoff

[timw]

Hi,
thanks for the tips Raymond and Geoff.

As I have already desoldered and removed ILA701, ILE701, ILE702, ILE703, ILE704, ILE705 I am wondering whether I can solder them back in a specific sequence to help diagose the problem ?

For example if ILE701 is the first set of memory registers (64 ?) and there are no other memory chips present, would XEQ SIZE 000 show 64 if ILE701 is ok ? With a faulty memory chip in-circuit would the XEQ SIZE 000 command then fail, indicating that the last chip fitted is faulty ?

Here I am assuming the ILA701 is memory registers 1-64, ILA702 is registers 65-128, etc, however this is just a guess.

Or should I put them all back in-circuit and proceed with fault finding ?

Thanks, Tim.

[Eric Smith]

1LA701 is the "status registers". The calculator needs that and 1LE701 at a minimum (along with all the ROMs) to work at all.

[timw]

Hi Eric,
when I said "....Here I am assuming the ILA701 is memory registers 1-64, ILA702 is registers 65-128, etc, however this is just a guess...." I should have said ILE701, ILE702, etc.

Anyway, I soldered the ILA701 and ILE701 back in (ILE702 to ILE705 are not in-circuit) and when I switch to program mode the display shows '000 REG 46'. GTO .. initiates 'PACKING' and a lockup. Does this mean the 41CV is only seeing the first 46 registers of the ILE701 and that it is a faulty chip ? If so, any tips on finding an ILE701 as I am not keen on buying another 41CV just for 1 chip.

I think the display also showed '000 REG 46' before I removed ILE701 to ILE705.

Thanks for you help. Timw.

[Eric Smith]

You are correct that 1LE701 contains the first 64 "user" memory registers. The "000 REG 46" is the correct display after entry to PRGM mode from MEMORY LOST, because the partition between registers registers and program space is fixed somewhere in the middle of the 1LE701 chip.

With all RAM chips installed, you should be able to access (STO and RCL) registers 00 though 272, but you have to use indirect addressing to get at registers above 99. For instance, you could do something like:

272 STO 00

1.23456789E41 STO IND 00

CLx

RCL IND 00

and you should bet the stored number back. (Press the gold shift key for IND.)

The other ways to look at the memory size are:

XEQ alpha SIZE alpha 000 -- configures for NO user data registers

PRGM - tells you how many program registers are available, e.g.,

00 REG 63, 00 REG 127, 00 REG 191, 00 REG 255, or 00 REG 319

Or, with the Extended Function/Memory module:

XEQ alpha SIZE? alpha

Failing during PACKING suggests that there is another failure. Most likely this would be either a ROM, the 1LA701 RAM, or the processor chip (1LA5-0001, 1LE3-0002, or 1LF5-0002). It is obvious that the ROMs, 1LA701, and processor are at least partially working, which makes this difficult to pin down.

The official service procedures would tell you to replace a series of chips until the calculator works correctly. This is obviously not practical for you, since there is no source of replacement parts aside from other calculators. At this point it sounds to me like your 41CV is only useful as a possible parts donor.

[Marcus von Cube, Germany]

Quote:

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At this point it sounds to me like your 41CV is only useful as a possible parts donor.

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...or as a home for a CL board. :-)

Edited: 8 Sept 2011, 2:15 a.m.