One of my 41's doesn't like modules in port 4

[damaltor]

(Old title: One of my 41's doesn't like its card reader)

Hi everybody,

i have one HP41C, tall keys, which doesnt like the card reader. If i plug it in, even before switching the calculator back on, the calculator makes a very silent noise (sounds like an inductor singing the song of a short circuit). After removing the card reader, the sound is still audible. If i switch the calc on now, it shows random patterns on the display, until i remove the battery and wait a while. No other way to bring it back as far as i can tell.

The calculator works fine, i tested the slot with a quad memory module (which also works fine) and the card reader works well with a different 41, even when i use the exact same battery. Any ideas?

[Harald]

(05-07-2016 11:57 AM)damaltor Wrote:  Hi everybody,

i have one HP41C, tall keys, which doesnt like the card reader. If i plug it in, even before switching the calculator back on, the calculator makes a very silent noise (sounds like an inductor singing the song of a short circuit). After removing the card reader, the sound is still audible. If i switch the calc on now, it shows random patterns on the display, until i remove the battery and wait a while. No other way to bring it back as far as i can tell.

The calculator works fine, i tested the slot with a quad memory module (which also works fine) and the card reader works well with a different 41, even when i use the exact same battery. Any ideas?

Maybe the power supply has a fault? Could be a bad capacitor causing excessive ripple with the extra load of the card reader. Just a guess though.

[damaltor]

Interesting. I am a bit scared to open it though, because it is one of the very early ones with the delicate connection between the pcbs.

[Harald]

(05-07-2016 08:07 PM)damaltor Wrote:  Interesting. I am a bit scared to open it though, because it is one of the very early ones with the delicate connection between the pcbs.

I am not sure which voltages are present on the expansion port. But maybe someone else has information on that? You could at least measure those that are accesible wirhout opening the calculator. Maybe that will give you a clue as to what is going on.

[BobVA]

(05-07-2016 08:07 PM)damaltor Wrote:  Interesting. I am a bit scared to open it though, because it is one of the very early ones with the delicate connection between the pcbs.

I had a similar problem with an HP-41 that refused to work with a card reader which turned out to be a defective pcb interconnect. The current to drive the motor runs though the interconnector. The elastomeric/"zebra" types are prone to developing high resistance.

[damaltor]

Harald: Will do, though I have already plugged a memory module in which works fine. I dont know if a memory module uses all Voltages though.

BobVA: I thought of that too. Who would drive a motor via zebra strips?? That is hilarious. But I don't think that this could be the problem, as the calculator malfunctions if I just plug the reader in it, I do not even have to switch it on or actually use the reader. Also it does not get better after removing the reader. Good idea though!

[Monte Dalrymple]

The card reader, unlike a regular module, is capable of driving the ISA line to wake up the processor. It sounds like the card reader ISA driver is always on. This is why the machine turns on when you plug in the card reader. It also explains the noise you are hearing - the card reader and the processor are fighting to drive the ISA line, putting strain on the switching power supply. It could be a short somewhere in the card reader, but more likely is that the controller chip in the card reader is bad.

[damaltor]

That might be. The card reader works fine on an other HP41 though, so the error is to find in the 41C. Maybe the ISA driver of the 41 is broken...

Also, shouldnt that be a problem only AFTER switching the device on? The Sound immediately comes up when i plug the reader in, not when i switch on the calculator.

[Monte Dalrymple]

(05-09-2016 06:05 AM)damaltor Wrote:  That might be. The card reader works fine on an other HP41 though, so the error is to find in the 41C. Maybe the ISA driver of the 41 is broken...

Also, shouldnt that be a problem only AFTER switching the device on? The Sound immediately comes up when i plug the reader in, not when i switch on the calculator.

A peripheral device can wake up the 41C CPU by pulling the ISA line High while the CPU is asleep. That's why I think that problem has something to do with that signal.

[damaltor]

Oh, thats interesting. I tested the reader again today with the second calc, it works fine. the (maybe) broken calc has a quad mem module in it which works fine, and as far as i know the isa line is needed for data transfer in both directions - so i guess i have to search deeper.... thanks for your help!

[damaltor]

Update: Though i was sure to have tested that before, i did now plug in a quad mem module into port 4. This produced the exact same results as with the card reader: The calculator made a faint noise, didnt turn on, and could only be reactivated by pulling out the batteries for >5 minutes. Removing and directly re-inserting them is not enough - it only brings garbage to the display.

The quad mem module works fine in all three other ports.

The contacts in port four look fine, and the calculator did not suffer from heavy battery leakage as far as i know. There was a rechargeable pack inside the calc when i bought it, and it had leaked a little, but not into the calculator - everything was still contained in the battery pack, and the battery contacts look like new.