HP-41C power on

[zixingcheche]

Hello all,

Today, I found my 41c (1937A00xxx) has issue on power on. (it works well previously)

1. when press "on", the 41c has no display;
2. after pressed "on", then press and hold any key, for example "R/S" key for 25 seconds around. the 41c powered on, and "0.0000" was shown on display.
3. everything works well.

Does anyone knows? Thanks in advance!

BR,
bai

[rprosperi]

It could be powering on, but the LCD is not visible due to LCD contacts not touching inside if the upper posts are broken. Try this:

Press down on the outside rails on both side of the unit in-between the 2 top rows of keys. Not super hard, but firmly.

While pressing down, push [ON]

The unit may well turn-on and you'll see the display. If so, it's possible that when you release the rails the display will go off, but the unit remains on - if you press the rails again, you'll see the display re-appear.

Possibly not the issue you're having, but this is a common symptom. If so, you'll have to repair the upper posts (of have it done for you, e.g. thecalculatorstore.com sells the repair parts and also offers repair service).

Please report results, it will help future readers.

Good luclk.

[zixingcheche]

Hello Bob,

Thank you for your reply! I tried as you suggested way. but it seems does not work on my 41c.
My 41c has issue on power on operation. but after it started power on, it will works. no need to hold the rails.

Now the only way to power it on is to hold any key around 25 seconds after a single press on the key [ON].

Is some capacitances defective? I just guess.

any suggestions are welcome..

BR,

[rprosperi]

Thanks for trying and for the feedback. I was speculating that holding down a key for a while was accomplishing effectively the same thing as holding the rails (which is pressing internal contacts together), but seems your machine indeed has a different malady.

On one of my 41CL's, I have to hold the rails initially to get the LCD to 'light up', but then once on, it will pretty much remain on until bumped or put down, confirming a barely broken post (or possibly cracked case boss where the top screws go in).

Keep hunting and please be sure to post the issue and solution once you find it.

[zixingcheche]

I changed the back case and the contacted ports module which is from my another well worked 41c, but the same symptom is still present.

so, I guess the defective part is CPU board? I believe the keyboard should be OK.

[zixingcheche]

This morning, I changed the CPU board from my another 41C.
Now it works well.

so, the original CPU board was defective. (maybe the power supply part)

but, one symptom coming. the auto-off function is around 45 seconds.

**the picture below is the CPU board from another 41c**

[zixingcheche]

I found a post here:https://www.hpmuseum.org/cgi-sys/cgiwrap/hpmuseum/archv021.cgi?read=232703

When the GFF version CPU installed into early 41C, the auto-off time will be 40 seconds around.

=================
Revision "F" with 470 pf

Frequency - 110 KHZ

Timeout - 40 seconds

Display - OK
=================

please check the pictures

[Garth Wilson]

I have my start-up routine set flag 44, the continuous-on flag.  I use 44 TOGF which is in the ZENROM module, since ON is not programmable and SF__ doesn't allow setting flags above number 29 (even with the ZENROM module, which surprised me).

[zixingcheche]

I checked the service manual, and found below:

SYMPTOM
NO TURN ON

POSSIBLE CURES
_Replace C5 (C5 0160-4685 CAPACITOR, 0.1uF, 50V)
_Cold solder joints between display and keyboard
_Replace CR1 (CR1,CR5 1901-0868 DIODE, Schottky)

then I checked the PCB, as below picture.
_C5 is easy to find maybe, just to looking for 0.1uF, 50V CAPACITOR
but
_CR1 is hard, as the picture shown, "1080 7908" this is hard to find new models.

anyone know how to find a Schottky CR1 model name to order from today's market?
thanks!

[Garth Wilson]

For the Schottky diode, I'd use a 1N5817.  It's pretty common.

[zixingcheche]

(08-17-2024 08:27 AM)Garth Wilson Wrote:  For the Schottky diode, I'd use a 1N5817.  It's pretty common.

Thank you so much! I will try to order.