My newly acquired HP19C seems to have died on me

[Harald]

I left it on the desk for a while and when I came back found the paper arround the printer head had become all blue.
It still prints, but a heater element on the bottom right seems to be turned on continuosly. Any idea why this could have happened? Is there a fix for this? So far the heater elements all seem to be OK. I turned it off for now..

Also a few keys only work when pushed rather hard. The keyboard desing seems to be different form the other woodstocks (domes instead of strips?). Is there a chance of cleaning the contacts?

Cheers,
Harald

[Harald]

Are there no 19c expersts present?

[Katie Wasserman]

(11-27-2014 06:28 PM)Harald Wrote:  Are there no 19c expersts present?

I'm not an expert on the 19C, but I'm curious about what you said:
"found the paper arround the printer head had become all blue"

That can/will happen if the paper is exposed to heat or certain chemicals -- isopropyl alcohol for example. If you left the calculator on, perhaps something inside got very hot, was it plugged in to change the batteries? Maybe something failed in the charging circuit, maybe one or more of the cells in the battery pack are shorted.

The stuck-on problem would seem to indicate that the print head driver has at least one bad transistor in it. According to Tony Duell's schematic the 19C uses a single chip transistor array for this, not discrete parts. But it should be possible to bypass the bad transistor in the array with a single NPN.

I've not taken the keyboard apart on the 19C, so don't have any suggestions for that problem.

[Harald]

(11-27-2014 06:47 PM)Katie Wasserman Wrote:  I'm not an expert on the 19C, but I'm curious about what you said:
"found the paper arround the printer head had become all blue"

That can/will happen if the paper is exposed to heat or certain chemicals -- isopropyl alcohol for example. If you left the calculator on, perhaps something inside got very hot, was it plugged in to change the batteries? Maybe something failed in the charging circuit, maybe one or more of the cells in the battery pack are shorted.

It was the printer head that got hot of course. It is just how I discovered this had happened.

Quote:The stuck-on problem would seem to indicate that the print head driver has at least one bad transistor in it. According to Tony Duell's schematic the 19C uses a single chip transistor array for this, not discrete parts. But it should be possible to bypass the bad transistor in the array with a single NPN.

Is that the RCA chip?

Unfortunately I don't have the schematics CD. I have been trying to get one for about half a year now as I am after an HP65 schematic as well. I got as far as sending the money, but then everything has gone quiet again. Looks like my mails end up in Dave Colvers spam folder.
Could you maybe email me the schematics? I think this should be OK, as I alreay payed for the CD.

Thanks,
Harald

[dct]

(11-24-2014 09:51 PM)Harald Wrote:  I left it on the desk for a while and when I came back found the paper arround the printer head had become all blue.
[...]

Until now my 19C works properly but I had also the effect the printer going mad: It was when the battery was near zero. Than it can happen the printer starts advancing paper without any reason until the battery is completely empty.

[Harald]

(11-28-2014 01:10 PM)dct Wrote:  

(11-24-2014 09:51 PM)Harald Wrote:  I left it on the desk for a while and when I came back found the paper arround the printer head had become all blue.
[...]

Until now my 19C works properly but I had also the effect the printer going mad: It was when the battery was near zero. Than it can happen the printer starts advancing paper without any reason until the battery is completely empty.

The battery is fully charged. The charger was plugged in as well, so I don't think this is the problem.

[Harald]

(11-27-2014 06:47 PM)Katie Wasserman Wrote:  The stuck-on problem would seem to indicate that the print head driver has at least one bad transistor in it. According to Tony Duell's schematic the 19C uses a single chip transistor array for this, not discrete parts. But it should be possible to bypass the bad transistor in the array with a single NPN.

Hi Katie,

I finally found the time to play with the 19C. Thanks for all your help! It was a bad transistor. For what ever reason it had a base emiter voltage of 0.2 Volts. After replacing it with a BC817 I now have a fully working printer! :-)

Unfortunately the 19C now has another problem. While typing in numbers, funny things happen. The display suddenly fills with zeros for example. Or somethimes segments c, d, e and g are lit on a few digits.

It seems, at least judging by it's smell, the calculator has been stored in a very damp environment for some time. Maybe the components suffered from that.

Cheers,
Harald

[Katie Wasserman]

(12-16-2014 06:57 PM)Harald Wrote:  I finally found the time to play with the 19C. Thanks for all your help! It was a bad transistor. For what ever reason it had a base emiter voltage of 0.2 Volts. After replacing it with a BC817 I now have a fully working printer! :-)

Unfortunately the 19C now has another problem. While typing in numbers, funny things happen. The display suddenly fills with zeros for example. Or somethimes segments c, d, e and g are lit on a few digits.

It seems, at least judging by it's smell, the calculator has been stored in a very damp environment for some time. Maybe the components suffered from that.

I'm glad to hear that you got the printer working at least! The other issues might be not enough current getting to one or more of the chips. Assuming that you have really good contacts from the battery (you can solder to these temporarily to make sure that you do have good contact) it might that you have a partially corroded trace. Or, as you said, a component that's failing. Or it could be just a single bad solder joint. You can re-solder all the connections for starters, that's easy enough to try.