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HP Forum Archive 20

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HP19C printer head...yeah! I know!
Message #1 Posted by Geoff Quickfall on 30 July 2011, 3:33 p.m.

I have searched the archives for print head replacement, repair, HP 19C repair and etc.

Lots of useful data there including resistance readings on older IR printers compared to newer printer heads.

The print heads are a different size in the IR printer then the 19C. It appears the print head in the 97 series is more similar.

The question is, and most of the postings cease at this point (going back to 2003):

Has anyone been successful in transplanting either the IR print head or the 97 or other series print heads into a 19C?

Cheers, Geoff

Edited: 30 July 2011, 3:34 p.m.

Re: HP19C printer head...yeah! I know!
Message #2 Posted by BobVA on 31 July 2011, 9:59 a.m.,
in response to message #1 by Geoff Quickfall

Did both of the 19's you were working on have duff print heads? Or are you trying to get both working?

Given the comments in this post it sounds like the 97 may be the only bio-compatible transplant donor. A repair procedure was all sketched out there, but if anyone tried it it they didn't post back.

If you take a shot at it, shoot lots of pictures and post the travelogue!

OT: I spent yesterday restoring a very forlorn HP-97S; practically like working on a tractor, compared to the brain surgery required for the 19c.

Interestingly enough the 97s didn't have an interface cable attached. I was wondering if the poor, battered fellow got promoted to office duty in his dotage and some fastidious engineer or accountant removed his cable.

Good luck with the 19c! Bob

Edited: 31 July 2011, 10:00 a.m.

Re: HP19C printer head...yeah! I know!
Message #3 Posted by Katie Wasserman on 31 July 2011, 1:20 p.m.,
in response to message #2 by BobVA

The 97/97s is indeed a pleasure to work on especially compared to the 19c. Unfortunately 97s' with missing cables and pods are pretty common I have one too. I was thinking of creating a pod of my own and invest,igated the signal lines in the (missing) cable. Once I had that I figured a single microcontroller with a ton of i/o lines would be an relatively easy way to replace the pod, but instead came up with this. One other regular on this forum followed my design (and caught a schematic error, thank you) and has enhanced their calculator too.

Re: HP19C printer head...yeah! I know!
Message #4 Posted by Geoff Quickfall on 31 July 2011, 1:36 p.m.,
in response to message #3 by Katie Wasserman

Well, I have two 19Cs, one prints the top half only and has a lower section printer head that is dead. I watched it happen but was not quick enough to save it.

The lighting was low. The printing had stopped but the head did not park. It started to glow. Immediately turned of the calc and cooled the head with compressed air.

Not in time to save it. The donor, which is a pretty looking battery charger with no hope of resurection (corrosion, missing traces and etc) actually melted the guide bar and imbedded the printing head in it!

So I have a working 19C with a half dead print head and a non working 19C which I got an LED to light up. A dead ACT chip. But it works as a charger!

I too found about 10 postings going back 10 years but there were no follow ups of the 97 procedure. I only have one 97 fully working and pristine with Katies mod on the printer and a fully functional card reader so I AM not experimenting with it. I do have four IR printers but the heads are different sizes and the resistance values are completely different.

This project will have to wait!


maybe printing two of the book!

97S Interfacing / 19C print head replacement
Message #5 Posted by BobVA on 31 July 2011, 4:41 p.m.,
in response to message #4 by Geoff Quickfall

... I watched it happen but was not quick enough to save it.

Uggh - I HATE it when something like that happens. My sympathies.

I'll keep my fingers crossed that TAS offers up the right half of a bisected 97 to you (perhaps the victim an unfortunate industrial accident in a saw mill.) They tend to work so well, that may be what it takes to get a junker. I've got one parts machine, but unfortunately it didn't have the printer assembly when I got it. (And some guy was standing on it at a ham fest.)

Katie: Thanks for that pointer. I've added that to "The List of Stuff I've Got To Do". Looks like a nice project. I haven't written any interrupt driven code in a decade or more, so I was glad to see you didn't need any. I'm pretty familiar with the BS2, so perhaps I'll be able to grasp the SX.

The photos were also interesting - whoever swiped the cable from my 97s didn't have the courtesy to replace the cap on the IDC connector.

I recently built a clock from a old power plant tachometer (whose scale was handily was numbered zero to twelve) using a BS2, a DAC to drive the meter movement and a 1302 RTC. One gimmick from that that you may find handy: I wrote a "signal" byte (i.e. known value) at the start of the 1302 RAM. My code uses it as a start-up check to detect a back-up power failure and react accordingly. (I'm using a cap for backup, so it's only good for a couple of days.) Might be fun to do something similar with your circuit, perhaps writing a checksum of bytes 0-30 in byte 31.

I'd been idly thinking about building a PC interface box for a spare 97 card reader to allow a PC to read/write 67/97 cards, but I'm now thinking the approach you suggested is a *lot* simpler.

Sending a program from a PC to the 97 using your interface looks pretty straight-forward, and I think that would cover 95% of the use cases for such an arrangement. (Probably not that much call for reading a card into a PC.)



PS: While I had the hood up on the 97, I used the technique described in this post of jumping test points "F" and "H" on the reader circuit board to allow writing to a write-protected card (I needed to fix a damaged HP Standard Pac card). It got me thinking about adding a switch to do this in the future, but perhaps it would be an ideal "f" function to add to your board (driving a reed relay to close the circuit between the points.)

Edited: 31 July 2011, 5:07 p.m.

Re: 97S Interfacing / 19C print head replacement
Message #6 Posted by Katie Wasserman on 31 July 2011, 7:01 p.m.,
in response to message #5 by BobVA


Yeah, this code doens't use interrupts (probably one of the only SX programs I've written that doens't) so it might work with a higher-speed version of the BS2.

You're idea for the DS1302 signature is a good one and I use something similar for the "macro" function in my 97 code, but it's not needed for knowing the the RTC needs to be reset. The backup CR1225 cell will keep the clock running for close to 20 years, in theory.

I like your idea of implementing an 'ff' function to override the card write protection!


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