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9866 printer troubleshooting help... - Printable Version

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9866 printer troubleshooting help... - Keith Lueck - 10-23-2007

I am working on a 9866a that's paired with my 9810a.

The printer accepts data and acknowledges it, but, no print action. Motor drive & power supplies are fine, manual feed works, all the status lines (e.g. paper out) are valid...

The little state machine that controls the thing seems to be running and getting data strobes, but, it's waiting on something else - I can't figure out what...

Does anyone have any documentation on the state machine, or detailed info. on its operation? I have the hp service manual and Tony Duell's schematics, but, I'm still banging my head on this one.

Also searched for a patent on the 9866, but had no luck...

BTW, I've created a card extender for this unit which will also work for the 9810a (and prolly the 20 & 30 as well). If you'd like artwork for the pc board and p/n's for the connectors (you'll need 2 for the calculator) I'll email them for free...


Re: 9866 printer troubleshooting help... - Keith Lueck - 10-24-2007

Well, I figured it out. Answering myself here in hopes that it'll help someone else... I've been chasing my tail over this one for a week! There's absolutely nothing wrong w/ the printer.

The printer was looking for a LF character. I thought this would be provided by the PRINT/SPACE key, but it is not. There is a gate that decodes the LF character and that signal was never being asserted. I momentarily shorted it (it's active low - s/b /LF on the schematic) to ground and got a print output. Reading further I discovered how to explicitly generate a LF on the calculator, and once I added that to my test code - voilla!

The examples in the printer interface manual are for a typwriter - not the 9866a. Apparently the typwriter produces output w/o needing a discrete LF. Not so for the thermal line printer.


Re: 9866 printer troubleshooting help... - Tony Duell - 10-24-2007

Quote:
Well, I figured it out. Answering myself here in hopes that it'll help someone else... I've been chasing my tail over this one for a week! There's absolutely nothing wrong w/ the printer.

The printer was looking for a LF character. I thought this would be provided by the PRINT/SPACE key, but it is not. There is a gate that decodes the LF character and that signal was never being asserted. I momentarily shorted it (it's active low - s/b /LF on the schematic) to ground and got a print output. Reading further I discovered how to explicitly generate a LF on the calculator, and once I added that to my test code - voilla!


If it's any consolation I was going to ask 2 questions :

1) Did it _ever_ work? My point was to ensure you were sending LFs, etc

2) Check the Linefeed-detect circuitry. There's a NAND gate to detect Linefeeds on the data path PCB, the output goes low when an LF is sent. This is actually an input to the state machine on the control board of course. If you weren't seeing LFs detected here, I would have suggested you checked you were sending them and then debugged the 9810's interface.

Yes, I realised (too late) I left the inverting bar (consistently) off the LF signal on all pages of the schematic!

Quote:

The examples in the printer interface manual are for a typwriter - not the 9866a. Apparently the typwriter produces output w/o needing a discrete LF. Not so for the thermal line printer.


It is of course a true line printer. It bufferes a line of text in the shift registers on the data path PCB (only 6 bits are stored in the upper-case only 9866A) and then when it prints a line of text it converts those characters into the dot pattern for the top dot-line of that row, stores that in shift registers on the printhead driver board, prints it, moves the paper up, then goes on to the next dot-line, etc. Actually, it's even more complicated than that, since each dot-line is printed in 4 (I think) interleaved sections.




Re: 9866 printer troubleshooting help... - Keith Lueck - 10-24-2007

Hey Tony - thanks for the help. It would've been impossible to work on w/o your schematics - I only mentioned the LF signal thing in case someone else was confused by it.

Yeah, I realized that either the 7430 LF detect gate was bad, or, it wasn't getting any LF characters - it turned out to be the latter... I'd also assumed that the printer would automatically print when its line buffer was full, but that's apparently not true either.

Basically, it was my own bone-headed misunderstanding of the equipment. Oh well, it was worth hours of entertainment (and heating my house w/ my Tek 547 o-scope...<g>).

All I need to do now is clean it up a bit and make some other cosmetic repairs...

Do you happen to know if the 9866 can be used to list programs from the calculator's memory? - my 2nd 9810a has no internal printer option....