IR Printer 82240A repair

[Miki Mihajlovic]

I got a non working 82240A IR printer. It powers up, it reacts to my HP-41 IR module commands, the head advances like it is printing but it leaves no imprint on the paper. I checked the paper with my other HP printer and it is OK so my assumption is that is something wrong with the thermal head. Next thing I opened it cleaned it inside and checked all the wires. They seem ok, all the solders seem to be firm and holding and the little knowledge about electronics I have, power is present pretty much everywhere I measured it.

Is there anything I could do here. It is quite a nifty little device and I would hate to have to sell it (give it away) for parts.

1234

[Michael Kaiser]

Hi Miki,

I'm owner of an HP82240A to.

Two suggestions:
1) Try new paper
2) Adjust the control slider for the printer head
(in the middle of the printer) totaly onto the right side

Good luck

Mike

Edited: 18 June 2004, 4:04 a.m.

[Miki Mihajlovic]

I tried those things first but it doesn't work. I am not really sure how those printers work. Are there tiny pins that actually hit the paper what crates the imprint or is it done differently. If the pins are there can they get stuck together due to dirt, gunk, or dirty lubricant that was present on the head when I opened it? Would some solvent help in that case?

1234

[Richard Garner]

It could be that the pins are dirty or that the heating element for the pins is not working. That is as far as my thinking goes on what you have described so far.

[Tony Duell]

The printhead on this printer consists of 8 (IIRC) tiny heater elements. They are driven by 7 sections of a ULN2803 octal driver IC (the other section drives the motor) together with a discrete transistor. Drive to the ULN2803 comes from one port of the 8048 (?) microcontroller. The user intensity control is part of an RC network that the 8048 'measures' and is used to determine the pulse width sent to the driver (longer == darker of course).

I'd start by carefully unplugging the printhead tapewire from its connector on the main PCB. Then check for low-ish resistance between the common connection (IIRC thickest track in the tapewire) and each of the others in turn. If it's open, then the printhead or tapewire is defective :-(

Then look for drive pulses at the inputs to the ULN2803 while printing. If there's nothing there, suspect the 8048 (custom programmed, you have to get one from another 82240A), or the intensity control and related components.

If you've got drive to the ULN2803 and nothing at the outputs, then that's dead.

[Miki Mihajlovic]

Thanks for the details Tony. Will try to do as you described.