HP-97 Printer Head

[aj04062]

I have a HP-97 that had a printer head failure. It has clearly overheated and burnt out. The plastic holder and rest pad are slightly melted, but usable, I think.

I have a new head. However, I am concerned about the failure mode of the prior head. Do you know how this would have happened? I don't want to install a new had just to see it burn out as well.

Could it have occurred if someone tried to print without paper?

I looked at the service manual on the DVD set, but nothing jumped out at me regarding this kind of failure.

[Randy]

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Do you know how this would have happened?

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No, but individual element failures are common. FWIW, I've never seen one that melted the surrounding plastic.

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I don't want to install a new had just to see it burn out as well.

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I would agree, not a good idea. It would be a very expensive fuse.

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Could it have occurred if someone tried to print without paper?

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I doubt it. Doing it long term might cause a few elements to fail but not melt things.

I would first measure the elements and see how many are failed. One or two is normal. More than that and I'd be concerned that the PIK is gone. A shorted driver transistor (Q1-Q7) would certainly cause a head element to fail if it was powered on for a long time and possibly generate enough heat to melt plastic.

You could provide seven dummy load resistors the same value as the head elements (~10-12 ohms) and power it up. See what the voltage drop is across each element - any with high drop are on all the time and should not be. Next step would be to print and verify that each transistor switches...