HP-97 troubleshooting

[Kees Bouw]

Hi All,

The mystery is solved.

I did a lot of testing and measuring, everything seemed quite normal with paper in the printer except for one thing: the paper advance button had no effect at all. Inspecting the connections on the switch and on the main board and comparing it with the service manual revealed that I made a mistake when connecting the switch to the main board. In my own defence, it was not really a stupid mistake. I am very careful with these things :-) I had looked at a photo from another HP-97 and connected the wires accordingly. But in that particular HP-97 the wires were connected differently from what the service manual says, something I had not noticed before. In the service manual it shows that the wires should be R B W (red black white) from top to bottom on the main board. But in my older HP-97 it was connected as B W R. To prove this I attach pictures of both switches which were wired differently as well of course. Left is the "irregular" one and at the right as it should be according to the service manual. The way I connected it the F1 from the ACT was connected to the OPS all the time. I do not remember exactly but the strange behaviour may indeed have been related to whether or not paper was present in the printer, meaning that way too much current was used when there was no paper and more-less normal behaviour with paper in it.
Anyway: a word of warning, be aware that the paper advance switch may not be wired as shown in the service manual!
Fortunately, no damage was done and after connecting it correctly everything worked fine.

Kees.