Looking for (idler?) gear wheel of HP-46 printer unit

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(04-09-2017 09:25 PM)Sadsilence Wrote:  Finally found some time to look for pictures I have done when creating my last gear wheel. I am quite impressed about your thinking process. Unfortunately I cannot drink coffee any more and switched to tea one and half year ago. Maybe the reason, why I choose a pragmatic try and see tactics.

Additionally I remember a HP-46 service manual (either coming from google to me or through Forum's document usb memory) which explains setting timings of printer unit electronically. Really difficult to understand and nearly impossible measuring signal forms with an oscilloscope within HP-46. It seems you need a special printer unit lab device. So I surrendered without a pratical test.

Attached is a picture showing positions between drum nubs and sensors that works for my unit. It needs one explanation: Left marker (green) should be aligned with it's magnetic head. With second (red marked) gear and it's two marks picture shows a position that does not work (I forgot to take one with right position). First marker of brass gear should be in perfect alignment with second magnetic sensor, with second marker targeting away from first magnetic head. In other words brass gear has to be rotated by around 45° counterclockwise compared to picture:

Why it is "nearly inpossible" to measure with Oscope? Is it impossible to measure with Digital storage oscilloscope? Or is the signal a type where you would need a logic alalyser. In these cases and if one is heavily on the restoration of these and similar units it might be worth to invest a few tens of dollars to some hobby level USB digital analyser & storage oscilloscope, which makes you look the life in different viewpoint if all you have used is analog oscilloscope without storage options (or very limited storage time).

Ie. I have both Analog (well digital and analog hybrid) and USB scope (not the cheapest on the market, but low end from respective manufacturer). My USB unit can decode UART and CAN protocols on fly, really handy. I know there is atleast one really popular chinese model (Digi analyser) in hobby use with 3rd party software, unfortunately I can not recall the name of the product or the 3rd partysoftware project atm. Cost were something like $25..$50 on ebay..

Edit: I found it or atleast similar project: http://www.sigrok.org/wiki/Supported_hardware