new to logic analysers

[Norton]

I have posted this in beginners because after a quick perusal of the the other forums, it is fairly evident that I am not as clever as I thought was.

I am playing with my first logic analyser (hantek 5022 (garbage)) in an attempt capture the data transimitted between a machine and a receipt printer (SII dpu-20) over a parallel port, with the intention logging the data as text.

Using the pinouts for a similar printer (I can't find a data sheet on the original), I have worked out the data pins, which are self-evident once seen on the screen.  The rest of what is happening is a mystery to me though.
Based on what I have learned about how parallel communications work, I would expect for find a strobe signal for each change of state on the data lines, followed by a BUSY and/or ACK, but I am reading several bits between strobes. 

My best guess as to what is happening is that I am reading electrical noise from the DC motor running the printer as bits.  No amount of screwing around with grounds has changed the nature of the signal..  The laptop, analyser, device, printer, and power supply are all connected to the same outlet, and I have even run jumpers between all of the ground points on all the devices attached without change.  The printer is printing everything it should be with the analyser attached.  In the sample provided, the printer is receiving the text "POWER UP", or "DATE:01:01:16".

in the attached screenshot, I have highlighted a gap between strobes to show the timing.  What made me suspect noise was that when I set the analyser to scan at 4Mhz, the strobe pulses register at 250 nanoseconds (or less), which I believe is a bit fast for such an old protocol.

Can anyone shed some light on what I am looking at here?

[Doctorandus_P]

The most common cause is to set the sample rate too low.
A decent minimum is to capture data at such a rate that you have at least 4 samples of each signal state before a bit flips.

Other common problems are:
* Logic levels that are different between the LA and DUT.
* Bad probing, long GND wires etc.

Also, in your next screenshot, please make it smaller. 1000 * 800 pixels is suficient for such screenshots, and allows web browsers to display them completely without scaling (which makes text very small).