Sinclair ZX80 / ZX81 / Z88 Forums

mhudson52 wrote: ↑Wed Apr 25, 2018 3:15 pm That is great news, especially the fit of the teeth in the sprocket grooves. I couldn't have gotten them that close without the actual pieces you sent.

As for not having the styli attached during your test, I would suspect that the printer doesn't know (or care) whether they are there or not.

With the exception of the mounting posts, TPU would indeed seem to be the filament of choice. We may have a situation where we have to deviate from the original design and use a small pin to attach the stylus. A little experimentation may be in order here.

On your next test, you might try something like a For-Next loop to tell it to "print" a defined number of lines and see if it stops normally.

My printer is currently down so I can perfect the perpendicularity of the X-Y axis, but should be back running in a day or so.

Great work!

Mike

I believe the styli need to be present the final paragraph in the quote taken from this site seems to confirm this.


http://www.worldofspectrum.org/faq/refe ... m#Printers




"ZX Printer
The ZX Printer was released in 1981 and is compatible with the ZX80 (with ROM upgrade), ZX81 and ZX Spectrum. It is an extremely compact 32 column printer which uses aluminium coated paper. The printed image is 'burned' onto the surface of the paper by two metal pins which travel across the paper. A voltage is passed through these pins which causes a spark to be produced, leaving a black dot. See the documentation section if you need a copy of the original manual or service guide. The ZX Printer is addressed in the same way as the Alphacom 32 and Timex TS2040, with the following notes:

D0 and D7 are both latched so that they remain high until the computer writes something to the printer. So even if you don't make use of the information you've read in, you should output an instruction (with appropriate data) to reset the latches until the next signal. These bits may be in either state on switch on, and aren't affected by the feed button.

The paper detect signal is also used internally by the printer to make sure that the styli stop off the paper. Note that if power is applied to the stylus, the paper signal will go high even if the printer is between scans, so the stylus must be turned off before attempting to detect the edge of the paper."


The noise is quite normal for this device.

Quote taken from here..

http://www.worldofspectrum.org/hardware/rep1.html

"Noise from plain gears
The noise is generated by the plain gears which drive the optical reader and the helical gears which provide the paper feed through two worm wheel drives.
Sinclair designs show very high quality innovative thinking in system design, but do tend to have a basic lack of technique in the more mundane engineering fields. There are several inexpensive ways of producing low noise drives and this design would have benefited enormously if some way could have been found to incorporate such techniques."


This page may also be of interest..

https://faqwiki.zxnet.co.uk/wiki/ZX_Printer

Thanks for pitching in, Moggy. Since I have Francois' styli held captive for the moment we'll have to wait until I get them back to him before a real test can commence.

I searched for hours to find the .016" music wire that came in and it is noticeably thicker than the wire used on the stylus. Not one to leave well enough alone, I spent more time today and found the correct 0.010" wire which is on order. As soon as it comes in and get a couple of prototypes dimensioned I will get Francois' back to him.



Mike

Here are some pictures:

The TPU belt just after printing and before post "cleaning"



The belt on the printer after its first dry run. Notice how the belt got dirty because of the dirty sprockets. You can also see the small posts, cleaned the best I could.



Another view from the top



François

Not sure if those involved are aware but I'll mention it anyway.

DO NOT clean the rubber platen roller as it's conductive and forms part of the electrical circuit, cleaning it usually means faint or no print at all.

Moggy wrote: ↑Fri Apr 27, 2018 2:42 pm Not sure if those involved are aware but I'll mention it anyway.

DO NOT clean the rubber platen roller as it's conductive and forms part of the electrical circuit, cleaning it usually means faint or no print at all.

Good point. I knew but I had forgotten. I was about to clean it with IPA as it has no grip anymore and slide on the paper instead of pulling on it. Would rubbing with a fine sandpaper could work without compromising its conductivity ? Any other idea how to restore grip ?

François

Great looking belt! I really like the way the teeth fit. Good to know that about cleaning.

mhudson52 wrote: ↑Wed Apr 25, 2018 11:08 pm
I searched for hours to find the .016" music wire that came in and it is noticeably thicker than the wire used on the stylus. Not one to leave well enough alone, I spent more time today and found the correct 0.010" wire which is on order. As soon as it comes in and get a couple of prototypes dimensioned I will get Francois' back to him.


Mike

McMaster has some 0.005", 0.008", 0.009", 0.010", 0.012", 0.014" etc

https://www.mcmaster.com/#music-wire/=1clhgyf

François

The platen roller grip on this printer is fairly good so I would look to the pinch rollers that hold/space the paper and see if they are spaced correctly and not causing any binding,if the tube-spacer-inside the-paper method as described in some articles is used incorrectly then it might cause the rollers to be spaced too wide causing excess friction.

Hi Mike,

You'll be happy to look at this



Congratulations, you did it.

Francois

Tears of joy.