Differences in height of characters on a TRS-80 Model 16

[retrobecanes]

The height of the rows of characters on the screen seem to be the smallest at the top of the screen and it increases with each successive row down to the bottom of the screen.
As a result the characters at the top are a lot shorter than the characters at the bottom of the screen.
What can I do to fix this?

 

[daver2]

That sounds like a monitor issue to me (on first thought).

I will look up the monitor schematics.

Dave

 

[daver2]

See PDF page 88 of 92 at https://www.progettosnaps.net/manuals/pdf/trs80m16.pdf.

There is a potentiometer (R25 I think) that is marked "VERT. LIN." (Vertical Linearization):



This potentiometer may have failed completely - or require adjustment. Sometimes the wiper of the potentiometer gets 'dirty' and fails to make proper contact with the carbon track. Note the position of the potentiometer's wiper and just adjust it slightly one way then the other (with the power OFF) and see if that fixes the problem.

If not, I will give you some other simple checks that you can perform to see if the control is faulty or not.

Of course, it may not be the potentiometer itself, but some of the associated capacitors (e.g. C8 and/or C9).

Dave

 

[retrobecanes]

@daver2 thanks for helping.
The numbering system on my model 16 video board is very different and I can’t seem to locate the vertical linearity pot. See picture below.
Any thoughts?

 

[Chuck(G)]

How about R211--looks like there's a legend (partly obscured in the photo) that says "V LIN" right by it. Being next to the SIZE trimmer, the position is correct.

 

[daver2]

+1, they have gone to the trouble of marking them on the screen print, so use that as your reference.

Dave

 

[retrobecanes]

You are right, I had missed it. I will see if it works. I am also recapping the whole board.