Re: Model 1 video tear (common) problem - how to fix?

Looking at your display, I can see you're not in the US. That will
complicate
things, but not overly so.

The problem with all the 'tears' on the model 1 video was that the 'white
level'
shifted things up and it would loose sync. In the US, this usually
manifested itself
when you displayed an entire white screen, but would occasionally also do
something similar to what you show when you just had a full screen of
characters.

The fix was a resistor change on the interface card in the monitor.

The US version had a small RCA black and white TV with the tuner card
removed and the TRS-80 interface card plugged in to the socket/slot for
the tuner. The TRS-80 logo on the monitor just covered up the channel
selector knob holes. I can only assume your monitor is similar.

Anyway, the fix for the US problem was NOT to replace the parts with the
same values, but to change the resistors and I seem to recall a cap as well.
The fix for your country may be similar, but I wouldn't know...

Mike



"Ian Mavric" <ianmav@xxxxxxxxxxxxxxx> wrote in message
news:Bp-dnfscOtq-WBbVnZ2dnUVZ_vadnZ2d@xxxxxxxxxxxxxxxxxx
Hi everybody,

I've got a Mod 1 here which exhibits the video tear (unable to sync
properly) problem which I am trying to fix. In fact, of my 6 Model 1s, 3
of
them have this problem, which makes me think that the problem might be
affecting a large percentage of Mod 1s out there.

Here is the @9 display on the M1 in question:


http://ianmav.customer.netspace.net.au/auctions/Picture%20or%20Video%201114.jpg

The monitor has been adjusted with a good M1, and you can see the picture
is
not central (not even close) and the sides concave (both are).

So far on this unit I've changed:

Z6, Z57, Z10, Z11, Z41
C20, C21, C26, C27
Q1, Q2, Q5
Z1, Z2

The voltages were adjusted to properly ready +12DVC, +5VDC, and -5VDC, and
with the roms plugged in it asks the normal "Memory Size?"

Given the (apparent) vastness of the problem (I've seen this problem on
probably 25 machines in my lifetime, and most of them I've parted-out
being
unable to solve the problem), I'm sure someone out there has fixed it...

Does anyone know which part/parts are causing this problem?

Thx.




.

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