TS 2068 Video Questions
5 messages · 2004-07-08 → 2004-10-10 · Yahoo Group era · View archive on archive.org
Participants: bryankvines, Jeff Burrell, Jarek Adamski, aralbrec
Preserved from the Timex/Sinclair 2068 Yahoo Group (2001–2019), which is no longer online. Text reproduced from the archive.org archive; email addresses masked.
Messages
1. TS 2068 Video Questions
bryankvines · Thu, 08 Jul 2004 15:22
Howdy folks.
I've got a couple of questions regarding the video output of the TS2068.
(1) If I build the RGB interface as described in the TS2068 tech manual, what sort of RGB
monitor can I expect to be able to drive? Would an old CGA or EGA-type monitor work?
Not that I have one, I'm just trying to figure out what I would need to buy.
(2) I note that there's at least one S-Video hack for the Spectrum; is there a way to get S-
Video out of the T2068, possibly by pulling signals from the LM1889 in the video
modulator circuit?
The four pins of an S-Video connector are Ground, Ground, Chrominance (the color info),
Luminance (the black & white or brightness info). Composite video is Ground and a
combined Chrominance/Luminance signal. Pin 13 on the 1889 is Chroma, which I assume
is Chrominance, but I don't see anything I would recognize as "Luminance".
I guess basically what I want to do is come up with SOME way to improve the video output
of my TS2068, which currently could best be described as "Ugh."
Thanks!
--
Bryan Vines
2. Re: [ts2068] TS 2068 Video Questions
Jeff Burrell · Thu, 8 Jul 2004 14:50:
Bryan;
According to the schematic in the 2068 TM pins 34
and 35 provide the B-Y and R-Y signals to the 1889.
These are Blue-Intensity and Red-Intensity signals
which, if I remember my old television teaching days,
are the two NTSC matrix signals that are modulated
onto the in-phase and quadrature color subcarrier.
Frankly, I don't believe several areas of the video
portion of the schematic. I suspect that the Y signal
is only connected to VR1 since that is the only way
Q5 (PN2222) can be turned on. I also suspect the base
of Q4 is connected through C75 to U4-13 and not to
ground at U3 for the same reason.
At any rate, U4-13 would seem to be chroma and the
top end of VR1 should be the luma/sync. It is
unlikely that the relative levels of the U and chroma
are correct, so you'd need to attenuate one or the
other and possibly phase shift one to align them in
time.
I have used the baseband composite output and it's
OK - certainly better than the RF output.
If I were going to do an RGB interface, I'd get a
wideband opamp (say LT1814) and rematrix the Y, U, and
V signals to regen the RGB. Then a sync separator
circuit similar to the one seen in the TM and you have
the signals you need. You may still need to combine
the sync signals with the green channel (I remember
this used to be typical on the old RGB montiors). Not
easy, but doable. In any case the bandwidth and
quality will suffer from all of this processing.
As to monitors, you would need an analog RGB monitor
with standard 60Hz/15750Hz rates (basically a TV
without all of the NTSC processing circuitry).
CGA/VGA monitors use TTL inputs and are completely
incompatible with the RGB signals the 2068 outputs.
Besides, the CGA monitor is the only one guaranteed to
work at 60/15750. VGA is out because the horizontal
rate is about 21KHz.
It would seem the S-video soulution would be the
best and easiest to implement. I hope this rambling
dissertation helps.
--- bryankvines <[email]> wrote:
> Howdy folks.
>
> I've got a couple of questions regarding the video
> output of the TS2068.
> (1) If I build the RGB interface as described in
> the TS2068 tech manual, what sort of RGB
> monitor can I expect to be able to drive? Would an
> old CGA or EGA-type monitor work?
> Not that I have one, I'm just trying to figure out
> what I would need to buy.
>
> (2) I note that there's at least one S-Video hack
> for the Spectrum; is there a way to get S-
> Video out of the T2068, possibly by pulling signals
> from the LM1889 in the video
> modulator circuit?
>
> The four pins of an S-Video connector are Ground,
> Ground, Chrominance (the color info),
> Luminance (the black & white or brightness info).
> Composite video is Ground and a
> combined Chrominance/Luminance signal. Pin 13 on the
> 1889 is Chroma, which I assume
> is Chrominance, but I don't see anything I would
> recognize as "Luminance".
>
> I guess basically what I want to do is come up with
> SOME way to improve the video output
> of my TS2068, which currently could best be
> described as "Ugh."
>
> Thanks!
> --
> Bryan Vines
>
>
>
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3. Re: TS 2068 Video Questions
Jarek Adamski · Fri, 09 Jul 2004 11:24
Hello,
--- In [email], "bryankvines" <bryankvines@y...> wrote:
> I've got a couple of questions regarding the video output of
> the TS2068.
I can partly answer, as I never tried sych things.
(I use the AVerMedia JOYTV scandoubler with composite
output and SVGA monitor.)
> Would an old CGA or EGA-type monitor work?
CGA should work, perhaps you can need slightly correct
the synchronization. EGA needs more work on the
synchronization - nay work, may not (unless you know
how to modify its circuit to 60Hz). All Multisync
monitors should work. You can also connect a TV with
RGB input (check the levels - may be TTL or 0.75V pp).
> Pin 13 on the 1889 is Chroma, which I assume is
> Chrominance, but I don't see anything I would
> recognize as "Luminance".
Luminance is the /Y signal (inverted?) outgoing from
the ULA (pin 33).
Perhaps this can help, I'm not a specialist in matter
of video circuits.
Jarek Adamski
4. Re: TS 2068 Video Questions
aralbrec · Fri, 16 Jul 2004 18:01
--- In [email], "bryankvines" <bryankvines@y...> wrote:
> (1) If I build the RGB interface as described in the TS2068 tech
manual, what sort of RGB
> monitor can I expect to be able to drive? Would an old CGA or EGA-
type monitor work?
> Not that I have one, I'm just trying to figure out what I would
need to buy.
Just to add here, the JLO expansion card thing
(the one with four slots where the disk interface card,
etc. plugged into) had this RGB interface constructed
on it. The JLO manual also had some discussion on
how to connect to a monitor and monitor brands.
I don't have my manual with me, but maybe someone
else has it? It may have been an insert rather
than part of the manual itself.
Personally, I was able to get pretty good
video out of the composite monitor output
on the back.
Alvin
5. Re: TS 2068 Video Questions
bryankvines · Sun, 10 Oct 2004 04:57
Hey everyone,
I just wanted to report that the RGB interface schematic provide on page 57 of the 2068
tech manual works very, very well. I'm impressed. I'm driving a Commodore 1084S
monitor, and the video is rock-solid.
I still have the circuit sitting on the solderless breadboard. I couldn't find any 64-pin edge
connectors, so I butchered a couple of old 34-pin floppy drive connectors (ribbon cable
type) and superglued them together. Super kludgey, but hey, it works. :) I'm not sure
whether I want to build the circuit into the 2068 or put it in an expansion box.
Anyway, I'm happy/excited. This is fun. :)
--
Bryan Vines
--- In [email], "bryankvines" <bryankvines@y...> wrote:
> Howdy folks.
>
> I've got a couple of questions regarding the video output of the TS2068.
> (1) If I build the RGB interface as described in the TS2068 tech manual, what sort of
RGB
> monitor can I expect to be able to drive? Would an old CGA or EGA-type monitor work?
> Not that I have one, I'm just trying to figure out what I would need to buy.