30 Jun
2003
30 Jun
'03
12:53 p.m.
I have read a lot about the SWTPC TV Typewriter, and I am interested in
how people modified a black and white TV for a video monitor. I have an
old black and white set that I thought would be fun to modify for use
as a video monitor. Now, granted, I don't really need another composite
monitor, I have plenty of old Apple monitors that will do the same
thing, I just thought it would be fun, since it would be a challenge to
find where to input the signal and how to do it. I found the PDF of
part of the SWTPC TV Typewriter manual on a web site, and it explains
the process, although not in great detail, and references a circuit
diagram of what needed to be added, but the diagram is nowhere to be
found. Does anyone have any instructions or hints that they may be able
to give me? Has anyone done this before? Any advice would be
appreciated.
Ian Primus
ian_primus(a)yahoo.com
30 Jun
30 Jun
1:22 p.m.
I would think the easiest and cheapest way is to use a plain old RF
modulator box that will put composite video on to channel 3 or 4.
I've taken apart one or two and they seem to have little more than a
few coils and small parts, a far cry from the rack mounted cable TV
modulators I just picked up(ooohh... so many trimmer caps and
coils...). I don't know a whole lot about it, but I'm slowly learning
as my interest in fast scan ATV increases... The converter box I have
goes with my TI-99, I probably have one in the box with my C-64, too.
I think you can still get them at Radio Shack. Otherwise, all you
need to do is dump the composite signal into an AM modulator and then
through a transmitter that the TV can pick up. I would guess these
small boxes having only coils just use a tuned circuit for channel 3
and the voltage from the composite signal to provide the signal. But
then I'm just guessing, I've never poked and prodded those little
boxes very much, I think I'll go do that now(when I find it,
anyhow...).
I have read a lot about the SWTPC TV Typewriter, and I
am interested
in how people modified a black and white TV for a video monitor. I
have an old black and white set that I thought would be fun to
modify for use as a video monitor. Now, granted, I don't really need
another composite monitor, I have plenty of old Apple monitors that
will do the same thing, I just thought it would be fun, since it
would be a challenge to find where to input the signal and how to do
it. I found the PDF of part of the SWTPC TV Typewriter manual on a
web site, and it explains the process, although not in great detail,
and references a circuit diagram of what needed to be added, but the
diagram is nowhere to be found. Does anyone have any instructions or
hints that they may be able to give me? Has anyone done this before?
Any advice would be appreciated.
--
/------------------------------------\
| http://jrollins.tripod.com/ |
| KD7BCY kd7bcy(a)teleport.com |
\------------------------------------/
1:48 p.m.
Those little RF boxes don't really convert from composite to RF, they
just provide a switch and a connection to a TV antenna input. The
output signal from the computer is already RF. Actually, what I
generally do with machines that have RF out only (i.e. Atari 2600) is
to just go to Radio Shack and get an RCA to F type screw connector
adapter. It's much smaller, and gives much better picture than those
little metal boxes do. It just doesn't provide a switch. What I want to
do is to actually input a true composite video signal into the TV. Of
course, this can be done by using a broken VCR with A/V inputs and a TV
output, but I want to modify the set as a learning experience, as well
as to create something useful for old computers.
Ian Primus
ian_primus(a)yahoo.com
On Monday, June 30, 2003, at 09:17 PM, John Rollins wrote:
I would think the easiest and cheapest way is to use a
plain old RF
modulator box that will put composite video on to channel 3 or 4. I've
taken apart one or two and they seem to have little more than a few
coils and small parts, a far cry from the rack mounted cable TV
modulators I just picked up(ooohh... so many trimmer caps and
coils...). I don't know a whole lot about it, but I'm slowly learning
as my interest in fast scan ATV increases... The converter box I have
goes with my TI-99, I probably have one in the box with my C-64, too.
I think you can still get them at Radio Shack. Otherwise, all you need
to do is dump the composite signal into an AM modulator and then
through a transmitter that the TV can pick up. I would guess these
small boxes having only coils just use a tuned circuit for channel 3
and the voltage from the composite signal to provide the signal. But
then I'm just guessing, I've never poked and prodded those little
boxes very much, I think I'll go do that now(when I find it,
anyhow...).
I have read a lot about the SWTPC TV Typewriter,
and I am interested
in how people modified a black and white TV for a video monitor. I
have an old black and white set that I thought would be fun to modify
for use as a video monitor. Now, granted, I don't really need another
composite monitor, I have plenty of old Apple monitors that will do
the same thing, I just thought it would be fun, since it would be a
challenge to find where to input the signal and how to do it. I found
the PDF of part of the SWTPC TV Typewriter manual on a web site, and
it explains the process, although not in great detail, and references
a circuit diagram of what needed to be added, but the diagram is
nowhere to be found. Does anyone have any instructions or hints that
they may be able to give me? Has anyone done this before? Any advice
would be appreciated.
--
/------------------------------------\
| http://jrollins.tripod.com/ |
| KD7BCY kd7bcy(a)teleport.com |
\------------------------------------/ 
2:21 p.m.
First - the TV itself is needed. When a unit is to hand, look up the
Sams Photofact for it - this will be the comprehensive data and
documentation package - numerous schematics, pictorials with all the
components marked, etc. I think they're, what - $15? Dunno, but it's
money well spent.
Then - most BW TVs from the 60s and early 70s (if tube) were
series-string type - they had no power transformer, rather the incoming
mains current was tied to a resistor string to power the tube filaments
and to diodes for the various DC voltages - this meant that one 'side' of
the mains always was connected to the metalwork of the set - thus posing a
signifigant hazard to persons **and to any other gear hooked up to the set
that didn't share the same ground polarity!!**
It is A Very Good Thing if you can score a simple mains<->mains
isolation transformer, just 110V in and 110V out, 1:1 windings. Be sure
its a two winding device *NOT* an 'autotransformer', which is typical of
most 'travel convertors' one buys for Journeying to dark and wild corners
of the world (Munich for instance). If you can't find a 100Watt (or so)
1:1 unit, you can make one by getting two identical power transformers and
and attaching thier secondaries to each other, thus a 1:5:5:1 for example.
Just be sure that the transformers will carry the load of the BW set
(total watts).
Now, using the Photfact schematics and data from the Web, here, and
other sources - locate the video and sync-separator circuits. Determine
the polarities of the signals involved, and what relative levels the
circuits want.
Buld up an interface circuit to accept TTL level (or standard NTSC
composite analog data) and feed it at the right levels and polarity to the
video input stage of the BW TV.
Power up both units and test.
After the Fire Captain tells you it's all right to go back inside,
salvage what you can from the sodden charcoal mess and try to find a new
hobby that carries less intrinsic risk.
;}
No but, seriously - after you have the BW TV set data, it is not a
particularly onerous task to suss out the points in the circuit where one
could ostensibly inject an external video sig.
I might also suggest that you look into opto-isolating the video feed
from your computer, just to be safe. Letting the Magic
Smoke out of one's
vintage computers is not exactly the best way for further
knowledge and
gain experience, though Mr. Wilde might have disagreed with me.
But hey - he's dead.
Cheers
John
2:48 p.m.
--- Ian Primus <ian_primus(a)yahoo.com> wrote:
Those little RF boxes don't really convert from
composite to RF, they
just provide a switch and a connection to a TV antenna input. The
output signal from the computer is already RF.
For the little ones with just a switch and a coil, that's all true. In
the case of a VIC-20, there _is_ an external composite adapter that
hangs off the DIN-5 for power, composite video and sound.
I _think_ the one for the TI-99/4a was also a true external RF modulator.
-ethan
3:16 p.m.
On Mon, 30 Jun 2003, Ian Primus wrote:
Those little RF boxes don't really convert from
composite to RF, they
The Sup'R'Mod II DOES convert from composite to RF (Channel 34).
Most of the other RF modulator boxes are channel 3, or 4, or switchable
between 3 and 4.
But some people don't know the difference between an RF modulator box and
a switch box.
But modifying a TV for composite input is a good project.
Maybe start with Don Lancaster's book(s) on the subject.
... and be careful! You will be working near high voltages; and some are
hot chassis
--
Grumpy Ol' Fred cisin(a)xenosoft.com
just provide a switch and a connection to a TV antenna
input. The
output signal from the computer is already RF. Actually, what I
generally do with machines that have RF out only (i.e. Atari 2600) is
to just go to Radio Shack and get an RCA to F type screw connector
adapter. It's much smaller, and gives much better picture than those
little metal boxes do. It just doesn't provide a switch. What I want to
do is to actually input a true composite video signal into the TV. Of
course, this can be done by using a broken VCR with A/V inputs and a TV
output, but I want to modify the set as a learning experience, as well
as to create something useful for old computers.
Ian Primus
ian_primus(a)yahoo.com
On Monday, June 30, 2003, at 09:17 PM, John Rollins wrote:
> I would think the easiest and cheapest way is to use a plain old RF
> modulator box that will put composite video on to channel 3 or 4. I've
> taken apart one or two and they seem to have little more than a few
> coils and small parts, a far cry from the rack mounted cable TV
> modulators I just picked up(ooohh... so many trimmer caps and
> coils...). I don't know a whole lot about it, but I'm slowly learning
> as my interest in fast scan ATV increases... The converter box I have
> goes with my TI-99, I probably have one in the box with my C-64, too.
> I think you can still get them at Radio Shack. Otherwise, all you need
> to do is dump the composite signal into an AM modulator and then
> through a transmitter that the TV can pick up. I would guess these
> small boxes having only coils just use a tuned circuit for channel 3
> and the voltage from the composite signal to provide the signal. But
> then I'm just guessing, I've never poked and prodded those little
> boxes very much, I think I'll go do that now(when I find it,
> anyhow...).
>
>
>> I have read a lot about the SWTPC TV Typewriter, and I am interested
>> in how people modified a black and white TV for a video monitor. I
7:49 p.m.
> I would think the easiest and cheapest way is to
use a plain old RF
> modulator box that will put composite video on to channel 3 or 4. I've
> taken apart one or two and they seem to have little more than a few
> coils and small parts, a far cry from the rack mounted cable TV
> modulators I just picked up(ooohh... so many trimmer caps and
> coils...). I don't know a whole lot about it, but I'm slowly learning
> as my interest in fast scan ATV increases... The converter box I have
> goes with my TI-99,
Those little RF boxes don't really convert from
composite to RF, they
just provide a switch and a connection to a TV antenna input.
Communication error!
While you where refering to the common (video game) switch boxes,
John did mention modulators! they are usualy the same size (ok,
the TI one is a true brick), but do what they are named, modulate
the composite signal onto a TV carrier.
The one I like most is the Amiga 520 (?).
Gruss
H.
--
VCF Europa 5.0 am 01./02. Mai 2004 in Muenchen
http://www.vcfe.org/
2:51 p.m.
----- Original Message -----
From: "John Rollins" <kd7bcy(a)teleport.com>
To: <cctalk(a)classiccmp.org>
Sent: Monday, June 30, 2003 8:17 PM
Subject: Re: Modifying a B&W TV for composite video input
I would think the easiest and cheapest way is to use a
plain old RF
modulator box that will put composite video on to channel 3 or 4.
I've taken apart one or two and they seem to have little more than a
few coils and small parts, a far cry from the rack mounted cable TV
modulators I just picked up(ooohh... so many trimmer caps and
coils...). I don't know a whole lot about it, but I'm slowly learning
as my interest in fast scan ATV increases... The converter box I have
goes with my TI-99, I probably have one in the box with my C-64, too.
I think you can still get them at Radio Shack. Otherwise, all you
need to do is dump the composite signal into an AM modulator and then
through a transmitter that the TV can pick up. I would guess these
small boxes having only coils just use a tuned circuit for channel 3
and the voltage from the composite signal to provide the signal. But
then I'm just guessing, I've never poked and prodded those little
boxes very much, I think I'll go do that now(when I find it,
anyhow...).
<SNIP> --
/------------------------------------\
| http://jrollins.tripod.com/ |
| KD7BCY kd7bcy(a)teleport.com |
\------------------------------------/
The SWTPC TV-Typewriter outputs baseband video, which is also a RF (radio
frequency) signal. What it is NOT is modulated. That is why it is called
baseband. Baseband is also sometimes called DIRECT video.
The Commodore 64 puts out a RF signal on TV channel 3 or 4 (switchable),
which is usually connected to a TV set using a RF SWITCH (required by the
FCC in the US). That switch is NOT a RF modulator, it is an isolation
device, to prevent your connection of your computer to an outside antenna
and the broadcasting your computer signal to your neighborhood; that
broadcast would be considered as unwanted interference by the FCC, thus the
isolation switch.
Please not that in the rest of this post that I am NOT talking about a RF
"switch" as described above, but about an actual RF modulator vs. baseband
video.
In my opinion, based on personal experience, it is cheaper, easier (if you
know what to do), and certainly provides a better picture if you use the
direct video approach when connecting a baseband device like the
TV-Typewriter to a TV set. When you use a RF modulator you cause the signal
to be modulated and then demodulated (by the TV); every time this is done,
some of the information is lost in the process. When you use the direct
video, little of the signal is lost or attenuated and the full bandwidth of
the TV's electronics are available. The lossy signal from a (cheap) RF
modulator causes the picture to be fuzzy or wavy and may not even be stable.
I used to have one of these TV-Typewriters and even modified it for 24x80
display by doubling the ram and making mods to the timing of the board.
There was an article published in one of the electronics / computer
magazines that showed how to do this, and it worked exactly as shown. I used
my TV Typewriter with a small black & white TV modified to have an RCA jack
for baseband RF input. It worked well for many years. My computer at that
time was a KIM-1, expanded with S-100 peripherals and memory, using a KIMSAI
motherboard / S-100 interface.
How one connects baseband to a TV depends on the TV itself; many small sets
have a "hot" chassis, that is to say that the chassis is connected to one
side of the 110 VAC mains, and insulated from the user by the plastic case.
This kind of TV can get you KILLED if you mess with it opened up or can
possibly blow your computer up if you connect to it improperly. This
procedure is therefore NOT recommended to the non-technically skilled. The
actual circuit can be as simple as a capacitor and a few resistors (for DC
restoration). What is done is to disconnect the TV's tuner and inject the
signal where the tuner did. Many people used a toggle switch so that the TV
or Video function could be selected as needed.
For what it is worth, TV doesn't use AM (Amplitude Modulation), it uses a
modulation technique called Vestigial Sideband, from before the days when
Single Sideband modulation was understood.
Also, RF modulators are ACTIVE devices requiring a power supply and ground
to operate; they do not derive their power from the signal; at least none
that I've ever seen do. With today's ultra-low powered devices, it may be
possible, but I doubt that anyone has gone to the trouble to design an
ultra-low power RF modulator considering that many TV's already have
composite (baseband having chrominance & luminance combined) video inputs.
Some specialty monitors, like those sold for use with the Commodore 64,
accepted separate chrominance (color) and luminance (brightness) inputs in
an attempt to give a better picture. The Commodore 64 has a special jack on
its back to connect to these monitors and uses a special cable to make that
connection.
Stuart Johnson
former electronics technician and present computer nut
4:48 p.m.
Ian Primus writes:
I have read a lot about the SWTPC TV Typewriter, and I
am interested in
how people modified a black and white TV for a video monitor. I have an
old black and white set that I thought would be fun to modify for use as a
video monitor. Now, granted, I don't really need another composite
monitor, I have plenty of old Apple monitors that will do the same thing,
I just thought it would be fun, since it would be a challenge to find
where to input the signal and how to do it. I found the PDF of part of the
SWTPC TV Typewriter manual on a web site, and it explains the process,
although not in great detail, and references a circuit diagram of what
needed to be added, but the diagram is nowhere to be found. Does anyone
have any instructions or hints that they may be able to give me? Has
anyone done this before? Any advice would be appreciated.
Ian Primus
ian_primus(a)yahoo.com
First you have to deterimine that the set isn't hot chassis, and has a
transformer operated power supply. Then get a Sams's Photofact, so you can
find where the video detector diode is.
Somewhere in there is a point where you can inject baseband video. Not
knowing the schematic, your guess is as good as mine. If you know basic
electronics, you can look for a point where the scope video is the right
polarity, and about 1v p-p and inject it there.
Gary Hildebrand
St. Joseph, MO
1 Jul
1 Jul
9:31 a.m.
I have read a lot about the SWTPC TV Typewriter, and I
am interested in
how people modified a black and white TV for a video monitor. I have an
old black and white set that I thought would be fun to modify for use
as a video monitor. Now, granted, I don't really need another composite
It's fun until you start working on a live-chassis set and you suddenly
apply mains across your video interface circuit and yourself....
Seriously, many large-screen (non-portable) B&W TVs have a live chassis
connected directly to one side of the mains (or worse to one side of a
bridge rectifier connected to the mains, so the chassis sits at half
mains voltage on average). Don't even think of adding a composite input
to such a set unless you connect the mains input to the secondary of a
double-wound isolating transformer. (OK, it is possible to isolate the
video input rather than the mains -- Radio Shack did on the original
Model 1 monitor, which has a hot chassis. But this is a lot harder to get
working right, and a lot more dangerous to experiment with).
Portable TVs that can also run off a 12V battery _normally_ have an
isolated PSU, but please check to be sure...
A circuit diagram of the set is _essential_. I am not sure where you are
-- if you're in the States, get the Sams Photofact for the set if you
can't get the original service manual. If you're in the UK, see if it was
covered in 'Radio and Television Servicing'.
Then all (!) you need to do is find the video detector stage and feed in
your composite signal at the output of that stage. Hopefully the sync
separater takes it's feed after that point (it's almost certain you can
find a point where this is the case) so you really can feed in a
composite signal and expect it to work.
-tony
10:46 a.m.
Tony wrote:
It's fun until you start working on a live-chassis
set and you suddenly
apply mains across your video interface circuit and yourself....
Yep. Nasty. Even with isolation still can get that ZAP!.
Seriously, many large-screen (non-portable) B&W
TVs have a live chassis
connected directly to one side of the mains (or worse to one side of a
bridge rectifier connected to the mains, so the chassis sits at half
mains voltage on average).
Every one you described for non-isolated sets are like this. Every
one, I'm referring to cheap color sets old or new. The - side of
rectifier bridge is "hot ground" in those. Very rare few I seen had
one diode and that was in old citizen sets usually 13" to 19". This
is really downright cheap. In those with non-isolated sets that
does have inputs, always have small signal isolation transformers and
or optical isolation. The others that is both hot/cold chassis be it
via flyback transformer like this one hitachi and about 7 yr old.
Other kind via SMPS is very common. Using mains isolation
transformer is *extremely rare*. In so many sets in 1
and half years of sets (cranks out about 30 sets every 5 days) I
worked on, only ONE did by design and that was really ancient Samsung
32" tv. So do your self a favor buy a newer used or new sets and
hook up things without modifying that set or be hackish on old stuff,
splice it on that internal mains wires a isolation transformer
and bolt it inside that set.
Portable TVs that can also run off a 12V battery
_normally_ have an
isolated PSU, but please check to be sure...
13" is considered portable also and almost always are hot chassis by
design. In RCA 13" AC/DC tv it's hot chassis, to run on 12V RCA
puts in an DC to DC converter! I'm talking about those that is made
from 1991 onwards. ( chassis TX8xx series) But what
nice about this
13" RCA has no B+ regulator and the pix is very stable
because of
direct control of horizontal pulses to regulate power in flyback
itself. Hence very little horizontal size swelling or jaggies with
bright parts. The later 13" RCA tvs gained mono audio and video
input after it got the SMPS but basic design of pervious 13" RCA
mostly unchanged.
By contrast I have seen so many other sets that doesn't have good
handle on the HV regulation the pix width swells with bright parts
and shrinks with darks. This drives me nuts. Those have same
chassis but has pincushion feature added (it is a module in RCA) had
better handle on this but not 100%.
If the vertical edges isn't straight (more of a flared or jaggies)
that what I mean by this poor HV regulation.
A circuit diagram of the set is _essential_. I am not
sure where you are
11:32 a.m.
Tony wrote:
True, but the mains is (IMHO) a lot more nasty than the EHT to the final
anode...
It's fun until you start working on a
live-chassis set and you suddenly
apply mains across your video interface circuit and yourself....
Yep. Nasty. Even with isolation still can get that ZAP!. Seriously, many large-screen (non-portable)
B&W TVs have a live chassis
connected directly to one side of the mains (or worse to one side of a
bridge rectifier connected to the mains, so the chassis sits at half
mains voltage on average).
Every one you described for non-isolated sets are like this. Every
one, I'm referring to cheap color sets old or new. The - side of rectifier bridge is "hot ground" in those.
Very rare few I seen had
one diode and that was in old citizen sets usually 13" to 19". This
is really downright cheap. In those with non-isolated sets that
does have inputs, always have small signal isolation transformers and
Other than an old, partly valved B&O colour TV, which had a transformer
isolated audio output (and no other I/O), I have never seen isolating
transformers for the signals on a UK TV.
or optical isolation. The others that is both
hot/cold chassis be it
via flyback transformer like this one hitachi and about 7 yr old.
Other kind via SMPS is very common. Using mains isolation
transformer is *extremely rare*. In so many sets in 1
Most UK TVs have an isoleted SMPSU these days
from 1991 onwards. ( chassis TX8xx series) But what
nice about this
13" RCA has no B+ regulator and the pix is very stable because of
direct control of horizontal pulses to regulate power in flyback
Are US TVs really so far behind European ones? We've had fully regulated
supply lines, including EHT, for many years... Over here we'd not accept
a TV where the picture changed in size with the average beam current!
A circuit
diagram of the set is _essential_. I am not sure where you are
>From original makers is asolute best please. Especially from RCA much better info and also have writings, and RCA also
put out
training manuals for particular chassis.
JVC doesn't do much on this just an schematic, troubleshooting charts
and raft of adjustment instructions in slim floppy books. Same thing
with Samsung, marginally better but their TV isn't my taste since it
tinkered too much with circuit that it is hard to troubleshoot.
Samsung liked to use philips ICs which is lousy and using AKB for
The advantage of Philips ICs is that you can generally get full data
sheets on them. And there's nothing wrong with them if correctly used!
only way u can probe around. Their philips schematics
is locked and
I can rememebr when Philips would send you a service manual free of
charge if you asked nicely.... Oh well :-(
-tony
7616
days inactive
7617
days old
11 comments
10 participants
participants (10)
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ard＠p850ug1.demon.co.uk -
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erd_6502＠yahoo.com -
ghldbrd＠ccp.com -
Hans.Franke＠mch20.sbs.de -
ian_primus＠yahoo.com -
jpero＠sympatico.ca -
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kd7bcy＠teleport.com -
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