Chroma/Luma (or s-video) Problems on 128DCR

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Chroma/Luma (or s-video) Problems on 128DCR

J. Alexander Jacocks
All,

I've asked a number of places, but I thought that I would get the thoughts of the fine folks, here, as well.

I have a C128DCR NTSC that has issues with signal level on chroma, from the video connector.  Signal levels seem to be just fine at the RF connector, and the picture is fine, from that connector.  From the video connector, to a modern TV or monitor, the picture is excellent quality, but monochrome.  Checking the output pins on the video connector, the level is very low, on the chroma signal.

I have changed:
1) VIC-II (8564) 
2) Clock generator (8701) 
3) Crystal (NTSC/14 MHz) 
4) RF modulator

All to no avail.  I'm scratching my head trying to determine what else could be awry.  I looked at the traces on the board, and I see no damage, between the RF modulator and the video connector.

Any other suggestions would be most welcome.

Thanks!
- Alex
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Re: Chroma/Luma (or s-video) Problems on 128DCR

Francesco Messineo
On Wed, May 2, 2018 at 4:55 PM, J. Alexander Jacocks <[hidden email]> wrote:

> All,
>
> I've asked a number of places, but I thought that I would get the thoughts
> of the fine folks, here, as well.
>
> I have a C128DCR NTSC that has issues with signal level on chroma, from the
> video connector.  Signal levels seem to be just fine at the RF connector,
> and the picture is fine, from that connector.  From the video connector, to
> a modern TV or monitor, the picture is excellent quality, but monochrome.
> Checking the output pins on the video connector, the level is very low, on
> the chroma signal.
>
> I have changed:
> 1) VIC-II (8564)
> 2) Clock generator (8701)
> 3) Crystal (NTSC/14 MHz)
> 4) RF modulator

according to the schematic, there're two jumpers that select different
levels of the chroma signal:
J10 and J11 and associated resistive divider R13-R14. I would check
these components as second step after having excluded EMI42 filter.
The filter should have basicly 0 ohms dc resistance between input and
output and basicly infinite resistance between either input or output
to GND.
Of course, you should make sure the "about 0 ohms" dc resistance is
present from the J10/J11 jumpers to the chroma output pin too, to rule
out any track/solder problem.
Almost all you changed, couldn't have been the problem judging from
the tests you describe.
I would have first checked with another monitor/TV.
HTH
Frank IZ8DWF

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Re: Chroma/Luma (or s-video) Problems on 128DCR

J. Alexander Jacocks
On Wed, May 2, 2018 at 11:12 AM, Francesco Messineo <[hidden email]> wrote:
On Wed, May 2, 2018 at 4:55 PM, J. Alexander Jacocks <[hidden email]> wrote:
> All,
>
> I've asked a number of places, but I thought that I would get the thoughts
> of the fine folks, here, as well.
>
> I have a C128DCR NTSC that has issues with signal level on chroma, from the
> video connector.  Signal levels seem to be just fine at the RF connector,
> and the picture is fine, from that connector.  From the video connector, to
> a modern TV or monitor, the picture is excellent quality, but monochrome.
> Checking the output pins on the video connector, the level is very low, on
> the chroma signal.
>
> I have changed:
> 1) VIC-II (8564)
> 2) Clock generator (8701)
> 3) Crystal (NTSC/14 MHz)
> 4) RF modulator

according to the schematic, there're two jumpers that select different
levels of the chroma signal:
J10 and J11 and associated resistive divider R13-R14. I would check
these components as second step after having excluded EMI42 filter.
The filter should have basicly 0 ohms dc resistance between input and
output and basicly infinite resistance between either input or output
to GND.
Of course, you should make sure the "about 0 ohms" dc resistance is
present from the J10/J11 jumpers to the chroma output pin too, to rule
out any track/solder problem.
Almost all you changed, couldn't have been the problem judging from
the tests you describe.
I would have first checked with another monitor/TV.

Frank,

I did indeed check with at least 2 TVs, and both showed the same issue, so it's not the TV/monitor.  I will open up my 128DCR this evening, and check the levels on those resistors and jumpers.

I didn't think that any of the parts were the problem, except for the RF modulator, which since the levels are low after the modulator, I thought might be faulty.

Thanks!
- Alex 

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Re: Chroma/Luma (or s-video) Problems on 128DCR

traymond160
Hi,

I hooked an older Bread Bin up to my Theatre view TV, only on the 
front panel has the RCA connectors for video and sound.

If you have just the C64 user manual it has the Video connector pinouts,
of course use the:
Video out and Audio out pins, using a multimeter double check which pins 
and the other end is the RCA connectors, see which one is video or audio.

If you're Monitor cables aren't marked, if you plug Video into Audio etc 
you will blow up the VIC and SID chips.

I believe you may only be using the RF anntenna connection but it's not very good.

Use a Commodore monitor cable.

Terry Raymond


On Wed, May 2, 2018, 9:23 AM J. Alexander Jacocks <[hidden email]> wrote:
On Wed, May 2, 2018 at 11:12 AM, Francesco Messineo <[hidden email]> wrote:
On Wed, May 2, 2018 at 4:55 PM, J. Alexander Jacocks <[hidden email]> wrote:
> All,
>
> I've asked a number of places, but I thought that I would get the thoughts
> of the fine folks, here, as well.
>
> I have a C128DCR NTSC that has issues with signal level on chroma, from the
> video connector.  Signal levels seem to be just fine at the RF connector,
> and the picture is fine, from that connector.  From the video connector, to
> a modern TV or monitor, the picture is excellent quality, but monochrome.
> Checking the output pins on the video connector, the level is very low, on
> the chroma signal.
>
> I have changed:
> 1) VIC-II (8564)
> 2) Clock generator (8701)
> 3) Crystal (NTSC/14 MHz)
> 4) RF modulator

according to the schematic, there're two jumpers that select different
levels of the chroma signal:
J10 and J11 and associated resistive divider R13-R14. I would check
these components as second step after having excluded EMI42 filter.
The filter should have basicly 0 ohms dc resistance between input and
output and basicly infinite resistance between either input or output
to GND.
Of course, you should make sure the "about 0 ohms" dc resistance is
present from the J10/J11 jumpers to the chroma output pin too, to rule
out any track/solder problem.
Almost all you changed, couldn't have been the problem judging from
the tests you describe.
I would have first checked with another monitor/TV.

Frank,

I did indeed check with at least 2 TVs, and both showed the same issue, so it's not the TV/monitor.  I will open up my 128DCR this evening, and check the levels on those resistors and jumpers.

I didn't think that any of the parts were the problem, except for the RF modulator, which since the levels are low after the modulator, I thought might be faulty.

Thanks!
- Alex 

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Re: Chroma/Luma (or s-video) Problems on 128DCR

MiaM
Den Wed, 02 May 2018 16:02:13 +0000 skrev Terry Raymond
<[hidden email]>:

> Hi,
>
> I hooked an older Bread Bin up to my Theatre view TV, only on the
> front panel has the RCA connectors for video and sound.
>
> If you have just the C64 user manual it has the Video connector
> pinouts, of course use the:
> Video out and Audio out pins, using a multimeter double check which
> pins and the other end is the RCA connectors, see which one is video
> or audio.

The C64 manual, at least the older ones, only has 5 of the 8 pins
documented...

> If you're Monitor cables aren't marked, if you plug Video into Audio
> etc you will blow up the VIC and SID chips.

No way. As long as ground is on the correct pin, VIC can of course
withstand the higher impedance / lower load of an audio input. I don't
think a SID chip would die by loading it with 75 ohm either.

What can kill stuff is connecting and disconnecting stuff while a
ground loop forms between the monitor and the computer (directly on a
C128/C128D with it's grounded PSU, via the disk drive on a C64 with
it's ungrounded PSU). The crappy RCA connectors usually makes contact
with the signal before the ground.

Disconnect all power leads for the computer and all accessories like
disk drives before connecting or disconnecting any cables to be on the
safe side, or run all stuff via a power strip (and don't connect
anything else like a cable TV aerial cable).

> I believe you may only be using the RF anntenna connection but it's
> not very good.
>
> Use a Commodore monitor cable.

For composite video and audio, any adapter cable intended for hooking
up old european 5-pin DIN audio equipment works fine as long as you use
the correct leads. Those have four RCA connectors and they will be (in
some order) audio out, audio in (don't use this unless you know what
you're doing), composite video out and monochrome video out.

For S-Video which this thread really is about, you need an 8-pin DIN
connector. Make sure to get the right one, there are two different
kinds of 8-pin DIN connectors. One where the pins form a perfect circle
except one pin is missing. The other has five pins in a perfect half
circle but the outer two pins (6 and 7) "sags" outwards. Can't remember
which one C64 uses. IIRC only one of theese two are truly a DIN
connector according to the (west) german DIN standard.

--
(\_/) Copy the bunny to your mails to help
(O.o) him achieve world domination.
(> <) Come join the dark side.
/_|_\ We have cookies.

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Re: Chroma/Luma (or s-video) Problems on 128DCR

Rhialto
On Wed 02 May 2018 at 22:03:55 +0200, Mia Magnusson wrote:
> For composite video and audio, any adapter cable intended for hooking
> up old european 5-pin DIN audio equipment works fine as long as you use
> the correct leads. Those have four RCA connectors and they will be (in
> some order) audio out, audio in (don't use this unless you know what
> you're doing), composite video out and monochrome video out.

Yes, I used one of those DIN <-> "tulip connector" cables to connect my
Amiga's 1084 monitor to my 64. Worked fine.

-Olaf.
--
___ Olaf 'Rhialto' Seibert  -- Wayland: Those who don't understand X
\X/ rhialto/at/falu.nl      -- are condemned to reinvent it. Poorly.

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Re: Chroma/Luma (or s-video) Problems on 128DCR

J. Alexander Jacocks
On Wed, May 2, 2018 at 17:21 Rhialto <[hidden email]> wrote:
On Wed 02 May 2018 at 22:03:55 +0200, Mia Magnusson wrote:
> For composite video and audio, any adapter cable intended for hooking
> up old european 5-pin DIN audio equipment works fine as long as you use
> the correct leads. Those have four RCA connectors and they will be (in
> some order) audio out, audio in (don't use this unless you know what
> you're doing), composite video out and monochrome video out.

Yes, I used one of those DIN <-> "tulip connector" cables to connect my
Amiga's 1084 monitor to my 64. Worked fine.

Just to clarify, I have three different cables, which I have been using with the 128DCR.

1) RCA-style RF cable
2) DIN8 -> s-video + audio
3) DIN8 -> chroma/luna + audio (all RCA connectors)

So, I do, indeed, have the proper cables.  The one particularly interesting question that has been raised is what are the normal signal levels for chroma, on the DCR?  I don’t know that, offhand, other than to say that I have gotten excellent picture out of the DIN8/s-video cable, in the past, to a modern LCD monitor.  Whether I used it with either of the LCDs (Dell 2001fp and HP 2025) that I am currently using is an open question, though.

Thanks!
- Alex
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Re: Chroma/Luma (or s-video) Problems on 128DCR

Bill Degnan
I made of post that details how I can switch between display modes on my C128D and 1084 display.  This may help shed light on what you'd need to do to get a color signal on an LCD display. In particular it's required that the 1084 be in the LCA setting to display color.  If you determine the difference how the 1084 processes in inbound signal from the C128 you'll learn what you need to do to make it work on the LCD, which I am guessing is in "CVBS mode" relative to the 1084.


If that helps, I will post the info on my site for future Commodorians

I did this to help confirm my theory that the issue is not with the C128 nor the cabling.  It's the LCD.  

Bill

On Thu, May 3, 2018 at 8:23 AM, J. Alexander Jacocks <[hidden email]> wrote:
On Wed, May 2, 2018 at 17:21 Rhialto <[hidden email]> wrote:
On Wed 02 May 2018 at 22:03:55 +0200, Mia Magnusson wrote:
> For composite video and audio, any adapter cable intended for hooking
> up old european 5-pin DIN audio equipment works fine as long as you use
> the correct leads. Those have four RCA connectors and they will be (in
> some order) audio out, audio in (don't use this unless you know what
> you're doing), composite video out and monochrome video out.

Yes, I used one of those DIN <-> "tulip connector" cables to connect my
Amiga's 1084 monitor to my 64. Worked fine.

Just to clarify, I have three different cables, which I have been using with the 128DCR.

1) RCA-style RF cable
2) DIN8 -> s-video + audio
3) DIN8 -> chroma/luna + audio (all RCA connectors)

So, I do, indeed, have the proper cables.  The one particularly interesting question that has been raised is what are the normal signal levels for chroma, on the DCR?  I don’t know that, offhand, other than to say that I have gotten excellent picture out of the DIN8/s-video cable, in the past, to a modern LCD monitor.  Whether I used it with either of the LCDs (Dell 2001fp and HP 2025) that I am currently using is an open question, though.

Thanks!
- Alex

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Re: Chroma/Luma (or s-video) Problems on 128DCR

J. Alexander Jacocks
On Thu, May 3, 2018 at 10:39 AM, Bill Degnan <[hidden email]> wrote:
I made of post that details how I can switch between display modes on my C128D and 1084 display.  This may help shed light on what you'd need to do to get a color signal on an LCD display. In particular it's required that the 1084 be in the LCA setting to display color.  If you determine the difference how the 1084 processes in inbound signal from the C128 you'll learn what you need to do to make it work on the LCD, which I am guessing is in "CVBS mode" relative to the 1084.


If that helps, I will post the info on my site for future Commodorians

I did this to help confirm my theory that the issue is not with the C128 nor the cabling.  It's the LCD.  

Interesting.  I'll try the C128 with my other LCD that has s-video, which is my Dell 2405fpw.  That's what I likely used, last time that I had the DCR hooked up to a modern monitor.  And, of course, I'll dig out my 1702 and use the chroma/luma cable.

If this is the case, as you suspect, then I think that maybe we should work on a general-purpose Commodore 64/128-to-LCD circuit.  I suspect that all that would be needed would be to amplify the chroma signal.

- Alex 
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Re: Chroma/Luma (or s-video) Problems on 128DCR

Gerrit Heitsch
On 05/03/2018 05:17 PM, J. Alexander Jacocks wrote:
>
> If this is the case, as you suspect, then I think that maybe we should
> work on a general-purpose Commodore 64/128-to-LCD circuit.  I suspect
> that all that would be needed would be to amplify the chroma signal.

The chroma output of the C64 is already too strong though. With some
displays you have to add a 330 ohm series resistor to the chroma signal
to get a stable picture.

  Gerrit


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Re: Chroma/Luma (or s-video) Problems on 128DCR

Bill Degnan
ALex,
For your exhibit, why not use a vintage display anyway?  Would it be easier to adapt to a CBM display rather than the other way around, given you have two weeks left?
b

On Thu, May 3, 2018 at 11:50 AM, Gerrit Heitsch <[hidden email]> wrote:
On 05/03/2018 05:17 PM, J. Alexander Jacocks wrote:

If this is the case, as you suspect, then I think that maybe we should work on a general-purpose Commodore 64/128-to-LCD circuit.  I suspect that all that would be needed would be to amplify the chroma signal.

The chroma output of the C64 is already too strong though. With some displays you have to add a 330 ohm series resistor to the chroma signal to get a stable picture.

 Gerrit



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Re: Chroma/Luma (or s-video) Problems on 128DCR

J. Alexander Jacocks
Bill,

Indeed, it would, but my display is on using vintage machines with modern peripherals.

So, unfortunately, I can't use my 1702 or my 1080.

- Alex

On Thu, May 3, 2018 at 1:10 PM, Bill Degnan <[hidden email]> wrote:
ALex,
For your exhibit, why not use a vintage display anyway?  Would it be easier to adapt to a CBM display rather than the other way around, given you have two weeks left?
b

On Thu, May 3, 2018 at 11:50 AM, Gerrit Heitsch <[hidden email]> wrote:
On 05/03/2018 05:17 PM, J. Alexander Jacocks wrote:

If this is the case, as you suspect, then I think that maybe we should work on a general-purpose Commodore 64/128-to-LCD circuit.  I suspect that all that would be needed would be to amplify the chroma signal.

The chroma output of the C64 is already too strong though. With some displays you have to add a 330 ohm series resistor to the chroma signal to get a stable picture.

 Gerrit