Panasonic CT-1350 RGB Monitor troubles.

[PgrAm]

I bought a Panasonic CT-1350MG monitor from a guy on craigslist in the hopes that I would use it with all my computers that support RGB. So I started with my amiga 500 and made a cable and I hooked it up and all the colors were off, they were a little too bright. I figured I could fix this by adjusting some simple settings but my monitor doesn't seem to have a contrast knob and the color/tint controls only seem to work with a composite input and not RGB. Does anyone else have this monitor or any info on it? Any general wisdom that might help resolve this problem would also be much appreciated.

Here are some pictures showing what the monitor looks like and some shots of the image with flash off compared to the real colors its supposed to be:


EDIT: also orange seems to show up as red

 

[modem7]

So I started with my amiga 500 and made a cable

Recently constructed home-made cable. That's definitely a possible cause. Is there any way you can eliminate that as the cause?

 

[PgrAm]

Well its a pretty good cable well shielded and all but I tried a composite input and had the same issues aside from orange being red which can be remedied with the tint knob when using composite. I think things would be pretty much solved If I could adjust black to be true black instead of grey and for that I need a contrast knob.

 

[PgrAm]

This is how it looks with a composite input. The brightness is set as low as it goes. This is ghouls 'n ghosts on the c64, the background should be black but its not. No homemade cables were used here.

 

[Maverick1978]

I know that on many RGB cable schematics that I've seen for both game consoles and Atari ST units, there have been many with resistors in-line with the R/G/B lines. Still, this looks like a brightness adjustment to me (although it COULD be a home-made cable problem). If you're sure that your cable's ok, pop the top off the monitor and look for some pots to adjust. Be careful not to touch any of the circuity, and most especially the big red anode wire that comes off of the picture tube! (that's lethal voltage). As with all things, if you're not sure, don't do it.

 

[PgrAm]

I know that on many RGB cable schematics that I've seen for both game consoles and Atari ST units, there have been many with resistors in-line with the R/G/B lines. Still, this looks like a brightness adjustment to me (although it COULD be a home-made cable problem). If you're sure that your cable's ok, pop the top off the monitor and look for some pots to adjust. Be careful not to touch any of the circuity, and most especially the big red anode wire that comes off of the picture tube! (that's lethal voltage). As with all things, if you're not sure, don't do it.

I modified my cable to add 220 ohm resistors on the RGB lines but they did nothing but desaturate the image, I had previously tried 220 uF capacitors but these had no effect. I'm almost sure the cable isn't the cause.

 

[modem7]

Inside your monitor are three channels: red, green and blue. Similar to the diagram [here]. When your monitor was assembled and then powered on for the first time, slight differences in the electronic components within the channels resulted in the 'colour balance' being out - white does not appear on screen as white. Colour balance is one of the alignments done by the maker. It's done by making slight adjustments to each channel until white is seen as white.

As monitors age, some components in the monitor slowly change value, with some of those component changes affecting the colour balance. I have a clone EGA monitor that has a slight red look to the colours. One of these days I will downwards adjust the red in the monitor to restore colour balance (to good-enough, not perfect).

To me, your monitor shows too much blue. But an amount that is not due to aged components. It looks as though there has been some kind of significant failure in the blue channel, a failure that has resulted in greatly excessive blue. Overdriven blue channel.

Regarding the screen shot in post #4. See how the numbers are not vertical. That is symptomatic of poor voltage regulation in the power supply (voltage regulation: maintaining constant voltage for varying levels of current being drawn). It could be that the main filter capacitors in the power supply need replacing, but another possible cause is the overdriven blue channel, which will be drawing a lot of current from the power supply, somewhat overloading the power supply.

The alternating dark/light blue bands might also be the result of a power supply struggling to supply the much-more-than-normal amount of current.

Does the symptom change when you 'bump' the monitor? If so, a bad solder joint could be the cause.

It would certainly be worthwhile to do a thorough visual inspection of the monitor's interior (including solder joints), because the cause may be visible.

 

[PgrAm]

Inside your monitor are three channels: red, green and blue. Similar to the diagram [here]. When your monitor was assembled and then powered on for the first time, slight differences in the electronic components within the channels resulted in the 'colour balance' being out - white does not appear on screen as white. Colour balance is one of the alignments done by the maker. It's done by making slight adjustments to each channel until white is seen as white.

As monitors age, some components in the monitor slowly change value, with some of those component changes affecting the colour balance. I have a clone EGA monitor that has a slight red look to the colours. One of these days I will downwards adjust the red in the monitor to restore colour balance (to good-enough, not perfect).

To me, your monitor shows too much blue. But an amount that is not due to aged components. It looks as though there has been some kind of significant failure in the blue channel, a failure that has resulted in greatly excessive blue. Overdriven blue channel.

Regarding the screen shot in post #4. See how the numbers are not vertical. That is symptomatic of poor voltage regulation in the power supply (voltage regulation: maintaining constant voltage for varying levels of current being drawn). It could be that the main filter capacitors in the power supply need replacing, but another possible cause is the overdriven blue channel, which will be drawing a lot of current from the power supply, somewhat overloading the power supply.

The alternating dark/light blue bands might also be the result of a power supply struggling to supply the much-more-than-normal amount of current.

Does the symptom change when you 'bump' the monitor? If so, a bad solder joint could be the cause.

It would certainly be worthwhile to do a thorough visual inspection of the monitor's interior (including solder joints), because the cause may be visible.

Just thought I should let you know that ghosts n' ghouls is supposed to have wavy text its not an actual problem and the alternating lines of dark/light are artifacts caused by temporal aliasing between the TV's refresh rate and the camera shutter, simply put they don't exist in real life. Here's a picture of the real ghosts n' ghouls title screen:


As for the blue channel I will look into it. Any advice for avoiding electric shock? I've worked on compact macs before which I just left unplugged overnight but I wasn't touching the CRT part.

 

[modem7]

Just thought I should let you know that ghosts n' ghouls is supposed to have wavy text its not an actual problem

So I was looking at phantom symptoms (pardon the pun).
That was a bad example for a 'look at this screen and tell me what is wrong with it'.

and the alternating lines of dark/light are artifacts caused by temporal aliasing between the TV's refresh rate and the camera shutter, simply put they don't exist in real life.

Relevant information.

As for the blue channel I will look into it. Any advice for avoiding electric shock? I've worked on compact macs before which I just left unplugged overnight but I wasn't touching the CRT part.

Some may say that this is overboard, but if you want to play safe:

* The disconnection from mains power and computer and then leaving overnight is good.
* Inspect with one hand behind your back.
* Do not touch any electronic components or the traces on a circuit board. You don't need to - this is a visual inspection.
* If the power supply is in a metal cage, then I don't see any point in you going into the cage. I can't see a power supply problem only affecting the blue.
* The video amplifier stages may be in a dedicated metal cage (as they are in the IBM EGA monitor).
* Wear safety glasses (in case you break the CRT neck).

 

[PgrAm]

I know what's wrong! I found the answer here when I was looking up color balance adjustment. This excerpt describes it pretty well.

One last setting you might need to make at some point is the master screen or G2 adjustment. It's a -very- coarse adjustment that sets the overall level of brightness. As a tube ages, the G2 may need to be set higher to compensate for a low-brightness problem. If this control is set too high, the image may be too bright and/or take on a milky appearance with faint diagonal "retrace" lines in the picture. If set too low, you will not have enough brightness even with the front panel brightness control at maximum. This master screen is on the flyback (line output) transformer, the large black plastic block usually located at the right rear of the main chassis. For identification purposes, note the thick (usually red in colour) wire that runs from the flyback to the top of the picture tube. The two controls on the flyback are the focus (top control) and master screen or G2 (bottom control).

If you look closely in the Turrican shot you can see thin lines during the horizontal retrace. Initially I assumed this was just interference from some other piece of hardware in the room (there's allot of random signals in there) and I wasn't concerned but I realized that this passage perfectly describes whats wrong with my monitor now I just need to find the adjustment and fix it.

 

[modem7]

Note that that adjustment will affect all three colours, not just blue.

 

[PgrAm]

Note that that adjustment will affect all three colours, not just blue.

AHAH! I found a Grille on the back of the monitor that quite clearly labels all of the adjustments and they are accessible without even opening it, independent pots for Red, Green, Blue, Screen and a few others. That's a life saver (quite literally).

 

[PgrAm]

Finally fixed! There is still a slight issue with colors when using RGB input but I think that may be a cable issue or possibly something wrong with the amiga. I'm gonna make a cable for my Sega Genesis and then I'll know for sure.