PAL red/green color moire, not in NTSC

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rmzalbar
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PAL red/green color moire, not in NTSC

Post by rmzalbar »

I have a 250407 breadbin C64 that was converted from NTSC to PAL, by replacing the VIC-II, setting the jumper, and changing the crystal. I also tuned R27 as accurately as possible to the correct color clock frequency for PAL.

So in PAL mode there's a red/green repeating vertical bars pattern present that's visible on all of my various displays. The more luma changes, the more visible it is. i.e. most visible in checkerboard patterns or with text, not visible with solid areas.

Just wondering if this is expected for PAL, or if there's something more I could do? Screenshot attached (from a CRT)
PAL.jpg



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eslapion
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Re: PAL red/green color moire, not in NTSC

Post by eslapion »

This looks more like a problem with the CRT you're using to display the PAL signal.

If you have a flat panel TV (most are both PAL and NTSC compatible these days) to check or perhaps one of those little boxes than can take an analog signal and convert it it for capture on the PC. I have a DVDXpress DX2 myself.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders

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Re: PAL red/green color moire, not in NTSC

Post by banman »

Hi rmzalbar,

I'm not am expert on these things.

I think eslapion's suggestion might work best.

I remember these color bands well on both PAL C64 and VIC 20's on tube style TV sets in the 80's.
I know the VIC had an RF modulator and we would just detune the TV receiver slightly. I think the same can be achieved on the C64 by off tuning the TV station a fraction. Assuming you are using the RF out on the C64.

Maybe switch out your current video RCA cable for a high quantity heavy duty shielded one. I think the thin ones pick up heaps of external EMI.

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Re: PAL red/green color moire, not in NTSC

Post by banman »

Hi rmzalbar,


Maybe the answer is here....



https://retrocomputerverzamelaar.nl/com ... -problems/


What do you say?

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Re: PAL red/green color moire, not in NTSC

Post by rmzalbar »

Eslapion: Oh man, I should have mentioned at the beginning that it is the same with all of my displays - I have 5 different types of CRT, and two LCDs I've used it on, and it looks the same with every one of them.

banman, it is assuredly the same as "non-fault #1" from your link. However, I do see screenshots from PAL systems that don't have any discernible color bars, yet on my system they are quite obvious in just about all graphics situations, not just in the stress-test of a black and white checkerboard pattern. I use Y/C (Svideo) and have also tried composite. I actually don't have any way to use PAL RF, as I don't have a PAL TV for that and anyhow the RF box is the NTSC version...

..which leads me to what I think might be the culprit, the NTSC RF modulator. I know it's connected to the video signal and actually helps generate the required signals to the video port, so perhaps the fact that it's optimized for NTSC is causing the issue?

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Re: PAL red/green color moire, not in NTSC

Post by banman »

Hi rmzalbar,


You might be right on that front with the issues being related to NTSC RF modulator.

Commodore went to great pains to keep EMI interference down in their machines to keep the FCC happy. Warranted or not.

I know personally that the difference is very great between the RF input vs composite on my Plasma. Composite is so much clearer. I would hazard a guess that S video is the next level up from that.

With RF input one gets a soft almost fuzzy not quite in focus feeling.




Do you have the shield and can lid for the VIC II chip in place as well as the top lid for the RF modulator securely fastened?

Can you access a PC capture card/usb device.

Here is a pic of a heavy duty RCA cable that I might use. Loads of shielding.
71QTYwPT-rL._AC_SL1500_.jpg
Here is one that I use. I would say without a doubt is low quality and is very susceptible to EMI.

s-l1600.jpg

Look, I am going out on a limb here. I know I'll cop a load full and I don't for a second say it's what you have. When I was testing different PLA's I had a dodgy one that gave very similar results to the one you have.

I don't suggest you go out and buy heaps of spares, however if you have a friend/ acquaintance you could borrow parts from to rule out things like the VIC II chip, PLA, color ram, etc... It may help.



I found a link that may shed some light on this discussion.

https://retrocomputing.stackexchange.co ... mmodore-64




I almost forgot there are several variants of PAL available...

https://en.wikipedia.org/wiki/PAL_region

PAL-B/G/D/K/I[edit]
Many countries have turned off analogue transmissions, so the following does not apply anymore, except for using devices which output broadcast signals, such as video recorders.

The majority of countries using or having used PAL have television standards with 625 lines and 50 fields per second, differences concern the audio carrier frequency and channel bandwidths. The variants are:

Standards B/G are used in most of Western Europe, Australia, and New Zealand
Standard I in the UK, Ireland, Hong Kong, South Africa, and Macau
Standards D/K (along with SECAM) in most of Central and Eastern Europe
Standard D in mainland China. Most analogue CCTV cameras are Standard D.
Systems B and G are similar. System B specifies 7 MHz channel bandwidth, while System G specifies 8 MHz channel bandwidth. Australia used System B for VHF and UHF channels. Similarly, Systems D and K are similar except for the bands they use: System D is only used on VHF (except in mainland China), while System K is only used on UHF. Although System I is used on both bands, it has only been used on UHF in the United Kingdom.

https://en.wikipedia.org/wiki/PAL#PAL_B ... _H,_K_or_I

Try out different ones and also adjust the aspect ratio of your screen if you can.

On some LCD monitors if you go into the clock time menu one can adjust the timing frequency slightly up or down. This can make changes to how the screen looks. It changes thing heaps. Try it......

Like this......
thumbnail.jpg
I just noticed looking at the photo I just took that that there are darker vertical bars and a fly-screen. I cannot see any artifacts what so ever when looking directly at the screen with the naked eye. Interesting.........




Something to think on too is that 'this' is the soul of your C64. It is unique to your C64 and you created it! One needs to remember that we are not using a VICE emulator which has a totally different scheme of displaying itself.

Every C64 I saw had it's own uniqueness. I cant ever recall seeing 2 the same. Think of the famous SID chip.....

Pretty awesome you converted it to PAL from NTSC! Have you tried any of the many PAL games on your system? Maybe after playing some great PAL games your mind might just filter out those small optical artifacts............ 8-)

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Re: PAL red/green color moire, not in NTSC

Post by rmzalbar »

Well.. the C64 itself is using the VIC-ii2 NTSC/PAL switcher board from Perifractic. It uses four bistable relays to switch the clock crystals, +5, +12, GND, and chip select lines between the two VICs. This slightly lengthens the path taken by the signals, but they are still strong enough to have no noticeable degradation in either mode. This also means that I don't have the "can" around the VIC area anymore.

The cable I'm using appears to be of high quality, it is a Y/C and audio-out cable made by a certain Canadian commodore/atari cable maker, resistored down to the correct impedance. I've also tested with a composite-out DIN adapter directly to a very good 75-ohm S/PDIF cable, and there was no difference. The colors appear regardless of the display type - LCD and CRT, so LCD tuning or scaling is not a factor here.

I even hooked up a scope to the color clock signal and tuned R27 to be as close as physically possible within the accuracy of a trimpot to the correct fundamental frequency (this actually did need some adjustment,) and this *did* cause the color bars to shift position a little bit left-to-right, but not go away. At any rate, I also tried installing the PAL setup *without* the VIC-II2 board just to be sure. No joy. Oh yeah - and I even tried another 6569 VIC-II, no difference.

It "feels" like a signal timing problem - like something is affecting the color timing in the PAL signal slightly out of phase (not totally unlike composite artifact color generated by luma, but not the same.)

I have a real native PAL C64-G machine on its way from Germany, so I can compare and contrast.

Here's a photo of the setup, just because photos are sexy and you've all been helpful:
NTSC2.jpg
ntsc.jpg

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Re: PAL red/green color moire, not in NTSC

Post by eslapion »

rmzalbar wrote:
Wed Jan 29, 2020 9:43 pm
I even hooked up a scope to the color clock signal and tuned R27 to be as close as physically possible within the accuracy of a trimpot to the correct fundamental frequency (this actually did need some adjustment,) and this *did* cause the color bars to shift position a little bit left-to-right, but not go away. At any rate, I also tried installing the PAL setup *without* the VIC-II2 board just to be sure. No joy. Oh yeah - and I even tried another 6569 VIC-II, no difference.

It "feels" like a signal timing problem - like something is affecting the color timing in the PAL signal slightly out of phase (not totally unlike composite artifact color generated by luma, but not the same.)
It seems very much the same way to me. The PAL color clock should be 17.734475MHz. Check it with a digital scope or good quality frequency counter on pin 21 of your 6569.

The board you added there has it's own PAL/NTSC crystals independent from whatever is on the C64 board.
Wealth, like happiness, is never attained directly. It comes as a by-product of providing a useful service. -Harland D. Sanders

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Re: PAL red/green color moire, not in NTSC

Post by banman »

Hi rmzalbar,


That is a nice setup. :)


That's a good thing you have another PAL machine on order.


Which version board do you have? Do you know of any known issues with this particular setup/version?


I agree I think it would be interesting to see the generated frequency of these crystals.....

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Re: PAL red/green color moire, not in NTSC

Post by banman »

Hi rmzalbar,

Apologies for being a pain.

I am assuming you checked for dry joints and filled up all the joints to the sockets on the board....

It wouldn't hurt just to gently run your hand and give things a wiggle while you are observing the output on your monitor....

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