Amigamaniac RGB to S-video v3 board troubles

[thgill]

I just recently received my version 3 board of the RGB to S-video adapter that Amigamaniac sells and having video problems with it. I have already spoke to Nathan about it and while he has given me some ideas, I want to see what some others thought.

I have a couple Amigas:

PAL A1200 - main machine
NTSC A500

Both machines work perfectly with a pair of 1084 monitors I have. No problems with the RGB picture output


I have a pair of TVs I am using with v3 adapter. a 47inch Vizio in the living room and a 26 inch Vizio in the bedroom. Both are LCD panels.


If I switch the adapter into NTSC mode (both dips) and plug it into my
NTSC A500, I get a perfect screen with no interference or wavy lines.
Looks really fantastic in s-video.


However if I switch it into PAL mode (both dips) and plug it into my
PAL A1200, I get wavy interfernce lines in the pictures. It overall
looks pretty good with the exception of this slight waviness in the
picture. I adjusted the tuner and it didn't have any affect on the
picture. Tried the adapters composite and it had the same
interference in the picture. I do get full color from both s-video and
composite.


However, if I unplug the adapter and just plug the composite into the
color composite out thats built into the A1200, I get a great picture
without interference. Well, as good as composite can give.

I am using a Vizio 47 inch flat panel to test. Since it works just
fine with the A1200's onboard composite output, I am assuming its
syncing to PAL frequencies fine. Checking the TVs on screen menu even
confirms its receiving a 50Hz signal and its in full color.

I also tried changing my PAL A1200 into NTSC mode via the early
startup menu and I get similar wavy picture symptoms. Again the onboard composite looks fine on the same TV and the RGB picture output looks fine on a 1084S monitor.


I am using the same power supply, same s-video and composite cables and same tv when testing the adapter. For some reason it just doesn't appear to work correctly with my PAL A1200. Works great in NTSC mode with my NTSC A500, but not with my PAL A1200.


So, any ideas on this?

[meega]

Shielding?

[thgill]

Shielding on what? The adapter or something else?

Both Amigas still have their internal metal RFI shields.

[kipper2k]

you cannot display pal correctly on a NTSC TV unless it is multi region, the purpose of the Pal/NTSC switch is for world wide usage

[Stedy]

Hi,

Can you take a picture of the display?

The AD724/AD725 used to convert RGB to Y/C have issues if the HSync of the input does not align with the colour carrier. This can cause cause some of the issues you describe.

Do you use separate H/V sync or the CSync input?

Have also had issues with ground loop problems on these devices.

Ian

[thgill]

Best of my knowledge this device uses H/V sync for the Amiga.

Honestly, it looks like a ground loop type interference.

Its just really weird that it only has that problem with my PAL A1200.


Where as my NTSC A500 is perfect with it.


I will try to take some photos or video of it tomorrow.

[Zetr0]

I think you will find my friend, that your monitor wont support NTSC 50Hz as that is what your Amiga A1200 is pumping out.

There are essentially two governing video clocks in the Amiga, the Colour Encoder and the Vertical Frequency.

The Output of PAL is 4.433MHz Colour Encoded @ 50Hz Vertical Refresh and I think this is why you are having some problems.

The Output of NTSC is 3.58Mhz Color Encoded @ 60Hz Vertical Refresh, hence an NTSC TV native screen mode.

I am surprised to read that after putting your PAL Amiga A1200 into 60Hz mode (from the early starup menu which should put a PAL amiga from 50Hz Vertical Refresh to 60Hz Vertical Refresh) didn't make any difference.

Another thing thats strange is the fact you got - good colour / stable screen not only from composite but from a PAL source on NTSC equipment - at best you should of only got a black and white image.

I assume you tried the composite in from the SVideo Adapter to the TV as well? do you get the same problem?

[amigamaniac]

Hmm, if it is a ground loop, why no problem with the NTSC A500? Could it be something with the A1200 MB design? I shall have to try the V3.0 RGB adapter with my A1200...

I have connected the H & V syncs from the Amiga to the AD724.

Could it be a power issue from the video port? My design takes the +12V pin of the video port, passes it through the big filter cap, then to the voltage regulator, which outputs the +5V needed for the AD724. After the +5V leaves the voltage regulator, it is further filtered by the decoupling caps at the power input pins on the AD724. I would have though that if the +12V from the A1200 was noisy, it wouldn't matter after all that filtering? Apparently the voltage regulator I have used can output +5V from an input of +7-35V. From memory though, the lower the voltage in, the lower the current out. Could this be a problem with the A1200 - i.e., there is less than +12V coming out of his A1200?

Could old leaky/dodgy caps be part of the problem?

It could be so many things, the mind boggles!

Nathan

[pandy71]

Different oscillators in NTSC and PAL Amiga - for NTSC it is simple 8 time chroma subcarrier and there is exactly 227.5 color ticks, for PAL it is more complicated - chroma subcarrier is multiply by 32 and divided by 5 to create proper oscillator frequency for Amiga, also length of line is 227 color cycles (exactly should be 227.00128 but it is truncated so it give us vertical frequency 25.000140969163Hz)
I can imagine that on PAL Amiga with NTSC hard or software NTSC mode only vertical frequency is switched to 60Hz (not even 60000/1001 as it should be) but maybe I'm wrong on this... but definitely main oscillator frequency remain the same as in PAL so this give us improper chroma subcarrier frequency on input of the NTSC encoder

I can only imagine that maybe some PLL that will use some clever PAL ref for creating NTSC (calculations need to be made) can help but... easier thing - add some clock externally (NTSC) and try to switch Agnus for real NTSC oscillator freq - at least this is is good starting point (search for 28636363.63636360MHz oscillator and remember about all safety related to those very sensitive input pins at the video port - _XCLKEN and XCLK - Agnus/Alice can be easily destroyed)

[Zetr0]

@Pandy

from the Adapter I have here, the AD724 uses an extenal clock for the colour burst, thus removing the truncation probem faced by a PAL amiga.

From the reading its possible that there is either an issue with a 50Hz horizontal NTSC or (and more likely) either a lot of EF noise from the machine or a ground loop problem.

Out of curiosity I would ask Thgill if he has tried the A500 set to PAL colour clock on the adapter (forcing a PAL 60Hz) whats the output like?

[pandy71]

is pin 15 on video port are used or not? this is output for CCK and Commodore designs for encoders always (not sure on this however on all schematics i've seen already it) is used for creating synchronous chroma burst subcarrier.

It can be both problems - ie frequency and old caps that in insufficient way filtering supply.

[Zetr0]

a thought just occured - have you tried changing the powersupply of the A1200 ?

[thgill]

Yes I have tried another PSU as well, same results. I have a third PSU I will also try tonite when I take some photos.

I have also tried the composite out on the S-video adapter (was mentioned in the original post). Same wavy line interference. Though to a lesser degree.

I haven't tried forcing the A500 into PAL mode and testing it. Perhaps I will do that tonite as well.

Looking at the video port diagrams, it looks like +12v is supplied by pin 22 on the RGB port.

Should I measure this tonite to ensure its actually outputting the correct voltage?

[pandy71]

Originally Posted by thgill

Should I measure this tonite to ensure its actually outputting the correct voltage?

Yes, check level - also if You think that power supply can be responsible mybe it is worth to measure AC current on line +12V - for example if You have access to oscilloscope You can select AC coupling and verify what is on this line...

[e5frog]

Get one more and see if it behaves the same.

Try a TV that's not Vizio and one that's not an LCD.

[thgill]

Looks like it might be one of my power supplies.

I was thinking I tested it with my modified ATX psu, but apparently I hadn't.


Plugged in my modded PSU and I get a stable, nearly perfect picture.

Took a couple quick pics.

This is from my 47inch Vizio LCD. Had it set to 4x3 mode (no stretch).

Excuse the poor iPhone quality.

[thgill]

I am picking up a 19inch LCD TV tomorrow thats suppose to be PAL compatible.

Will test it with all three of my psus and see if there is any change.

[Matt020]

How did you go with the 19 inch LCD TV?