Interference lines?

[Neil79]

Anyone know what causes this? Is it because it's via Scart, as this happens on both the Amstrad 464 Plus and the GX 4000. Two different TV's... Amstrad CPC 464 and 6128 through original monitor is fine.

[chinnyhill10]

Anyone know what causes this? Is it because it's via Scart, as this happens on both the Amstrad 464 Plus and the GX 4000. Two different TV's... Amstrad CPC 464 and 6128 through original monitor is fine.

When I used the Plus lead supplied by a certain online retailer, I had many odd artefacts until I cut the RGB select pin and used a 1.5v power source instead. Then the picture was free of all problems (which varied from a blank screen on some TV's, black and white picture on others, and colour with distortion on some).

[Neil79]

When I used the Plus lead supplied by a certain online retailer, I had many odd artefacts until I cut the RGB select pin and used a 1.5v power source instead. Then the picture was free of all problems (which varied from a blank screen on some TV's, black and white picture on others, and colour with distortion on some).

It's odd as it's two different connection types, one scart/scart the other 464 plus scart.


Oh well

[chinnyhill10]

It's odd as it's two different connection types, one scart/scart the other 464 plus scart.


Oh well

But regardless of connection at the TV end presumably the select pin is still in use.


Might not be. Might be bad SCART termination. But I'd head for the RGB select pin first of all.

[arnoldemu]

Anyone know what causes this? Is it because it's via Scart, as this happens on both the Amstrad 464 Plus and the GX 4000. Two different TV's... Amstrad CPC 464 and 6128 through original monitor is fine.

I've seen this pattern before from a plus on a cm14 monitor I think.

It's unique to plus.

[Bryce]

Any chance you are using a switchmode PSU?

Bryce.

[Neil79]

Any chance you are using a switchmode PSU?

Bryce.

The recommended one


ECP-11-9U | 9V dc, 1 Output, 2.1 x 5.5 x 9.5 mm Centre Positive Switch Mode,

[chinnyhill10]

The recommended one


ECP-11-9U | 9V dc, 1 Output, 2.1 x 5.5 x 9.5 mm Centre Positive Switch Mode,

You didn't plug that into the Plus did you?

[Bryce]

Recommended by who? Switchmode PSUs will always introduce interference on a system that doesn't have its own regulation stage (ie: the CPC). My guess is that the lines you are seeing are coming from that. Do you have a linear supply you could try?

I assume it is a 5V version you have? 9V would fry a CPC instantly.

Bryce.

[Neil79]

You didn't plug that into the Plus did you?

Of course not


This was for the 464 plus
AMSTRAD CPC 464 & 6128 + (PLUS MODELS) TV CONNECTION KIT - PSU ADAPTER & SCART |


This was for the GX4000 ( Recommended by nearly every one  in the GX4000/Brick thread )
ECP-11-9U | 9V dc, 1 Output, 2.1 x 5.5 x 9.5 mm Centre Positive Switch Mode,

[Bryce]

The GX4000 has some internal regulation with filtering, although it's not really made to filter out switching noise, but the CPC has nothing and lets the entire switching noise through. I'd still recommend that you look for a linear solution for at least one of them and see if that resolves the issue.

Bryce.

[chinnyhill10]

The GX4000 has some internal regulation with filtering, although it's not really made to filter out switching noise, but the CPC has nothing and lets the entire switching noise through. I'd still recommend that you look for a linear solution for at least one of them and see if that resolves the issue.

Bryce.

I've never seen any machine have issues with the RS switched mode supplies. They are superb quality and aren't some Ebay rubbish with no filtering. They are filtered and the price reflects the quality of the units.


The world has moved on from linear supplies with poor regulation. I would be VERY surprised if its these PSU's causing the issues especially since I have many of the RS units here including ones I use with all my CPC's including a 464+ with no issues at all.


In fact with the Spectrum its now been proven that certain switched supplies not only help the machine run cooler but improve the picture quality due to the vastly improved filtering over the supplied Sinclair unit.

[Neil79]

I shall try a different TV tomorrow, one that is a small CRT!

[chinnyhill10]

I shall try a different TV tomorrow, one that is a small CRT!

Are both LCD's the same brand? I ask as for example Samsungs have known issues with composite sync and I ended up getting special cables for my Master System and Megadrive to stop patterning on certain colours.


Also, as I mentioned earlier, some brands (especially cheap brands) have poor termination on the SCARTS which leads to patterning.


Still think its voltage problems on the SCART select pin mind. Does it get worse or better with different colour combinations on the screen? Ie what does it do if the screen has lots of peak white or you flash the border between white and black?

[gerald]

The GX4000 has some internal regulation with filtering, although it's not really made to filter out switching noise, but the CPC has nothing and lets the entire switching noise through. I'd still recommend that you look for a linear solution for at least one of them and see if that resolves the issue.

Bryce.

When powered from 9V, the GX4000 already use its own linear 5v regulators.
I've use several GX4000 and plus with the same monitor/power supply (switching 5V)
They all exhibit some 'interference' but these are not the same strength according to the plus/gx used. Some does not exhibit anything at all.
I am more thinking of aging voltage filtering.

[Bryce]

You mean dried out capacitors?

@chinnyhill: Even good and expensive SMPSUs will still have a certain amount of noise on the rail. Connect one to a scope and see for yourself.

Switchmode supplies didn't replace linear supplies, they are just an alternative and there are many places where a linear supply is still the only option.

Bryce.

[CraigsBar]

Anyone know what causes this? Is it because it's via Scart, as this happens on both the Amstrad 464 Plus and the GX 4000. Two different TV's... Amstrad CPC 464 and 6128 through original monitor is fine.

My plus machines (all 4 of them) have this on LCD TV's when connected with scart or rgb to VGA connections. I find it most noticeable on things like the 3d bat logo on batman forever where a large part of the screen is a solid colour. They all work fine on the cm14 monitor, CRT and plasma TV using the same cables. So yeah, I guess it's a plus thing! Not seen it at all with the gx4000 tho.

[Bruce Abbott]

Vertical lines synchronized to the display suggests inadequate decoupling of logic chips rather than switch-mode power supply noise.  here's an example of the same problem in an MSX computer, and the fix (extra decoupling capacitors close to the VDP chip).

 

[Bryce]

The plus also deleted the AC-coupling capacitors on the RGB lines which also probably doesn't help.

Bryce.

[gerald]

I just had a look at the schematic :
The GX4000 has a blocking inductance (L3) on the supply line of the DAC with local filtering.
That self does not exist on the Plus. There is a global self at in 5V input port, but this does not prevent HF spikes to reach the video signal.

[arnoldemu]

The plus also deleted the AC-coupling capacitors on the RGB lines which also probably doesn't help.

Bryce.

I think the absence of these are causing the lines I see.

[Bryce]

I just had a look at the schematic :
The GX4000 has a blocking inductance (L3) on the supply line of the DAC with local filtering.
That self does not exist on the Plus. There is a global self at in 5V input port, but this does not prevent HF spikes to reach the video signal.

That's why I mentioned that it has filtering / regulation, but isn't tuned to remove switching spikes.

Bryce.

[chinnyhill10]

Vertical lines synchronized to the display suggests inadequate decoupling of logic chips rather than switch-mode power supply noise.  here's an example of the same problem in an MSX computer, and the fix (extra decoupling capacitors close to the VDP chip).

C64 and C16/Plus 4 suffer badly from this as well.


But I've not seen any sign of it on my 464 Plus whereas my Plus 4 and C64's suffer from it badly on the same equipment (go and watch ChinnyVision to see how clean my Plus is and the bars down the screen on the C64 and Plus 4).

[CraigsBar]

Damn! So I posted you the *wrong* plus then. LOL

[chinnyhill10]

Damn! So I posted you the *wrong* plus then. LOL

Until people start cutting their RGB select pins on the SCARTS, I remain to be convinced. I had all sorts of weird shit going on until I put a steady 1.5v in there. The effects varied depending on what was on the screen and from device to device as well.


Mind you, if people are reporting the bars also on their Amstrad monitors this would probably point to a fault in the CPC. Possibly caps going bad somewhere. My XE has weird display issues and I know its the caps causing it.