RF Output

[bootlegger]

Hi All,
Bit of an odd one.
I have two QLs that both produce a bleeding effect when using RF. I have tried both machines in an old CRT and an LCD and both produce the same effect.
Now the strange part. If I remove the RF from the back of the QL so that just the centre pin is connected and the Ground is disconnected, then the picture quality is perfect (for RF at least).
So it seems when GND is connected between LCD/CRT and QL that the picture bleeds. I since bought an RGB to Scart adapter and that works perfectly well, but in my testing, I noticed that when using the RF lead with the RGB connected, that the picture was perfectly clear over UHF! So to sum up, when just RF connected with centre pin only, picture is good. When using RF only with centre pin and ground connected, picture is bad. With RGB cable connected and RF connected with centre pin and ground, picture is good.
I have purchased 2 Motorola MC1377P RGB to PAL/NTSC Video Chip from sellmyretro because from a little research I did it sounded like this was the likely cause of the screen bleeds, but these replacement chips did not make any difference.
On a last note, when using purely the RGB to Scart adapter, although the picture is very good, there are some vertical lines down the display. Is this common?

I am happy that I have a clear picture using RGB so am not too worried about this, but it would be nice to understand why it occurs, and whether its worthy of any further time/money for repair to get it as good as new.

I have pictures of all the effects too, but am not sure how to attach pictures to this post?

Thanks in advance,
Jason

[Martin_Head]

It could be a problem with the RF modulator.

It could also be some sort of earthing/grounding problem.

When you connect the RGB/Scart connector. The QL's and the TV's grounds will be connected. But when you use an RF cable, the two grounds may not be connected if the RF socket in the TV is isolated from the TV's ground (as they usually were when TV's had live chassis).

Also are you using a standard power supply? If you have some other sort, or a switch mode power supply, you might have some voltage difference between the TV's ground and the QL's ground.

Martin Head

[1024MAK]

For the RF/UHF problem, try another known good UHF lead, clean the outside contact of the socket on the QL's modulator.
For the vertical lines on a SCART connection, this is most likely the TV switching between RGB video and composite video. Try another TV (preferably one with manual input source selection via on-screen menu or remote control button). Which SCART lead did you buy?

Mark

[Cristian]

I have pictures of all the effects too, but am not sure how to attach pictures to this post?

You may use some file hosting service (like "Dropbox"), then paste the picture links here.
Checking your pictures would be very useful for us in order to help you.