CRT TV installed in cab with VGA RGB-->Scart cable - weird picture

[repetto74]

Hi Guys,

I am desperate to obtain a decent picture with the 15khz CRT TV I have installed in my cab (my previous arcade electronics has gone bad and the flyback is no more available). It is a 25" TV with scart inputs so I purchased a quality RGB to scart cable with +12v and +5v molex connector for the A/V commutation and RGB switch.

Unfortunately I cannot get past this video quality where the image looks dim and some weird horizontal lighter coloured bars appears where text is displayed.

What I am sure of is that the cable is not the cause. I have tried to connect a DVD player with a standard scart cable and I do have the same issue when displaying the DVD menu. What this can be? I have a lot of pots on the TV chassis I can adjust and also the focus and brightness on the flyback. Is that a problem with the sync?

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[buttersoft]

Yer, might be a sync issue. What's the setup? Is it a PC, and if so, what PC, what OS, what GPU, how are you getting 15kHz, and composite sync? Does the VGA-to-SCART cable plug directly into the PC and go straight to the TV?

[repetto74]

Hi Buttersoft,

It is a standard PC config of 2004 with 4 GB of Ram and two IDE HDD. I am using an ArcadeVGA video card at 15khz and the VGA to Scart cable is directly connected to the video card output and the TV scart input.
This setup was working with my past arcade monitor and had to remove it due to a bad FBT so I choose the option of placing a TV in the cab. I have tried to hook a DVD player directly to the TV scart and I do have the same issue when displaying the DVD menu so the issue has somehow to do with the TV set and not the PC config and cable.
The TV electronics has a lot of pots I can tweak like B+ voltage, Trap, Delay, all the screen size and shift. I did not touch any pot up to now and even no tried to turn the screen of the FBT yet.

UPDATE : Last time I took out the TV Pcb to unsolder the cable wiring I did myself from the scart pins as I do no need it anymore (brand new cable directly connected to the Scart plug). By mistake I did turn the pot for the B+ adjustment just to check with the screw driver then I moved it more or less to its original position. Now the TV won't turn up (no raster) so I did check with a voltmeter at the check point for the B+ (It is a resistor so I put both voltmeter leads on each side of the resistor and I read only 65 VDC where it should be normally 155 VDC for a 25" monitor. There is not enough B+ voltage to carry on the FBT I hope this is the problem now cause I had a screen lighting up before moving the B+ pot.

[Mr. Peabody]

B+ is the main drive. If your other issue(s) persist, show us some pictures.

[repetto74]

Actually the situation is as follow :

I have measured the B+ at the Testing Point marked on the PCB (where a 68 kohms resistor is mounted) so red lead on one leg of the resistor and black lead to the box of the TV tuner, well I measure just around 87 VDC where I should read almost 155 VDC. Turning the B+ trim will just change the voltage range of about 7-8 VDC not more. So I am definitely missing voltage somewhere but the actual B+ is actual enough to drive the flyback and display a very dim image.
Turning the G2 pot on the flyback is very sensitive. The image changes from a full picture with retrace lines to no picture at all by just moving the pot a little bit. The "sweet spot" is just a dim picture.

The B+ is the problem. I have measured the resistance of the 68k resistor and I read 160-170 kohms fluctuating. Weird, I am supposed to read a value close to 68K.