COLECOVISION SCREEN SCRAMBLED or distorted

[uveprom]

Hi,

 

It was with only black screen for long time,,, now check it again, i did see L14 2.7uh open, so i replace with 10uh because i dont have 2.7uh,

 

now it show this: i need to know if by the L14 value or is other problem ?

 

 

 

 

 

 

thanks for answer,

 

 

 

[+nanochess]

Is it a PAL Colecovision? never have seen so weird synchro.

[uveprom]

NTSC, but my ask is, L14 2.7uh is open, i replace with 10uh, it can be the problem for that ?

[uveprom]

I think is ntsc . i will try in other tv set,

[uveprom]

My colecovision uses 9928

[+nanochess]

My colecovision uses 9928

 

It's NTSC then. I never have seen this problem.

 

I would suggest checking the pin 36 of VDP using a RCA jack for composite output, connect it to center, put the other side to ground and it should display a black and white picture in your TV.

 

If the synchro is bad then the VDP is fried, it happened me one time.

 

If the synchro is good then the RF modulator is the problem, there are two potentiometers that can be adjusted but I never tried moving them because I don't know what purpose are these.

[uveprom]

I have a new 9928, but nothing change in it, so both 9928 are ok,

 

thanks for the tip. i will try,

 

the pots in rf is one for audio and the other for fine tunning,

 

i think the problem is the VDP clock, is generated for 2x 7404 gates, and it uses a 2.7uh to generate the vdp clock, i dont have the 2.7uh to replace, im usisng 10uh, i will try to find one to see,

 

thanks for post,

[uveprom]

The problem was L14, is for VDP clock,

 

problem solved,

 

thanks for answer,