First RGB mod questions - Philips CRT 29SX8976 G8 Chassis

[Gazscart2]

Well ive finally joined the forum after reading and absorbing all the amazing information regarding CRT mods and general. Thank you to all firstly.

I am hoping I can ask for your support with RGB modding this particular TV. The schematic is the G8 chassis and I've attached the link to the file here if you are able to have a look.....

https://freeservicemanuals.info/en/serv ... e_vignette

I have repaired CRTs with convergence and neck issues before (tilt). Replaced some transistors and a couple of caps (Geometry circuits) so I feel comfortable working with CRTs and discharging. However my technical knowledge of electronic diagrams is limited and I'm learning all the time. I have all the relevant tools solder gun remover, avo meter I just need to improve my knowledge of the TV.

I wonder if the community would be able to help me identify the IC for the RGB signal and the OSD. I think its on page 14 here but cant be sure? I'm just following the outputs back tot he signal processor

Any help would be much appreciated!

All the best

G

[MarkOZLAD]

Looks like TDA4681 (IC 7551) is the target chip for the mod. It has two RGB inputs, one for PIP and one for OSD. I'd be looking to hijack the pins for PIP 10,11,12,13.

I'd probably try removing the PIP chip 1140 (or at least lifting legs 1,2,4 and 5), make sure resistors 4562, 4563 and 4564 have 75 Ohm resistors in them (these will be the termination). I would inject my RGB into the holes for the PIP chip pins 4,2 and 1 respectively. I'd then take 5V to a switch and then into Pin 5 of the holes left by PIP chip.

Need to make sure capacitor positions 2565, 2566 and 2567 have capacitors in them. Factory ones should be fine but if not there some 10nF capacitors will work in there.

(Page 10 of Manual)

[Gazscart2]

Thanks MarkOZLAD

My next question is that I only have a universal remote and I have not found the PIP option. As I can still access the OSD via the universal remote could you advise what to do to hijack the OSD with muxing?

I really appreciate your help

G

[MarkOZLAD]

I don’t think you’ll need to access the PIP. I believe the 5V into the fast blanking will force RGB without the PIP being selected via remote.

Happy to have a look at the OSD circuit when I get the chance.

[MarkOZLAD]

Mux method would be to do a twist of 75R and 200R into holes left by removing 3562, 3563 and 3564. Blanking 5V into switch into 470r onto not grounded leg of 3565.

[Gazscart2]

Well, I have now had the board modded by a contact of mine as I didn't feel 100% confident. It looks like he's nailed it.... I will be trying this weekend... Shall I post pictures to help the community?

[Josh128]

By all means, please do.

[MarkOZLAD]

By all means, please do.

I’d go as far as to say “Hell yes!”

[Gazscart2]

https://www.dropbox.com/s/1tstogngqzcfo ... 2.jpg?dl=0

https://www.dropbox.com/s/nh4owjynxttz1 ... 7.jpg?dl=0

https://www.dropbox.com/s/0yougp6iy5wwv ... 2.jpg?dl=0

https://www.dropbox.com/s/2la9bvdgbrwen ... 8.jpg?dl=0

Hopefully that has worked, I received the board back from my contact and wired up the rest of the bnc connectors after a good clean down.

I must say I think I'm going to replace my jvc pvm for a while as I've checked geometry and convergence with a few tweaks and it's damn good.

Thanks again community!!!

[Gazscart2]

Hi all,

Need some more assistance. The RGB mod of the tv works fine, apart from a weird issue with either linearity or pinamp/cushion.

The best way to explain this is when there is a scrolling image from top to bottom the middle of the screen looks pinched but the top and bottom seem to extend outwards.

I've adjusted convergence and this is fine but the geometry is really frustrating. On a fixed image I. E. Circles it looks fine but as soon as it starts to scroll it looks like the image is going through pasta roller.....

With these tvs there is no service menu only pot adjustments and I'm getting somewhat confused as to why its doing this. Do I need to replace some caps?

Appreciate and help. I will take a video later and upload to dropbox if anyone can help.

Thanks all.

[MarkOZLAD]

That’s likely how it came from the factory. It’s a consumer TV, made to watch the 6 o’clock news.

[Gazscart2]

That’s likely how it came from the factory. It’s a consumer TV, made to watch the 6 o’clock news.

Good point to remeber...