# Rear Projection TV Convergence Board Project

#### sjgallagher2

Joined Feb 6, 2013
131
I'm not sure if I need help on this project or not, but I felt like sharing to sort of log my work and recap what I've done for myself and anyone interested. My friends and I picked up a large rear-projection TV from the curb several months ago and brought it back to our dorm. I've been working at fixing it ever since, on-and-off. When we first turned it on, the colors were very misaligned, and we only had red and green- no blue.

After probing around the thing for a while, I realized the smart thing to do would be to just google it. I did, and found solutions: The convergence board in the tv had a pair of blown ICs, which messed up the colors. The blue wouldn't show up because of algae in the coolant in the CRT. I replaced the coolant first, and cleaned out the CRT with alcohol to make sure that stuff stayed away. Like magic, the blue came back! Happy moment.

At the same time, I'd ordered new ICs from ebay for around $8, which seems like a cheap price. I was skeptical if they would be good or not. After desoldering the old ICs and putting in the new ones, I fired up the TV and found no change. I realized that if something had blown - e.g. a resistor or something - I might have destroyed the new ICs. Googling the problem more confirmed it, and I felt stupid. So I went to work on the board, checking resistances everywhere. As of yet, I've found no shorts, but one capacitor connection was open. So I soldered that back, and with blithe hope I checked how the tv would work with the board. No dice. So I unplugged the output from the board and turned the TV on again, as I began to fear a firmware problem. No change! That was good news since I know that the problem is almost definitely on that board. It could as well be with the inputs, or the output, but I have a little more of an idea of where to go from here. The next step is to get familiar with the ICs I replaced. They're op-amps, heavy duty I might add. Lots of pins, lots of redundancy with the power. So my next step, I figure, is to test if the ICs are blown or not. I have the datasheet in hand and I'm getting to work on a quick test circuit once I finish writing this! A few pictures and schematics: The left most is the CG amp board, then the flyback used to power the CRT (included for no particular reason other than I figured since I had the picture I would include it), and the convergence board, and CG amp schematics. CG amp is what I'm working on. Schematics are low quality since they're picture versions of the PDF manual, but I didn't want to post the PDF. Sadly, pdf to image converters aren't too high quality. If anybody has had issues with rear-projections before and has any tips for us, that'd be welcome! Or any stories in general. These things used to go for big$\$, but today they're next to free, and I've noticed a large crowd has taken to fixing them up for a big, free TV. Great stuff.

That's all for now! Until next time, all.
Sam Gallagher

#### Dodgydave

Joined Jun 22, 2012
9,317
Do you have red green and blue signals present on the the crt pcb at the tube, to see if the tube is at fault you can swap the blue for a working colour and see if it appears on the screen.