I hope someone can help me with this issue. I would like to try and repair this myself.
I started loosing red sporadically and it increased in frequency to the point that now I only have blue and green. I have checked other inputs and it also occurs on the DVD input and front video input, so I know it is not just an input cable. When I take the front panels of the TV off, I can see a faint amber glow at the base of all 3 CRT tubes. I am just not getting any light from the red CRT. I assume the CRT is not burned out? Occasionally I will still see it come on for 10 to 30 seconds.
I have a full set of service manuals, but not much experience with TVs. Any idea where to start? Is this a convergence board issue?
Thanks, Bruce
doubt i the converence would cause is problem, could be the red driver board, or an rgb circuit fault. swap the red driver board with the green driver board and see if the green stops working, and if the red comes back you know he red crt is good, if the green does not work then the red crt driver board id bad, if the green does work with the red crt driver board then the red crt is bad,
Thanks for the response, Larry. Great idea!
I took of the front panel to access the CRT driver boards. From the front the red is on the left, the green in the middle and blue on the right. There are wires running from the blue driver board to the green driver board that were not long enough to let me just switch the red board with the green board. So I had to move the green board to the red CRT, the blue board to the green CRT and the red board all the way to the right to the Blue CRT. Now I have red and green with no blue on the display. So it looks like the red driver board is suspect. It could also be no red output from the RGB PCB? Do I try switching the the red and green inputs to the driver boards?
Thanks again, Bruce
yes thats what you need to do now to pin it down
OK, I switched the SG and SR CRT driver board inputs. The red output from the RGB PCB does provide a good signal to the CRT driver board. So it likes like I have a problem with the red CRT driver board
I will pull the board and look for any bad solder connections. Are there some likely components that would fail on this board? I do have a digital multimeter and soldering experience, but I am not sure what to check.
Thanks, Bruce
I don't see any bad solder connections and none of the components look physically stressed. There are three transistors on the board.
2SC3790 NPN Epitaxial Planar Silicon Transistors High-Definition CRT Display Video Output
2SA1480 PNP Epitaxial Planar Silicon Transistors High-Definition CRT Display Video Output
2SC3942 Power Device - Power Transistors - General-Purpose power amplification Panasonic
Do you think I shold try to pull these transistors and test them?
This is the schematic.
Thanks, Bruce
make sure the 230 and the 12 volts are there and for sure check C6R02 capacitor I have replaecd many of those caps
It's fixed!
I found the parts I needed at B&D Enterprises. With a $15 minimum, I got a good selection of components. I suspected that it was the 2SC3942 power transistor, but replaced the C6R02 capacitor first. At 8 years, it can't hurt. That wasn't the problem, but replacing the power transistor fixed it.
Thanks for your help, Larry!!
Well, excellent thread guys! Had no green signsl. Had a "repairman" come and tell me the crt board and convergence board were blown, but said he could not find replacement boards. I did the swaparoo on the CRT boards, and there was certainly a green signal coming into the crt board. Could not find a replacement one ANYWHERE. (note to self, never buy mitsubishi electronics products again as they do not support their customers). Bought the transistors, some of the caps, and some of the diodes shown on above schematic. Just replaced them all. B&D electronics is a good find, they had most of the stuff needed and even suggested an alternate for one of the transistors that was obsolete. TV turned on and problem is now solved.
BTW, had to unsolder the mounting pins on the big heat sink and remount it a little higher off the board to match the replacement transistor.
ALso, I drilled some ventilation holes in the front pressed board panel. I think these CRT boards overheat and fail. That might help longevity
Yeah, I pulled the pressed board completely off my pioneer, that thing gets smokin hot!! Plus putting it in the basement will probably give it an extra year of life! i have even considered putting a 120V fan right on the heatsink for convergence chips!! Great times!
Well, excellent thread guys! Had no green signsl. Had a "repairman" come and tell me the crt board and convergence board were blown, but said he could not find replacement boards. I did the swaparoo on the CRT boards, and there was certainly a green signal coming into the crt board. Could not find a replacement one ANYWHERE. (note to self, never buy mitsubishi electronics products again as they do not support their customers). Bought the transistors, some of the caps, and some of the diodes shown on above schematic. Just replaced them all. B&D electronics is a good find, they had most of the stuff needed and even suggested an alternate for one of the transistors that was obsolete. TV turned on and problem is now solved.
BTW, had to unsolder the mounting pins on the big heat sink and remount it a little higher off the board to match the replacement transistor.
ALso, I drilled some ventilation holes in the front pressed board panel. I think these CRT boards overheat and fail. That might help longevity
Yeah, I pulled the pressed board completely off my pioneer, that thing gets smokin hot!! Plus putting it in the basement will probably give it an extra year of life! i have even considered putting a 120V fan right on the heatsink for convergence chips!! Great times!