My adventures in HL67A750 repair...
I have a 67", purchased in '08, and it has performed flawlessly for 6 years ( and still works fine). Been reading this forum since '08, and I have become familiar with most of the reported problems. A few years ago I bought a set of replacement modules, while they were still available and cheap, to be prepared for my set's demise.
This past spring, I contacted a fellow thru this forum, who lives nearby, about his dead HL67A750, and agreed to take it off his hands for a pittance. Its been sitting on my workbench all summer, and I finally got the motivation to work on it this weekend. The symptom: no picture, reboots 3 times, then the 3 status leds flash. Each reboot produces a short (50ms or so) flicker of white light on the screen, barely visible. The guy said he replaced the power supplies, which didn't help, then gave up.
I tested the R, G, and B LEDs, all are good.
The sub-SMPS supply produces 16V to the LED driver, so I assume the supplies are good (since the main board is operating).
So I replace the LED driver, does not fix the problem.
So I replace the DMD board (keeping the original DMD chip), does not fix the problem.
So I pull out the main board + main SMPS combo, to swap the main board. I notice one of the SMPS big electrolytic caps has a slight bulge, so I swap the main SMPS board first. Bingo, problem fixed.
In retrospect, now I understand the problem. The main SMPS provides low voltage to the main (control) board, and high voltage (300+ volts) to the sub-SMPS. The bad caps in the HV supply to the LED driver cause the 300V to fold when the high current draw from the LEDs begins, killing the 16V output. The control board senses the loss of light and reboots.
I guess the previous owner didn't replace the main SMPS, or put in a bad one. Too bad I replaced the DMD board first, as that means I had to go thru the optical alignment, which is a chore, and requires service menu steps to reprogram the CCA data. Live & learn. I discovered the tilt (image rotation) procedure, which I wasn't aware of before. Glad that I have the service manual to guide me.
Now I have a working spare HL67A750, and no place to put it