Repairing a Mitsubishi WS 55909 CRT projection HDTV

[hardwareguy]

Got a call on a Mits WS55909 55" CRT projection TV with the continuous flashing green light of death.

Here is a basic overview of what was wrong.

One blown pico fuse near the main SMPS transformer on the main power board (the one in the middle of the set). The convergence amplifier had failed. Amp #5 output in the STK 393-110 module was shorted to +VCC.

Fixed that so I thought the TV would power back up.....wrong!

The flashing green light of death continued..... some Googling later and I had a lead on another issue...what else but our old nemesis, bad caps, this time in the "DM" module.

The DM module contains the DTV tuner and all the MPEG decode stuff. There are 3 big chips under heatsinks, a lot of RAM and some ROMs on the board among other things. The problem isn't on this main board, its on a daughterboard inside the same box labeled "DM POWER" This is a simple SMPS that runs on the standby voltages from the main power board. There are 7 Nichicon VR 1000uF 16V caps that like to die. Mine failed without any external sign of failure although others report bulging.

I pulled one and it measured 3 nano farads! I then knew I had found the issue. As luck would have it, I had exactly 7 Nichicon HZ 1000uF 16V caps in my toolbox and I was able to complete repairs that night.

The owner and I performed a rough convergence calibration and then he regretted giving this TV to his daughter and buying an LCD. The contrast on CRT just cant be beat. They are still worth fixing.

[hardwareguy]

Re: Repairing a Mitsubishi WS 55909 CRT projection HDTV

Update....if you find Nichicon VR on the DM Power board, replace them regardless of their apperance. VR is not a low ESR type and as such it has no business being on the output filter of a switch mode regulator that powers what is essentially a computer!

Im surprised Mitsubishi of all firms would make such a silly mistake on such an expensive set.

[Maxxarcade]

Re: Repairing a Mitsubishi WS 55909 CRT projection HDTV

Mitsubishi had cap issues even back in the 90's. Nichicon and Rubycon both were commonly bad at the time. They always smelled like fish when heated with a soldering iron

That said, once repaired, they always look great. I have several Mits sets in arcade games that have over 25,000 hours on them and still running.