Rifaa
Rifaa
Branch Unspecified
10 May 2009

Cross a sharp LCD TV with a BenQ, what would you get? (Part 2)

Continued ...

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Here is a comparison of both the Inverter Assy. As you can see there is a major difference in them. The High Voltage generation technics is obviously different and the Input Vcc is also quite different. The BenQ uses a 14V Supply and the HV generation is quite similar that of a LCD monitor.
It uses a step up Tx and the primary is driven in push pull stage with a common low profile high Voltage transistor that is typically found in LCD monitors. Now these transistor's failure rate is quite high as I have found, mainly shorting out but in this case for the time being none of them have any faults besides the Tx and connector. So I bypassed the faulty stage feed back and Powered the Invereter using a separate supply and enabled the switch on terminals, the back lit switched on as before and went pssssssst, pssssst and pooooooooof and up came smokes 😕, I went like What the.???
I mean bypassing a stage never did this to me before. And to make things worse a few of the output stage transistor went up in smoke too. So the sharp inverter is next in line. The Sharp Inverter uses 400V DC to power up and it's drive technics is quite different. It a uses a single output stage to drive a single transformer coupled to a number of isolation transformers and uses opto's in the feed back loop to sense the HV loading. Quite complex and the best part is all the inverter boards are functional, so my guess is this technics is quite reliable and it also generated less heat. The difficulty was to get 400V DC without using the sharp PSU, even if I rectify AC mains the max is 280V DC. It uses a charge pump to increase the 280V to 400V. So I had to use the sharp PSU some how. So that's final. Next part is to interface the BenQ tubes to the Sharp Inverter.
Below is a picture of both the Tube Assembly dismantled.

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As you can see the number of tubes is same and identical, even though they from different manufactures. The Connectors was different, so I have to compromise.
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I removed the BenQ tube connectors and replaced them with sharp ones so that I can use the sharp inverter. A hectic job though. Never the less it was assembled as shown below and ready to power up.

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After connecting all the interconnects and the PCB's, I switched on, it lit for a few sec and went off, too bright and too fast to notice any thing, I have to take a picture to see what was wrong. ( @ fast shutter speed )

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So here was the main source of the problem, faulty tubes. The sharp Inverter LV feed back senses the burned tubes and switches off the inverter. Donno when this has occurred, it could be their before or might be there as a result of my second attempt, either way no one is there to complain.
The sharp Back lit is not turning off proving that it's tubes are OK.
Now I have to replace the tubes, something I haven't dream of doing before.

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The tubes removal was very tricky. As I can see the tubes were quite fragile, but I was able to remove all of them without breaking a sweat.

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Removed Tubes. ( quite nice I'll say, come to think of it, these are the kind of light tubes used by Jedi's as there light saber, don't you think, I can make a mini light saber 😁. but no saber fights with this fragile tube)

Next was to remove the sharp ones, and it goes along fine
And as I was cleaning the solder at their terminals to be assembled in the BenQ tray, it was the last tube, was very careful, but at the very last minute....crack. I broke one. So I have to replace one with a benQ tube, something I did not like since most of the tubes were dead but I have no other choice

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Here is the final Assembly. And it never switched off to my delight.
Here is a pic of the BenQ TV
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https://www.crazyengineers.com/forum...-lcd-tv-benq-what-would-you-get-part-3-a.html
10 May 2009
Woa ! 😁

Super!
Rifaa

Rifaa

Branch Unspecified
11 May 2009
think so? Biggie.
Thanks
silverscorpion

silverscorpion

Branch Unspecified
11 May 2009
Great going.. Waiting for the next part..😀😀
Harshad Italiya

Harshad Italiya

Electronics and Communication
11 May 2009
Keep them coming Rifaa
Ashraf HZ

Ashraf HZ

Communications
11 May 2009
respect, my friend.
Rifaa

Rifaa

Branch Unspecified
11 May 2009
thanks for the motivation. the best part is yet to come. A little busy right now

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