Fix for Benq FP737s 17" (Q7T3)

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

Well found. The data sheet certainly has same digits. Are you able to verify that the the good one to the PCB has the same connections and is a P channel device as per data sheet? If it all checks out all should be well. Just have to find one to buy, maybe available from LCD parts web site

I agree the Benq PCBs have lousy tracks. Easily detach.

Hi again here is a status report on the HP (Benq Monitor). I replaced the transistors and the monitor came on and worked flawlessly.

However I found another problem as soon as power is applied one of the two inverter circuits come on and when the power button is pressed the other inverter circuit comes on along with the video. In other words when I press the power button to power the monitor down only 2 of the 4 CCFLs shut off.

So I take the board out again and find the problem a blown SMT MOSFET IC. The IC package has a small bubble in it which is never good. I saw it while working on the board but I denied there was a problem .

So I measure the SMT FET that is not bubbled from Source To Drain (the side of the inverter that was shutting off) and I get a voltage drop.

Then I measure from Source To Drain on the bubbled FET and its Open Circuit.

For future reference I have circled the FETS that shut down the inverter circuits there are two one for each circuit which drives 2 CCFL lamps.

Well now I've found my shutdown problem now here is my question.

I think I've found a replacement MOSFET IC but would like an opinion. I have plenty of experience soldering these things so its no biggie for me.

The IC has the following numbers on it.

4431

BP (Triangle) Probably Vishay's Logo

L47C (Probably A Lot Number)

Here is a link to the datasheet of what I think is a suitable replacement:

http://www.vishay.com/docs/71803/71803.pdf

What do you guys think?

Thanks for any help in advance.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

I see Mouser has these SI4430 in stock.

[Krankshaft]

Re: Fix for Benq FP737s 17" (Q7T3)

Thanks for the reply.

I was able to get them from Newark.com with them I get the parts in 2 days via UPS ground since they are closer to NJ hopefully I'll get them the day before Thanksgiving or at least the day after.

In case anyone ever needs these here is the link:

Note: The T1-E3 designation just means its lead free.

http://www.newark.com/jsp/search/pro...sp?SKU=06J7725

Mouser is another lifesaver along with Digikey which is where I get my Panasonic FC caps from but shipments from them via ground take around a week to get to me.

I removed the FET and checked the traces underneath pins 1-3 on one side are tied together for the source pin 4 is the gate and pins 5-8 are for the drain.

I'm lucky that this FET went short circuit rather then open or I'd probably be probing the Inverter PWM IC and ringing the transformers right about now.

Oh yeah and correction the faulty FET showed a short circuit from source to drain wow I almost wrote open circuit again bad hands .

[Krankshaft]

Re: Fix for Benq FP737s 17" (Q7T3)

Well I replaced the shorted MOSFET and the other working one just to be safe and the monitor is back in business.

Both inverter circuits now shut off when I hit the power button .

This thing is great with a 1000:1 contrast ratio.

The only better device contrast wise that I have is my DLP projector at 2000:1 and the DLP panel on that is only 1/2 inch wide!

The MOSFET IC was an exact replacement all of the manufacturer symbols were the same as the ones on the old IC.

Alldatasheet.com was a lifesaver as well which found the IC for me just by typing the four numbers .

Yet another perfectly good monitor saved from the landfill with just a few bucks.

Now if I could only find a broken LCD TV on a curb somewhere and I'll have a nice TV to go with my Wii and 360 .

[shadow]

Re: Fix for Benq FP737s 17" (Q7T3)

Now if I could only find a broken LCD TV on a curb somewhere and I'll have a nice TV to go with my Wii and 360 .

We can only hope!

[thekingmtg]

Re: Fix for Benq FP737s 17" (Q7T3)

hi, i have a benq q7c3 modell, it's very similar, the sympton is the same, tha fuse of 3a is blown, i checked the board and find one fet and one 2sc5707 shorted, the only difference in that circuits is that the fu9024n is a std10pf06, but the specification are practically equal, in fact the 9024 is a replacement of the st. Well i changed the three transistor, one std10pf06 and two 2sc5707 and the fuse, the monitor now gets on but of in 2 seconds, well i tested it hard, well at the end i put a 2k2 resistor from ground to the out of the tl1451 pins 7 out1 and pin 10 out2, and in one side the lamps get on ok, and in the other get on but a little poor than the other and th transistors gets very hot, i changed the transistor in pairs, and the fail change from the other side, i didn't tell that the transistors that gets hot are ¡¡ the newer ones !!, the older works great and don't become hot, can be the new transistors bad?, it tested ok in the diode mode 0,56 b-e b-c , i can't believe that, this fail turns me crazy, i never suspect of the new transistors, well if you can help me thanks, sorry for my english, i'm form uruguay, thanks friends.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

Sorry to hear that the monitor still does not work correctly. Transistors get hot. First check that you inserted correctly for e.b.c. If that is correct check capacitors connected to the inverter transformers, may need replacing. If the caps are OK check the output caps usually blue, look for shorts. If all caps are OK check transformers, this is hard, it needs a ringing tester.


The transistors will get hot if:
1. There is insufficient drive ( incorrectly inserted)
2. Excessive loading (failed caps or transformer or lamp)

Lamps can be tested by swapping to the good inverter to see if this cuases a problem.

Most unlikely the transistors are the problem if they are 2SC5707.

[Krankshaft]

Re: Fix for Benq FP737s 17" (Q7T3)

Yes make sure that you insert the transistors properly there will be a white line silkscreened on the board make sure that the transistors metal back faces this white line. My HP monitor manufactured by Benq had this hopefully yours does too.

If so the transistor is in backwards be sure to diode check them in this case and hope they are not blown out.

As Dav said be sure to check the caps if any are bulged replace them.

The transformer on the suspect inverter may have shorted turns which would cause the new driver transistors to fry as well. The fuse in question cuts off power to the inverter in the event of excess current draw. The fuse for the main power supply is a 250V fuse on the AC side.

These transistors do get warm but they shouldn't get so hot that you can't comfortably put your finger on it (after unplugging it of course).

I can't tell you how many times I've accidentally touched a live MOSFET heatsink in a switcher .

[thekingmtg]

Re: Fix for Benq FP737s 17" (Q7T3)

ok thanks, but i tell you before that i swapped the transistors?, i mean i swapped with the old ones, swapped the inverters, you understand?, i put the old transistor in whichever inverter and works fine so neither capicitor nor transformers are the problem, and the new transistor gets very hot in both sides i mean in both inverters, the inverters (2) works fine with the old transistors and bad with the new ones, and of course that i put htem well, i mean the old ones don't get hot, so?, thanks again.

[Krankshaft]

Re: Fix for Benq FP737s 17" (Q7T3)

What type are the new transistors did you replace them with the original Sanyo C5707 transistors or did you substitute?

[thekingmtg]

Re: Fix for Benq FP737s 17" (Q7T3)

i tought that are originals, it said c5707 and under that 4j, maybe are defective from the factory?, the appearance are like the originals, did i mention are smk, i mean superfical mount, but i think this is not the problem, well thanks.

[kc8adu]

Re: Fix for Benq FP737s 17" (Q7T3)

if you swap the pairs of transistors and only the new ones get hot you may have gotten remarks or counterfiets.

[Krankshaft]

Re: Fix for Benq FP737s 17" (Q7T3)

Indeed this heating up seems fishy. Do a search for C5707 on e-bay thats where I got mine and they worked great. The monitor they repaired I am using right now.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

I also confirm that the eBay supplier of 2SC5707 provides transistors that work well.

Having swapped transistors and the fault follows the transistors is does seem that the replacement transistors are the problem. Could they have been harmed/damaged at the first install? Either by incorrect insertion or overheating when soldering.

I do have another concern if the circuitry is the same as the FP 737s. If the MOSFET failed it is also possible that the drive transistors for this FET have also been damaged. Because these transistors are intended to quickly charge the FET input capacitance they deliver a short burst of charge current that is just fine. But if the FET fuses a much longer current duration is delivered into a short circuit (the capacitance no longer exists).

[Flavior]

Re: Fix for Benq FP737s 17" (Q7T3)

Salutes are again me,
The question is:
1) Does an alone wing of the inverter succeed in making to turn on both the lamps?

2) Is there way for ingannar the integrated one and to make him/it work with an only wing?

Thanks for the help

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

It is stated that both inverters work with original transistors, so problem with new transistors.

Not a good idea to load more that one lamp per section of inverter. There are good reasons why it is made with one lamp per inverter section or transformer.

[thekingmtg]

Re: Fix for Benq FP737s 17" (Q7T3)

it was the transistors, i can't believe that the seller give me those ''china'' replacements, i put other replacement 2sd843 it works well, there are to-200 capsule, but work fine, thanks to all.

[davmax]

Re: Fix for Benq FP737s 17" (Q7T3)

You said the transistors get hot in the inverter. I would expect the SD843 to be hotter than 2SC5707. For speed, the SD is much slower (higher switching loss) the ft is 1/33 less (10:330). The gain is about 1/3 and the ON saturation voltage is close to double. The 2SC5707 is hard to beat or replace.

I will interested to hear if there is a noticable heat difference. You have certainly proved that you had a transistor problem, well done.

[thekingmtg]

Re: Fix for Benq FP737s 17" (Q7T3)

yes i know the differences on 2sd843, but beleive me i don't think that the inverter work at very high speed, it goes well with 843, and the answer is no, they don't get hotter, just a little more of the 5707 but really insignificant, one of the 843 gets a little more hotter than the other, i believe is the transformer that have some turn burn or somethin, is the transforemer of the original and only burnt transistor, (the first cause of the fail, but the temperature problems is not a problem the double diode ic702 and ic 703 (to-220) capsule, are the diodes that seems like transistors with the bigger sink gets much more hotter, these ic's are before fuse (3A), i tought you understand, this diodes with capicitors give the source of the inverter (secondary part), well tell me if you don't understand something, alex.

[thekingmtg]

Re: Fix for Benq FP737s 17" (Q7T3)

i forget it, i test the tft from about 2 hours and nothing burn.