LCD 19" BENQ T905 problems

[silverdr]

Re: LCD 19" BENQ T905 problems

Hello group, I've got the 48.L1J02.A02 board which blows fuses (the main 2A one) - I found one leaking capacitor (C605 - 100uF/450V) but this couldn't be shorting, could it? When removing it one leg simply fell away.. What else should I be looking at? I use this schematic. Things before the 4 diode Graetz rectifier are OK. I suspected the rectifier itself but it also seems OK. Right after the rectifier the best looking candidate seems the Q601. Is the STP7NK80ZFP "Power MOSFET" (on the schematic called Q601 - 2SK3264) a typical failure? How to check it. What the ohmmeter should show? Every bit of help appreciated.

[jetadm123]

Re: LCD 19" BENQ T905 problems

D10PF-06-6K036534 is probably:

std10pf06

[adjnabi]

Re: LCD 19" BENQ T905 problems

Hello everyone

First say that I am from Spain and sorry for my English , I am using google translator.
My monitor is a Benq T905 . Has the problem of two seconds and off . If I connect it to pc , I see the desktop and two seconds and off, after shotdown continuous green LED and shortly after passing yellow

With a multimeter checked

Picofuse (PF801*) = 0.04 ohms, ¿Is good?
Two C5707 = Bad
Two D10PF-06-6K036534 (Q812* - Q805*) = Bad

*See Photo

I have doubts:

¿Where to buy or compatible D10PF-06-6K036534?, I do not find
What Picofuse buy considering that I live in Spain ( 220V ) ? This is good for me?--->Fuse3A 125V. Reading the post 99...Yes, I think so

First photo.....

Green star = Changed
Yellow star = Good
Red star = Bad

I will change the yellow and red stars , but any suggestions? (Also I will review welds as stated in the manual....A guide on how to troubleshoot 2 seconds to black)

Second photo....

Is the pic not find it anywhere , any equivalent ?

Wrote the best I could , thanks for your time and work. A greeting

[R_J]

Re: LCD 19" BENQ T905 problems

I just repaired a Dell E173FPb (Benq board) that had one shorted 2sc5707, and the cause was poor solder connections on components in the inverter, (transformer and cap. c735) plus other misc. poor connections. check the connections with a magnifier, I use an old eye piece from an old camcorder, but any magnifier will help, just look for what looks like a small dark circle around the components lead where it is soldered, and just resolder it. They will look something like this more or less

[manthi]

Re: LCD 19" BENQ T905 problems

hey looks like it's working.

i replaced the 2 c5707 and the pico fuse, and the problem is gone.
but now i have the most challenging part to do, if i want to do a proper job

My standard operating procedure with these monitors is:

• Replace all of the secondary caps.
  
• Desolder all 4 inverter transformers legs and reflow them with new solder.
  
• Desolder all 4 transistors and the polyester caps (between the transistors) and inductors (nearby the transistors) for the inverter and reflow them.
  
• Check the rest of the board over with a magnifier for other bad joints.

If you haven't done all 4 steps in the list you will have a repeat failure.

since soldering is not my specialty, i am afraid that by trying to unsolder and redo all of the above steps, i might to more bad than good.
if i look at Capullaco story i think that is what happen to him
he bite off more than he could chew, and ended up with a big spark, and a dead lcd.
what do you think i should do the required steps and risk a total failure, or take a chance and leave the job as is (2 new c5707 1 picofuse and resolded polyester caps)

and a BIG THANKS to all the people that contributed to this thread, it is always fun to learn new things, in the end, it cost me more than buying a used lcd, but learning something knew is priceless

[manthi]

Re: LCD 19" BENQ T905 problems

i ordered a kit 4x c5707 2x fu9024n 1x 3a 125v fuse,
so it should be enough to replace my parts even if i damage one or two, the fuse is the only piece i don't have any spare, but my local store has it (the only part he has actually).
so time to practice now

[selldoor]

Re: LCD 19" BENQ T905 problems

You should replace the 5705s in pairs even if one is ok it is likely to go when paired with a new one. That is why I said order extras.
2 weeks will give you lots of time to practice soldering and learn what the parts
are called. We cant always see the numbers

You REALLY do need to resolder ALL if you dont the 5707s will blow within a week
(often quicker)

[manthi]

Re: LCD 19" BENQ T905 problems

i bought a 25w weller iron,
i removed pf801, it is dead
removed q808 q809, one is dead but the other one looks good, when test it i get same result than q815 q816 (over range)
i resolded the c826 leg,
now i need to buy the 3a 125v fuse and the c5707 , couldn't find them at my local store, so i am going to order them from ebay,
so it's going to take at least 2 weeks to arrive
i will post an update

[manthi]

Re: LCD 19" BENQ T905 problems

Have you not read this thread it is mentioned over and over again
Recently post 145 and 153

yes i read the entire thread, but for a novice like me, all those name transformer/inverter/caps/mosfet/capacitor diode..etc it get confusing.
it is easier to understand if for exemple you say check pf801
or resolder c824 c826 , then i know what you are talking about,
anyways no matter what, all of you are of a great help, i sure couldn't fix that screen without your help

[selldoor]

Re: LCD 19" BENQ T905 problems

when you say [resolder ALL the high voltage joints ] do you mean the 4 inverter transformers t801-802-803-804?

Have you not read this thread it is mentioned over and over again
Recently post 145 and 153

[manthi]

Re: LCD 19" BENQ T905 problems

You dont actually say what your meter was set on if 200ohms then 808 and 809 are off but assuming the "1" is on the left of the meter screen indicating over scale then q815 q816 q805 and q812 are good.
If you are ordering get at least 2 extra. As already said it best to resolder ALL the high voltage joints - suggest remove as much of the old solder as you can and replace with fresh leaded solder.

yes it was set at 200 ohm.
when you say [resolder ALL the high voltage joints ] do you mean the 4 inverter transformers t801-802-803-804?

i am going to practice soldering on a scrapped board, and see how it goes.
what material should i buy?
http://www.canadiantire.ca/en/tools-...soldering.html

[selldoor]

Re: LCD 19" BENQ T905 problems

so
q808 and q809 give me reading of
leg1 to leg 2 03.4
leg1 to leg 3 03.0
leg2 to leg 3 00.8

q815 and q816
leg1 to leg 2 1
leg1 to leg 3 1
leg2 to leg 3 1

q805 and q812
leg1 to leg 2 1
leg1 to leg 3 1
leg2 to leg 3 1

so if i understand this correctly, my pico fuse pf801 is dead so are q808 q809
and c826 has a broken soldering ,
am i right, what else?

You dont actually say what your meter was set on if 200ohms then 808 and 809 are off but assuming the "1" is on the left of the meter screen indicating over scale then q815 q816 q805 and q812 are good.
If you are ordering get at least 2 extra. As already said it best to resolder ALL the high voltage joints - suggest remove as much of the old solder as you can and replace with fresh leaded solder.

[manthi]

Re: LCD 19" BENQ T905 problems

ok thanks guys, now i need to get some equipment and spare parts

[budm]

Re: LCD 19" BENQ T905 problems

That fuse is open, then you need to check those transistors/MOSFETs for shorts/low Ohm, it looks like you do have some with low Ohms readings. Remove them and test them off the board.

[manthi]

Re: LCD 19" BENQ T905 problems

1 Ohm? or over range? Touch the two probes together and tell us what you read, the fuse should gives about the same reading, it sounds like the fuse is open.

if i touch the prob together i get 00.3, but on the fuse it says 1 so i think it means over range, check picture

[manthi]

Re: LCD 19" BENQ T905 problems

Some browning is normal.



Here is how I test transistors in circuit.

a) put black probe (com) on pin 1 and red probe on pin 2 - read ohm
b) put black probe (com) on pin 1 and red probe on pin 3 - read ohm
c) put black probe (com) on pin 2 and red probe on pin 3 - read ohm

If any ohm reading is less than 50 ohm you have a shorted transistor and it will need to be replaced.

edit:

Some boards will have a fuse or picofuse and they may be open because a transistor was shorted or some other component went bad.

You can test for open fuses by (with power off and unplugged)

a) put black probe (com) on one pin and red probe on other pin - read ohm

If the reading is 0.3 or 0.4 ohm you have a good fuse. Anything higher is a sign of an open fuse. Do NOT replace fuses and turn on the power back on without checking for what caused the fuse to go open otherwise you will just be replacing the fuse again.

so
q808 and q809 give me reading of
leg1 to leg 2 03.4
leg1 to leg 3 03.0
leg2 to leg 3 00.8

q815 and q816
leg1 to leg 2 1
leg1 to leg 3 1
leg2 to leg 3 1

q805 and q812
leg1 to leg 2 1
leg1 to leg 3 1
leg2 to leg 3 1

so if i understand this correctly, my pico fuse pf801 is dead so are q808 q809
and c826 has a broken soldering ,
am i right, what else?

[budm]

Re: LCD 19" BENQ T905 problems

1 Ohm? or over range? Touch the two probes together and tell us what you read, the fuse should gives about the same reading, it sounds like the fuse is open.

[manthi]

Re: LCD 19" BENQ T905 problems

ok i set my multimeter on 200 ohm, and when i check pf801, it stays at 1

[manthi]

Re: LCD 19" BENQ T905 problems

ok sorry guys i didn't see there was already answers, i am going to check what you ask

[manthi]

Re: LCD 19" BENQ T905 problems

Check also the polyester capacitors at the switching transformers. C824 and C826 (220 nF, 160V) usually have dry solder joint in 90% of the cases due to ultrasonic vibration from the switching current.

Chris

i think it's what i have here no? it is one of c826 leg