samsung y buffer ic's

[sidecutter_5]

hi,this is my first post (be gentle with me) i'm going to try to replace two of the ic's on my y scan upper buffer board,part no-lj41-05121a.has anybody got any tips before i start? I have access to a hot air smd rework /hot plate setup.it's access to experience im missing. thank's

[Ohm Supplies]

Hello.

Yes, I've removed the ic's several times from this board & of sounds like you have the right kit to do it, what are you going to replace them with or are you going to make 1 good out of 2?
Regards
Andy

[daz]

Hi Andy
I had this very idea myself after realising only one IC would fail, I thought I could make one board out of two, but while removing and replacing the IC provides no problems I encounter problems removing the silicon cleanly, and this caused problems when re sitting the IC.
Any tips for removing the silicon easily?
Thanks
Daz

[brainstorm]

Hi all,

Is there a big saving replacing the IC ?
The complete board is not usually very expensive

Also, then there is the cause of the buffer IC failing,
Andy, I'm sure you make a fine kit for this very scenario!!

Brian

[sidecutter_5]

hi,sorry for the late reply.Had a go at this with the rework station, but due to my inexperience with the equipment i had a problem or two.
1,removing the pins and the ic together.
2,removing the ic,
At first i stupidly thaught that it was only the pins that held the ic in position on the board,it is as you all probably know is held on by a approx 10mm square pad soldered on to the board.
Binned the rework station idea and the soldering iron came out.Cut the pins off the ic and working from the back of the board with a hot iron, diluted the lead free stuff with some nice lead/tin mix solder, the chip came off the board ok.
Taking the pins of the chip off the board was a bit of solder wick.cleaned up ok.
will be replacing with new fe 3407f chips,ex china @£1.50 each.
It,s worth a go.
regards ste

[Ianm]

Hi All
New On here but been in the trade for a long while now and I am workshop based (that's the intro over    )
I replace these Ic's  and use a PCB preheater and a hot air rework station with a Quad flat pack nozzle on it, works great,
to remove the silicon glue I first remove the thick of it with a sharp blade then go around the IC with a fiber pencil,
the IC's I get are from China  and re flowing the new ones onto the pcb are no prob , use good smd reworking flux

[leo_the_noob]

I'm a newb myself and am going to attempt the replacement of the IC chips myself . I also have the LJ41-05121A and 5122A Samsung buffer boards. I need to decide how many chips need replacement first. I have a hot air station and some experience with BGA reflows so I think I'm up for the task. What is the proper procedure to test these buffers and identify good/bad IC chips? One board has a burned IC on it so that is obviously bad but I'd like a way to check them with a meter if possible. Thanks in advance for any help.

[sidecutter_5]

hi,leo best policy is to replace all the chips on both upper and lower y buffers.if one has burned out it's only a matter of time before another one craps out.and taking your ysus board fet's out again.
these buffer boards are a crap design in my opinion,as there are no heatsinks on the chips and as it's usually the top buffer that fails i can only assume that it is a heat problem.
have done this repair myself having limeted knowlege of smd chips so you will not have a problem.
If you are keeping the tv for yourself fit two silent 50 mm pc fans over the buffers/ysus fixed to the chassis rails.
I used a seperate 12v psu and added another 240v 5v coil relay on the psu linked to the 5v start up relay
get a good laptop charger or simalar (fits nice inside the tv)

[sidecutter_5]

checking the ic's
i will probably get reamed for telling you this
In the center of the buffer boards there is a matrix of holes about 3/4 inch square this is the ground,
make sure you have a good connection to this (flux in the holes etc)
test for shorts on each connector going to the screen cables
you can trace the tracks on the board to the bad chip.

[leo_the_noob]

I had not received a reply for a while so stopped checking on my post. Thanks for the help sidecutter. Using your instructions it looks like only the top IC im my upper buffer is shorted. I only ordered 3 buffer IC chips about 3 weeks ago so I'm still waiting on them. So in your experience replacing the 1 bad IC will be a temporary fix? How many of these repairs have you done and what has been their life expectancy so far? Thanks again for your help!!

[sidecutter_5]

hi leo,this trio of boards(upper,lower buffers and ysus) are legendary for causing problems if you only replace one of the chips it can cause an expensive chain of events.
all the chips have had the same amount of use so when is the next one going to let go?
when a chip shorts out it usually takes out the ysus fets as well so when you put your refurbished buffer in and fire it up it burns that board and your lower buffer as well.
check your ysus board fets for shorts first.
q5500
q5501
q5502
q5503
q5504
q5506
one of these is surface mount
i know it takes a long time for delivery of these fe chips be patient or it will bite you.
done two of these now one a phillips.
put fans in it if you are keeping it
regards ste

[Tellyfix]

Multimeter on diode range, check pins 34 and 36 on each IC. If you get a short circuit or about 0.8 (depending on polarity of probes then you have a faulty IC (usually top 1 or 2)....