RCA rlded3950a-b sound but no video

[wiseowl9000]

Re: RCA rlded3950a-b sound but no video

Whoops. I misread the resistor value, 47 Ohm not 470 Ohm. I ordered ERJ-P08J470V 47 Ohm Surface Mount Resistors. Will desolder the 470 Ohm ones and replace with the above.

Usually use the TV without the inbuilt sound, tried using sound and nothing. Not sure when that part of the system failed. Might be related to the power supply issue or might not.

[wiseowl9000]

Re: RCA rlded3950a-b sound but no video

The repair ran for a month then the same cap blew again. Looks like a fault I hadn't found to repair. It seemed to be running hot over that month too. I'm going to take it in to the repair shop now (having let them know I had a go at fixing it). Could in part be due to my poor soldering skills (poor solder joints).

Mosfet is burnt out and underside of board is browned (possibly excess resin from soldering the surface mount resistors).

Still, I had a good time trying to fix it and have spare components to send along with it to the repair shop.

[d8341]

Re: RCA rlded3950a-b sound but no video

I have a RCA 39 inch led hdtv that made a serious pop noise and picture went black but sound was ok. Thankfully I came across your forums and read for a couple of days now and decided to try and fix it myself. After the pop and video going i unplugged the tv right away. I plugged it back in and tv came on normally but only lasted about 15 minutes and video went black but still had sound. If I turn it off and back on right away it wound not change but if I wait just a minute or two it would come on normal again but only last five minutes and gone again. It doesn't matter if you unplug it and plug in again does it change anything. It seems like you have to wait about 10 or 15 minutes to get it to work 15 minutes at most no matter how long i wait plugged in or not. I also noticed when the video goes black...I can still see video if i use a flashlight near the screen. So needless to say the tv is 12 days over its 1 year warranty "lesson learned lol" and no help from RCA except to ship it to them and they will fix it for $175.00 + shipping and handling. So I took the cover off the back after finding and reading your forums and found a blue ceramic cap blown at C22 on the board. the cap is a 221 1kv. I replaced the cap and tried the tv but the tv does the same thing. So i took the back off again and noticed the voltage regulator " I think it is" I'm a newbie at this lol it's black and has three legs and is screwed to a heat sink. It looks like two legs shorted when the cap blew. Could this cause the problem and how would i go about checking it with a meter? Sorry for the long post.

Hi, MrBowtie: Thanks for your post!

I think I am facing the same situation and trying to fix my RCA tv. Are you able to get schematic of this power supply board? What is the value for C22, D5, R44, R45 and that MOSFET? I am going to order these parts to see if I can fix my TV.

[d8341]

Re: RCA rlded3950a-b sound but no video

OK, so the power MOSFET has Source (3) to Drain (2) shorted. The high voltage cap that blew up is for the RC Snubber circuit (the snubber RC network is connected in parallel with Source and Drain of the MOSFET), the cap is connected in series with R44/R45 (R44, R45 are connected in parallel), You need to check R44 and R45. If the snubber circuit failed, the the MOSFET will be damage.
There is also RCD snubber network (D5, C16, R39 that should be checked) which is connected in parallel with primary side of the transformer.
You also need to check the MOSFET Gate drive network (R23, R26, R26, R30, D25) for damage. The Gate drive network is connected between the Gate of the MOSFET and the GD (Gate Drive) pin 5 of that SMPS IC. You should check the resistance reading between pin 5 and the one end of the jumper JP9, report the reading. We also need the P/N of the SMPS IC.
You also need to check the Source resistor (R13?) that has heat shrink tubing on it sitting between the heat sink and the Main 450VDC filter cap, it could have blown open when the MOSFET shorted out.
So you have lots of components to check, if you don't, you can easily blow up your new parts.

May I ask what is the part number of IC2? Is it th e SMPS IC you mentioned in post? It seems gone on my power supply board and I need to find out its replacement. Thanks!

[lotas]

Re: RCA rlded3950a-b sound but no video

Ic2 - fan7930