Samsung LE40R76BD

[tom66]

Got this TV for a quite reasonable price! When plugged in and turned on, there is sound, but there are various multicoloured single pixel vertical lines on the display and no visible image as such.

After leaving it to warm up for about 20 minutes and turning it on again, I did get a nice picture.

I am thinking this is either a bad T-con (bad solder joint or maybe a bad MLCC/ceramic cap), or a bad cap on the PSU. None of the caps are bulging, but I'll test them with my ESR meter later. It doesn't have any problems turning on or off, it seems to be a later Samsung using Samxon capacitors instead (GF(?) series).

I'll post pictures shortly.

[tom66]

Re: Samsung LE40R76BD

Tested the capacitors. I'm getting 0.06 ohm ESR at worst for the 1000u/10V; this is just within specification, so I'm going to say the caps are most likely good, and give replacing the T-con a shot - could just be a bad solder joint under a BGA.

[tom66]

Re: Samsung LE40R76BD

I found a failed voltage regulator on the T-con.

The part # is LD1117-C549. STMicroelectronics.

Given the placement of resistors from the output to the ground/adjust pin, I'm guessing it's probably an adjustable regulator. These LD1117 regulators seem to fail all the time.

Input measures 5.2V, output measures about 1.1V and adjust is 0.57V.

There are two other regulators on this board, they test okay.

I'm wondering if when the set warmed up, this regulator started working properly again?

Also noticed the boost rail on the T-con sits at 4.3V, probably due to the main chip not working.

I just found my SD card reader, will upload pics very shortly...

[tom66]

Re: Samsung LE40R76BD

Pics attached.

[tom66]

Re: Samsung LE40R76BD

Since the other regulators are rated for 2.5V output and the faulty one is too I decided to fiddle around with bridging it to one or the other, just as a test. Once I did this, I got a picture - although a bit flickery it doesn't surprise me as it's clear one regulator isn't up to the job of powering the load of two. I've ordered a new regulator & will post if it fixes the problem.

[bbjunkie]

Re: Samsung LE40R76BD

Since the other regulators are rated for 2.5V output and the faulty one is too I decided to fiddle around with bridging it to one or the other, just as a test. Once I did this, I got a picture - although a bit flickery it doesn't surprise me as it's clear one regulator isn't up to the job of powering the load of two. I've ordered a new regulator & will post if it fixes the problem.

You have nerves of steel!

I think I would have bottled out and just tried a new regulator

[tom66]

Re: Samsung LE40R76BD

You have nerves of steel!

I think I would have bottled out and just tried a new regulator

A new T-con is £18 and a regulator is £2.50. Worst case I fry the T-con but I needed a new one anyway, might as well try and fix it.

[tom66]

Re: Samsung LE40R76BD

Just fixed this TV. I did a REAL bodge job trying to replace the LDO but eventually got it on. My main problem was I lifted the ADJ/GND pad so had to run a jumper wire, but it's now working.

I was at the office, where I only have a basic soldering iron, ideally I'd use my hot air station to remove the LDO then stick it on with a bit of solder paste and apply solder to the pins.

[bbjunkie]

Re: Samsung LE40R76BD

Sometimes the traces can be so easy lifted. I noticed the Vestel psu I am currently working on has very poor tracks, they lift if you even look at them the wrong way!
Sometimes difficult to get a good compromise between a hot enough iron to melt the solder quickly and too hot that it lifts tracks.

Another one saved from landfill though and another one for your tally!


Congratulations

Jim

[tom66]

Re: Samsung LE40R76BD

Tally updated. Total 18 monitors/TVs fixed.

The board uses ENIG, electro plated nickel-gold (basically gold plated pads). I'm not sure myself if these are more prone to coming off but I've heard they are.

It will undergo a soak test for a couple of hours to see if it lasts and I will glue the wire down properly and fix the bad soldering, but it looks like another TV fixed.

RRP sticker still left on back of TV from Cash Converters: £1,099.99. USED price.

These things were expensive back then. The people I picked it up from had replaced it with a DigitalArt (?) LCD TV, shame that one is going to die as I can already hear the intermittent "skip a beat" hf whining you get from nearly failed caps...

Shame the regulator failed, seems like poor design. I guess the designers think thermal protection will save the regulator but that's not true. If the regulator runs close to thermal protection for long periods of time it will eventually fail. Every 10degC rise in temperature approximately halves lifespan. Most of these parts will do 10,000,000 hours at 25degC junction but at 150degC junction that is only 100 days extrapolate that to maybe 2-3 years and you can see it must have been running hot.

In this case it didn't fail s/c or o/c but was walking wounded - occasionally powering up to full 2.5V but mostly sitting at 1.1V. LDOs are great, but their limitations must be understood. I reckon if the designers had used a 2.5V buck converter they could have ditched all three regs and have a far more reliable solution... but that would cost extra (probably £1.)