This is my first foray into flat screen tvs. This was given to me as I was interested in having a look round it as I have never had anything to do with these type of sets.
I saved it from its final trip to be recycled and it came with the fault of "lines on the screen".
The usual electrolytics in the power supply were very bad and after replacing them the set worked perfectly. I had it running on the bench for about an hour and all seemed well.
Since then it will run for 2-3 mins and then start turning on and off. I turned off Anynet and Auto power and checked that no timer settings were active and it settled down for three hours with an input from a dvd player. Now the problem has returned and is exactly as it was on and off relentlessly. I can see all the voltages from the power supply are perfect including standby, but the standby return from the main board to turn the power supply on is turning on and off and I know that this set did not have this fault before it came to me.
The net is full of owners with this problem and I have followed the advice given but to no effect. I have toyed with the idea of bypassing the instruction to the power supply to turn on so that the set is always on if plugged in but I'm wondering if any members have better knowledge or advice.
Just to eliminate it I disconnected the remote sensor as I've heard they can go bad. No difference. Can anyone point me at a service manual or a circuit diagram of the main board? I will try bypassing the start function which returns the standby voltage via the main board but it would be good to understand what I'm dealing with.
I have found some service manual here: Electrotanya
True to form with Samsung they never include the PSU board schematic in their manuals. What I have often done is to find the board reference number in the manual and do a separate search for it. I believe the PSU board is BN44-00156A (need to check) and only found a schematic here Eserviceinfo
I have had many issues with older Samsung TV's, mainly due to the lead-free solder developing dry joints. The power supplies are monitored by the system microcontroller and if a glitch in the regulated voltage occurs the uC will shut down the power rapidly. You may have to monitor the various supply lines with a 'scope as the transients are too fast for a DMM to even realise!
Samsung TV's can be fussy for the correct capacitor ESR and when comparing original part numbers usually find Panasonic FM and FR 105°C series work OK. Might be worth checking operating temperature of the electrolytic capacitors.
Hi, Although i rarely sign in these days i visit the forum everyday. I will try to offer some help on this tv although its pretty old as modern junk goes. One of the first things to try is disconnecting the buttons on the side of the set, this is a common problem. Next to try is checking the esr of capacitors on the main board. They are associated with the smd regulators, they are all 100uf 16v smd capacitors. I usually fit low esr high temperature caps and bend the legs to suit. If you still have problems it’s time to desolder the metal can. Inside here you will find 2 1000uf 10v smd caps, change them even if the esr seems ok, you can squeeze normal caps in on their side. While in the can check for greasy goo on the ic’s, if thats present clean it off with ipa and wipe the pads that push onto the ic’s. That will normally get these going and if not i suspect the recycling centre is the place for it. Sorry for the long winded post. Norman
Rich, thank you for your advice. The caps I replaced are now 105 degree Nichicons and have an esr below o.1 ohm. As soon as I have time I'll scope the voltages although the problem is always "wait 2 minutes then cycle on and off at perfectly regular intervals"
I have also had times when the set has run for a while, so I don't know if these sets are just over designed for protection or maybe a part is hot or otherwise upset.
So far the problem tends to be unpredictable and I'm noticing that physical movement can sometimes affect it. I bypassed the trurn on/off return to the power supply and found the set still turning itself off even though the power supply is now permanently running. When I disturbed the small board at the top of the set it began to run continuously for a long time and I began to suspect a bad connection. However the problem returned and even with that circuit and the side control panel disconnected the set is switching at will.
Pressing on the main board produces no results but the set will occasionally run for extended periods which makes me think it's a contact issue. Am I right in thinking a capacitor problem would be more permanent? The set was subject to a lot of handling and transport before it landed here and given its age I'm left thinking it could be a solder issue.
Hard to say, some of these sets had firmware issues which could and did causes weird and wonderful symptoms.
EEprom corruption on a few models was common especially if excess ripple on the supply line due to duff caps was the root cause, the eeprom itself was usually ok just data corruption, reprogramming normally sufficed.
Last Friday I got called out to look at a Samsung LE26R74BD LCD TV set. The problem with it was it wouldn't tune in Freeview stations. Easy enough to enter the DVB tuning menu, press OK for auto tuning, the scan would start and within less than a second or so the tuning operation would cancel itself out. Anyway, it turned out to be an easy fix, just two bulging elcos on the power supply board.
Well, guys, I've spent enough time on this set. The set is old and power hungry and I only had it to look round inside it out of curiosity. Nothing I do affects it and the switching has become more frequent without the initial 2 mins of running well. It just sits there doing its thing. I scoped the power supply outputs but found nothing to suspect any problems. I've taken the repaired power supply out and dismantled the rest. Fascinating stuff. It has tubes for illumination and I suspect they might be tired, some are slightly dark. I read somewhere that the set monitors the current to the tubes and will shut down if it sees a fault. Lots of guesswork but I'm glad I tried.
I'm in a similar position with a nine year old Panasonic plasma TV set.
The board you see in the attachment was found to have a short circuit FET. Finding the faulty FET was no simple task because all the components being tested didn't unsolder easy. Anyway, after removing the heat sink it was possible to pick out each transistor and diode until the short circuit one was found. A replacement transistor was purchased and duly fitted. Short circuit across the power supply gone. Success! Not so. I was about to sign the job off but before doing so I decided to to check other components and sure enough more short circuit transistors. So that's it, continue to attempt to repair the board, or find out if a new replacement PCB is still available and at what cost? Or like the Samsung being discussed or just advise the the owner of the set to buy a new model. Like the Samsung this plasma set is a power greedy thing.
And on the other hand, I have an ancient Sanyo badged Vestel, which, behind the screen is working perfectly, but the screen itself seems to be 'delaminating' and has some weird on-screen artefacts. A pity really because I actually liked that old LCD display. So old is the set that it doesn't even sport DVB reception, but the sound quality is outstanding for an FP set, and the picture rendering was as good as any I've seen (at 1080 resolution). Comfortable on the eye, is how I'd describe it, but no chance of finding a replacement panel for the old beast. Electronically, it's a real trooper!
I'm in a similar position with a nine year old Panasonic plasma TV set.
The board you see in the attachment was found to have a short circuit FET. Finding the faulty FET was no simple task because all the components being tested didn't unsolder easy. Anyway, after removing the heat sink it was possible to pick out each transistor and diode until the short circuit one was found. A replacement transistor was purchased and duly fitted. Short circuit across the power supply gone. Success! Not so. I was about to sign the job off but before doing so I decided to to check other components and sure enough more short circuit transistors. So that's it, continue to attempt to repair the board, or find out if a new replacement PCB is still available and at what cost? Or like the Samsung being discussed or just advise the the owner of the set to buy a new model. Like the Samsung this plasma set is a power greedy thing.
Till Eulenspiegel.
I imagine it's a difficult call when doing professional tv repairs. It's always a risk it will backfire on you when someting else fails soon after. Good luck with this set.
My business was vehicle repairs and (generally) the state of a vehicle is more predictable. Most customers could understand the risks of spending on an older vehicle and could see that a later gearbox failure had nothing to do with a rebuilt engine.
Today, I took a chance and accepted a Toshiba LCD TV for repair which turned out to have a Vestel chassis similar to the Sanyo Marion mentioned in an earlier post.
I was lucky with this one, just two electrolytic capacitors needed replacement. The plug and socket to the on-off switch was making bad contact, played safe and fitted a wire link. On-off switch inoperative but the owner of the set wasn't bothered about that.
