Samsung PS42C91AHD on 15sec off repeated

[maxvalutech]

This set only done about half usual usage its 2007/8 model and owner reported it went phttt and turned off. Gave it to me rather than dump it. Plugged it in and obvious standby was present so took the back off to be met with a pile of dust and fluff, cleaned that up and examined all boards except logic which is hidden behind metal shield to which main board is attached, also reseated connectors and checked fuses all OK. Plugged it in again and turned on at PP - this time relay clicking on then straight off again. Took out the power and main board to look at reverse side and clean properly behind them also checked logic and its fuse but nothing obvious. Put back together and turned on at PP again now smoke coming out from behind main so quickly switched off - then thought well damage already done so switched on again - set starts!! Connected DVD as no antenna input in work area - it plays full picture all good for 15 seconds then click to off then immediate self restart for another 15 seconds etc etc. Checked voltages Vs Va spot on but 5.3 was turning off at test point on power board but of course not at standby. Disconnected Y same problem disconnected X same problem. The smoke was from R3286 R3279 and perhaps R3185 which are now kaput, although no circuit diagram, I think maybe part of signal inputs circuitry (knowing my luck probably digital tuner). It seems some component is going oc or breaking down when it warms up a bit but then the restart is immediate and goes for exactly the same time each time. Logic has the 1 second heartbeat plus another green led flashes once at restart. Power BN44-00161A Main BN41-00888C Logic LJ41-05136A. Anyone have an idea of what component likely to be the culprit in these circumstances?? To me it seems likely power or main problem. I did try a jumper on connector cable from power to main at main end to isolate it (ps-on to rtn) but set stayed dead.

[maxvalutech]

Re: Samsung PS42C91AHD on 15sec off repeated

Pics but sorry quality not good.

[syaoran123]

Re: Samsung PS42C91AHD on 15sec off repeated

I would check the solder joints of the small transistors attached to the thin heatsink in the middle of power supply. That could explain the intermittent issue.

[maxvalutech]

Re: Samsung PS42C91AHD on 15sec off repeated

Thanks for the suggestion I have visually inspected for dry joints but will reflow these just in case as it does seem odd that off time is so consistent.

[ReeceyBurger123]

Re: Samsung PS42C91AHD on 15sec off repeated

I would check the solder joints of the small transistors attached to the thin heatsink in the middle of power supply. That could explain the intermittent issue.

+1 also the relays on these can get cold joints.

[maxvalutech]

Re: Samsung PS42C91AHD on 15sec off repeated

Reflowed items on PS but no better then finally managed to isolate main (used a paper staple) from PS and the Vs and Va came up and were stable so looks like its the main. Found another main same set specs not far away and for $40 delivered which is about most I would outlay on set this old. Will report result when new board fitted.

[maxvalutech]

Re: Samsung PS42C91AHD on 15sec off repeated

New used board fitted and the set is working aok - the only difference I note is chimes do not play at turn on so eeprom data possibly just a little different. I did find circuit diagram for same model 50" but it only seems to show sections of main board - there are resistors numbered in the 1000 and 2000 prefixes but nothing with 3000 and the ones burnt out were in that series so I am none the wiser if they were the problem or not !!??

[ReeceyBurger123]

Re: Samsung PS42C91AHD on 15sec off repeated

These do chime lol, you can turn it off in the menu. Also good work buddy

[maxvalutech]

Re: Samsung PS42C91AHD on 15sec off repeated

Thanks for that advice I will look for it and yes all seems OK. Owner has this in on-site holiday van setup so I'll let him have it back but that will cost him a box of beer!!