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General discussion

HL-S5687W ignores front panel buttons and remote

Mar 6, 2009 12:13AM PST

Hi, new here. Would definitely appreciate pointing in the right direction. HL-S5687W powers up fine, but within a minute or two acts up. If I go into 'service mode' quickly after power-on, it shows the different service mode options, but soon it starts racing through them as if you are holding down either the UP or DOWN button. Ignores all front panel buttons, except eventually it might respond to the Power button. No LEDs on front are flashing (like they do if you press a button on the remote), so it's definitely not getting a 'bad' signal from the remote control. If you press a button on the remote, the front LED does flash, but has no effect on the TV's actions. Picture itself seems OK (no light engine problems). Any ideas where to start looking?

Discussion is locked

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HL-S5687W ignores front panel buttons and remote
Mar 6, 2009 6:21AM PST

avrguru,

The source of this problem is likely in one of two places.

1. The touch panel on the television (up or down button) is either depressed or unintentionally making contact.

2. The problem may reside on the board making contact where it shouldn't be.

I don't have any way of knowing which one is the way to go; that said, until you can control the cursor, I might suggest not going into the service menu and possibly enabling something that will have an ill-effect. Just a friendly thought.

--HDTech

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Not likely the front panel itself...
Mar 6, 2009 6:58AM PST

Thanks for the quick response!
Since the problem doesn't appear immediately when turned on, it seems unlikely that it's a 'bad' button. Which board processes input from the front panel as well as the remote? Please note that the LED correctly indicates when a key on the remote is activated, so it also seems unlikely to be a bad IR receiver or decoder (although the decoder could be generating an output even though not getting any IR input, I suppose). I'm trying to narrow down which board would need repair or replacement.
Thanks!

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Not likely the front panel itself...
Mar 6, 2009 8:47AM PST

avrguru,

I'm not sure which part it could be - it's extremely difficult to diagnose a television or symptom based on a text description. I don't have the technical architectures on the units to pinpoint a board, unfortunately. If forced to guess, I'd lean towards the main PCB, but of course, I can't say that conclusively.

--HDTech

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Definitely on the main board...
Mar 9, 2009 12:06AM PDT

I tore it apart and left front panel keys/LEDs unplugged, but left IR connected. Still does it. Very temperature sensitive in one corner of the PCB, but appears to be 1.8V voltage regulators, so this is probably a secondary effect as a tiny shift in operating voltage is affecting the REAL chip that's got the problem. There was quite a bit of 'some' material on the PCB. Not sure if they use a no-wash flux during manufacturing, but it almost looked like someone dumped a can of Coke and left it to dry (no evidence of this happening post-manufacturing as everything else is sparkling clean in the set). Did a lot of cleaning (isopropyl & Q-tips), improved, but still present. Can't figure out which chip receives the signal from the keypad, since traces are routed on inner PCB layers. Suspecting partial short due to unknown material. Really need a schematic, or at least a block diagram, to trace this out. Any hope?

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Narrowed down...
Mar 10, 2009 5:02AM PDT

Measured resistance on the 4-pin connector from front panel, two wires labeled KEY1 and KEY2. One is 5.2K to GND/5V, the other is 500ohms. Clearly there's a short somewhere. Traced the line back to a Samsung chip, but the chip is not the source of the short. The affected line loops back through a 100ohm R and goes to a different 6-pin front-panel connector which has LED signals and 5V/GND for the keys. Not a clue what that extra signal does, it's labeled S5V. At one point during troubleshooting the short disappeared, but reappeared after trying it in the set again. The lack of even a block diagram is causing a huge time waste. Anyone know where I can get detailed servicing info? A schematic would be awesome.
Thanks!

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FIXED!
Mar 13, 2009 2:29PM PDT

Turned out to be a short on an inner layer of the PCB, near the Samsung chip that reads the front panel signals (with an A-to-D converter). I cut the trace at both ends, where it came up to the top side, and replaced it with a jumper wire, and all is good! The short was actually temperature-sensitive; when I would heat up the PCB near the Samsung chip (where I believe the short was located), the short would disappear. Cool off that spot on the PCB, and it would re-appear.

The S5V signal appears to be the front panel Power button.