Samsung SyncMaster 710MP - TV mode not working

[drgst]

Hello everyone! This is my first post so forgive me if I miss something to explain.

This TV suddenly died on me. I had to replace all of the caps in the power supply and one resistor in the feedback circuit between the two legs of the optocoupler (pins 3 and 4) to be able to get the proper 5V and 14V from the IP board. Additionally I had to replace IC103 G960T45R (3.3V Voltage regulator) from the mainboard, before I get some kind of signs of life from this TV). Now I have it working in PC mode, but still not in TV Mode. When I'm cycling through the TV options in the main menu they look grayed out and when trying to select them the message "not available" appears. The PC mode options all appear fine and respond well. I measured the voltage from all of the voltage regulators on the mainboard and all voltages appear all right: 2.5V, 3.3V, 5V, 8V are all there. I still haven't replaced any cap on the mainboard but I don't think that this could be the cause for the TV mode not working, because the voltages are fine. One problem I noticed only is that the 33V for the tuner is down to 4V, but I think that this could only be a problem for finding channels and not for the TV mode not working at all. The other 5V for the tuner is all right. I measured the pin on the tuner that receives the 33V for resistance and saw Mega Ohm resistance. I disconnected the pin from the tuner and received around 32V from the circuit.

I fear that the problem could be due to some processor on the mainboard or maybe the tuner. Has anyone else experienced something like this, or has any idea what could be the problem?

I have attached the schematic of the mainboard. The link is:

http://www.eserviceinfo.com/download.php?fileid=63029

Thanks in advance for your help.

[vtech]

Common sense says that the 33v line should not have anything to do with the TV mode but based on your description, the 33v line drops to 4 volts when tied to the tuner. At first glance it points to a bad tuner however, you read megaohms resistance from that pin to ground!
Hmm.. lets see, when you load a 33v line with a megaohm resistance, no way it could be loaded down to 4volts? Something is definitely amiss here; either your ground reference is not correct or the 33v is infact not all there.
Back track the source of the 33v and make sure it is solid (it is usually sourced from a higher line in the power supply and clamped to 33v)
Is there any activity on the SDA & SCL lines going to the tuner? I have seen a short on either line could possibly defeat the TV operation.
Also, is there a possibility of an EEprom corruption? I do not have the specific schematic of the set but these are somethings to check on.

[drgst]

Thank you for you answer vtech.

Here is the schematic for the 33V:

http://i43.tinypic.com/2czeb21.jpg

As you can see this circuit is driven by 5V, which I measured good. When I remove the load (disconnect the pin from the tuner) the voltage reads around 32V. Since the load is very big this shouldn't fall at all. Could there by some dynamic load that brings down the voltage?

I also measured the SDA & SCL lines with a multimetar and there's definitely some activity. On both lines I measured a fluctuating DC voltage going from 3.7V to 5.2V.

A link to the schematic of this TV is posted in my first post.

[jts1957]

You found a 33 volt destination. There is a second on same page.

In case you don't have whole manual...

http://elektrotanya.com/samsung_710mp.rar/download.html
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[drgst]

Does anyone maybe know how to access the service menu?

[jts1957]

Try:
Power, off, MUTE, 1, 8, 2, Power on
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[bargougui]

Bonjour tout le monde si vou plait
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[bargougui]

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