Mlt166a Megmeet ltc2701td

[Bigbe]

I have an mlt166a that shows a hot ground. 86 volts at the heatsinks on the primary side. Some of the capacitors tops show the same voltage as the heatsinks. what should I look for to try fixing this one.
Thanks, Bigbe

[budm]

Re: Mlt166a Megmeet ltc2701td

When you work on the primary (hot side), you do not use chassis ground as the ground ref for voltage readings, you use the ngative leg of the main filter cap (the 450vdc rating) as the ground ref point for the meter. Also do not touch the heat sinks, it can be part of the primary circuits.
So any pictures of the board and the symptom of the problems?

[Bigbe]

Re: Mlt166a Megmeet ltc2701td

Well Budm, The TV won't turn on just blinks red. The 5v jumps around from 4.4 to 4.9 very unstable. when connecting the 5v to the pson pin nothing happens with the 12v or 24v pins. I've changed the common caps that go bad.

[budm]

Re: Mlt166a Megmeet ltc2701td

OK, at least the stanDBY 5V is kind of working but not stable, that can be due to too much load or due to bad caps such as the start up cap (22~47uF 50V) in the primary side. You can try heating the board with hairdryer to see if it becomes stable. Then we still have to find out if the PFC voltage booster circuit is working or not. When TV is plugged in but not turn on, you should have about 160~170v right at the two legs of the main 450V filter cap, when you force on the power supply on the PS_ON pin, it should jump to around 370~400VDC range on that cap, if it does not, then the 12v/24V power supply will not run.
Pictures of the boards?
SCH from tom66 web site.

[Bigbe]

Re: Mlt166a Megmeet ltc2701td

I'll have to get the camera out and take some snaps. give me a bit to do that, might be tomorrow.
Thanks

[Bigbe]

Re: Mlt166a Megmeet ltc2701td

Budm, The SCH did the trick, I had it powered up in an hour. Z3 and the two 10 ohm surface mount resistors were the problem.
Thanks

[budm]

Re: Mlt166a Megmeet ltc2701td

Glad to hear, tom66 has lots of SCH.
http://www.tgohome.com/ServiceManuals/