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New at this, trying to test Va, Vs

 
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mmastera
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PostPosted: Tue Jun 01, 2010 8:09 pm    Post subject: New at this, trying to test Va, Vs Reply with quote

I have an LG 42PC3DD-UE (Insignia NS-PDP42) with audio but no picture. Doesn't appear the display lights up at all. I've checked the two fuses on the YSUS and two on the PSU and all seem fine.

My question: this seems silly, but is there a trick to testing for Va and Vs? With the TV already on, if I test for them at the PSU I get 0.0v for Va and 3.7v for Vs. I started thinking the PSU was bad. On a whim I watched the meter while I turned the TV on and I see Va and Vs at their expected values (60V, 190V) for awhile (up until the audio kicks in) then they drop to the above mentioned values.

Many people on the net have already said to replace the YSUS and I have no problem doing that, just trying to be thorough and more importantly learn something so I was trying to rule out the PSU...

Any advice?

thanks!
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minnie



Joined: 18 Aug 2005
Posts: 2877
Location: Hell

PostPosted: Tue Jun 01, 2010 9:36 pm    Post subject: Reply with quote

What do the voltages do with the boards up plugged? It could be your power supply.
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PostPosted: Wed Jun 02, 2010 3:25 am    Post subject: Reply with quote

Hey minnie, thanks for the reply...

I was just going to update the thread, as that's the next thing I tried...I removed all connectors from the PSU (except AC power of course). When I plug it in I hear the relay click and check Va and Vs - I get the same results as before. I could use a little education here. Should the PSU normally output Va and Vs even with nothing plugged in, or is the main board required to give it a signal to start supplying Va and Vs?

If it's supposed to be showing Va and Vs all the time, even with nothing plugged in, then I'd say you hit the nail on the head - bad PSU. I started to suspect the PSU a little bit ago and now I'm trying to figure out how to test capacitors - all I have is a DMM without a specific capacitance testing function...

thanks again!
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minnie



Joined: 18 Aug 2005
Posts: 2877
Location: Hell

PostPosted: Thu Jun 03, 2010 4:24 am    Post subject: Reply with quote

Keep the digital main connected if VS and VA do not come up with the X and Y sustain unplugged suspect the power supply. Unless the problem is obvious it's board level only.
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