Low Voltage To CCFL Tubes - Sony 55EX500

[max1636]

Im currently waiting on an inverter board for a Sony 55EX500 TV but realized after working on another TV that the problem might actually be that the tubes aren't getting the right voltage. Reading each output to the CCFL tubes I get 175v AC. But on another Sony I was working on which is now functional the tubes are given 230v AC. Im going to open the TV up again tomorrow to see what voltage the PFC board is being given to investigate but I just wanted to know is 175v too low?

[tom66]

Re: Low Voltage To CCFL Tubes - Sony 55EX500

If you are using a digital multimeter to measure the tube outputs you've probably just destroyed the meter, as a 55" will drive tubes with about 3000V to start, 2000V to run.

[max1636]

Re: Low Voltage To CCFL Tubes - Sony 55EX500

If you are using a digital multimeter to measure the tube outputs you've probably just destroyed the meter, as a 55" will drive tubes with about 3000V to start, 2000V to run.

I do it all the time and the multimeter is still fine. I have heard it's not recommended but its not a super expensive one its just a cheap model Fluke. So what you are saying is 175v is too low? The TV turns on for a few seconds and only dimmly shows the Sony logo on screen.

[Ltank]

Re: Low Voltage To CCFL Tubes - Sony 55EX500

I just bought a Tenma H.V. Probe 1000:1 ratio can safety measure these voltages without damage to self or your DVM

[max1636]

Re: Low Voltage To CCFL Tubes - Sony 55EX500

I just bought a Tenma H.V. Probe 1000:1 ratio can safety measure these voltages without damage to self or your DVM

Thanks I might pick one of those up.

[tom66]

Re: Low Voltage To CCFL Tubes - Sony 55EX500

I would not trust that meter after doing such a measurement. I haven't heard of any commercial portable battery powered meter capable of measuring beyond 1200V? 175V would only cause the ends of the bulbs to glow slightly...

[selldoor]

Re: Low Voltage To CCFL Tubes - Sony 55EX500

Hi Tom -I have already told him that!! but even budm didnt pick up on it and neither did the the op.
I am wondering if we are talking about the same transformers.

For me an Inverter transformer is the one that connects directly to the
ccfl socket.

There are other transformers on the board that supply the inverter transformers
so if the OP means one of those then 175v would be possible.

Perhaps the OP can confirm exactly which transformer he is testing.

[max1636]

Re: Low Voltage To CCFL Tubes - Sony 55EX500

Sorry guys I understand the reading I'm getting may not be correct but I thought it was weird that on one TV I was getting 230v AC and on another I was getting 175v AC. I was just wondering if that seems unusual? I will open the TV up today to test other voltages. Also the 175v AC and 230v AC reading I am getting from the test points going into the tubes from the inverter board.

[budm]

Re: Low Voltage To CCFL Tubes - Sony 55EX500

The AC of output of the inverter transformer can be from 60~100 KHz, the meter will not have the bandwidth to read that high AC frequency. It is also high impedance power source so the probe and the meter can easily load down the power supply.