CMV CT-934D won't power on - secondary voltages disappear

[retiredcaps]

Re: CMV CT-934D won't power on - secondary voltages disappear

Although 'logic' says the fault is on the 'Logic' PCB(pardon the pun..).I assume that if you had another Logic PCB,you would have tried that to confirm that is the case ????.

I got this monitor for free from the local ad. If I had another one identical monitor, yes, I would have tried swapping boards.

Set up the PSU/Inverter ONLY..ie NO Logic PCB,Plug in the CCFL's,and on the connector which normally goes to the Logic PCB,apply Approx 3volts DC(from an external battery perhaps),between the ON/OFF pin and Ground.This will light the Lamps.HOWEVER I had lying around a little PC Fan,a Standard 12v,250Ma one,and a little experimenting showed that applying 12v to it, it actually took 62Ma,BUT applying
5V to it the current increased to approx 160Ma,So with the Set up as above,if you have a Fan,or similar, put it on the same connector between the 5v pin and Ground.The question is DO the CCFL's light ???and the Fan spin ???

Funny, I was thinking about a test like this for the last couple of weeks and what I have at home to do this.

Thanks for the idea, I'll see what I can do to test this in the next few days.

[URAD_Harvey]

Re: CMV CT-934D won't power on - secondary voltages disappear

Did you ever get it fixed?

An old trick we used to use long ago was to use a 6V lantern battery in series with a resistor on the 5V supply line to limit the current just below operating current for the traces being evaluated. Then you take a meter and measure the voltage along the supply line traces, it will be a few micro volts higher at the source but will drop to zero at the short. Of course in those days the boards we were testing were 17" double sided - not these 4" 6-layer jobs.

Let us know what you found out

[retiredcaps]

Re: CMV CT-934D won't power on - secondary voltages disappear

Well, almost 20 months later, I figured out the problem. I originally got the idea from momaka way back around Dec 2011 when he did a lot of detailed posts on troubleshooting the t-con boards.

https://www.badcaps.net/forum/showpo...9&postcount=13

He explained that smd ceramic caps fail shorted on the t-con boards. Somehow this gave me the idea to look at all the ceramic caps on my logic board (not t-con) and sure enough CP18 was shorted. See pic.

It wasn't until March 27, 2012 that I actually replaced the ceramic cap with a 22uF 25V Samxon electrolytic cap. I took at guess at the capacitance value based on the size of the other caps on the logic board.

Once I replaced it, all the voltages came up and stayed stable. I have been running burn in tests for the last 48 hours and everything works great so far.

[budm]

Re: CMV CT-934D won't power on - secondary voltages disappear

Those MLCC can easily be damaged due to poor handling during assembling of the board, or the board got flexed too much. I replaced those caps in T-CON, Inverter boards, main baords before, the bad part is that some time there will be 5~10 in parallel, and as always, the last one I remove to test will be the one that is shorted out, I can see cracks on the body using high magnifying glass to see.
MLCC info
https://www.badcaps.net/forum/showthread.php?t=19663

[kallyd]

Re: CMV CT-934D won't power on - secondary voltages disappear

Do you still have it after so much time?

[retiredcaps]

Re: CMV CT-934D won't power on - secondary voltages disappear

Do you still have it after so much time?

Still works and staring at it right now. It is on at least 4 hours daily.