TV set shutdown after few seconds of coming on.
Set will stay on longer if you continuously change channel.Problem was
intermittent before but goes hard now. I have done some resoldering thinking that is just some cold solder issue.
Screen flickers with green, and sometimes red color before shutdown. I have checked the power supply section, voltages seems to be ok. The main supply output of SMPS(B+) bothers me because per schem. diagram it should be 130Vdc for the 21" set and I'm reading 139dc volts. What could be causing this "abnormal" voltage output of SMPS? I have replaced the swithcing regulator IC and some electrolytic caps in the horizontal driver ckt. I have read that most of the Philips product having this chassis no. encounter the same problem but no one seems to solve the problem. Glad if anyone from the masters can help. Thanks in advance. God bless.
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Re: Philips 21" L01.2A Chassis HV Shutdown
The increase in voltage may be to some circuit loading being removed this is a sign that something may have increased in resistance or something may have opened in the attached circuit. Have you taken any voltage measurements in the video section of the set, if not check the voltages on the pins of the video processor IC and follow the connections up to the CRT socket, be sure to pay special attention to the focus and screen grid voltages. If those are ok check the voltages in the horizontal section including oscilloscope measurements for drive signals.
Please inform me of your findings.
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It sounds like you are describing high-voltage (HV) shutdown. As a safety feature, if the voltage in the TV rises above a set limit, the TV will shut off to prevent possible x-rays from the picture tube. The only way to reset the shutdown is by unplugging the TV, then reconnecting the power.
This shutdown can be caused by several things. The power supply may in fact not be regulating the voltage properly because of component failure. Your power line voltage may be a little higher than usual and causing nuisance shutdowns. Or the HV shutdown control may simply need to readjusted because components have aged and changed value slightly, also causing nuisance shutdown. The HV transformer may be defective, or the picture tube is going bad.
Unfortunately, it's not possible to say what's wrong without seeing the set to check operation and determine the cause. So I can't suggest anything you might do yourself to fix this. If you want to keep this TV you should let a professional servicer check it over, determine what's needed and give you an estimate. Or you can use this as an excuse to purchase a new TV. Flat screen sets are quite reasonably priced now, and depending on what turns out to be wrong with your TV, it might be more economical to replace it.
Re:"shutdown after video comes up the green power light stays on but the set will not shut down while changing channels."
I do not think this has anything to do with logic circuits and video processing. When you stay on one channel the horizontal and vertical alignment circuit works more than if you change channels all the time. This is just a guess, but have a look at convergence ICs. when you keep changing channels the power amp ICs (or transistors) go on and off, if one of them is defective it will overheat and shut down. Other possibility is an internal tuner failure. Also test using a DVS or VCR.
Sounds like you have a bad picture tube. More than likely the CRT could be shorted, which would cause the set to shut down. My first advise would be to power up the set with an isolation transformer with the voltage about 60% approx. 72 Volts AC, and monitor what happens when you increase the voltage slowly. If the set remains on at 60 -70 %, then when increased to 90 - 100% it shuts down, you have something drawing too much current ( which could be the CRT )
Check for stuck button on front of set or on remote. Probably ch. down button. Wiggle button free from jammed condition and ch. should stop changing. If that doesn't solve it unplug set from the wall or power strip for 30 seconds and restart in an attempt to reset. Take batteries out of remote to eliminate it as the culprit, also. And you can change the tv input and use audio/video input if the tuner in the set has gone haywire.Good luck, Russmann.
sounds like an intermittent shut down which is heat related. some part , maybe one stuck on a heatsink is warming up and running too much current triggering shutdown.
to find it you can tell what is shutting down with a voltmeter, or you can heat suspected parts with a blow dryer to speed the shutdown .. or freeze spray to see if it goes beyond your shutdown time.
Ed did you change the yokes when you put the DPTV series CRT into the PTV chassis? If not its most likely the vertical output or the Horizontal output that got destroyed. If you changed the yoke its most likely the HV generator.
On the DPTV chassis that should shutdown the vertical deflection which would leave audio working worse case scenario would also be the HV generator and Horizontal output.