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.
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.
That chassis has a couple of problems I'd check first before writting it off as a bad crt... The vertical Ic can cause the problems you're experiencing. In that unit it's a TDA8177 (vertical Ic) and if it fails you'll find no 10v supply to the HV generator - thus no HV to light the cans. Could also be the HV generator module itself, but more likely vertical Ic before suspecting the HV module. If you hav a dmm you could measure the voltage on pins 7 & 8 or pins 1 & 2 on the HV plug. If you have nothing there it's the generator - if not highly suspect the vertical.
To answer your question - if the blue can were bad red & green would still light depending on the internal short. If all three are out I'd suspect a loss of HV (high voltage) or B+ as it's referenced.
I gave this advice to someone with this same problem so here it is again:
It sounds like your shutdown circuit is being activated. This is due to excess current being drawn. This usually happens in the High Voltage section of the TV or one of the deflection stages. Due to the nature of this problem I would suggest that you take it to a local TV repair shop or have a TV repair person come out and take a look at the issue. The HV section is dangerous and should be dealt with by a qualified TV repair technician.
This could be a High- Voltage shutdown circuit problem. The reason it will stay on longer with a bright picture, is the high voltage is slightly reduced, not allowing the shutdown circuit to shut off the set. But I believe your problems to be in the shutdown circuit.
A common failure in these units is Q401, Toshiba p/n# Bz510004 is a 2SA1624 (HV amplifier) which finally fails due to a resistor R408 Toshiba p/n# Bz210285 a .47 ohm/1w metal oxide having changed in value and at last opening... This isn't an expensive repair for a qualified shop - but I would suggest not continuing to test your shutdown circuit. What's happening is that HV (high Voltage) is builds beyond tolerances and the shutdown circuit turns your unit off to keep from causing any severe damage. If it failed you could likely burn out the SMPS or cause some substantial damage.. Good Luck! Bill
If the set runs at all, your flyback and output transistor are good. If the set shuts down after a few seconds and the sides are wavy, it usually means that the main B+ in your power supply is too high and not regulating properly. I do not know what kind of power supply that model uses, but if has an old-style STR regulator (like the STR30130) then it is probably shorted, and if the set uses a switching power supply then look for an open or leaky electrolytic cap on the primary side. If the power supply is working correctly and the set shuts down, check for an open safety cap (the large 1.6 - 2Kv cap connected to the collector of the horizontal output transistor).
Phillip you have a problem in the main power supply or in the High voltage shutdown circuit. Now the longer you wait to have this fixed the more its gonna cost ya Unless your a tech then get a schematic and measure the voltage on the hv shutdown pin on the video junglke ic when the set shuts down If the voltage at the time of the shutdown sodent spike up then you know your problem is in the power supply. Good luck