Please help. Phillips 22PFL3504D/F7 mfd 11/09. No power. Power supply makes high pitched noise. Caps look OK. No bulges. No leaks. R603 to R606 approx 470 ohms (analog meter). No voltage out. Please help me troubleshoot this. Thank you.
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Phillips 22 inch no power high pitch transformer noise
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Re: Phillips 22 inch no power high pitch transformer noise
The diagram below shows how to connect a digital meter to test the diode. There are a number of things to remember:
• Make sure you are using the diode range.
• Using a digital meter, connect the black lead to the cathode and red to the anode (forward bias - around 1kΩ).
• Reverse the meter connections (reverse bias - infinity reading).
* Note some times depending on how diode is wired into circuit may need
to remove or lift one side for more accurate reading.Ron Driver,BSEE,CET,ISCET,NESDA
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Re: Phillips 22 inch no power high pitch transformer noise
Interesting results. I did unsolder one side of each diode to check them out of the circuit. When I put the meter on diode check, it said 0l. So I assume that is an open circuit.
D607 gave readings of 0l in one direction and 707 in the other. No sound. Diode D668 read 1s in both directions and the meter made a continuous sound.
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Re: Phillips 22 inch no power high pitch transformer noise
Did a google search for 20BSB-T26 and came across a thread that the poster was looking for the exact diode you need. It was said that it's a 1W 20V zener diode. Did a simple seach at digikey for a 1W 20V zener and came up with this.
http://www.digikey.com/product-detai...DICT-ND/190282
Does this look like the diode you have (size)? The part number wasn't helping either. Maybe someone with alot more experience in this department will chime in.
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Re: Phillips 22 inch no power high pitch transformer noise
Had similar issue with Philips model 42PFL5432D/37. Problem: ZD906, called transient voltage suppressor. Purchased this as replacement:
http://shop.vetcosurplus.com/catalog...tbq9rj2dgg2j13
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Re: Phillips 22 inch no power high pitch transformer noise
Check the circuit that diode is on, and replace the capacitors. Even if they don't look bad. The zener is there to protect from overvoltage - if it shorts, it means the voltage on that output is higher than it should be, which usually happens as a result of bad caps. When the ESR of a cap increases in a regulated power supply circuit, the power supply increases the duty cycle to keep voltage in regulation. However, with bad caps, while the average voltage remains the same as required (since this is set by the feedback circuit), the peak voltage increases, sometimes dramatically so.
An ideal DC source would have peak voltage equal to average voltage, however, in practice, there's always a small amount of AC ripple on top of the DC voltage, it's not quite a straight line as seen in textbooks, it's got peaks and dips, hence its peak voltage is a little bit higher than its average. The better the caps, the straighter the line and the smaller this difference. As they go bad, the peaks and dips in the voltage become larger and your device isn't happy anymore.
Without the zener to short first, a lot of stuff would fry.Last edited by Th3_uN1Qu3; 10-05-2012, 04:34 PM.Originally posted by PeteS in CARemember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
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