Philips 37PFL5322D/37 Chirping from psu

[orgwood]

Re: Philips 37PFL5322D/37 Chirping from psu

My son put it in his TV and everything is working fine including the remote so that means the 12VDC rail and the 24VDC rails are firing up in the right order...12VDC for standby and 24VDC for power on. Thanks so much for all your help and patience. Peace, Dave

[orgwood]

Re: Philips 37PFL5322D/37 Chirping from psu

https://www.badcaps.net/forum/showthread.php?t=34579
Here's the link to the Magnavox SMPS thread since they're basically the same.

[sherrygarris]

Re: Philips 37PFL5322D/37 Chirping from psu

this is an awesome forum. i currently have 2 of these Phillips with chirping in my shop. Since the 2 zeners in question were in the snubber circuit i removed them from both sets and briefly turned them on (after I'd done basic checks of course) to confirm that these would fix. Both sets powered up fine. I'm ordering the p6ke120a times 4 and will have saved 2 sets from the landfill and made a bit of cash. Thanks to all who continue to contribute and to all who continue to work in the ever changing and sadly shrinking field of TV repair

[orgwood]

Re: Philips 37PFL5322D/37 Chirping from psu

I would like for you to help me understand the purpose of those zeners. You said they were in the snubber circuit so I would expect them to limit the voltage that appears across that primary. Is that right? If so, how does removing them and powering on the PS not cause the voltage to go too high. Thanks, Dave

[itzklove]

Re: Philips 37PFL5322D/37 Chirping from psu

Good morning, I ma having a problem with my Philips Power Supply 715T2454-2 which is in a 42" Philips TV. First started out the 24VDC was missing but with the help of this forum trend I replace an IC TEA1507P the 24 VDC is now there, Now I am having another issue.

Just powering up the Philips Power Supply 715T2454-2, using a Multi-meter I can read the 24VDC at connector J13, pin-1 and pin-2 but after awhile you can see the 24VDC dropping (counting down) 0V; this is with the Philips Power Supply still connect to the AC power source. Here is where it get a little con fusing for me. At first I thought the IC TEA1507P went bad again, so i decided to change it again the next day.

The next day for some strange reason I decided to powered up the Philips Power Supply again before changing IC TEA1507P, and using the Multi-meter I could again read the 24VDC at connector J13, pin-1 and pin-2, and after awhile "again" the 24VDC begin to dropping and I watch it counting down from 24VDC to 0V. After seen this I let the power supply sit for 12 hours and once again I was able to read 24VDC then watch it count down again.

Can someone here direct me to the source of the problem.

[orgwood]

Re: Philips 37PFL5322D/37 Chirping from psu

Are you powering up the SMPS with a load on the 24VDC? It may be going into overvoltage shutdown without a load. The 24VDC should not come active until you have the 12VDC running and then apply a turn on signal to activate the Stand By pin.

[itzklove]

Re: Philips 37PFL5322D/37 Chirping from psu

Thanks for assisting, and I think you maybe right, because while powering up the power supply board there were no load connected. I had the power supply board out of the TV on a table with the AC plugged in while reading the voltages at connector CN902, pins 1 and 2 (which should 24VDC) and pins 3 and 4 (which should 24VDC).

When i get home later I will put it back in the TV and complete all the connections and see what happen.

Thank you
Kevin

[Ivan_Ryger]

Re: Philips 37PFL5322D/37 Chirping from psu

Dear all,
please does anyone have a spare transformer HJC-S6192 in a working condition?
I replaced shorted TVS diodes and a couple of secondary capacitors. The rest seems to be OK and my LCR meter shows most probably shorted winding.
Thank you.
Ivan

[tvtimmy]

Re: Philips 37PFL5322D/37 Chirping from psu

I will check when I get home. I cant send you a PM because you are so new to the forum. Send me a PM with your email address and I will let you know.

[Ivan_Ryger]

Re: Philips 37PFL5322D/37 Chirping from psu

Dear all,
finally after a long struggling I made my PSU working. At the beginning I found popped three parallel filtering capacitors popped at the secondary side (C952,953,956). In addition to that at the primary side of the transformer, two TVS diodes (ZD902,904) were shorted. You can easily check them by multimeter in the forward direction. After replacing these components, the power supply was still chirping, though.
I measured all the passive and active components (resistors, capacitors and diodes) with emphasis on the snubber circuit (D925 checked for forward voltage drop and reverse breakdown voltage, as well, C944 for capacitance). Secondary diodes D922 and D926 were checked for forward voltage and reverse leakage, everything OK. The critical component could be also the source current sensing resistor R949, so i checked it for a resistance by passing 100mA through it and measuring the voltage drop across it. Again everything OK.
also tried to swap the active circuits (IC904, Q901) with others - no change.

So my suspicion fell on the transformer. You can easily check it with oscilloscope and square wave generator by measuring the Q-factor of the primary winding.
I found it somewhat low (somewhat below 10), implying some problems there.
The method is described here

http://www.giangrandi.ch/electronics...ingdownq.shtml

. Luckily, a member TvTimmy found one used transformer in his old stock.
The new one had a Q-factor of about 30.
So I tried to swap it. The chirping sound has changed but was still present.
By measuring the voltage at the pin 8 IC904 I found that this was regularly dropping under UVLO threshold level. Thus the IC was getting into undervoltage lockout state.

Next measurements revealed something interesting. When I grounded the base of Q913 through 5kOhm resistor, the power supply started running correctly even with a small 80 Ohm load connected to the output of the 24V line. In this case the main SMPS was powered from lower voltage (170V present on C907), since the PFC pre-reguator was turned off.

However, by shorting the optocoupler (IC909) at the phototransistor side the PSU was chirping again. In this test, the PFC pre-regulator was running at full voltage on C907 (about 370V, can be up to 400V). I realized that during this test the voltage was again dropping under UVLO threshold. So it implied an increased power consumption by two chips IC902 and 904. Since I could not find the reason of this problem, i fixed it in slightly different way. By increasing the base current of Q914 I decreased the voltage drop across the next switching transistors. I increased the current by adding a 5kOhm (value not critical) resistor in parallel to R915. In addition to that I had to increase the capacitance of capacitor C958? (47uF/25V original) by changing it with a new one 100uF/35V.

After all these steps the PSU finally started working correctly.