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FP-29 Yaesu Switching Power Supply Problem

WHen first applying AC, the two DC voltages (+30 and +13.8 VDC) try coming up but suddenly fall back to zero. Recycling power switch a few seconds later gives same results.

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The power supply is running, but there is a failure in the protection circuitry. Usually a shorted Zener diode or small signal transistor. The Op-Amp for the current limiter can cause the same symptom.

If the supply does this ONLY with the radio connected, there is usually one or more shorted PA transistors.

Bob W1GWU

Posted on Jul 21, 2011

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I have a dcs 1565 alarm, replaced battery but no lights or anything on keypad. Power is on


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No visual lights on display, but vcr works


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How do i turn on a compaq ps-7231 power supply?


Pin Name Color
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Power supply problem no switching


( "Power Supply Problem Not Switching "???? )

How do you know it's Not Switching? Do you mean the TV wont turn on when you push the power button on and off on the TV and also with the remote control unit? Is that what you mean? If YES! Then, If your Vizio TV wont turn on and has NO-PICTURE, NO-SOUND and a BLACK SCREEN, Then the TV has an AC or a DC Voltage Problem.

1 - First, check the wall outlet socket by pluging in a lamp to see if you have 110 AC-volts there. If the lamp works, the wall outlet is OK! That means the problem is inside the TV.

2 - Before, you remove the back off the TV. I want to *(CAUTION - YOU)* The Power Voltages inside your TV are Very, DANGEROUS!!! There is 110 AC Volts at a 20-AMP-Rating ***CAN BE A LETHEL DEADLY SHOCK HAZARD to HUMANS!!!*** Also there are DC Voltages ranging from 3.3 to 24 volts. And R-F- VERY-HIGH-VOLTAGE of 20,000 Volts or More.

3 - You will need hand tools and a Digitle Volt Ohm Meter to check AC & DC Voltages and the OHMS Meter section to check resistors, capacitors, coils, grounds and contacts.

4 - With the Back removed, and no-power to the set. Inspect the power board for any signs of BURNED, LOOSE or BROCKEN parts like resistors, capacitors, coils, fuses on all boards. If you discover damaged parts, make a list of them. Then you must deside if you are qualified to do the on board repair or just order a new replacment board.

5 - If on the other hand you didn't discover any damaged parts by your inspection, It's time to put the Meter to good use. Plug the TV power cord to the wall outlet. Set the Meter for AC - voltage range of 200 or more. check for 110 AC volts going to the power supply board fused inputs.
If NO replace the cord. If YES, look on the board for voltage test points marked on the board. (SAMPLE!) 3.3 vdc, 5 vdc, 12 vdc, 24 vdc, and so on. Set Meter for DC Volts now, range 50 to 100. Put the black lead to ground and the RED lead to each test point marked on the board while repetetedly pressing the TV power on & off button..

6 - If ANY of the DC voltages were LOW, WRONG or MISSING, The Main power board is defective and needs to be removed and replaced with a new one. Write down the board number that is on the board and use that number to order the new one. You can order it on the Net!

*****(NOTE)***** If you are not an electronics tech. don't try to fix the old defective board... but, keep it handy, you might need it for parts later. :-)

Hope This helped... GOOD LUCK! NOW, GO FIX YOUR TV!

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Pin Name Color Description
1 3.3V Orange +3.3 VDC
2 3.3V Orange +3.3 VDC
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4 5V Red +5 VDC
5 COM Black Ground
6 5V Red +5 VDC
7 COM Black Ground
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10 12V Yellow +12 VDC
11 3.3V Orange +3.3 VDC
12 -12V Blue -12 VDC
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15 COM Black Ground
16 COM Black Ground
17 COM Black Ground
18 -5V White -5 VDC
19 5V Red +5 VDC
20 5V Red +5 VDC

/PSON activated by pressing and releasing the power button while the power supply is in standby mode. Activating /PSON connects the power supply's /PSON input to ground, thereby switching the power supply to full-on condition.
18 AWG is recommended for all wires except pin 11, which should be 22 AWG. For 300W configurations 16 AWG is recommended.
There are several ATX variants.
Hope this helps.
If this helps you resolve your problem, please
consider giving me a rating of 4.It will help me as well. Thank you.

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1 Answer

MY RCA 27" WILL NOT TURN ON, HAVE POWER TO THE FUSE, THE FUSE IS GOOD ALSO BUT THE DEGAUSS RELAY DOES NOT CLICK AND NO OTHER CLICKS ARE HEARD EITHER, WHAT COULD BE WRONG?


you need to check the voltage output of your power supply section.This power supply supply is a switching type power supply.there is a chopper transformer in there.its supply is a dc voltage unlike any other transformer which is AC supplied on the primary..First step.
1.Using a multitester measure the primary supply it is a DC voltage around 220v - 110 VDC
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good luck!Hope i helped you..

please rate my help..god bless!

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1 Answer

ESA Plasma PDP4294LV No video,sound


 checked voltages meter set to AC referenced to chassis VA, VE, etc no voltages. 
Do not try to measure voltages on the primary side of the power supply with a meter; you may damage the meter and cause new damage to the supply. There are switching frequencies somewhere between 50,000 - 100,000 Hz and possible voltage peaks of several hundred volts. 

Checking AC is only useful before a diode bridge that converts incoming AC into raw DC that is then chopped at higher frequency into an approximate HF AC, coupled to the secondary, then tapped and connected to more diodes to produce DC, finally regulated and sent on its way.
Your plasma set uses some higher voltages that could have caused the cracking sound they heard but the DVD player didn't cause the problem directly; maybe just caused the HV for the display to surge for a moment.
You may have additional fuses on the secondary side of the supply. If test points are accessible there, check for DC voltages and be suspicious of any fuse or test point that measures nothing at all.
I can't tell you which voltages to expect since that varies from one design to another but you should find several lower voltages such as 5 VDC for logic circuits and perhaps a 12 V point. The plasma's HV could be produced from a separate board fed from the AC line or get its supply voltage from the main supply. There aren't many standards to rely on here.      

The most likely semiconductor failure would be on the secondary side and diodes come in many different packages, many cylindrical, some in the TO-220 package with a metal flange and mounted on upright aluminum heatsinks. These will have only two leads and there will be some in the same package with three legs. The latter can also be checked statically but unless you know what kind of transistor or regulator (look about the same) you are measuring, you will not be able to ferret out a defective one with any luck. 
While you have the set open, check for any dust bunnies that can act as sponges, collect moisture and create a discharge path for higher voltages. 

Dec 26, 2008 | Akai PDP4294 42 in. EDTV-Ready Plasma...

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