Question about Akai PDP4294 42 in. EDTV-Ready Plasma Television
I have this TV given to me. They said they heard a spark while hooking up up a DVD player, so they say. Well brought it home, no picture sound. Steady RED light, hear relay. When turn off, LED flash 5 times. Took off back, Power supply looks good nothing burned. Checked main fuse in -ok andcheck the 8 black can type fuse- all good. checked voltages meter set to AC referenced to chassis VA, VE, etc no voltages. I see it is all SAMSUNG inside. Is the Power supply bad?. If so,where can I get one? Is there schematics somewhere? Please advise. Thanks, Mike
> 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.
Posted on Dec 27, 2008
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Posted on Jan 02, 2017
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