Question about Zenith Televison & Video
I have a good sound and I have in board 42T-YSUS , Fuse 202, 204 Volts.but I do not have High voltage. Please Answer
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Posted on Jan 02, 2017
> 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
to test the zsus board check for a low resistance on the fuse to ground. sadly if the zsus is bad, the ysus and one or both of the driver boards is probably also bad. best to change all at once as a defective one can tacke out the others.
Posted on Dec 31, 2008
I have the same issue with my LG 42PC3DVA and I narrowed it down to the Y SUS board. After a little research there are a few items that are prone to go. The ceramic fuses (as you found), sometimes the capacitors on the Y SUS, Z SUS, and power supply go along with them You can tell because thy will be bulged at the top instead of flat. I replaced a few of my capacitors - they are only $0.89 each so it was MUCH cheaper than a board.
The other thing that is common on the Y SUS in particular are the FETs (also called MOSFET). They can be replaced if you are good with a soldering gun but they are static sensitive so be grounded. They are also a bit tricky to test so you may want to do some research on how to determine if this is the issue... or you can just replace the whole board.
Posted on Oct 28, 2009
It's not the x main. 90% of the time it's a y buffer that goes out. It's usually the top buffer. 3/4 of the time the buffer takes out the y main board too. You cannot just replace the y-main or buffer because it will just burn out the other within seconds. Also about 1/4 of the time it'll take out the top transformer on the power supply too. The solution? First disconnect the power to the y main board. turn on the television and check the voltages coming off of it. Careful it's high voltage 208V! Remember it's DC too. Then disconnect the buffers from the y main board. You can try powering the y-main up to see if the little LED lights up. This does not indicate it's working though but it'll tell you if it is possible to fix. The fixes for these boards is only for electronics guys. It usually involves replacing 1-3 capacitors and 1-4 FET's. Since a bad buffer can take out a good y main in seconds it's usually recommended that one replace all 3 boards at the same time. It's a $250 fix. How do I know all this? I've now repaired 5 of these televisions. I owned one and spent close to 600 repairing it. I bought misc parts and broken sets online for months before I had 2 different repair guys walk me through the process of repairing them. I had so much cash tied up in parts that I bought 3 more dead sets and repaired them to justify all my spending. I've never had an x board fail. I've had EVERY top buffer fail. I've had all but 1 y-mains fail. and 1 lower buffer fail. I've also had the y buffer fry it's top chip, blow a capacitor and FET on the y-main, and fry the top transformer on the power supply before my eyes. It only took 5 seconds. Replacement of the 3 y boards will almost always fix the sound but no picture problem. Hope this helps!
Posted on May 26, 2010
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