Fuse fired (ON SECONDARY STAGE OF POWER SUPPLY) when you turn on the tv.
There is a tranformer to divide the cool ground from the hot ground and in the secondary in every stage(coil) there is a fuse and when you turn on the tv, one of these fuse is fired and the tv turn off. I saw the board and you can´t see any problem, just the fuse. I have the schematic, i can send to you in order to see it. Regards.
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Re: Fuse fired (ON SECONDARY STAGE OF POWER SUPPLY) when...
There are alot of problems with this set. I do not have a manual but have worked on several in a shop while I was in NY. If you want, send the manual to [email protected] amd I will see what you are talking about. Please include a note on the exact fuse that keeps blowing.
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This is fairly straight forward---if it got the fuse, input filter (big cap!) and the fuseable 7 watt-----
Understand (I do not know how savy you are) the power supply uses two grounds----on the primary side of the transformer (in power supply) it is from earth ground and on the secondary side from hot ground--when checking voltages= these are the key! you have to be on the correct ground to get correct readings.
Follow the money---the primary raw should be on that cap---follow it to see when it stops downstream.
220 can pop a lot of things---the set should also have a regulator IC in the power supply (could also be a big transistor) and if a chip--raw from that cap goes into it---and regulated comes out another pin---see if you have the raw and then see if at horizontal output collector and from there to flyback( with set off what is resistance reading from the collector of the output transistor to earth ground?
what kind of experience do you have with troubleshooting?
This problem causes and problems is the power supply board.Those tranformers on the power supply board one of those tranformer output coil not working anymore.That the board,where the power a/c cord plug into it.Tries websites like Shopjimmy.com.Ebay.com to buy a whole refurbish power supply board for the replacement.
The whole dawn power supply board is shorted and dead.U have the equipments,a good trouble shooting and electronic skills,trouble shoot all those transformers out put,check all the primary and secondary out put of those coils of those power transformers?Some of those power tranformers are dead needed replacement.Or try website like Tvrepairworld.com to buy a whole refurbish power supply board for the replacement
Please check the horizontal output transistor for leak, base-emitter. Change it.If there is any kind of short in the board, the power supply will sense int and will shuts down. Line out put transformer [LOT] may also suspect. On the secondary supply stage from LOT, the secondary power supply section, check all the rectifier diodes, and its filter capacitors for leak. Even a slight leak will effect the proper function of the set. Check it with good qulaity analongue multimeter, with setting it to meg ohms range; check the suspected componets off board. Likewise check the primary rectified DC voltage at SMPS stage. It should be aroung 380V DC accross main filter capacitor. If it is not check the main filter capacitor [usually 330Mfd 450V] for low capacity. and check the four main rectifier diodes.
TVs and monitors usually incorporate some kind of startup circuit to provide drive to the horizontal output transistor (HOT) until the flyback power supply is running. Yes, TVs and monitors boot just like computers.
There are two typical kinds of symptoms: power on click but nothing else happens or a tick-tick-tick sound indicating cycling of the low voltage (line regulator) but lack of startup horizontal drive.
Check the voltage on the horizontal output transistor (HOT). If no voltage is present, there may be a blown fuse or open fusable resistor - and probably a shorted HOT.
However, if the voltage is normal (or high) - usually 100-150 V, then there is likely a problem with the startup circuit not providing initial base drive to the HOT.
The startup circuits may take several forms:
Discrete multivibrator or other simple transistor circuit to provide base drive to the HOT.
IC which is part of deflection chain powered off of a voltage divider or transformer.
Other type of circuit which operates off of the line which provides some kind of drive to the HOT.
The startup circuit may operate off of the standby power supply or voltage derived from non-isolated input. Be careful - of course, use an isolation transformer whenever working on TVs and especially for power supply problems.
Note that one common way of verifying that this is a startup problem is to inject a 15 kHz signal directly into the HOT base or driver circuit (just for a second or two). If the TV then starts up and continues to run, you know that it is a startup problem. However, this is a risky procedure for both you and the TV.
I have also seen startup circuits that were designed to fail. Turning the TV on and off multiple times would exceed the power ratings of the components in the startup circuit. Some Zenith models have this 'feature'.
When this situation exists, it could be that the circuit is not providing the proper drive or that due to some other circuit condition, the drive is not always sufficient to get the secondary supplies going to the point that the normal circuits take over.
You can still check for bad connections - prod the circuit board with an insulated stick when the problem reoccurs.
Fuse blowing is due to excessive current drain and the the first clue is the blown fuse itself. If the fuse blows with a flash a bang and splatters copper across the inside of the glass you have a hard blow caused by a dead short on the power supply, check for power switch flashing over internaly. Short circuit main filter capacitors. Shorted turns in power transformer primary winding. If fuse just separates check for short on output transistors C to E. Try isolating fault by disconnecting LT pos/neg supplies to output stage. Also check for partial shorts on speakers and speaker wires using an analog ohm meter on low ohms setting.
If you have power to the outlet, then remove the back cover of tv. Check that the glass bus fuse isn't bad. It should have the thin wire inside running all away across the fuse.
If the fuse is good, then the high-voltage tranformer (power supply) is bad. You can get a replacement from tigerdirect.com
Check the volatage regulator in the mainboard resolder all you found dried unsolder parts inside mainboard. Voltage test the regulator IC if have a voltage flow 2.5 to 5v DC. check ribbon cable connector from mainboard to controller board if properly connected. In the controller board find the small fuse test it for open. Reminder:
When you voltage test in the power board
in the primary section of power supply
use hot ground. Do not use the hot ground
when you voltage testing the secondary
power supply, mainboard and controller
because it will cause of damage
semiconductor. For safety use cold ground
for secondary, mainboard and controller
Most TVs today use a "hot-chassis" design and a switch-mode power supply. You should use an isolation transformer when doing any service work on a TV. This helps protect you and your test equipment, and can prevent accidental damage to the TV by grounding parts to the wrong point.
Hot-chassis sets use two different grounds. The power supplies have one ground reference for the primary side (hot ground) and a different point for the secondary (cold ground). The point you pick will depend on what part of the TV you're measuring.
If you are troubleshooting a dead set and working on the primary side of the power supply, use the negative lead of the large electrolytic capacitor you'll find near the AC input connection. There's almost always a bridge rectifier and filter cap (300 to 400 uF range, 180 to 250 volt rating, so physically pretty large) in that area to make the raw DC. That's a guaranteed good hot ground. Sometimes the set will have a labeled hot ground point right on the circuit board for you.
For measurements on the secondary (output) side of the supply, almost any shield can is ground. The tuner cover is a good choice.