Tip & How-To about Televison & Video

How to test an LCD TV or monitor PSU and inverter

Hi.

Before proceeding I assume you have technical training along with the multimeter. A full testing must be done with power on, and for safety reason must not be done by an untrained user.

The tip contains only general indications. The reader is supposed to have the training to apply in practice the testing method below.

If there is no power at all, then the responsible is almost always the PSU.

When there is no power, test AC in to PSU. If there is no AC in (read volts, or read ohms on power cable), that means that the power cord must be replaced.

If there is AC in, then test the PSU section near to AC input. You always find a resistor or a fuse in there . Check if it has blown.
After that you test the rest of PSU component. If there is no power at all , and problem is not power cord, it is often possible to spot at a glance a leaky or bulged capacitor.

If there is power, but the monitor stays in standby, then te PSU is forced to low voltage only by controller board. This happens when a fault had been detected.

In this case testing the PSU becomes more complicate. The technician must locate the control lines from controller board. This control lines operate at lower PSU voltage (often +5V), and turn on higher voltages on PSU board.

The inverter may use for example a +20V line from PSU. The +20V line is turned on by the controller board, closing a +5V control line to PSU. When PSU is in standby mode, the technician testing the PSU must bridge the +5V line with the PSU low +5V circuit, and test if the +20V line to the inverter gets turned on.

As explained this kind of test must not be done by the unexperienced user, as the chance to waste the unit beyond repair is high, and there are also many safety concerns.

After testing the PSU, next part to test will be the inverter board.

The inverter is tested reading DC voltage in from controller board, and AC out to back light system.
The inverter is an high voltage board, remember, safety first when testing AC circuit.

If the inverter has no DC from controller, then test PSU, if PSU is OK, and inverter has still no DC in when PSU line to inverter is on, then replace controller board.
If the inverter has DC in, and no AC out, then replace the inverter.
If the inverter has DC in and AC out when higher DC voltage to inverter is turned on, then test at component level the main controller board, and if present test LCD controller.

Regards.

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john deere will not start


First, check the obvious. Check your battery. Next, if you have a multimeter, turn your multimeter to continuity setting (where you hear a beep when two ends touch). Then with multimeter, check all safety switches, push in and let out with probes of meter on leads of switch, you will hear meter beep as you push switch in and out. If all switches are good, test keyswitch with test light. You should have power at back of terminal that red wire leads to on your keyswitch. Next, take test light and touch to small single post on solenoid(not large red leads). Turn key over and observe light. If test light comes on all is good and you need a new solenoid. You can find a lot along the way. This process will narrow down your search. Remember, brake pedals and seat switches will need to be depressed to test solenoid or no power will be going to post. Goodluck!

Aug 09, 2014 | John Deere Gx75 Rx75 Srx75 Sx75 130 9hp...

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put in gaer and dies


Some bikes have one or more safety features regarding the clutch and gear box. One feature is a micro-switch at the clutch master/lever, it tells the safety system if the clutch lever is out or in. If the switch fails the safety system will think the lever is out (allowing power to rear wheel) and kill the engine to prevent the bike from lurching forward, potentially causing the bike and rider to go down. The other feature is not as common, it is a similar switch at the side stand. This prevents the rider from starting off with the side stand down. Which can also cause the bike and rider to go down. If that switch fails then the bike will think the side stand is always down and will kill the engine as soon as it put into gear. If you know how to use a multimeter you can test the switch(s) for function and determine if it is failed. Otherwise have it checked by a competent mechanic.

There is also a recall on your bike (and many others with the same gearbox) regarding the power train. A good reason to get you bike in, fix this safety issue and your original issue.
2002 Yamaha Midnight Star POWER TRAIN MANUAL TRANSMISSION Recall

MGM

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1 Answer

wiring


Check your power cord and power supply, check the plug is clean and free from corrosion or dirt.
Plug another appliance into the same socket to check there is power at the socket.

Note: Electricity can cause serious injury even Death.
Isolate your power supply from the mains switchboard.
Switch off and Unplug your appliance from the wall socket before attempting any repairs.

If its still under warranty, take it back to the store or manufacturer for replacement.
Call a serviceman to test the appliance for you,

If not you could...
Check your fuse in the device, you will have to dismantle the appliance.

Get your Multimeter and do some tests...
Test the flexible cord connections
Electrical tests included, visual inspection, Earth continuity, Polarity and Insulation resistance.

Examining cord for Damage
Disconnect flexible cord from power supply.
Check cord along the whole length for obvious damage

1: Visual Inspection
A visual test is necessary before using test instruments to ensure that all specific safety requirements are meet.
Check the general condition and safety of the cord, plug, cord anchorage, terminations and of the appliance itself.

2: Earth Continuity.
The earthing system of an electrical installation must be installed in a manner that will allow circuit protection devices to operate if there is a fault between live parts (other than Neutral) and the mass of earth.
What to check: For class (one) 1 protectively earthed appliances only, test for very low resistance between exposed appliance metalwork and the earth pin of the plug. this resistance should be as low as possible and must not exceed 1 ohm. Note: the Exposed metal parts of a class 2 double-insulated appliance must not be earthed.
Equipment requirements:
A Multimeter (Digital or analogue) Set on a ohm scale or an insulation tester that also has a continuity scale.
A set of leads.

3: Polarity
Why is this test necessary:
An incorrect connection of phase and neutral conductors to fittings and appliances is extremely dangerous and has been the cause, either directly or indirectly of many shocks and fatalities.
What to check:
Polarity tests are carried out to ensure that every single-pole switch operates in the active conductor or the circuit in which it is connected.
Equipment requirements:
A Multimeter (Digital or analogue) Set on the resistance scale when the SUPPLY is NOT connected.
or a voltage indicator set on a suitable voltage rating when the supply is not connected.

4: Insulation Resistance
Why this test is necessary:
All live conductors (including Neutrals) and live parts must be insulated to prevent - Electric shock hazards from inadvertent contact.
- Fire hazards and equipment damage from short circuits.
What to check:
Insulation resistance tests must be made between:
- Active conductors of a poly-phase circuit
- Active and Neutral
- Active and Earth
- Neutral and Earth
The insulation resistance between appropriate components shall be not less than 1 mega-ohm minimum
Equipment requirements:
An insulation resistance tester which maintains an output of 500 volts when loaded with a 1 mega-ohm resistance.
A set of leads.

Different countries adhere to spicific Electrical (safety) Regulations and standards

This information is only intended to enlighten the novice, guide and remind someone already in the field of electrical installations.
DO NOT attempt any electrical repairs unless you have the appropriate background or training.

Jun 11, 2013 | Yamaha RX-V757 Receiver

1 Answer

I have sound but no picture


Hi.

If the display is completely dark, then it is usually a faulty inverter.

You can find some general troubleshooting here:LCD TV has sound but no picture.

Below general steps to test the inverter:
Before proceeding I assume you have technical training

To contact a technician or to verify warranty status call the number that you find in the owners manual.

Here parts:LTV-32W1

Sep 28, 2010 | Westinghouse LTV-32w1 32 in. HD-Ready LCD...

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