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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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...

1 Answer

How do I service a multimeter with a eepr err on it. All the manuals just say to get it serviced and I want to learn to do it myself.


Hi Russ, Unfortunately, unless you've got an EEPROM programmer and a system for wiping and recoding the Eprom (chipset), along with the specs and coding of the logic circuit, you're not going to be able to learn to do this yourself.

Fluke makes some very nice test measurement equipment, but they will not release their confidential programming codes to anyone outside of their authorized service centers, etc., so having the proper data needed to perform the repair, from a technical standpoint, isn't feasible.

Even with my basement with all sorts of test, diagnostic, and repair equipment for working on electronics, I still need a full schematic of the product needing servicing, for without that, it is extremely difficult to resolve problems with many electronic devices. Not to mention that Fluke uses mostly SMC (surface mount components) which are pretty darned small and typically installed by automated equipment during manufacture.

Wish I had better news for you, but in this situation, you would be well advised to have the service repair done by Fluke.

I hope you find this Very Helpful and best regards!

Nov 10, 2009 | RTO Fluke Insulation Multimeters # 1577

1 Answer

Heat element does not kick on. Checked both limit switches OK. Have 120v to both sides of the element however it does not heat up. Help!!


Hi.

If you have volts at the element , and the element does not heat up, then the element has blown.

The element is tested using a multimeter on Ohm on the element contacts.
To do this you need to disconnect the element and point multimeter probes at element contacts. Multimeter must be set on a low impedance scale, eg Rx1. If the multimeter returns open, or go to infinity (same thing), then the element has blown.
In a similar way you can test the thermostats. This can also be tested bypassing them.

Do all test with power not connected. Repairs must be done by trained personal.

You can find parts and diagrams here.

Regards.
Enter mode

Nov 09, 2009 | Kenmore 63952 Electric Dryer

2 Answers

BOTTOM ELEMENT DOES NOT WORK


If the top element is working, then it is either the element, the wiring harness , or the control board.

Since both elements are controlled through the same temperature probe, then the temp. probe should be OK.

The heating element must be removed and tested using a multimeter.

The part is tested disconnecting wiring from element contacts, setting a multimeter to read impedance at Rx1, and reading Ohms on element contact.
If the circuit is open (no continuity and infinite Ohms value), then the element has blown and must be replaced.


If the element has continuity, test the wiring harness, then replace wiring harness or control board.

All the test must be done by a trained repairer, strictly observing all health and safety rules.

Regards.

Oct 21, 2009 | DeLonghi EO1238 Toaster Oven with...

1 Answer

Power light is not turning on. I have replaced the 2 15 amp fuses in the washer (not ASKO fuses) and I have confirmed that the beaker panel is working fine and the dryer which is linked to the washer is working so power seems to be getting to the washer, but no power on light.


There is need to check if there is power getting at the fuses and power getting to timer control board.That is done reading volts with a multimeter.

For safety reasons I need to remind that all test with live power must be done by a trained repairman.

If there is no power at all and you already replaced the two fuses, then problem can be power cord, internal wiring harness, control assembly .

Sep 08, 2009 | Asko Washing Machines

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