The closest I came to repairing the motherboard was washing it. (It was full of dust)

I used demineralized water. (yes, water.. an advice I got from long-time electrician) I let it dry and it worked afterward.

Well.. it worked before that too, but the dust was covering most of it.

Remeber.. dust + airflow = static charge.

there is nothing else BUT replacing the capacitors and maybe re-soldering the slots if you feel lucky. this is not a CRT monitor, it cannot be repaired.

never never open a crt monitor

true, unless you know what you're doing

Wow JBennet: what electronics school teaches that? How to fix a monitor or replace a fuse without opening the chassis.

You can open a monitor, but only after you are trained. and know what precautious to take. and be careful of the corona discharge, even when it is unplugged.

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back to original question.
1: if unit has no lights, no power

• (a)check the voltages on the AC adapter

• (b)check the battery - try with and without battery

2: if the unit has power light(s) but won't come on (ie batt charging light)

• (a)check the on/off button or button panel

• (b) check the connector of the power button (male & female)

• (c) disassemble unit removing Batt, CD/DVD/HD and try with just the bare board and power power panel.

NOTE: you can leave the heatsink off for test purposes but do not run the unit more than 30sec to 1min without it. - if it comes on.

3: if the unit has no lights

• (a) Check the fuses behind/near DC Jack (esp. toshiba and sony)

• (b) check the power resistors, MOV's (RV1, RV2, RV3) in DC jack area (DELL)
  ii. if you have a docking station, you can test to see if it will power on with voltage going through the docking station. (even when a DC jack is bad)- in USA check goodwill, salvation army and other thrift shops for a backup plan ~$4 to $9USD.

• check the power controller chips MAX1999 or MAX1632 (DELL, HP Compaq,Gateway, eMachines, and others)

4: if the unit has no lights & the LED on the power adapter turns off when plugged in.

• you have a dead short - usually power chip, cap, MOV, or DC jack area.

Hope that helps some....

its very easy for people to kill themselves when dismantling crt screens hence not reccomended

Voltage checks are important too, checking the various voltages help isolate problems. Also checking the various power regs on a board to see if they are ok can help you.

Resistance checks on certain IC's and BGA's can give you a clue to where the problem may be. However you do need to have an idea of what this resistance should be at when in a normal booting state.

*

jbennet, I have worked for 7 years in a company that repaired CRT screens, providing warranty repairs for the entire country. Do you think I wouldn't know what I'm talking about?

repairing a motherboard is not easy as chewing a gum..if you really want to go down to component level..first you must know how to read a diagram..use an oscilloscope, spectrum analyzer...and so on... better buy a new one..don't waste time.

This is a great thread. Glad to see there are some who at least share some info on chip level reoairs. In India chip level repairs of motherboards is still common. Generally you can get a board fixed for around 10USD or sometimes less.

It goes without saying that whoever wants to repair boards needs to know electronics well, should be able to read schematics and test components. An oscilloscope is helpful, but in a tight fix sometimes a good digital multimeter with a frequency counter can help.

Electrolytic capacitoers generally fail on old boards. Also mosfets are prone to fail in some places where power is irregular. If mosfets have failed, one should also check voltage regualtor modules (VRM ICs).

One should check clock ICs once all voltages are seen to be ok. Sometimes crystals can fail or have dry joints.

Am pasting some info on VRM testing below.



Procedure for testing Voltage Regulator Modules (VRMs):
(This assumes that any bad capacitor problems have already been fixed.)

1. Turn off power to the computer.

2. Remove CPU, memory, and all peripherals from motherboard. Disconnect power supply.

3. This step verifies that the board is not damaged, and the VRM is not shorted:
a. Measure resistance from power supply pin (+3.3, +5, +12, -5, -12) to input of VRM. Resistance should be zero (too low to measure).
b. Measure resistance from output of VRM to load supply pin. Resistance should be zero (too low to measure).
c. Measure resistance from input of VRM to ground (should be greater than 1 megohm, usually much greater).
d. Measure resistance from output of VRM to ground (should be greater than 1 megohm, usually much greater).

4. Install CPU, memory, and all peripherals to motherboard. Connect power supply.

5. Turn on power to the computer.

6. This step actually tests the VRM (all voltages taken with respect to circuit ground):
a. Measure voltage at the power supply side of the power connector (+3.3, +5, +12, -5, -12).
b. Measure voltage at the motherboard side of the power connector (+3.3, +5, +12, -5, -12). Anything less than the value obtained in step 6.a indicates a high resistance in the power supply connector.
c. Measure voltage at the input to the VRM (+3.3, +5, +12, -5, -12). Anything less than the value obtained in step 6.b indicates a high resistance in the PC board traces to the VRM, and is probably not repairable, even with a schematic.
d. Measure voltage at the output of the VRM. The value obtained depends on the functions being powered by the VRM, so knowledge of the expected value is required. Anything different than expected indicates a failed VRM (note that output may be higher or lower than expected if bad).
e. Measure voltage at the device being powered. This requires knowledge of the device (which pins are power pins). Pinouts are readily available on the Internet for 30-pin, 72/144 pin, and 168 pin memory, as well as ISA, PCI, AGP, USB, etc. Pinouts for CPUs are either on the Internet or may be obtained from the manufacturer. Anything less than the value obtained in step 6.d indicates a high resistance in the PC board traces from the VRM, and is probably not repairable, even with a schematic.




VRMs (voltage regulator modules) are a specific class of MOSFETs; MOSFETS are a specific type of FETs. FETs have several advantages over bipolar transistors. For a basic description on the workings of a voltage regulator, search on "7805 data" on Google or Yahoo (7805 is a basic 5-volt regulator).

VRMs take one voltage (such as +5 VDC) and produce a different, lower voltage that is needed by various components (microprocessor, memory, etc.). Each VRM can only produce one output at a time, so two different VRMs are needed if the CPU and memory operate at different voltages. The output of the VRM can be varied slightly, depending on how external components are connected and controlled, so some motherboards are able to have settable voltages for memory. CPU voltage is usually, but not always, taken care of automatically. True variable power supplies, where the voltage is variable over a large range, aren't used in PCs. The middle leg is usually cut off, because it is connected to the case, which is soldered to the board. The case is often, but not always, connected to ground. To test one, you need to know what the input and output should be, then measure them with respect to a known ground. If the VRM produces no or low output with proper input, either it's bad, or an external controlling component is bad. If the input is bad, look for upstream damage. Usually, it's best to test a VRM in-circuit (with CPU, memory, etc. removed!) so that the output can be checked at the immediate output of the VRM, as well as at the point of connection of the powered device.


I got this procedure on another site. If i can recollect who the author was i shall psot the info in a later post.

Hope this helps those interested in fixing motherboards.

Cheers!