Viewsonic E70 monitor cannot switch on What is the likely cause and how to repair it

[Steve]

I have a old Viewsonic E70 CRT monitor(about 3 years old)whose
warranty has already expired. I can't swtich it on. That is no LED
light at all/no sound at all. What could be the problem and how to
troubleshoot it?
How to repair or correct the problem?I have no experience at repairing
monitors but is keen to learn and get it repaired myself.
I only have a multimeter at hand and some electronics knowledge and
yes I do know the dangers of high voltage in the capacitors CRT tube
etc.
I do not have the circuit schematics of the E70 monitor.Does anyone
have one?
The fuse is definitely OK, I checked. I did look up
http://www.repairfaq.org for help.
It should be a simple problem what would be the likely cause for a
monitor to not start or no power at all?Any help would be much
appreciated. Could it be the on/off swtich cause I remembered I switch
it on and off a couple of times before it just went off and cannot be
turned on again.

 

[Thias Russell]

Hello Steve

First of all it is normally the power supply that is faulty when there is no
led on. So in that case it could be faulty cap. faulty swich transistor and
so on.

I have a 40 page service manual as PDF file if you are interested.

If so please Email me at: [email protected]

Best regards Thias Russell

 

[Bob Parker]

Hello Steve

First of all it is normally the power supply that is faulty when there is no
led on. So in that case it could be faulty cap. faulty swich transistor and
so on.

I have a 40 page service manual as PDF file if you are interested.

If so please Email me at: [email protected]

Best regards Thias Russell

Just for the information of anyone seeking this manual, Thias is
*selling* it for the price of 50 Danish crowns, not giving it away.

Cheers,
Bob

 

[Steve]

The servicing manual for Viewsonic monitor e70f can be found at the
following site ftp://147.213.74.111/Schemy/Monitory/ or other monitor
schematics can be found at
http://schema99.host.sk/my_page/monitory/b.htm.

According to Page 27 of the servicing manual for viewsonic e70f for no
power supply dead set.
I checked the fixed output voltage after the transformer there was
nothing no dc voltage at all.
I checked the C807 capacitor and there was a dc voltage of around
320Vdc
as the input supply is 230Vac which should be right as it is twice as
in the example for input supply 110Vac(US) should be 150Vdc.Even with
no power supply there is still this 320Vdc across it.
I then checked the resistors R819, R805 & R829 which is ok no open
circuit
The funny thing is the Q805 n-channel power mosfet Fuji 2SK2645-01M
with the very large heatsink on it. The resistance across the
source(black -terminal) and drain(red +terminal) is 0 ohm and the
resistance between the source(black -terminal) and gate(red +terminal)
is 0 ohm. Is this right? or do I have to take out the mosfet from the
board in order to check??I,m thinking of replacing this component.
The IC801 pin7 is 0V.

How to remove this mosfet from the board? I have a desoldering tool
and iron and wick. The large heatsink seems to be glued onto the board
by some white mixture and screwed onto the mosfet tightly.
I can,t get to the component or unscrew the heatsink cause there are
lots of short wires connected to the board and the CRT. Can any
experienced monitor technician please advise a newbie on how to
replace such a component and is this the right action to take.

 

[Wild Bill]

You should read the safety precautions and procedures for discharging and
working around CRTs in the SER Repair FAQ.
http://www.repairfaq.org/REPAIR/

I don't think an ohm meter will help you determine if an FET is in working
condition, that's what FET testers are designed for.

To perform component replacements on pcb repairs, it's generally best to
remove the board from the case. This requires disconnection of the yoke
plug, HV lead, CRT board and other wiring connections. Marker pens are handy
for marking connectors.

Testing individual components on the board doesn't always require complete
component removal. If the solder around the pins can be removed completely,
the component is essentially out-of-circuit.
Where heatsinks are involved, there may be solder tabs from the HS soldered
to the board, other times, there are screws from the bottom side holding
them in place.

The PS FET regulator circuit probably/definitely has provisions for sensing
other circuit faults, and shutting the regulator off.
See the repair FAQ section about monitor repairs, and notice that many types
of other circuit faults will shut down the PS section.

I didn't see the original posted message, but there are quite a few other
items to check before replacing the PS regulator, if that's what you're
considering.

WB
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