Nec 1860nx no power

[rippergr]

Hello
I have a nec 1860nx lcd monitor which doesn't power on.
I measured fuses, jack they are ok.I measure the cables that go from power board to vga board and I don't have power.
I can't find schematics for this monitor either.
I am attaching pictures(I took a picture of the back of the power board only because I think somewhere there is the problem)

[selldoor]

Re: Nec 1860nx no power

Hi - can you test the voltage on the BIG cap.
Meter on vDC600 should be around 350vdc so take care.
Also can you post a full picture of that black box mains in- have not seen one
in a monitor before.

[rippergr]

Re: Nec 1860nx no power

I have 40v in big capacitor.
What part exactly are you reffering? I don't understand what do you mean. Can you show it to me in a picture?

[selldoor]

Re: Nec 1860nx no power

In and out most of today.
Pic attached

Also test the the voltage on the red and white wires marked with yellow box.
I think it should be mains voltage ac.

[rippergr]

Re: Nec 1860nx no power

this black box its where the ac cable goes and those 2 yellow cables are the main voltage 220V.
I saw that you put in one component pink and green lines. Shpuld I check those too and if yes how will I measure them? Its just voltage there?

[selldoor]

Re: Nec 1860nx no power

Ok so is the voltage on the red and white wires 220vAC

and the blue and brown ? just the on off switch?

[rippergr]

Re: Nec 1860nx no power

exactly

[selldoor]

Re: Nec 1860nx no power

OK well in that case, the red and green marks are on the bridge rectifier so next
test is on the RED center pins - Meter on 600vAC - it should be your mains voltage. Then change your meter to 600vDC and test the two GREEN outer pins. should be mains voltage x1.41

[rippergr]

Re: Nec 1860nx no power

voltage in red pins is 220V-230V , voltage in green pins is ~310V

[selldoor]

Re: Nec 1860nx no power

ok hehehe hadnt noticed the damage to the board at the bottom of the picture
I will have another look at that.
310vDC on the bridge - they are connected almost directly to the BIG cap - 40v DC??
(please say if AC or DC) - Can you test it again. If still 40vDC with the power off ,test
the resistance from -(minus) on the bridge to - on the cap. Then do the same for the (+)

[selldoor]

Re: Nec 1860nx no power

Also on the back of the board there is a label F902 on the top of the board is it the bright green component mainly under a blob of grey glue?

[rippergr]

Re: Nec 1860nx no power

I measured big cap again in AC and it showed 680V.
Yes there is a green component with F902 I measured in diode mode and it it is ok.

[rippergr]

Re: Nec 1860nx no power

Something very strange happened.
When I measure the big cap again and saw that the voltage is 680V I connect the cables again to the vga board and it worked.
Can you tell me how this happened?
Can it be a faulty component that somehow "fixed" for a while?

[selldoor]

Re: Nec 1860nx no power

F902 is a fuse- You dont test in diode mode ?? Please test in ohms mode, it is probably ok but I need to be sure. - Should read the same as touching the probes together on the meter in ohms mode.

680 vDC PLEASE always say if AC or DC.

That is most unlikely the cap is rated for 400vdc or 450vdc which is the maximum voltage it can take. I am pretty sure 680vDC would have blown it up. Check the battery in you meter?

As to it working - well looks like there are quite a lot of bad solder joints and
possibly a broken trace near IC 901. Maybe they just momentarily re connected.

Is C909 burnt (looks black on top) Can you post close up of the
top and bottom of the IC 901 area. Can you read the part number on IC901.
Is there a crack in board/ break in the trace between pin1 and 2/3.
If you hold it up to a very bright light it might help.

[rippergr]

Re: Nec 1860nx no power

Those are not bad solder joints. Its just flux in one pin and the crack you see it's not a crack its just the board it has a line there.
I am attaching a new closeup photo with flux cleaned

[selldoor]

Re: Nec 1860nx no power

Wow cant believe it , mind I am now viewing this on a better screen and even the old pic looks a bit better.
So now what to do - keep it on test switching on and off now and again to see what happens?

[rippergr]

Re: Nec 1860nx no power

So far I left irt open for 1 hour switch it on and off 10 times and still working