Viewsonic VA720 - 2 secs to black

[shovenose]

To make a long sotry short, aunty got this crap from a relative (for free)... used a Mini-DVI to VGA adapter to attach it to her MacBook...

damn it! 2 seconds to black!

Opened the back,
removed all the covers and stuff...
nothing noticeable bad
Of course all caps are crap (Hermei, Elite, Ltec, etc)

but none are bloated.
I'm not at home right now so I don't have any tools... just the screwdriver I used to take it apart...

The picture does show fine for almost exactly 2 secons... no reddish tinge or any shit like that...

Picture coming soon!

Can I test it with certain boards detachhed? what can I test? thanks!


EDIT: image too big for here, no image resize software on her computer, so here is an image:
http://img716.imageshack.us/img716/1...1121220631.jpg

[retiredcaps]

2 seconds to black can be

a) bad caps
b) bad ccfl and/or wiring (return wire)
c) bad inverter transformer
d) bad fuse especially if there is more than one fuse on the inverter board

All discussed in posts #13 and #14 at

http://www.badcaps.net/forum/showthread.php?t=10419

[shovenose]

Thank you. Will take a look tomorrow, I'm off to bed now!

[PCBONEZ]

I did one of those.
The only cap actually blown was the large one next to the yellow wrapped transformer.
[Mine was bloated though.]
I replaced just that and it fixed it.
- Then I recapped the rest of it because I don't wanna take it apart again.
.

[shovenose]

Originally Posted by PCBONEZ

I did one of those.
The only cap actually blown was the large one next to the yellow wrapped transformer.
[Mine was bloated though.]
I replaced just that and it fixed it.
- Then I recapped the rest of it because I don't wanna take it apart again.
.

are you referring to the 3300uf 16v one on the power board?

[shovenose]

Alright well I disconnected one of the two what I assume to be the CCFL connectors from the inverter. Tried it again. Same problem. Plugged that one back in and disconnected the other one. No change...

I'm inclined to say that from this analysis the logic board is OK and we can completely ignore it. Right?
Thanks.

I don't have my multimeter with me here in SF, so what I'm limited to ATM is unplugging boards, hitting it with a hammer, and dousing it with water....
(just kidding, I want this shit to work when I'm done with ti)

[PCBONEZ]

Originally Posted by shovenose

are you referring to the 3300uf 16v one on the power board?

Yup.
I remember because the cap I initially used was a Samxon RS 10mm [the PSU favorite], and it was either too tall or I it needed for something else, so I temporarily used it to run-test the rest of the screen [leaving back off] while my caps order went through.
Because of were it sat, the open back of that thing was the first thing I saw when I walked into the shop for about a week.

[shovenose]

on mine it's an Elite crapacitor. I'm sure I've got some sort of cap at home that would fit there but until I replace that any other ideas what could be causing this???

[shovenose]

I googled the part number of the PSU (jt178/188a) and I got this:
http://www.discount-merchant.com/SYL...-p/1125162.htm
Click on the picture to enlarge it. IT HAS NO CAPCITOR WTF??
edit: slightly different overall layout. but can i just remove the whole capacitor and try turning it on?

[PCBONEZ]

Looks to be missing other parts too.
The dummies showed a board that wasn't complete yet.
Replacement boards often get you more crap caps so if you want it to last you still have to recap.
.
I didn't have any other problems so I dunno.
.
If you'd like to fry more expensive [and possibly harder to find] parts then turning it on with missing caps is a good way to do it.
.
Elite are as bad as or worse than Capxon.
Make them all go away.
.

[shovenose]

Step 1: getting my aunt to give it to me
Step 2: digging through my c(r)ap collection to find a suitable capacitor. I hope you don't mind if I don't match up the ESR/ripple specs
Step 3: replace that 1 cap
Step 4: if it works, be happy
Step 4.5: if it doesn't work replace more caps
Step 5: thank you


^that's my plan...

[PCBONEZ]

Plan B.
Charge her $50 to fix it.
.

[retiredcaps]

Originally Posted by shovenose

Alright well I disconnected one of the two what I assume to be the CCFL connectors from the inverter. Tried it again. Same problem. Plugged that one back in and disconnected the other one. No change...

The test you did above will show if a ccfl is completely broken. That is, no light will come on. The problem can still be a bad ccfl or wiring.

[shovenose]

OK. Good to know. Since I don't have any weird reddish tint either I'm going to pretend the CCFLs are a-ok...
I will not charge her $50 - but I told her I might have to charge her a $1 material fee

[retiredcaps]

Originally Posted by shovenose

Since I don't have any weird reddish tint either I'm going to pretend the CCFLs are a-ok...

No, you still can have a ccfl problem. The return wire (the thinner one) could be frayed or loose. The ccfls themselves can be blackened. See

http://s807.photobucket.com/albums/y...klight%20lamp/

[shovenose]

Alright, I did some testing. Using my Analog Multimeter, I placed the black lead on the metal inner casing of the monitor, and the red one on the two red wires going from the power supply board to the mainboard. It was at 12V when the monitor was off. It was at 12V when the monitor was displaying for a few seconds. It was still at 12V when the monitor CCFLs had turned off. In other words, it was ALWAYS at 12V. I think we can rule out the power board. More troubleshooting steps please!

[retiredcaps]

Originally Posted by shovenose

More troubleshooting steps please!

Post #2, c) bad inverter transformer

[shovenose]

Originally Posted by retiredcaps

Post #2, c) bad inverter transformer

Alrighty, how would I test that?
Thanks!

[retiredcaps]

Originally Posted by shovenose

Alrighty, how would I test that?
Thanks!

Well, if you read post #2 again, it is included in great detail if follow the URL.

[shovenose]

4) Bad transformer
----------------------

The transformer (T designation) converts the low voltage into high voltage to drive the ccfls. These can be bad.

If you have a manual range multimeter, set it to 2k ohms (two thousand). You can test for open windings "in circuit" on the transformer by (with power off and unplugged)

Power off and unplug monitor. WAIT 5 MINUTES BEFORE STARTING the ohms measurements. Waiting allows the capacitors and other components to discharge.

a) Number the pins on the transformers anyway you like
b) black probe on pin 1, red on pin 2 - record ohm
c) black probe on pin 1, red on pin 3 - record ohm
d) black probe on pin 1, red on pin 4 - record ohm
e) etc
f) black probe on pin 1, red on pin last - record ohm
g) black probe on pin 2, red on pin 3 - record ohm
h) black probe on pin 2, red on pin 4 - record ohm
i) etc
j) black probe on pin 2, red on pin last - record ohm
k) black probe on pin 3, red on pin 4 - record ohm
l) etc
m) finally, black probe on pin last-1, red on pin last - record ohm

I'm guessing the secondaries should read 950 ohm (this will vary for different transformers). If one secondary is 950ohm and the other is 750ohm, that would indicate a problem. A 4% variation or more in the secondaries suggests a bad transformer.

Alright I see that. Now, how would I measure this on an analog multimeter?

I'm assuming the inverter transformers are the ones market PT1 and PT2.