VX 724 black screen green light flashing

[stevepw]

Re: VX 724 black screen green light flashing

HI All

just an update , got some new caps to day to replace a duff H154 put them in and WOW a working screen again, been on for an hour now looks good with no funny smells..

to get it working I replaced

5 domed caps on the power board
one burnt transformer (many thanks rtech, I would have struggled without this )
The 2 small transisitors underneath above
both of the H154 caps one of which had gone

Thanks for the diagnosis, tips, help ive enjoyed the learning and repairing so much I bought another duff one of ebay to play with!

[Rtech]

Re: VX 724 black screen green light flashing

Well done, glad to be of help......I hope the one you bought was NOT the one I was bidding on.....lol

[stevepw]

Re: VX 724 black screen green light flashing

HI Rtech, If is was sorry, couldnt let it go
Got my VX912 off Ebay, same board as the VX724, but screen is 2" bigger, it had the 2 seconds to black flashing , simple fix, swapped about 4 domed caps over and Bobs your Uncle

YEEE now got a 2 screen set up

[Rtech]

Re: VX 724 black screen green light flashing

Well done.The problem comes when its not caps,thats when the fun starts.I suppose a lot of us on here ,get a lot of satisfaction, by turning a non-working electronic/electrical item,into a fully functional item once more.

[cheebster]

Re: VX 724 black screen green light flashing

Resurrecting an old thread here ! Got my hands (was on the side of the road) on a vx724. Flashing green light..

I recapped it, no joy. I got some other inverters i could scavenge parts of here, but i was wondering... are those transformers all the same (if they're the same size, with 4 inputs, 6 outputs) ?

I was wondering if i could use them. I got a board with 2 transformers that say: EST0029A.. The ones in the viewsonic are STJ00029

Looks pretty similar to me, but just don't want to kill the board here so any advice would be really appreciated !

Another Q about it.. I had on the same donor board, some transistors marked as DK QM, and the original ones on the viewsonic were DK QN.

Can those be used as well, of they're different ?

Thanks !!!

[Rtech]

Re: VX 724 black screen green light flashing

The transistors 'DK', can also have codes with it of QA,QB,QO,QP,QF etc, and these are production codes, the original part was 2SC4672.
As far as the transformer is concerned,then you need to be 100% sure it is the same,eg the secondary resistance being the same as the original, but you really need a schematic or tech details of each to be certain.

[cheebster]

Re: VX 724 black screen green light flashing

Ok. I've removed both transformers now and they have all the same readings. A wild guess would be that both are good...

I'm unsure where to look and what to test now, but i do know there's still something to fix since it doesn't fire up..

I don't see much continuity in the transformer, only shorts between pins

1-6, 2-4, 3-5. I see 0.7 ohms there.. Do i need to test it some other way ? I've read the tutorial but i'm not so sure i'm testing it the good way.

[Rtech]

Re: VX 724 black screen green light flashing

Its the secondaries that you have to measure..that the two pins on the ends nearest to the lamp connectors,they must be very very close to the same reading.Also the other problem with these, is the Blue or Brown Capacitors near to the transformers...if one of them is 'bulging' compared to the other, then that is the problem.

[cheebster]

Re: VX 724 black screen green light flashing

Rtech, i'm unsure how to properly measure the secondaries. I got 4 pins on this secondary side, 2 pairs. I got to measure between the 2 pins on each side ?

The capacitors i got near the transformers are red, marked H154J, they both look fine (no shorts.. but i sold my esr meter, never used it, so i can't test further)

:|

[cheebster]

Re: VX 724 black screen green light flashing

One thing i've tried and noticed, is that when i put the PSU by itself, just plug the ac cord to it, it fires up fine and gives 12.55V on the ouput, and it doesnt struggle to fire up. Does that mean something is bad in the controller board ?

[PlainBill]

Re: VX 724 black screen green light flashing

The usual problem with this monitor is the transistors for the Royer oscillator - DK Q*, AKA 2SC4672 short. Before you get too carried away, make sure they aren't shorted. You can also turn on the inverter by applying 3.3 volts to the BL_ON pin on the connector to the signal card.

If the transistors are not shorted, and the power supply is stable when the inverter is turned on, yes it is possible that the signal card is bad. I'd say it is not a common problem, but it would be foolish to assume it NEVER happens.

PlainBill

[cheebster]

Re: VX 724 black screen green light flashing

I've replaced the transistors with some i had on another inverter, they were DK QM.

With them installed, same result. The original ones were shorted !

I've also tried applying 12V and GND to the controller board with a bench top PSU, i get the steady green light and the controller board seems to work.

I'm missing something here, but not so sure what.

I've placed an order for 2 transistors a few minutes ago on digikey, just wondering if i should cancel the order (ain't sure if the ones ive put it are a good replacement ?)

Kinda bad to pay 8$ shipping for 1.50$ worth of parts when i'm not even sure i need them hehe

Out of ideas here :/

[cheebster]

Re: VX 724 black screen green light flashing

Ok, there's still something wrong... (eh)

I notice that i get really different readings on the 2 inverter sides.

On the good one :

Q8/Q9 Readings

From ground plate (middle) to left pin : .73kohm
to right pin : .75kohm

Bad side..

From ground plate (middle) to left pin : .26kohm
to right pin : 0.22kohm

So it's really different on both sides..

On the transformer secondaries, i see .44k on both transformers (in circuit).

[PlainBill]

Re: VX 724 black screen green light flashing

Ok, there's still something wrong... (eh)

I notice that i get really different readings on the 2 inverter sides.

On the good one :

Q8/Q9 Readings

From ground plate (middle) to left pin : .73kohm
to right pin : .75kohm

Bad side..

From ground plate (middle) to left pin : .26kohm
to right pin : 0.22kohm

So it's really different on both sides..

On the transformer secondaries, i see .44k on both transformers (in circuit).

Several points:

1. If you are in the USA, use Digikey's USPS First Class Mail shipping option. Something ordered today would arrive Thursday and shipping would be in the order of $2.75.

2. How badly do you need this monitor? I've got the same monitor waiting for me to get to it. The transistors short as soon as power is turned on; I'm going to use a variable power supply and a scope to see if I can figure out what is going wrong. But that won't be this month.

3. The Belinea 101910 monitor is identical to this one; the service manual has schematics.

PlainBill

[retiredcaps]

Re: VX 724 black screen green light flashing

1. If you are in the USA, use Digikey's USPS First Class Mail shipping option. Something ordered today would arrive Thursday and shipping would be in the order of $2.75.

The (eh) and $8 s/h says to me he is in Canada.

[cheebster]

Re: VX 724 black screen green light flashing

I don't 'need' the monitor any time soon, just a spare really.. was on the side of the road.

I redid a lot of the soldering on the board, with fresh solder.. No luck still.

Yes, i'm in Canada.

[cheebster]

Re: VX 724 black screen green light flashing

Hi Plainbill ! Did you play a bit with this one since we last posted ? I got mine still sitting on the shelf waiting for some love. Thanks !!

[PlainBill]

Re: VX 724 black screen green light flashing

Hi Plainbill ! Did you play a bit with this one since we last posted ? I got mine still sitting on the shelf waiting for some love. Thanks !!

Sorry, not yet. And moving toward the back of the queue.

PlainBill

[cheebster]

Re: VX 724 black screen green light flashing

Hehe, ok. I've ordered a replacement board on ebay for 23$ shipped. Guess i'm somehow giving up on this one, up to some point.

[Nocta]

Re: VX 724 black screen green light flashing

Sorry for bumping this thread again but I have a ViewSonic VX724 monitor too and it is not working.

I changed all the capacitors and now it shows the image but just for a second and then it powers off (even though the green light is on).

I took out a 2SD1628 transistor because it was broken (I don't know how it could've happen).

The problem now is that THAT lamp (the one where I took off the transistor) doesn't light on. It's not the lamp because I tried switching them, it's the output.

I attach a couple of images. I hope you can help me.

I got the follow reading (at 200 ohm) from the transistor from the other lamp. I write it the way I marked it in the picture.

Working lamps:

1-2 Nothing
1-3 1 ohm
1-4 Nothing

Not working lamps:

1-2 1 ohm
1-3 1 ohm
1-4 1 ohm

I tried but I can't find the 2SD1628 transistor where I live but maybe there's other way to cheat the BI3101A (the one that 'controls' the lamp).

Thanks in advance.





PS: I'd appreciate your input. Consider that i'm not an technician or something.