Proview Pro576 (Model 568) delays to start when cold.

[EGuevarae]

Re: Proview Pro576 (Model 568) delays to start when cold.

The transformer has the same number of turns on both sides (? isolation?). The maximum V on the board is 12v.
I replaced all 100uf with ELNA caps of 5mm that I don't remember where I got, and used one 6mm when the one in the red square is but I had to put the board back a little loose for it to fit.
I couldn't find 220uf 16/25v in 5mm size so, for the 220uf I had to put all but one of the original su'scon back (the one in the green circle was not a su'scon, it was a jamicon on it's side, not flat against the board). The cap in the blue circle was changed for a ELNA too.
All the changed ELNA caps were rated at 85C.
Now the LCD turns on always on the first try, but I lost the audio on the monitor, but that is not important, as the sound was not that good ...
I know it was not the best solution, but the LCD is working now. Before it had audio, now it does not. But it wasn't used anyway, so I'm fine.

[PCBONEZ]

Re: Proview Pro576 (Model 568) delays to start when cold.

Isolation xfmers only work with AC. You have DC 'in' jack on that PCB.
Xfmer might be part of a filter or might be part of an SMPS.
I really can't say without tracing out the circuit.

[This is in general, I dunno if SMPS circuits are used on that kind of board.]
SMPS works by switching current on/off alternately through primary winding to create a high[er] voltage AC frequency.
[Usually in the KHz range somewhere.]
AC is then coupled through Xfmr into a Rectifier and tuned into DC.
Xfmr could be 1:1.
AC volts at Xfmr would be higher than DC out of the SMPS.
And, if you have meter on DC you won't see AC volts.
.
Just saying volts on some of the caps might be more than 12v DC.
.

[kc8adu]

Re: Proview Pro576 (Model 568) delays to start when cold.

filter choke.
mainly to keep smps hash from radiating from the dc input cord.

[PCBONEZ]

Re: Proview Pro576 (Model 568) delays to start when cold.

The two coils in the frame is just a choke?

[EGuevarae]

Re: Proview Pro576 (Model 568) delays to start when cold.

Isolation xfmers only work with AC. You have DC 'in' jack on that PCB.
Xfmer might be part of a filter or might be part of an SMPS.
I really can't say without tracing out the circuit.

[This is in general, I dunno if SMPS circuits are used on that kind of board.]
SMPS works by switching current on/off alternately through primary winding to create a high[er] voltage AC frequency.
[Usually in the KHz range somewhere.]
AC is then coupled through Xfmr into a Rectifier and tuned into DC.
Xfmr could be 1:1.
AC volts at Xfmr would be higher than DC out of the SMPS.
And, if you have meter on DC you won't see AC volts.
.
Just saying volts on some of the caps might be more than 12v DC.
.

I replaced them with mainly 16v after checking voltages (per your suggestion) and after I found 12v and 5v only. The diode in the center of the picture, near the yellow Jamicon had 5v, the outputs to the inverter are 12v & 5v, plus a varying voltage that I know for sure is for bright control. I didn't test the output to the LCD panel. I missed it now that I rethink the issue, but I could not found more than 12v. And I finally found the meaning of the distressed solder and a circle (picture) after you (PCBONEZ) said it looked like something was there (and it didn't when I opened it the first time). A guy I contacted on eBay had a board like this on sale and I asked if he could check. He said that his board has a 22uf 16v but a different one he has does not have it. So I actually soldered one to see what happened, but as nothing happened, I removed it. It was my first use of soldering iron in years, so the holes are a mess. Mystery of the missing cap solved!

[PCBONEZ]

Re: Proview Pro576 (Model 568) delays to start when cold.

If you checked voltages you are good to go.

My point was really that the designs of these boards varies so much there might be cases where say a 35v cap NEEDS to be a 35v cap.
-
I've only had to do caps in LCD screens so far so there a bunch of people in here with a wider range of experience specific to LCD's screens than I have.

I'm pretty sure that includes you and one of these days I'll probably be asking you questions.

.

[EGuevarae]

Re: Proview Pro576 (Model 568) delays to start when cold.

If you checked voltages you are good to go..

Yes, I checked them (again, per your suggestion) and that gave me the confidence to go ahead and change them all.

My point was really that the designs of these boards varies so much there might be cases where say a 35v cap NEEDS to be a 35v cap.

I think I now really get what you are trying to say : as of design, it had to be of a specific voltage, not because it would be that high (lower, in fact), but because taking into account other factors (the infamous ESR, by example...) they have to be that rating or that series.

I've only had to do caps in LCD screens so far so there a bunch of people in here with a wider range of experience specific to LCD's screens than I have.
I'm pretty sure that includes you and one of these days I'll probably be asking you questions.

Your help has been of great value to me, and I'm pretty sure that to others too. And in the event I can help you in the near/far future, it will be a real pleasure to give back (to you and to all other forum members) some of what the forum had given me so far.

[robsonq]

Re: Proview Pro576 (Model 568) delays to start when cold.

Hi, i know it s an old post but i am looking for an answer here i got first post :3.
Hello Guevara, nice to greet you, I am from México, I have the proview monitor PRO558 model 568.
My display delays to turn on, but just the backlights, I know it because after turning on the computer I can see images when I focus my eyes on the screen and when I put the light from my Iphone on it. My question is that if you had the same problem, or your old Proview didn´t even show images without the backlights, the first & last time I opened it just found one bad Cap and I changed it, but the problem persists, actually it delays to turn on and use to do it when the LCD enters in stand-by after 15 mins, I was near to buy a generic inverter but after I saw your post I was thinking of change the most of the caps. I see that our problems are similar(I know you fixed it), and just want to know your opinion before buying the new inverter.
Thank you!