Myria 17" monitor - a mini nightmare so far

[mariushm]

I was bored a few days ago and decided to buy a 17" monitor from a local ebay type of site... paid about 15$ for it.

It's a Myria vl7a9px-e33 - 17" with speakers and headphones output at the back side. It's also sold in supermarkets and similar style shops around Europe as Auris, or something like that.

The guy was saying it turns off and on every few seconds so I assumed it was just a case of bad caps.... oh man, i only wish now.

Here's how it looked inside:



the display board with a TDA7496L audio amp (2x2w)



Yeah... it's a bit hard to see from this picture, but it's the only one i have in the original state.
The monitor was fixed already, the main switcher, a couple of capacitors and an inverter transformer were replaced and the guy that fixed it soldered like a noob... looked like cold joins everywhere.

The inverter transformer had different pin count and size so he just bent the pins on one side and on the high voltage side he just soldered the pins to some wires and through the holes.

In addition, look what the genius used on the inverter circuit:



Can you spot the problem? Let me give you a hit. The switching power supply peaks at start at 13.5 then stabilizes after about 2-3 seconds to 12v.
The moron took a 10v rated capacitor and just put it there.

sidenote: everything inside is samxon.. some even had those crappy chinese standard codes like CD2678 on them.

When testing the monitor it indeed made a noise like arcing/sparks in inverter transformer, and the cycle kept repeating... so assumed it's the same inverter transformer.

Mcguyvered an inverter transformer from a working psu (had a monitor with broken display) and installed two 1200uF 16 caps .. hell, no service manual, a 1500uF and 1000uF originally, figured 1200uF x 2 would work.

Here's the new board layout



and the back side



Looks like crap but whatever. No go, still resetting. Replaced the other inverter transformer as well, no go.

There was still that arcing noise, but now with both inverters replaced I assumed the main transformer is shot, even though with nothing connected it was giving good voltages.

So I figured why not, soldered some wires on the back on the output of the rectifier diodes and connected them to my linear power supply's outputs, set at 12v and 5v - there's a 3.3v linear regulator on the same heatsink pulling from 5v, so I was all good.

Started the power supply... the 12v shot right to 3A (the current limit of my psu), so either something is shorted or... I guess that's why the main transformer was making noises, it was overloaded.

Assumed it might be either the inverter side or the audio amp, as that's fed from 12v - removed the 12v wire from the connector, put my meter on current measurement and powered the psu. Nope, current on the 12v on the board is fine.
So my inverter side of the psu is still shot... I can't picture the lamps pulling 30 watts to get my linear power supply into current limit.

Now what's even stranger is that the moment I put the vga cable from a computer I have, the load on 5v goes to the 3A on the psu, and again i doubt the monitor uses that much power on 5v.. it's a fricking 17 incher.

I should get one of those chinese universal inverter boards in a few days so then I'll be able to test with just that and my power supply... or I'll use an ATX power supply for the 5v and 12v to be sure it's not current limit the issue.

[Th3_uN1Qu3]

Re: Myria 17" monitor - a mini nightmare so far

As a rule, i don't buy anything smaller than 19" widescreen, too low profit margin. But it'd be interesting to see the outcome of this one. You can test the lamps with a laptop inverter if you happen to have one around.

[mariushm]

Re: Myria 17" monitor - a mini nightmare so far

I didn't buy it for reselling purposes, it's just a junk monitor for the workbench, it's a pain to keep looking down under the desk at the 17" Eizo CRT which is too heavy and large.
That PC is to connect the scope and my multimeter to, test monitors with its vga card's output etc etc, it's not my regular desktop system.



Yeah. I made all the tests using the lamps from another monitor I knew they were good. They are from a 20" though, maybe they're too strong... I don't know. I'm waiting for the universal inverter to arrive and if I manage to do something with it I'll post here.

I'm puzzled why the 5v would go to 3 amps when the vga cable is plugged in, I figure it's probably a short somewhere. The capacitors on that board aren't that great but they measured ok in circuit. The capacitors on the amp outputs have issues, they measured about 395uF each instead of 470uF.

[ben7]

Re: Myria 17" monitor - a mini nightmare so far

I didn't buy it for reselling purposes, it's just a junk monitor for the workbench, it's a pain to keep looking down under the desk at the 17" Eizo CRT which is too heavy and large.
That PC is to connect the scope and my multimeter to, test monitors with its vga card's output etc etc, it's not my regular desktop system.



Yeah. I made all the tests using the lamps from another monitor I knew they were good. They are from a 20" though, maybe they're too strong... I don't know. I'm waiting for the universal inverter to arrive and if I manage to do something with it I'll post here.

I'm puzzled why the 5v would go to 3 amps when the vga cable is plugged in, I figure it's probably a short somewhere. The capacitors on that board aren't that great but they measured ok in circuit. The capacitors on the amp outputs have issues, they measured about 395uF each instead of 470uF.

Hmm, IDK why the 5v logic board supply be greater than 3A. Perhaps your PSU is tripping too quickly?

To get the invertor working, see if the mosfets are bad. It occasionally happens, but the control chip might be bad too.

[Th3_uN1Qu3]

Re: Myria 17" monitor - a mini nightmare so far

If you can't fix it, i'll post you this here 19" HP. It's been sitting here for over 1 year. It is in working condition, but it has some dust inside the LCD and i can't be bothered to take the panel apart to clean it.

[mariushm]

Re: Myria 17" monitor - a mini nightmare so far

Thank you Unique, I'll definitely keep your offer in mind. There's no rush though, I'd like to keep working on this for a bit before giving up.

The inverter arrived this morning, and for about 4 Uk pounds I paid, it doesn't look bad:





The chip is DF6109A, some Chinese controller. My only concern was that it says on the pcb 10-30v while the controller's absolute maximum rating is 20v.

It turns out there's a small 78L12 linear regulator (12v 100mA), so even with 10v input, the regulator should still output about 8v, which is within the actual 4.5-18v range of the controller.

Yeah, it's not nice that the regulator will always stay outside proper regulation, even with my 12v input but on the other hand... i might just use a 19v laptop adapter to power this directly and maybe use a 7815 for the tda7496 amplifier (because the capacitors all around the board are 16v max and don't feel like replacing all)

Anyway, I'll probably install this tomorrow morning, I'm too tired to work on it now - slept only a few hours today, i'm sleeping in front of the pc.

[mariushm]

Re: Myria 17" monitor - a mini nightmare so far

Updating this because i don't want to leave it hanging.

I took the time to install the universal inverter and I have to say... it works great!
Connected it to my linear power supply on 12v, wired the on/off and adjust wires to the display board and it started right up.

The monitor now keeps the lights on for about 5 seconds, then it goes to standby (leg goes orange/yellow) and lights turn off. While they're on, there's about 1.4-1.7 amps drawn from the power supply, which is reasonable, no concerns.

With the longer time the lights stay on, i managed to check the panel more thoroughly. Unfortunately, it looks like there's a darker spot on the panel in the top right corner, about as big as a finger tip. I may live with that, as it's just a monitor for workbench like i said but the biggest problem is ...

I still have that 5v short simply by plugging the vga cable into the display board. Actually not even plugging, just by touching the exterior metal of the vga connector to the metal that's supposed to be grounded on the display board, i have a short on the 5v rail and my linear power supply goes to 3A current limit.

I grabbed my multimeter and put the probes on the metal "jackets" of the connectors and I get 5v between them and if i slightly adjust the output of the power supply, i see it changing.

I'm puzzled as to why 2 points that should be grounded suddenly have 5v between them when they touch.

Checked the vga cable and tested it against the ground in the mains socket and the back of the pc and it's no 5v between them.

Could it be an issue that the linear power supply's outputs are floating? Could it be that the computer has live and neutral inverter (if i accidentaly plugged it the other way around)? I'm just throwing out ideas, i don't have much experience with earth reference, grounds, these notions...

What's worse is that this may have blown some fuse on the actual panel - when i got it it used to say no signal at start, now it doesn't show anything when powering the monitor with or without vga cable in the back. The connector outputs 5v to the panel so it's probably some fuse or resistor blown up or in the worst case the actual chips on the panel.

As it's not really a monitor that *has to* be fixed, just a side project, I almost can't be bothered to open up the panel, it's just a pain to take the back metal lid off, lots of screws. I'll probably do it when I have some spare time