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.
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.
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