Hey there,
I've been silently lurking around here for many many moons now, all the while reading bits and pieces here and there "absorbing" all these useful tips and info by the masters. This thread here have been particularly helpful on fixing a Viewsonic lcd issue below and hopefully my notes can be of some help to others.
About a month ago, I bought a faulty Viewsonic VG2021m from a guy claiming that it just needs an IC replacement for the backlight (read: someone attempted to fix it but got stuck). Upon opening it up, it was missing the power FET (Q102) and the two backlight FETs (Q204,Q205). I went hunting for and found a copy of the DAC-19M005 schematics and parts list somewhere on the web.
For the primary FET, I stuffed in a STP6NK60ZFP and for the backlight FETs I used Fairchild RFP45N06. The AP40T03GP is non existent around here and the ones on ebay (with shipping) actually costs more and is way too much hassle for me. After checking/comparing datasheets, I'm convinced that the RFP45N06 is a good alternative. The track for Q204 was broken, probably by someone who attempted a previous repair, so that needs a bit of track fixing. I didn't have any SMD-1206 fuse for F200 and the ones I have on hand was SMD-451 4A, so that one will have to do for now. All the secondary capacitors were replaced with whatever I have on hand (mostly Nichicon HE or Panasonic FC).
Once all done (or so I thought), I powered it up, a blue led lights up, a bit of whining was heard somewhere near the main transformer or secondary capacitors, backlight flickered for a second then the whole thing shuts down. Oh crap! I also was jolted by a "mildly" shorted chasis. I took a test pen and the chasis lights up! Oh crap crap!
I re-inspected the power board and found the grounding pads dirty (oxidized?). Cleaned that one up, screwed the board back in tightly and powered it up. Same thing happened, blue led lights up, backlight flickered then shuts down. Well, at least the chasis is not making me jump anymore. I found that the main filter caps was not discharged but I've previously confirmed that the primary side is okay. So, I check the secondary side again and all seems to be okay too. All secondary voltages output are fine. Fuse F200 is still good. So, what gives ?
I'm guessing it's the inverter section. So, I removed fuse F200 and power it up again. This time I get a blue led light, a bit less whining, then the led turns amber but it doesn't shuts down anymore (and the main filter caps discharged properly when powered down).
Ok, that tells me the inverter side is where the problem lies now. I remembered reading about R210 goes bad here and indeed, R210 was way off at 2K ohms (should be 10 ohms). I also checked all the rest of the resistors just to be sure. Apparently, only R210 is bad. Alas, I don't have any smd 10 ohms on hand to make a quick test. So, I wired x2 4.7 ohms resistors in series, insulate it and put in into R210 for a quick test run.
Now, I powered it up and was rewarded with a nice desktop. All secondary voltages are good, no more whining heard and most importantly, the backlight works! Yay!
The repairs was finally completed with proper parts over a day ago and the LCD monitor has been running fine since then. So, big thanks goes to EGuevarae, PlainBill, Welchs101, gfgray and billy66 for their inputs (and outputs) on the DAC-19M005 boards.
I've been silently lurking around here for many many moons now, all the while reading bits and pieces here and there "absorbing" all these useful tips and info by the masters. This thread here have been particularly helpful on fixing a Viewsonic lcd issue below and hopefully my notes can be of some help to others.
About a month ago, I bought a faulty Viewsonic VG2021m from a guy claiming that it just needs an IC replacement for the backlight (read: someone attempted to fix it but got stuck). Upon opening it up, it was missing the power FET (Q102) and the two backlight FETs (Q204,Q205). I went hunting for and found a copy of the DAC-19M005 schematics and parts list somewhere on the web.
For the primary FET, I stuffed in a STP6NK60ZFP and for the backlight FETs I used Fairchild RFP45N06. The AP40T03GP is non existent around here and the ones on ebay (with shipping) actually costs more and is way too much hassle for me. After checking/comparing datasheets, I'm convinced that the RFP45N06 is a good alternative. The track for Q204 was broken, probably by someone who attempted a previous repair, so that needs a bit of track fixing. I didn't have any SMD-1206 fuse for F200 and the ones I have on hand was SMD-451 4A, so that one will have to do for now. All the secondary capacitors were replaced with whatever I have on hand (mostly Nichicon HE or Panasonic FC).
Once all done (or so I thought), I powered it up, a blue led lights up, a bit of whining was heard somewhere near the main transformer or secondary capacitors, backlight flickered for a second then the whole thing shuts down. Oh crap! I also was jolted by a "mildly" shorted chasis. I took a test pen and the chasis lights up! Oh crap crap!
I re-inspected the power board and found the grounding pads dirty (oxidized?). Cleaned that one up, screwed the board back in tightly and powered it up. Same thing happened, blue led lights up, backlight flickered then shuts down. Well, at least the chasis is not making me jump anymore. I found that the main filter caps was not discharged but I've previously confirmed that the primary side is okay. So, I check the secondary side again and all seems to be okay too. All secondary voltages output are fine. Fuse F200 is still good. So, what gives ?
I'm guessing it's the inverter section. So, I removed fuse F200 and power it up again. This time I get a blue led light, a bit less whining, then the led turns amber but it doesn't shuts down anymore (and the main filter caps discharged properly when powered down).
Ok, that tells me the inverter side is where the problem lies now. I remembered reading about R210 goes bad here and indeed, R210 was way off at 2K ohms (should be 10 ohms). I also checked all the rest of the resistors just to be sure. Apparently, only R210 is bad. Alas, I don't have any smd 10 ohms on hand to make a quick test. So, I wired x2 4.7 ohms resistors in series, insulate it and put in into R210 for a quick test run.
Now, I powered it up and was rewarded with a nice desktop. All secondary voltages are good, no more whining heard and most importantly, the backlight works! Yay!
The repairs was finally completed with proper parts over a day ago and the LCD monitor has been running fine since then. So, big thanks goes to EGuevarae, PlainBill, Welchs101, gfgray and billy66 for their inputs (and outputs) on the DAC-19M005 boards.
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