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Old 05-08-2019, 11:48 AM   #1
pbig
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Default Viewsonic VX2255WMB-DAC 19M011

dear sirs,
please excuse my English if any mistakes, I'm coming from France. I have a faulty Viewsonic VX2255WMB display that I would like to fix. I have disassembled it and found the DAC 19M011 that seems to be the culprit. I first changed the CapXcon C204, CE101/102103/104/105 capacitors. No other capacitors seemed doomed. After this, I connected the board to wall plug, the ON/OFF led got blue and red, and had a bad smell on the left side of the green DELTA coil. I could not identify the source and some component(s) start chirping. I checked the transistors and fuse that seem ok.
It have bought from Aliexpress a replacement board that is completely faulty : when plugged, the ON/OFF led doesnot even light up!
I wonder if the large capacitor on entrance could be the culprit: after being connected to wall plug, I measured ~300V with voltmeter on the Aliexpress board and ~30V on the original board. Any other guesses or suggestions? Best regards,
Pierre
Attached Images
File Type: jpg DAC 19M011-1.jpg (137.4 KB, 7 views)
File Type: jpg DAC 19M011-2.jpg (426.4 KB, 8 views)

Last edited by pbig; 05-08-2019 at 11:50 AM..
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Old 05-08-2019, 06:13 PM   #2
R_J
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Default Re: Viewsonic VX2255WMB-DAC 19M011

A chirping sound is usually a sign of a dead short in the secondary, Check for solder splashes, check for shorted diodes in the secondary The DC voltage across the main capacitor should be about 300v

Last edited by R_J; 05-08-2019 at 06:22 PM..
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Old 05-09-2019, 01:04 AM   #3
pbig
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Default Re: Viewsonic VX2255WMB-DAC 19M011

thank you for your answer R J. I will test for that. But you confirm that the main capacitor DC voltage is incorrect on my original DAC card and it should be replaced. I'm trying to obtain a refund from Aliexpress seller for his dead card.
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Old 05-09-2019, 09:15 AM   #4
R_J
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Default Re: Viewsonic VX2255WMB-DAC 19M011

The main capacitor should be around 330 volts, There is not much that can cause it to be that low, basically the a/c line voltage comes into the ~ ~ of the bridge rectifier and out the +- charging the main capacitor, this cap rarely goes bad, I suspect your fuse may have blown and you are measuring 30 volts which is just the left over charge on the cap.
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Old 05-10-2019, 09:04 AM   #5
pbig
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Default Re: Viewsonic VX2255WMB-DAC 19M011

Dear RJ, yes, the capacitor DC voltage before discharge is about 30V and slowly decreases when connected to multimeter probes. This blown fuse may be responsible for the bad smell I felt after I had changed the CapXcon caps and connected to mains. Could you please indicate me on the pictures where is this fuse I should check (recto/verso) or give its reference number? F101 seems ok. I found on a Russian website the schematic but am not able to decypher it.
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