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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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Viewsonic GS790 19" monitor needs above 121VAC to power on
Hi again from Montreal to all fellow techs !!
This is my third posting about this problem. (last one was 6 months ago). Most monitors will power on normally with only 110VAC. This one refuses to power on unless I apply 122VAC. (I use a variac to boost the input voltage a little). I checked all power supply caps with an ESR meter.(no problems)Thanks again to Bob Parker and his famous ESR meter. I also checked all power supply resistors for correct values. (no problems) All diodes and transistors seem OK around the power supply. I have the schematic and service manual. Is there something else I should check ?? Many thanks, Jacques Carrier |
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Jacques Carrier wrote:
Hi again from Montreal to all fellow techs !! This is my third posting about this problem. (last one was 6 months ago). Most monitors will power on normally with only 110VAC. This one refuses to power on unless I apply 122VAC. (I use a variac to boost the input voltage a little). I checked all power supply caps with an ESR meter.(no problems)Thanks again to Bob Parker and his famous ESR meter. I also checked all power supply resistors for correct values. (no problems) All diodes and transistors seem OK around the power supply. I have the schematic and service manual. Is there something else I should check ?? Many thanks, Jacques Carrier What's the rectified voltage at the filter cap? Ripple? I've seen one diode go and drop the voltage enough to cause problems. Low capacitance value can be a problem. Not sure if an ESR measurement always picks this up. Had a power supply just the other day. Voltage at the output of the supply seemed close enough to work on my voltmeter. Turned out that there was 60 Hz ripple on it that I didn't discover until I looked with a scope. All the diodes checked good with the ohm meter. The scope told me which one "had to be bad". When I pulled it, the lead was loose in the package. Checked fine at low current, but wouldn't rectify the high current required. mike -- Return address is VALID. 500MHz Tek DSOscilloscope TDS540 $2200 http://nm7u.tripod.com/homepage/te.html Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121 Bunch of stuff For Sale and Wanted at the link below. http://www.geocities.com/SiliconValley/Monitor/4710/ |
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is there wax on the PCB for holding wires?
it can absorb moisture and cause all sorts of weird problems Mark |
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