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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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Benq T905 power supply repair
Phil Allison wrote:
Jeroni Paul wrote: Here is its schematic: http://www.rom.by/files/q9t4-fp91g-power_bd_1.pdf ** If the mosfet blew, R615 must have too. Did you maybe replace it with a wirewound type ? That would explain most of you symptoms, running OK at low loads but failing if the current in the switch is higher - also made worse if the AC supply voltage is lower as it will be with a lamp in series. R615 ( 0.22 ohms 2 watts ) must be a metal film or composition type. IOW *low* inductance is crucial. ..... Phil Thank you Phil. The resistor you mention was good and is the original. Finally I got it working by wiring 4 100W bulbs in parallel, so I removed the bulbs and all is fine. |
#2
Posted to sci.electronics.repair
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Benq T905 power supply repair
Jeroni Paul wrote:
** If the mosfet blew, R615 must have too. Did you maybe replace it with a wirewound type ? That would explain most of you symptoms, running OK at low loads but failing if the current in the switch is higher - also made worse if the AC supply voltage is lower as it will be with a lamp in series. R615 ( 0.22 ohms 2 watts ) must be a metal film or composition type. IOW *low* inductance is crucial. Thank you Phil. The resistor you mention was good and is the original. Finally I got it working by wiring 4 100W bulbs in parallel, so I removed the bulbs and all is fine. ** That SMPS is unusually sensitive to low AC supply voltage. Normally they work from 85V and up. ..... Phil |
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