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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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![]() Hi , please,forgive the form of my English i have to repair an industrial motherboard, model ITOX G4S300, it is necessary to make a machine working,capacitors were already changed in recent past. Disks diconnectd,CPU and memory replaced,tried with onboard and AGP video card,no video outputs,beeps neither ,the only sign of working are spinning fans . +12V,+5V and +3V are present on ATX connector The most noticeable thing is the lack of any PWM activity on the gates of each of 6 MOSFETS forming the buck converter, commonly placed close to the CPU. The question is: is this dependent only by the PWM controller itself or something wrong from the BIOS (that of course i can't check) or from other hardware could stop the buck converter from working? In other words,the PWM should run in any condition or not? Many thanks for your help and your time spent reading this Diego Milan,Italy --- Questa email è stata esaminata alla ricerca di virus da AVG. http://www.avg.com |
#2
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On 1/21/2018 2:24 PM, blisca wrote:
Hi , please,forgive the form of my English i have to repair an industrial motherboard, model ITOX G4S300, it is necessary to make a machine working,capacitors were already changed in recent past. Were ALL the caps changed? I once had a cap over by the video circuit fail and cause the system not to boot. Did the system function after that? What were the circumstances leading up to the current failure? Disks diconnectd,CPU and memory replaced,tried with onboard and AGP video card,no video outputs,beeps neither ,the only sign of working are spinning fans . +12V,+5V and +3V are present on ATX connector Did you check those supplies with an oscilloscope looking for spikes? I've had circuits destroyed or weakened causing later failures from voltage spikes allowed by the caps previously replaced. I had one repeat failure from a cold solder joint on one of the previously replaced caps. The most noticeable thing is the lack of any PWM activity on the gates of each of 6 MOSFETS forming the buck converter, commonly placed close to the CPU. I don't think there's any chance that the cpu can run with no supply voltage. The question is: is this dependent only by the PWM controller itself or something wrong from the BIOS (that of course i can't check) or from other hardware could stop the buck converter from working? In other words,the PWM should run in any condition or not? First thing I'd do is look up the specs on the PWM controller chip, look at the circuits in the app note to see if there's a control input and look at that with a scope. Many thanks for your help and your time spent reading this Diego Milan,Italy --- Questa email è stata esaminata alla ricerca di virus da AVG. http://www.avg.com Did you check for source volts right at the PWM controller with an oscilloscope so that you can see if the supply is trying to start? Fuses in the path? |
#3
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In data gennaio 2018 alle ore 01:37:49, mike ha
scritto: On 1/21/2018 2:24 PM, blisca wrote: Thanks Mike i have to repair an industrial motherboard, model ITOX G4S300, it is necessary to make a machine working,capacitors were already changed in recent past. Were ALL the caps changed? Many,but let me check again I once had a cap over by the video circuit fail and cause the system not to boot. Did the system function after that? Yes ,it did for months What were the circumstances leading up to the current failure? Normal use,the board is mounted in a rack,not much air,but 2 minifan helping cooling Disks diconnectd,CPU and memory replaced,tried with onboard and AGP video card,no video outputs,beeps neither ,the only sign of working are spinning fans . +12V,+5V and +3V are present on ATX connector Did you check those supplies with an oscilloscope looking for spikes? Yes,no negative spikes tirggers the oscilloscope I've had circuits destroyed or weakened causing later failures from voltage spikes allowed by the caps previously replaced. I had one repeat failure from a cold solder joint on one of the previously replaced caps. I will keep it in mind The most noticeable thing is the lack of any PWM activity on the gates of each of 6 MOSFETS forming the buck converter, commonly placed close to the CPU. I don't think there's any chance that the cpu can run with no supply voltage. The question is: is this dependent only by the PWM controller itself or something wrong from the BIOS (that of course i can't check) or from other hardware could stop the buck converter from working? In other words,the PWM should run in any condition or not? First thing I'd do is look up the specs on the PWM controller chip, look at the circuits in the app note to see if there's a control input and look at that with a scope. I'll check it,thanks Many thanks for your help and your time spent reading this Diego Milan,Italy --- Questa email è stata esaminata alla ricerca di virus da AVG. http://www.avg.com Did you check for source volts right at the PWM controller with an oscilloscope so that you can see if the supply is trying to start? Fuses in the path? Yes i tried but even at start i can't see any PWM attempt to start the buck converter -- Creato con il client email di Opera: http://www.opera.com/mail/ |
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