Hi guys
I have a faulty Xilence ATX PSU here
The fault basically is I have two short circuit power transistors on the primary side of the large SMPS transformer - they are 2SC3320.
There is another smaller transistor on the primary side C3866 which tests ok
The PSU has three transformers - it looks like the 2SC3320's drive the big one and the C3866 drives one of the small ones. There is a separate PFC PCB with it's own controller and MoSFETS
There is also a short on the 3.3V output and a near short on 5V - I suspect this probably blew the two 2SC3320
However, What has me interested (not for the repair but for increasing my own knowledge) is how this PSU actually works
The only 'connection' between HV and LV sides are the three SMPS transformers and one opto isolator
There is no PWM controller on the primary side. Normally I would expect to find two - one for the 'big' transformer and another for 5VSTB
The only PWM controller I can see is on the low voltage side KA7500C. There is another 8pin IC nearby, but the datasheet says this is a Diode array. SG6510D
It is concievable (to me) that either the opto-isolator or one of the small transformers provides drive from the KA7500C to the 2SC3320 pair. In any case no feedback via an opto-isolator would be needed as the controller appears to be on the low voltage side
And the other small transformer could provide 5VSB and also power the KA7500C - but this begs the question, where is the controller for that SMPS transformer? I did also check just to see if it is a small linear transformer connected to 220V input but that also appears not to be the case - it does appear to go to the C3866 but there is no IC driver here, just another small NPN transistor part 8055S and a few resistors/capacitors. The opto-isolator transistor also seems to connect into this area.
So possibly I am quite wrong in my guess how it works - the main thing I would like to know is how does the PWM controller on the low voltage side get it's power and why is there nothing like a 'TNY' chip or similar to drive the Standby supply?
See pics.
I have a faulty Xilence ATX PSU here
The fault basically is I have two short circuit power transistors on the primary side of the large SMPS transformer - they are 2SC3320.
There is another smaller transistor on the primary side C3866 which tests ok
The PSU has three transformers - it looks like the 2SC3320's drive the big one and the C3866 drives one of the small ones. There is a separate PFC PCB with it's own controller and MoSFETS
There is also a short on the 3.3V output and a near short on 5V - I suspect this probably blew the two 2SC3320
However, What has me interested (not for the repair but for increasing my own knowledge) is how this PSU actually works
The only 'connection' between HV and LV sides are the three SMPS transformers and one opto isolator
There is no PWM controller on the primary side. Normally I would expect to find two - one for the 'big' transformer and another for 5VSTB
The only PWM controller I can see is on the low voltage side KA7500C. There is another 8pin IC nearby, but the datasheet says this is a Diode array. SG6510D
It is concievable (to me) that either the opto-isolator or one of the small transformers provides drive from the KA7500C to the 2SC3320 pair. In any case no feedback via an opto-isolator would be needed as the controller appears to be on the low voltage side
And the other small transformer could provide 5VSB and also power the KA7500C - but this begs the question, where is the controller for that SMPS transformer? I did also check just to see if it is a small linear transformer connected to 220V input but that also appears not to be the case - it does appear to go to the C3866 but there is no IC driver here, just another small NPN transistor part 8055S and a few resistors/capacitors. The opto-isolator transistor also seems to connect into this area.
So possibly I am quite wrong in my guess how it works - the main thing I would like to know is how does the PWM controller on the low voltage side get it's power and why is there nothing like a 'TNY' chip or similar to drive the Standby supply?
See pics.
Comment