Fujitsu Siemens Scenicview P19-2

[Behemot]

I am quite surprised there s no thread yeat about this wonder, I got quite a few of them already. Always blown caps, sometimes it takes down fuse and inverter transistors.

You can get some images here http://diit.cz/clanek/fujitsu-siemens-scenicview-p19-2, that is the first one I repaired. It was already serviced with transistors before, they used bad caps so I recapped that. You can also see the input cap was getting bad. Sicne than it was usually just caps, sometimes fuse.

Now I got one more stubborn, also with input cap vomiting insides out. After recap, it seems there is more problems on primary than just the capacitor. Transistor and freewheeling diode measure good but I still do not have Vdd for the SG6841 PWM controller. Vin/pullup pin is OK with 3 V but I got nothing else but some 0,8 V at Vdd. Both the diodes there (one diode as rectifier with cap and than probably zener with another smooting cap) seem to be OK so this leads me into thinking the transformer is bad, either the main winding or auxiliary winding for the PWM controller.

Is there anything I can try to have a look at before high-voltage O-scope probe I have already ordered will come so I can scope the transformer than?

[budm]

Re: Fujitsu Siemens Scenicview P19-2

What resistance reading are you getting between VDD (7) and Ground (1)?

3V at Vin is too low. The VDD has to be at 16V for start-up condition to occur, the Vdd cap is charged (uisng high Z) through the Vin pin during start-up, then the Aux winding will take over when the SMPS is in running mode. VDD has internal Zener diode which may be damaged, or Vdd cap has high leakage

Under-voltage lockout (UVLO)
The turn-on and turn-off threshold of SG6841 are
fixed internally at 16V/10V. During start-up, the hold-up
capacitor must be charged to 16V through the start-up
resistor so that SG6841 will be enabled. The hold-up
capacitor will continue to supply VDD before the energy
can be delivered from auxiliary winding of the main
transformer. VDD must not drop below 10V during this
start-up process. This UVLO hysteresis window insures
that hold-up capacitor is adequate to supply VDD during
start-up.

[budm]

Re: Fujitsu Siemens Scenicview P19-2

Some thread about SG6841:
https://www.badcaps.net/forum/showth...841#post155965

https://www.badcaps.net/forum/showth...841#post335348

[Behemot]

Re: Fujitsu Siemens Scenicview P19-2

I have replaced both the capacitors, those were CrapXon GF, with Nichicon PW (47 and 10 uF, 25 V). Got ordinary cap response there - resistance increasing from 0 to infinity as cap is charging.

[budm]

Re: Fujitsu Siemens Scenicview P19-2

Will it be difficult to swap the IC with the working unit, at this point 3V at Vin is the key point, may be take the measurement voltage on the working unit so you will ref. reading to compare to.

[Behemot]

Re: Fujitsu Siemens Scenicview P19-2

I have two other non-working units so I can do that…or I can just recap them and compare it under operation, both options possible.