Dell E2009WF schematics or service manual

[(*steve*)]

I would tend to encourage hooking the probes to the circuit before powering on. Even that can be "interesting" as you may not have sufficient patience to allow all the caps to discharge (often these supplies will have nothing to leak that charge away).

It's really a high voltage thing, but keep your left hand in your pocket.

 

[SebaX75]

Hi,
I've done the measures requested... considers that it is the first time I used the oscilloscope after reading many guides ... I hope it's used properly (the bigger problem was the trigger).
The ticketing frequency is at 3Hz, with load or not, all timings are always at about 3Hz.
I've monitored output, with or without load, always starting from 5V or something more, without load it remain at about 5V, decreasing very slowly and not more than 10/20mV, but with the load it drops to zero and then restart from 5V, remaing at 5V for some milliseconds.
The voltage on C855 is always the same, with or without load, a sawtooth like wave between 10 and 15V.
I designed the graphics on a sheet and done a photo.
On R859 there is no voltage, it seem only noise (2mV/div), but modifying the trigger you can see something other... I've done two photos with different trigger setting.

What I must check now?

Do you know some links where I can find schematics with the waveforms of the output stages that should I expect? I've another dead switching supply (a network switch) and I would try to repair it.

Thanks,
Sebastian

 

[Resqueline]

Getting the trigger right is always a challenge. It seems you're doing ok.
So it ticks even without a load.. Does the 12V (or whatever) reach full voltage too? If not try to remove J2. Is the C853 (C863?) negative solder joint ok?
Reading the voltage (curve) on R859 may prove difficult. It will be a spike just a few µsecond(s) wide - every 333ms. The amplitude may be in the volt range.
To (try to) read this you'll have to set the trigging to Normal Mode, DC, adjust the trigger level until you get a 3Hz response, and crank up the intensity.

 

[SebaX75]

Hi,
the other voltage was ok (about 28V), the problem was on 5V section, an SMD resistor near PWM chip, R856 that extenally was ok, was interrupted... found in an empirical way, by testing all resistors around the PWM (a friend of mine has told that voltage on D852 was very strange).
I replaced the resistor and now all is working, I tried it for 10 minutes and all was ok.
Very thanks for the help and support; with the knowledge that I learned from you and the equipment I've bought now I can try to repair other more complex equipment.

Thanks,
Sebastian

P.S.: Now I've a new problem, but I do a new post... the oscilloscope is very old and there is the EHT in dispersion; it works as an ionizer on the edges toward the case...

 

[Resqueline]

Kudos to you (& your friend)!
Rare fault, but I should've figured it out. It makes sense now, the C855 voltage dropping so rapidly from 15 to 10V.
D852 & R856 is a high-current recharge circuit for C855. It's put into action upon the first few pulses at startup.
Lacking this recharge C855 quickly runs out of juice and the IC shuts down due to undervoltage.
R841/-2/-3 is what's slowly recharging C855 (from the +330V) so it can try again.

 

[SebaX75]

Yes,
probably the short circuits of the fast diode (D854) has caused an excessive current for the resistor R856.
This was my first complex repair, in 90% of cases had always been the capacitors for power supply (always found with ESR meter).
Now I've two others power supply with good capacitor but not working (one with output at 3,3V, even without load, vs 12V, and one fully dead, but the fuse is good), these will be my next repairs... however, all suggestions are welcome.

Thanks,
Sebastian