Fixed a ViewSonic N3260w

[budm]

Re: Fixed a ViewSonic N3260w

Looks like mistake. The one I got from Fairchild site is dated July 2014.

[12rounds]

Re: Fixed a ViewSonic N3260w

it threw me off. replaced it with a fmmt593 for the time being - will post results when i get home and test it out.

[12rounds]

Re: Fixed a ViewSonic N3260w

results: a small amount of magic smoke can out of an unseen part. couldn't ID which one and nothing was hot to the touch by the time i took power off. now i don't have any power on CNS1 once again.

i really wish i had a schematic for this...

[budm]

Re: Fixed a ViewSonic N3260w

The output of Q7 (Emitter) feeds the Voltage to the switched transistor Q11 which supplies the voltage for running the PFC IC and the 24V SMPS IC.
Did you recheck the soldering works and no solder bridge any where? see if Q7 is damaged.
Check the Collector of Q11 and the primary circuit ground to see if it shows low Ohms.

[12rounds]

Re: Fixed a ViewSonic N3260w

checked the solder under the scope earlier - it's fine. q7 appears dead with diode check in circuit. q11 collector is still low to primary ground.

[budm]

Re: Fixed a ViewSonic N3260w

"q11 collector is still low to primary ground" How low is it, it should be low enough to draw so much current to make smoke.

[12rounds]

Re: Fixed a ViewSonic N3260w

missed the point of what i was doing there. 25ohms form q11collector to gnd.

...which indicates c32 is short? no, that's not right - try to follow jumper wires....

it seems like i need to replace the 5 remaining electro caps as there is one filtering the vcc leg of the pwm ic. then r&r q7, check vcc to gnd and make sure i don't have 25ohms and more, power it on and see if i killed the pwm ic.

thoughts?

[budm]

Re: Fixed a ViewSonic N3260w

25 Ohms reading is more likely to be caused by the ICS, we know that the Collector is connected to the VCC pin of the PFC IC, is t also connected to the VCC of the SMPS IC for the 12/14v section?

[12rounds]

Re: Fixed a ViewSonic N3260w

what is ics?

[12rounds]

Re: Fixed a ViewSonic N3260w

q11 collector is not connected to smps ic vcc. it is decoupled via c32.

i have 2 of these boards - both nonfunctional. i haven't touched to other one, but it does not read 25ohhs from pri gnd to q11 collector.

[budm]

Re: Fixed a ViewSonic N3260w

The SMPS IC for the 12V/24V should get the VCC from switched transistor some where, I only see Q11 as the only one.

[12rounds]

Re: Fixed a ViewSonic N3260w

got wires crossed. i have the 16 pin soic as a high voltage resonant controller - for step up transformer i assume -and ic2, an 8 pin soic, as the smps controller (by part number and data sheet cross reference).

i have the 16pin ic vcc coming from q9 collector. q9 emitter is tied to vcc of pfc ic.

[budm]

Re: Fixed a ViewSonic N3260w

OK, so they have another switched transistor for providing the VCC to the SMPS IC, I assume the VCC pin to ground on the 12v/24v is not at 25 Ohms, right?
So it looks you will have to start removing parts to find out which one is giving you that 25 Ohms reading.

[12rounds]

Re: Fixed a ViewSonic N3260w

you are correct - 16pin ic vcc pin is not 25ohm to gnd. pfc ic is internally short to gnd...

i just found this - it is for a different supply, but the parts that i have checked are VERY similar.

[budm]

Re: Fixed a ViewSonic N3260w

I have that diagram, it is closed but not sure how close it is to your board.

[12rounds]

Re: Fixed a ViewSonic N3260w

pretty close so far. after work going to go through the pfc network and see is i can find anything wrong that would short out the ic. any ideas?

[budm]

Re: Fixed a ViewSonic N3260w

If the MOSFET for the PFC failed, it will take out the IC.

[12rounds]

Re: Fixed a ViewSonic N3260w

spent some more time with this - after replacing the rest of the electro caps, the pfc ic, dead q7, and incorrect q11 the supply comes one without any more smoke. have to start looking at the schematic again and see what else is supposed to turn on now. no backlight comes on, so there is still something wrong.

I'm trying to understand how the DRV output on IC3 is supposed to work. I think i might be getting hung up on this...

[12rounds]

Re: Fixed a ViewSonic N3260w

update:

I poster printed the available schematic and sat down for a couple hours to see if i could understand what is happening with my broken supply. I am pretty confident that my PFC circuit is functioning properly at this point - IC3 and Q3 seem to be playing nice with each other and functioning as a boost converter; I now have 346V across the main filtering cap c1.

That is the good part. the bad part is it looks like this is remaining 346V is DC across the transformer. I don't think that IC2 (smps ic) is pulsing its drive for q4's gate. there is only 0.95vdc on the gate of q4 - the datasheet list the gate threshold at 2-4vdc. There is a fluxing voltage on the source of q4 measuring 14.5vac and 345vdc at q4's drain. I am not sure how to determine if ic2 is bad, or if these is a problem in it's CTRL or SENSE network.

[budm]

Re: Fixed a ViewSonic N3260w

OK, IC2 (TEA1532) is the SMPS IC for making 5V STBY, so it must be working since you are getting the boosted Voltage on main filter cap C1 (180uF 450VDC) and the main board is sending the PS_ON to turn on the PFC Voltage booster.
IC1 (L6598) is the SMPS for the 24VDC and the 12VDC, are you getting those two voltages?
BTW, your meter AC frequency bandwidth is not high enough to measure 70~100KHz AC,