Dell ONE All In One Computer

[budm]

Re: Dell ONE All In One Computer

If the MOSFET failed Drain to Gate, the High voltage on the Drain pin will dump through the Gate, the GD pin and internally shorted to the VCC pin and try to flow back through the switched transistor and back to the AUX winding circuit of the TNY SMPS IC, the AUX supply also supplies the running voltage for the SMPS IC. So it depends on how badly the circuits are damaged, you need to check all or you can just keep blowing up your new parts.
The PFC section is the PFC Voltage booster, so when it is on, the B+ will go up to about 370~400VDC range for the other switched power supply section to run, need to get it fixed.

[Davi.p]

Re: Dell ONE All In One Computer

If the MOSFET failed Drain to Gate, the High voltage on the Drain pin will dump through the Gate, the GD pin and internally shorted to the VCC pin and try to flow back through the switched transistor and back to the AUX winding circuit of the TNY SMPS IC....

Here you are talking about the st.by psu i think.. or the main supply?
Because the OP don't have found bad power mosfets in the 2 flyback sections..

The PFC section is the PFC Voltage booster, so when it is on, the B+ will go up to about 370~400VDC range for the other switched power supply section to run, need to get it fixed.

But the 2 psu can't run at 166/320v (depending on mains voltage) directly?

[budm]

Re: Dell ONE All In One Computer

"Here you are talking about the st.by psu i think" Yes.
"But the 2 psu can't run at 166/320v (depending on mains voltage) directly?" Yes they can.
The PFC voltage booster will boost the voltage to 370~400Vdc, it does not care if the in put is 120 or 230V, that is why there is no line selector switch on the unit. Read up on switching power supply and PFC voltage booster.
In the old day, the line voltage selector will put the main DC into Voltage double mode or direct rectification depends on the line voltage selector. How do you think those power supply runs from 80~240VAC without having the line voltage selector switch? You need to look up on lots of circuits to get familiar with how they work.

[Davi.p]

Re: Dell ONE All In One Computer

"How do you think those power supply runs from 80~240VAC without having the line voltage selector switch? " I know monitor psu can run with 90~260Vac input.. but you said: "PFC need to get it fixed" so its not bypassable?

[budm]

Re: Dell ONE All In One Computer

No, unless you have the circuit to boost the voltage to run that second power supply. If you do not install the MOSFET, the PFC will be basically will be disabled. Did you look at the circuit of the PFC? The voltage on the main filter will be only equal to the line voltage x 1.414 minus voltage drops on diodes.

[Rolin]

Re: Dell ONE All In One Computer

I've been reading the posts between Budm and Davi.p. Very interesting stuff! Really appreciate the help - I'm learning so much!

The resistor metered as shorted (removed from the board). I'll clarify, my meter measures .1 - .2 when the leads are touched (I guess low batteries). And when I measure the resistor it shows the same .1 - .2 ohms - appears to be shorted unless it's a very low ohm resistor as you mentioned.

The original TO220 diode measured 0 ohms both directions (out of circuit) - it was shorted both directions. The new one still measures different in both directions - I tested in circuit this time - hopfully that means it's still OK.

The 20N65C3 MOSFET is not shorted (tested in circuit). The original 20N60C3 was completely shorted (was removed from the circuit). So this also appears to be OK. Also, the fuse never blew this time either - very strange!

The SG6961: Reading between Pin7 and Pin8 is 34.3ohms. Pins 6-7 are 0 ohms. But measuring pin7 and one of the screw holes (should be gound?) it's open. Is that correct? I just looked at the spec sheet again - it looks like a capacitor should be between this pin and ground - that would explain it.

Diodes: I checked all the diodes (out of circuit) before I replaced the parts. I rechecked the following. Leaving in circuit this time (hope OK): On top of the board: Diode near TVS841, D841, D821 (this one is completely open in one direction and has some resistance in the other direction in circuit).

I looked over Diagram 15 and I'm just not sure how to find D3 and D4. The only diodes I can see in that area are near the TNY chip (listed in this paragraph). There are some smaller surface mount diodes on the back of the board, but I might need some assistance in how to test them.

BTW: I dont know if this will help but it appears the TO220 Diode BYV29X-600 (one leg) is directly connected to the large cap.

Sounds like it will be OK to leave the BYV29FX-600 as a sub for BYV29X-600 at least for testing - after I get it working I might put in the correct one if you guys think I should.

Let me know if I forgot to check something you guys asked for. If you need a clearer picture or one from a different angle, don't hesitate to ask.

Rolin

[budm]

Re: Dell ONE All In One Computer

The Catode of that TO-220 (equivalent to D4 in fig 15) should be connected to the + leg of the cap (same as shown in the fig 15), the Anode will be connected to the Drain and one leg of the PFC inductor. So the PFC IC is bad for sure. The circuit ground of the primary (hot side) is not the chassis ground, the ground ref point for the primary side of the circuit is the negative leg of that main 450VDC filter cap. The secondary (cold side) ground ref is tied to the chassis.
So when you are working in the primary side, DO NOT TOUCH anything with your hands or body, it is deadly and you should at least plug what you are working on into the GFCI outlet or use isolation transformer.
BTW, how is the GD pin of the PFC IC connected to the Gate of the MOSFET? There must be some kind of resistor/s and may be diode in that signal path to the Gate of the MOSFET, you must check that section real well.
Right now if you power up the unit without having the PFC IC, and the MOSFET installed, you should be able to get the standby power supply working, I would do that first, get the STBY power supply working first.

[Rolin]

Re: Dell ONE All In One Computer

yes, Pin 1 the cathode (TO220 Diode BYV29FX-600) is connected to the "+" on large cap (And I do see in the diagram now). And, yes it looks like the anode is connected to the PFC Inductor (had to look up what a PFC Inductor is - it's the coil next to the MOSFET and TO200 Diode).

I see what you mean on the diagram. Pin 7 on the SG6961 (PFC IC) appears to go through a resistor then to the gate of 20N60C3 MOSFET. I've checked for direct conectivity to any components in the area, and found connection to a small surface mount resistor marked "200" location R12, then the other side of that resistor is directly conducted to Pin 1 of 20N60C3 MOSFET (which is the gate). There isn't any traces, so it must be in one of the lower layers of the board.

BTW: R12 is also directly connected to R13 (marked 2R2), which is connected to a small smt diode location D1, which is connected to R11 (right next to it). And the other side of R11 appears to conduct to Pin3 of 20N60C3 MOSFET (source). Does this info help? I think most of it is clear enough in the picture of the back of the board.

So you are saying the SG6961 (PFC IC) will need to be replaced along with the TNY277PN (PWM IC). Not sure about the resistor yet...

BTW: I don't have a GFCI outlet in this room, and I don't have an isolation transformer. As long as I am taking readings while not plugged in I guess it won't be a problem. If we get to a point where we need to take readings while plugged in, I'll have to bring to another outlet such as the bathroom. I should mention that there is a plastic shell this board fits into, so it is safely contained when I do plug it to test. Thank you for the warning!

[Rolin]

Re: Dell ONE All In One Computer

BTW: I looked at the resistor again. Here's what I think it is. Bands: Black/Gray/Silver/Gold/Black I think the second band is gray. I also think the last band "black" is for temperature. Is it .08 OHMS??

I found this that helped me: "5 band resistor with a 4th band of gold or silver" Five band resistors with a fourth band of gold or silver form an exception, and are used on specialized and older resistors. The first two bands represent the significant digits, the 3th the multiply factor, the 4th the tolerance and the 5th the temperature coefficient"

[Davi.p]

Re: Dell ONE All In One Computer

"Diode near TVS841, D841, D821" are theese as the schematic the 2 diodes on the vcc pin of pfc ic? If yes test them.. "I'm just not sure how to find D3 and D4. " I'm watching a datasheet took from another source, anyway D3 in mine is the fast diode that goes from + output of bridge diode and cathode of D4, i don't know if it must exist, but if yes test it, test also bridge diode, BYV29FX-600 is good enough to stay there.. "I've checked for direct conectivity to any components in the area, and found connection to a small surface mount resistor marked "200"" i'm not an expert but the diode in parallel of that resistor not always exist i think, "So you are saying the SG6961 (PFC IC) will need to be replaced along with the TNY277PN (PWM IC)" Only PFC IC for now, as budm said you can dismount the mosfet to test the st.by psu with current in it (test its output on the cathode pin of diode near the smaller transformer, "Not sure about the resistor yet" no is good.. "As long as I am taking readings while not plugged in I guess it won't be a problem." it is, you must discharge the large cap every time you switch off the board, use a 2W resistor or more, if you dont have use a less but discharge time will increase to 1-2 min., i use an ambient perfume for the 220v, i put it on the cap terminals for 10-20-30 sec. then i measure it, if voltage is very low to be sure i also short circ. it with a piece of metal.. "Is it .08 OHMS??" Yes i think..
The pfc inductor is that like a transformer (the mid size of the three)

[Rolin]

Re: Dell ONE All In One Computer

I'm trying to put this together in my mind - since I don't do this very often, I might be a little slow.

At this point you recommend to remove the SG6961 (PFC IC) and remove the 20N60C3 MOSFET, and of course the TNY277PN (PWM IC), reattach the .08 resistor (I assume you believe it's a good very low ohm resistor not showing up on the meter well enough to measure) and power up to test the standby voltage?

Just want to make sure I understand correctly.

Once I do this, should I be carefully probing anything? Or are we just powering up to see if there are further obvious shorts?

Davi.p, I have tested "Diode near TVS841, D841, D821" for shorts (in the circuit) - they seem OK. You mentioned to test the Bridge Diode (Bridge Rectifier as I know it) - tested in circuit and its not shorted, different readings in opposite directions on pins 1-2 and 3-4.

"test its output on the cathode pin of diode near the smaller transformer". Not sure which diode and exactly how to test it.

I'll be careful around the large cap - I'll use something to discharge the cap - I'm sure I can find a 2 watt resistor around here.

[budm]

Re: Dell ONE All In One Computer

TNY277PN (PWM IC); New one since you have indicated that it blew up as in post 1. Also anything else burnt in that area of the STBY power supply section? Once we get the STBY working and you have for sure verify the components around the PFC IC controller are not damaged, then install the new MOSFET and the new PFC IC. Put 100W lamps in series with the power cord so the lamp will be in series with the power supply HOT (Line) wire.

[Rolin]

Re: Dell ONE All In One Computer

No nothing else is burned in the STBY section or anywhere else that I can tell.

So first I should order a TNY277PN (PWM IC) and install. Then resolder the resistor back on the board (again, I believe you feel it's good). Also remove the SG6961 (PFC IC) and remove the 20N60C3 MOSFET - then power up to check the standby voltage?

The 100W light bulb sounds interesting - I might have a question about that a little later...

[budm]

Re: Dell ONE All In One Computer

Yes. You can make some of these box.
http://s807.photobucket.com/user/bud...?sort=3&page=1

http://s807.photobucket.com/user/bud...tml?sort=3&o=7

[Davi.p]

Re: Dell ONE All In One Computer

I don't remebered the TNY blown in the 1st post, i watch now better the closeup photo and the IC seems exploded or is your bad desoldering work as we can see from the bottom, it lack 1 pin so the mosfet must be checked well, i don't see it so it could be integrated with IC, it seem that the drain pin is the one exploded, the sense resistor it's probably internal but to be sure check if there's one low value external, have you tested the optoisolators? You can check insulation between its secondary and primary side, it's a transistor and a led, test for shorts at least, watch it's datasheet if you have doubts on pinout.. the TNY must be present when you will do the first test. testing the st.by output is quite safe but better if you use lattice or rubber gloves, you must place the blk probe to around a screw hole with copper, the red to the cathode, side with band, of the diode marked in red below, the bridge diode cannot be tested with 2 tests, it has 4 diodes, you have to put tester in diode test, put +probe to - sign of bridge - probe to one ~, read, -pr. on the other ~, read, after put + probe on one ~ , - probe on + sign of br., read, + probe on the other ~, read, all must read not near 0 and not infinite, repeat all steps with probes inverted, all must read infinite.

[Davi.p]

Re: Dell ONE All In One Computer

For the lamp you can solder 2 big wires (0,75mm- 1inch=2,54mm) to the main fuse holder and the other ends to a lamp holder..
Budm: the lamp serves only to show shorts and prevent main fuse to blow or limits damages?

[budm]

Re: Dell ONE All In One Computer

Main fuse has to be removed if you are going to install the lamp in place of the fuse. The lamp is used for automatic current limiter. The lamp should flash on bright (as main cap charged up), then it should go dim, if it stays on bright, then it means there is short circuit. The Wattage of the lamp will have to be picked based on how much the unit under test (UUT) current requirement is.
What ever the OP does, he will have to inspect the circuits real well for any damages.

[Rolin]

Re: Dell ONE All In One Computer

I'll see if I can make one of those 100W light bulb contraptions. I have read the recommendations in other areas of this forum to wire in a light bulb across the fuse to prevent damage from shorted components, didn't know it could also be done on the cord as well. One thing I should mention again, the fuse didn't blow this time - not sure why, maybe I pulled the plug fast enough to prevent further damage when I saw the sparks.

I'll look over the STBY area again and try to check any of the parts as best as I know how. I understand once we get the STBY area stable, then I need to test any part around the PFC IC controller. I believe I'm looking for shorts mostly?

I'll order these parts for now: TNY277PN (PWM IC), SG6961 (PFC IC)

Once I get the parts, I'll install the TNY277PN (I'll remove the SG6961 and remove the 20N60C3 MOSFET) and power it up. I'll use rubber gloves and I'll see if I can build the light bulb tester and use it during my first test. At that point I report back with my findings and further advice.

Davi.p, you have a good eye! Yes I desoldered the TNY277PN (and it had a heatsink over it as well that I removed), but I placed it back in the holes for the picture. And yes, PIN4 (the drain pin) didn't come off with the chip - I wasn't sure if it "exploded" on pin4 or I just didn't unsolder it completely and broke off. If I had to guess, I think PIN4 did explode off the chip - I wouldn't have forced the chip off hard enough to break it off.

Are the optoisolators PC3 and PC2? If so, I'm not sure how to test them. I read your post and I'll do my best to figure it out.

I know I'll be a little nervous powering up for the first time. I might just clarify everything one more time when I have all the parts and testers ready to go!

[Davi.p]

Re: Dell ONE All In One Computer

For the optoisolators you must desolder it, from the bottom picture take off only the upper one that is relative to st.by circuit, be sure to remember wich versus it had, test the 2 near pins in side of the primary (to the left on photo) in diode test mode one direction and the other, it must read infinite (is like test a bjt between C & E), test the other side like a diode, it must read between 0,3 in one direction and infinite the other..

[budm]

Re: Dell ONE All In One Computer

Typical Vf of the LED inside the Opto is about 0.9~1.5V range, that is what you should see in Diode test mode (Diode test mode will show the Vf of the semiconductor).
For example: