Asus PTGD-LR

[sceva]

This mb is out of an HP Media Center PC, about 5 years old, model 557z. One day it did not power on. I had replaced the power supply a couple of years ago. It is a small form factor/custom ps. This time when looking up the part it was about $150. It was for my work and they did not want to invest that much into an old computer, so I brought it home to see if I could salvage it, or at least some parts.

I found some bad caps in the power supply, recapped, tested, looked ok. Plugged it into the mb, and saw some smoke between the usb ports and the cpu. Wasn't sure if it was from the caps or the transistors. Turned it off, then for some reason turned it back on and the ps blew the fuse and something else as I am unable to repair it.

Then taking a closer look at the board I noticed 5 bulging caps, and one of the transistors (mosfet) where the smoke was tested bad. I replaced the caps (with Panasonic caps) and transistor (with exact replacement), found another ATX 24 pin power supply (too big to fit inside the case, but ok for testing) and it powered up perfectly. It worked for a couple of hours and then the transistor went out again.

Here is what I need help with: the transistor is the kind that has two legs and the back soldered to the board. I only have a soldering station and don't know how to solder/unsolder these components well. Is it possible the new transistor failed because I was only able to get a little solder tacked onto the back? I also might have applied too much heat trying to get it soldered onto the board. If you look at the first pic you can see the mess I have made trying to unsolder/solder this twice. (I had not cleaned up the flux and extra solder when I took the pic.) I did test with continuity and it seems the board has not been damaged severely.

I still have one more new transistor to try, but wanted some help before trying to attach it again. The only idea I have come up with was to clean it up good, then cover the area with ChipQuick, and place the transistor on that quickly before it hardens. But I don't know if ChipQuick will work over the long term.

The caps that were replaced are the larger caps (two are removed in the pic) I have tested the other caps in the area with an esr meter without removing them, and they test ok, but I don't mind ordering some more and replacing them if they could be contributing to the problem.

I have repaired a lot of LCD monitors with the help of this forum, but this is my first motherboard!

[PCBONEZ]

Re: Asus PTGD-LR

You can't check ESR or uF on caps in a VRM without removing them.
- They are in parallel.

The large area on the back of those chips acts as a heat-sink as well as a connection.
Yes full contact is important.

I would tin the back of the chip and tin the pad with enough solder for a bond.
Then position it and hold the heat on the tab until you feel it 'sink' into place.
Do that before you mess with the legs....

Good luck. Those are a pain in the as*.

.

[PCBONEZ]

Re: Asus PTGD-LR

Check the other MOSFETs very well.
They may be open so this one is trying to do the work for all of them.

[seanc]

Re: Asus PTGD-LR

They are a pain in the ass, but a good deal easier to remove with Chip Quik.
When re-applying, use normal solder. The method PCBONEZ describes for installation is good.

I've done this repair on an ASUS SLI board which is working perfectly fine and a Gigabyte board, which hasn't been tested for long, but suspected fine.
In both cases of my repairs, the mosfets had blown due to a short on the rear of the board.

Perhaps your mosfet overheated the second time. What Panasonic caps did you use?


You need to clean up that mess, invest in a good bottle of isopropyl alcohol and a tooth brush.

Also, your PSU may be salvageable, there are many people knowledgeable in salvaging damaged PSUs - such as everell. Might be worth it in this case where it's a custom PSU.

[sceva]

Re: Asus PTGD-LR

I would tin the back of the chip and tin the pad with enough solder for a bond.
Then position it and hold the heat on the tab until you feel it 'sink' into place.
Do that before you mess with the legs....
.

I followed your directions, got the new cap on without much trouble, and it worked for less than an hour before failing. When it fails all three points on it are shorted. The other two seem ok.

Check the other MOSFETs very well.
They may be open so this one is trying to do the work for all of them.

I tried removing the MOSFET next to the one I replaced to test it off the board... I naturally destroyed it in the process. (using chipquick and my iron set to 480 degrees, I leave the iron on the tab for way too long - several minutes, and then use various tools to pry and pull on it. Twice it has come apart before it came off the board. Maybe there is some glue in addition to the solder. I noticed that I had not cleaned up the solder on the first one very well after getting the next one off, so that might have had something to do with it failing.

I've done this repair on an ASUS SLI board which is working perfectly fine and a Gigabyte board, which hasn't been tested for long, but suspected fine.
In both cases of my repairs, the mosfets had blown due to a short on the rear of the board.

When I remove the MOSFET I can't find any shorts, and the points on the board seem to test ok with continuity.

Perhaps your mosfet overheated the second time. What Panasonic caps did you use?

I used Panasonic cap #EEU-FM1C102, which is a 1000u, 16v, ECG type. I also pulled off one of the small caps nearest the bad MOSFET and it tested very good.

You need to clean up that mess, invest in a good bottle of isopropyl alcohol and a tooth brush.

I have removed all three of the MOSFETS in that area and cleaned it up nicely!

Also, your PSU may be salvageable, there are many people knowledgeable in salvaging damaged PSUs - such as everell. Might be worth it in this case where it's a custom PSU.

Nice to know. If I get the board working I will tackle that next.

I am considering buying some more MOSFETs and trying again, hoping I just did a lousy job of soldering that piece in. Please let me know if you have any further ideas on things I should check. Thanks.

[seanc]

Re: Asus PTGD-LR

You're definitely using exactly the same type of moset for replacement?

[sceva]

Re: Asus PTGD-LR

You're definitely using exactly the same type of moset for replacement?

I think so. The part number on the originals is:
IPD06N03LA
The part number on the new ones from Digi-key is:
IPD06N03LA G
The G being the only difference. They are both Infineon Technologies, and both have an R in the lower right corner.

[Th3_uN1Qu3]

Re: Asus PTGD-LR

Yeah it's the right type, should work. Here's a tip on how to remove them. First heat up and lift the two terminals off the board (gate and source). Then keep your iron on the tab (drain) on the highest setting, and after about a minute use whatever tool you desire to wiggle it left and right till it comes loose. Never attempt to lift it as it will break, like you experienced.

When soldering a new one in, bend the gate and source pins upwards first. Then solder the drain, push down gate and source, solder those, done.

[kc8adu]

Re: Asus PTGD-LR

except some of the leads are quite stiff and will break out of the case when you attempt to bend them.

[sceva]

Re: Asus PTGD-LR

I have some new MOSFET's on order and will update my next try. Thanks again.

[sceva]

Re: Asus PTGD-LR

I replaced all three transistors with new ones, and figured out if I tin the board first, and hold the iron there for about 15 seconds before applying the transistor, then quickly place the transistor and apply heat to the tab, I can get a good joint under the tab.

But, less than 5 minutes after turning it on the same transistor failed again... All pins are open to each other. Obviously there is something else wrong, but I have not been able to figure it out. Any ideas where to look? Thanks.

[seanc]

Re: Asus PTGD-LR

Check for shorts on the back of the board. Perhaps replace that transistor and test the board on a cardboard box?

You've put the two missing caps back, next to the transistor, in the correct orientation?
Are you sure the PSU you're testing with is good?

[Th3_uN1Qu3]

Re: Asus PTGD-LR

But, less than 5 minutes after turning it on the same transistor failed again...

But the board DID work for those few minutes? We're getting somewhere. Do you have an oscilloscope? There might be a fault with the controller chip causing shoot-through, or maybe there's too little gate drive and the MOSFET isn't switched to its lowest resistance state.

[seanc]

Re: Asus PTGD-LR

Some more thoughts:
Could there have been damage to the CPU when the PSU failed?
You didn't mention if you noticed the blown caps before or after the PSU failure.

[sceva]

Re: Asus PTGD-LR

Check for shorts on the back of the board. Perhaps replace that transistor and test the board on a cardboard box?

You've put the two missing caps back, next to the transistor, in the correct orientation?
Are you sure the PSU you're testing with is good?

I can't see/find any shorts. The caps are installed correctly, BUT the first time I replaced the caps (before replacing the transistor) I replaced all three of them backwards and powered it up. No smoke, but it the computer must have recognized something was wrong because it did not power up. It is a used PSU, but the voltages test ok, the 12v lines that power this area show 12.4v without a load attached.

But the board DID work for those few minutes? We're getting somewhere. Do you have an oscilloscope? There might be a fault with the controller chip causing shoot-through, or maybe there's too little gate drive and the MOSFET isn't switched to its lowest resistance state.

I don't have an oscilloscope, although I have thought about making one from some kits, but don't know if they would be helpful or not. (can't afford a good one right now, been watching craigslist).

Some more thoughts:
Could there have been damage to the CPU when the PSU failed?
You didn't mention if you noticed the blown caps before or after the PSU failure.

Here is the order of events:

1. computer would not power on.
2. repaired the power supply.
3. turned on computer, saw some smoke in the area around the caps/transistor I have been working on.
4. Turned it off quickly. Couldn't tell where the smoke came from, and noticed the caps were bulging. Plugged it back in and the power supply POPPED and went dead.
5. Replaced caps (in the wrong orientation) and the computer would not turn on.
6. Replaced the transistor, and noticed the caps were backwards and re-installed them correctly.
7. It came on and booted up to Windows. I actually restarted it a couple of times over a 1/2 hour time, and then shortly thereafter the transistor blew again.
8. I then replaced the transistor again, trying to do a better job of soldering.
9. It came on for about 5-10 minutes before blowing the same transistor.
10. Replaced all three transistors in that area and it came on for about 5 minutes before blowing.

If the cpu was damaged, would it boot up to windows?

[PCBONEZ]

Re: Asus PTGD-LR

If you are still wanting to fix it then you are going to need to trace out the circuit checking for bad resistors, bad diodes, bad 'other', open traces, shorted traces, and look to see if the MOSFET controller is bad. [For the controller you'll have to look up the data sheet and figure out how to test it.]

When it gets that far I trash the board because the easy ones are more fun to play with.

.

[sceva]

Re: Asus PTGD-LR

When it gets that far I trash the board because the easy ones are more fun to play with.
.

I agree with you, but since this is a custom board and I would like to use the media center features, I will try to poke around a little more and see if I can come up with something...

[PCBONEZ]

Re: Asus PTGD-LR

I hate to burst your bubble but, except for the price, I don't see anything 'special' or 'custom' about the board.

http://h10025.www1.hp.com/ewfrf/wc/d...x&lc=en&dlc=en
http://www.skyline-eng.com/index.cfm...roduct_ID/6536

Should be easy to replace with a core architecture mobo which will give you more power with less watts.
.

[sceva]

Re: Asus PTGD-LR

I hate to burst your bubble but, except for the price, I don't see anything 'special' or 'custom' about the board.

Should be easy to replace with a core architecture mobo which will give you more power with less watts.
.

Thanks for the link to the mobo. The computer comes with an ir remote, and has audio out which are both built with direct connections to the mobo that I would like to keep using if possible. If not, I may take your suggesting and transfer the rest of the components to a new mobo.

I have been tinkering around and found some more info, but I am not sure if it identifies the problem or not... Here is what I have found:

1. The small cap, 100u/16v right beside the 4 pin connector for the power supply had very high esr. I replaced it with a 100u/25v nichicon.
2. Pins 6 and 7 on the MOSFET close to the same connector are shorted. I removed it from the board and found the MOSFET pins are not shorted, but the tracks on the board are shorted. Pin 6 is Power Ground, and Pin 7 is SW, which the datasheet says is "This pin is connected to the buck switching node, close to the upper MOSFET’s source. It is the floating return for the upper MOSFET drive signal." Is this ok?

I also traced the tracks and tried to draw it on the attached picture, and then did a drawing also. There is also a diode in the pic that is loosely connected to the trace that connects runs thru the smd cap and 1R0. By loosely I mean when testing it for continuity it acts like it is running thru a cap instead of being a closed circuit.

I wanted to get some feedback before replacing the transistor again to see if the bad cap was the problem.

[PCBONEZ]

Re: Asus PTGD-LR

Look at figure 1 in the data sheet below. It is a reference drawing for the MOSFET driver chip and may not be exactly what you have, but you can clearly see pins 6 & 7 should not be shorted together because if they were Q2 wouldn't work.

http://pdf1.alldatasheet.com/datashe...DP3418KRZ.html