Stick the card in the slot and start it up. If there is nothing (computer still halts), unsolder the other two mosfets on the other end of the card, near the choke, as well. Check if one is connected paralel on the bottom.
With the MOSFETs near the Molex connector removed, it still won't start
Just as before, there's a slight twitch from the CPU fan, and that's all there is
better to keep quiet and be thought a fool, than to open your mouth and remove all doubt
With the MOSFETs near the Molex connector removed, it still won't start
Just as before, there's a slight twitch from the CPU fan, and that's all there is
That means there's still a short and we (read: you ) gotta hunt it down.
Basically, it all comes down to remove components until any short circuit between 5v/ground and/or 12v/ground disappears.
Start with the easy components - D1, D3, D4. Then check for short circuit. If still present, continue with any other mosfets and voltage regulators on the card that measure continuity/0 resistance between output and ground or output and 5v/12v.
Also, referring to the picture I attached below, check resistance between the pads circled in blue and the pads circled in green. What resistance do you get? Now check resistance between the cyan pads and the green pads. Again what resistance do you get?
Thanks for the colour coding - I can cope with that (still trying to work out what is the choke, mentioned by Pyr0Beast in post #19 - is it the component marked R68M ?)
Resistance between the blue & green pads is 85.5 ohm
And between the cyan & green pads is 87.9 ohm
better to keep quiet and be thought a fool, than to open your mouth and remove all doubt
Resistance between the blue & green pads is 85.5 ohm
And between the cyan & green pads is 87.9 ohm
Good. That means nothing else is shorted down the line.
Next, check for continuity again between the 5v pin and ground on the power connector. Also check for continuity between 12v and ground. If you're still getting a low reading on any of these, proceed to remove D1, D3, D4. Then check for continuity again at the power connector. If you still get a low continuity reading, remove the MOSFETs Pyr0Beast mentioned (one is on the front of the card, near the choke R68M, the other is in the back, right under the first one).
Then, yet again, check for continuity at the power connector. Post a log of the results you get here.
Once the short circuit between 5v and ground or 12v and ground is removed, the computer should hopefully start. After this, all you'll have to do is get replacements for the components you removed, and you may get a working video card.
In the meantime, keep the old components (or try not to loose them ) - some of them, like the diodes, may still be good.
Thanks for the colour coding - I can cope with that (still trying to work out what is the choke, mentioned by Pyr0Beast in post #19 - is it the component marked R68M ?)
Yes.
Remove both mosfets. One is on the upper side of the board. Otherone on the bottom.
With mosfets removed and short still detected I would check tantalum capacitors on input.
Also replace the PSU if they are shot - as seems voltage surge killed them.
I did look at Farnell - they said No Longer Manufactured for the Infineon part, and choose a substitute
If they are in stock, no problem with that.
Next, check for continuity again between the 5v pin and ground on the power connector. Also check for continuity between 12v and ground. If you're still getting a low reading on any of these, proceed to remove D1, D3, D4.
Was still getting a continuity beep between 12v & ground, although removal of the first set of MOSFETs near the Molex connector had fixed between 5v & ground
Removed the diodes on the back, as per this pic, but no change
Attached Files
better to keep quiet and be thought a fool, than to open your mouth and remove all doubt
Then check for continuity again at the power connector. If you still get a low continuity reading, remove the MOSFETs Pyr0Beast mentioned (one is on the front of the card, near the choke R68M, the other is in the back, right under the first one).
Then, yet again, check for continuity at the power connector. Post a log of the results you get here.
Removed one MOSFET on the back, as per this pic - was already suspicious of this one, because previous testing showed a continuity beep between the centre (ground?) and right legs
No more continuity beeps on the Molex connectors, so on to the acid test ...
... and motherboard powers up with this card in its AGP slot
Now I'll need handholding for replacements of the diodes and the MOSFET(s) - am I correct in thinking the one still in situ should be replaced also, being a pair ?
Anyway, the diodes are marked with a W logo, and underneath that M72, and underneath that 383 or 3B3
The removed capacitor is marked D452 and BA627H
The capacitor still in situ, on the fan side of the card, is marked D472 and BA632G
Attached Files
better to keep quiet and be thought a fool, than to open your mouth and remove all doubt
Now I'll need handholding for replacements of the diodes and the MOSFET(s) - am I correct in thinking the one still in situ should be replaced also, being a pair ?
Yes.
As a matter of fact, check the rest of the large MOSFETs as well (circled in blue, see attached images). That is, get their datasheets first, see which pins are Source and which are Drain, then measure resistance between Source and Drain. Those that show very low resistance (less than 20 Ohms) should be removed from the board and measured again. If they measure normal out of circuit, you can put them back on the card.
Anyway, the diodes are marked with a W logo, and underneath that M72, and underneath that 383 or 3B3
Check them for continuity with your multimeter. They should show continuity only in one way, but open circuit/infinity when the probes are reversed.
If they pass this test, you can put them back on the card.
The removed capacitor is marked D452 and BA627H
The capacitor still in situ, on the fan side of the card, is marked D472 and BA632G
Are these tantalum capacitors? Where were they located?
If they aren't shorted, I think you can put those back in as well (though it would be good if someone else could confirm that this is okay).
Are these tantalum capacitors? Where were they located?
If they aren't shorted, I think you can put those back in as well (though it would be good if someone else could confirm that this is okay).
Sorry, Senior moment on my part, plus wife on my case to get off the bl.... computer
Should have read:
The removed MOSFET is marked D452 and BA627H
The MOSFET still in situ, on the fan side of the card, is marked D472 and BA632G
better to keep quiet and be thought a fool, than to open your mouth and remove all doubt
Remember that by the time consequences of a short-sighted decision are experienced, the idiot who made the bad decision may have already been promoted or moved on to a better job at another company.
That is, get their datasheets first, see which pins are Source and which are Drain, then measure resistance between Source and Drain. Those that show very low resistance (less than 20 Ohms) should be removed from the board and measured again. If they measure normal out of circuit, you can put them back on the card.
The removed MOSFET marked D452 has been replaced, as per picture, by one marked 70T03H cannibalised from a dead motherboard
I wasn't sure what normal should be for "measure normal", so I selected a 70T03H which gave a short beep for Continuity/Diode test between Drain & Source (which, in my limited experience, indicates a working MOSFET)
Afterwards, no continuity beeps between 12v or 5v and ground pins on the card's Molex connector
And a motherboard still powers up with the card in its AGP slot
Attached Files
better to keep quiet and be thought a fool, than to open your mouth and remove all doubt
Check them for continuity with your multimeter. They should show continuity only in one way, but open circuit/infinity when the probes are reversed.
If they pass this test, you can put them back on the card.
The three diodes passed this test, so they're back on the card, as per picture
Again, no continuity beeps and motherboard powers up
Now I have to buy some replacement SO8 MOSFETs and see what happens - those parts don't seem to be used on motherboards, and possible to cannibalise
Pyr0Beast, I haven't disregarded your advice about replacing the electrolytics - it's on my list of things to do
Attached Files
better to keep quiet and be thought a fool, than to open your mouth and remove all doubt
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