2x Electrolyte capacitors on Nvidia Gt7300 graphics card for Macpro - Page 1
Forum section: electronics / beginners

author: vinlove
author_rank: Frequent Contributor
timestamp: September 24, 2016, 12:49:49 pm
content: hi AllI was checking the capacitors on the Nvidia gt7300 graphics card from my macpro 2.1 because the display went dead on it.2x of the Electrolyte capacitors on the card are being read on the Meter as resistors of 0.2 ohms rather than capacitors.Would I be right in thinking these caps are gone off, and causing the display go dead? The macpro tries to boot, but after displaying the Mac logo for a few seconds, it just goes blank. The monitor loses signal from the graphics card.If it is right assumption, would it be ok to replace them to new ones? I am asking this because having a close look on the pcb of the gt7300, solder is not visible on the parts. It looks like soldering is done in special way, or maybe it is a kind of pcb, normal soldering is not possible?I will try to get the photos of them later to show what I mean. cheers.

author: Ammar
author_rank: Regular Contributor
timestamp: September 24, 2016, 01:36:15 pm
content: Are you measuring correctly? Are you sure you are not measuring the case? To be sure, you could de-solder them and measure. They are likely decoupling capacitors, so measuring 0.2is certainly problematic.There is no reason why you can't replace them. Make sure the voltage rating of the caps you replace them with is equal or greater than that of the current ones. Otherwise, Good luck!

author: wraper
author_rank: Unknown
timestamp: September 24, 2016, 01:54:33 pm
content: If you are measuring them in circuit, then you are measuring not capacitors. It is extraordinary rare case for electrolytic capacitor to fail short. If those are on GPU Vcore, 0.2 ohm probably is fine.

author: vinlove
author_rank: Frequent Contributor
timestamp: September 24, 2016, 02:46:18 pm
content: The first photo - the one on the right black 2x el. caps are reading as resisters of 0.02 ohms.The lone one on the left reads as capacitor as normal.https://flic.kr/p/M6Q4wJThe second photo shows how the soldering on pcb is barely visible. It looks more clear on the photo, but on bare eyes, they look as if not existent.https://flic.kr/p/MnLF3YThe third photo shows the meter reading the caps as resisters.https://flic.kr/p/MnLF4EAs you say maybe they need to be taken out before measuring, but why the one on the left read as normal cap?cheers.

author: wraper
author_rank: Unknown
timestamp: September 24, 2016, 02:57:05 pm
content: Are you using in component type auto detect mode?

author: wraper
author_rank: Unknown
timestamp: September 24, 2016, 03:05:48 pm
content: Such meter unlikely to use DC for measurement. But at high frequency capacitor will appear almost as resistor. Basically what happens, meter measures ESR of the capacitor and shows it. But it cannot detect it as capacitor because of parasitic resistance in the circuit in parallel to the capacitor. You shouldneverexpect component type detection to work properly in circuit.

author: jitter
author_rank: Frequent Contributor
timestamp: September 24, 2016, 03:10:15 pm
content: Yeah, indeed. Desolder the caps you suspect and measure again.Looking at the pics, the caps look healthy. Bad caps show pronounced bulging of the tops and, in even worse cases, electrolyte leakage.BTW, did you try to measure the voltage across those caps during the brief moment it works at power on?Edit: the soldering of the caps leads looks normal, except for the right most pin. Either there's too much solder on it, or it did not wet properly. My guess is that there's a groundplane connected to that pin. If not designed properly (using thermal reliefs around the pin) soldering that properly can be very difficult. Bad wetting could lead to a weak joint that easily cracks.

author: wraper
author_rank: Unknown
timestamp: September 24, 2016, 03:22:30 pm
content: Quote from: jitter on September 24, 2016, 03:10:15 pmIt looks like manual touch-up with a soldering iron at factory after the reflow soldering. And thereisthermal relief. Nonetheless even with thermal relief present it is difficult to hand solder parts on multiplayer boards when they are connected to heavy power plane on multiple layers.

author: rob77
author_rank: Super Contributor
timestamp: September 24, 2016, 03:39:46 pm
content: Quote from: vinlove on September 24, 2016, 02:46:18 pmif you measure in-circuit , then the circuit does affect the readings... that 3rd cap is apparently in a different circuit and therefore the circuit affects the reading differently. de-solder the caps and measure them with a correct LCR meter.btw.. the 0.02ohm might be a short on that power rail not the capacitor itself (e.g. shorted mosfet or diode)

author: vinlove
author_rank: Frequent Contributor
timestamp: September 24, 2016, 04:16:06 pm
content: Thanks for great advice.Will de-solder them and measure again.yeah the meter is in auto mode, and it detects components types very well.But components in circuit - it is first time I tried with the meter.As you suggested, maybe the caps may be ok.The gt-7300 had died before this summer, and been resurrected by baking inthe oven for 11 minutes, and it has been working great until it decided to die againthis week.Due to this event, I am on my ipad. I hate using the ipad, so the macpro needs to comeback to life again soon.

author: jitter
author_rank: Frequent Contributor
timestamp: September 24, 2016, 05:14:08 pm
content: Baking in an oven temporarily resurrects it? Hmmm...I know next to nothing about Apple products but I've heard this before somewhere, probably in a Louis Rossman video.Is this perhaps a model with known issues? Does it by any chance have tantalum caps?

author: wraper
author_rank: Unknown
timestamp: September 24, 2016, 06:12:51 pm
content: First of all, electrolytic capacitors shouldn't be baked ever. Secondly, as baking helped, it's 99% chance that it's faulty GPU chip itself.

author: vinlove
author_rank: Frequent Contributor
timestamp: September 24, 2016, 10:09:55 pm
content: Quote from: blueskull on September 24, 2016, 08:23:00 pmI saw them. I was actually going to get a used Quadropro FX4500 with 512mb for £79.But they are all ancient, likely to have been pulled out of dead macpros, or resurrected by baking in the oven. Only God would know how long they will work.BTW, baking the dead gt7300 in the oven worked. It came back to live from non working dead card to a perfectly working and running like new card. I was stunned by it. Only problem is that it died again within 2 months.

author: Monkeh
author_rank: Super Contributor
timestamp: September 24, 2016, 10:20:44 pm
content: Quote from: vinlove on September 24, 2016, 10:09:55 pmBecause it didn't 'work'. That's like claiming taking some paracetamol cures a cold.. You relieved the symptoms briefly, nothing more.

author: jitter
author_rank: Frequent Contributor
timestamp: September 25, 2016, 07:50:06 am
content: Your baking the card only alleviated some symptoms that now have become prominent enough for it to stop working again.Baking in an oven, I'm guessing you were expecting a torn solder joint and attempted to reflow it. It did work for two months, but it's died again.You only live twice, so now the real problem solving starts and you will need to trace the fault.What does Dave always say? Oh yeah: "thou shalt measure voltages". Good luck!

author: wraper
author_rank: Unknown
timestamp: September 25, 2016, 08:38:07 am
content: Quote from: jitter on September 25, 2016, 07:50:06 amThis has nothing to do with solder joints under the chip. This is because of internal bump fail under the silicon die in the chip itself.

author: vinlove
author_rank: Frequent Contributor
timestamp: September 25, 2016, 09:48:51 am
content: Quote from: jitter on September 25, 2016, 07:50:06 amAt the time when it died first time, I tried everything to get it working, but it didnt work at all. So I was going to toss it in the bin. Baking it in the oven was the last measure. I really didnt expect it to work. But when it did, I realised that most of the used ancient graphic cards for sale on ebay could be from the oven resuurected by 11 miniutes of baking. Thats why I didnt buy them.But yes, I should have done some measuring at the time. Then I had no meters and no knowledge about these things. Now I am learning and reading about Electronicss and fault findings, this is a good opportunity to learn something.If it came back to live another time, I would be overjoyed

author: brabus
author_rank: Frequent Contributor
timestamp: September 25, 2016, 10:15:05 am
content: This remembers me of a friend wanting to buy an used TV for pennies, and demanding a two-year warranty for it.The only way you have to relief you ancestral, human fear of being scammed is buying a brand new card - if you find one.On the other hand, thinking that every used board on ebay is being sold because it was defective and has been processed with 11 minutes in the oven, well... it doesn't really work like that.Having bought plenty of used stuff, I have been seldom disappointed. Keep in mind that you get what you pay for. Original package is missing, sometimes the board is sent in a box without protection at all, sometimes it' a DOA. You can ask for a refund or another item to be sent; in general, buyers are supposed to be right - I am a lot more worried when I sell something!Of course, if you still like the idea of a piece of paper that screams "warranty", you can bring the whole thing to an authorized repair store.

author: vinlove
author_rank: Frequent Contributor
timestamp: September 25, 2016, 11:00:06 am
content: Quote from: brabus on September 25, 2016, 10:15:05 amI think there is big difference between demanding 2 years warranty for used electrical item and deciding not to buy it.