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Replacing faulty RAM on video cards?

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    #21
    Re: Replacing faulty RAM on video cards?

    I would think the stovetop makes more sense, given that the 'real' BGA rework machines use heaters on the bottom, and hot air/IR on top.

    The oven doesn't make sense to me except that people do it because it's all they've got.
    "Tantalum for the brave, Solid Aluminium for the wise, Wet Electrolytic for the adventurous"
    -David VanHorn

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      #22
      Re: Replacing faulty RAM on video cards?

      Originally posted by Agent24 View Post
      The oven doesn't make sense to me except that people do it because it's all they've got.
      Well, no, everyone has got a stove top too. It's just much easier to explain to someone non-technical to set the temperature to X degrees for Y minutes and "reflow" whatever video card they desire.

      But you are absolutely right - it doesn't make sense to do it in the oven at all, and I am personally against oven reflows, even if you have nothing better. Reason being is that ovens tend to vary quite a bit in design - from what type they are (gas, electric) to how fast they heat up and how much they overshoot in temperature. And with that, you can get quite varying results as well. That's why some people end up literally baking their video cards to a crisp while others don't get any results at all, because their card didn't heat up enough. (And then of course, there's the fact that you just may not actually have a repairable GPU to begin with.)

      Originally posted by Agent24 View Post
      I would think the stovetop makes more sense, given that the 'real' BGA rework machines use heaters on the bottom, and hot air/IR on top.
      Well the really real BGA machines use a large IR pre-heater for the whole board and two hot air heaters for the top and bottom of the area/BGA chip that is meant to be heated. In fact, most of the BGA industry (real factories that make boards, not repair "shops" with those cheesy eBay IR stations) still use and prefer hot air over IR.
      Why?
      - Because IR is highly dependent on the object's absorption rate - i.e. is it a white/silver shiny object or a black object with rough texture. The two would obviously absorb IR differently (hence why if you leave a dark and a light shirt in the sun, the dark shirt will get hotter.) With hot air, you don't have this problem. However, hot air is much more inefficient and thus requires more energy (and that's why most BGA machines on eBay are IR... because if they had to do it all with hot air, the machine would require a lot more power, which could be a problem for some customers.) Also, IR is easier to setup compared to hot air. This has mostly to do when using thermocouples for temperature probing. With IR, there is no or little moving air over the thermocouple, so you can read the temperature of an object with the IR heater directly over it, and it won't affect the reading. With hot air, the temperature of the air is usually a lot hotter than the desired "target" temperature (and again, that's because not all of the energy/heat from the hot air is transferred to the object). And because of that, a thermocouple probe will read much higher temperature when it is blasted with the hot air heater than when it isn't. Thus, to get an accurate reading, either the thermocouple has to be "calibrated" for the specific hot air heater it will be used with -OR- the heater can be turned off for a few moments, then the reading can be taken from the thermocouple, and then if needed, the heater can resume again.

      So that's why those IR machines are more popular - they are just easier to set up and deal with. Hot air is more work but gives better results due to more even heating. Also, with hot air, the PCB will rarely brown/darken after being reworked, unlike with most IR stations.

      But anyways...
      Now try explaining all of that above in a simple short YouTube video (or wherever you prefer) to all the people out there looking to "reflow" their video cards and consoles at home. I bet most would probably close the video not even half-way through.

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        #23
        Re: Replacing faulty RAM on video cards?

        Originally posted by Agent24 View Post
        Good point - and even if you find which address(es) are bad, which physical IC does that correspond to anyway... no schematics for these things.:
        One solution I found intresting:
        https://www.youtube.com/watch?v=6LOp4IMulEk
        QT#1: Crude way to find a defective video RAM bank

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