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Hello everyone, in this lesson we will continue to look at the timing of the A card

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In the last lesson, we learned about the generation of VPP power supply.

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Next, let's look at how the memory power supply and the GPU memory module power supply are generated.

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We open the drawings and find their generating circuits in the catalog, on page 21

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After finding this power supply chip, you can see that it has a lot of pins

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Its model number is NCP81022

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This chip is a relatively common chip in the A card.

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Its workflow will be slightly more complicated than that of ordinary PWM chips

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First step, it needs to be powered

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The power supply of this chip has three pins

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VCC pin, 5V power supply

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VRMP pin, 12V power supply

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VDDIO pin, 1.8V power supply

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In the second step, it needs to get an open signal

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The third step, after the power supply is turned on, the chip will work,

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and it will generate MVDD power supply and VDDCI power supply through PWM pin control.

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The fourth step, when the VDDCI and MVDD power supplies are normally generated,

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these two power supplies will return to the chip to adjust the output voltage through the chip

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The fifth step, when the power supply is stable, it will send a PG signal

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But after the PG signal, the workflow of this chip is not over yet

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Here is a set of SVID buses

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It is connected to the GPU

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When the GPU works normally, it will adjust the output voltage through the SVID bus

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But the SVID bus does not affect the voltage generation

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In the end, the external conditions required by this chip are actually power supply and open signal

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With the power supply and open signal,

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it will output the two power supplies of MVDD and VDDCI

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If these two power supplies cannot be generated,

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generally there is a problem with the current detection or voltage detection pin,

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or there is a problem with the chip body

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So let's take a look at where its power supply and start signal come from

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Its power supply comes from 5V, 12V gold finger and 1.8V respectively

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These three power supplies have all been generated in the previous lessons

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Let's draw this step

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Let's look at the open signal

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Its turn-on signal needs to be high

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Let's see where its high level comes from

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It can be seen that its high level is directly converted from PWRGOOD of VPP

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And VPP PWRGOOD has been generated in the previous course

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So there is a open signal

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With the power supply and open signal, the chip will work and generate MVDD and VDDCI

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So far, all the power supplies in the A card sequence have been generated normally

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The difference between it and N card timing is that their timing relationship is not so strict

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For example, VPP power supply is not controlled by the core power supply,

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but directly controlled by 0.75V

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And the EN signal of the power supply chip of some A cards is not 3.3V high level

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Therefore, when we repair the A card, if there is no EN signal,

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it is not recommended to directly pull them up to 3.3V high level

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Pulling them up directly won't work either.

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If you want to create an EN signal, you can only remove the triode or MOS tube that controls the pull-down EN