6min

Diagnostics Power Draws

Once we have confirmed we have a working BQ24193 it is time to hook up our bench power supply to the Switch for the remainder of all our diagnosis and repair.

Without a bench power supply telling us the current draw we are flying blind with nothing more than a multimeter and the hopes of a full working LCD and console. However, with a bench power supply we can tell if a system is booting fully into the OS with 100% certainty without even having a screen connected.

We can tell if the eMMC is bricked/bad or stuck in first-stage boot not going to second stage boot. We can tell if we have dead shorts, if we are failing to go to sleep mode, and so much more. All from the current draw of the bench power supply. So if you are going to be repairing Switch consoles I cannot recommend enough a good bench power supply.

We sell a nice priced mid-range bench power supply with accurate current readings enough for the task. A high-end one will cost you several thousand, but these mid-level accurate bench power supplies are good enough. Cheaper ones are of no use, their current measurements are nowhere near accurate enough to rely on for any diagnostics.

Bypassing the battery

It is simple to power up the console from the bench power supply. Install the 10K bypass resistor between the two test pads above the battery connector, remove the battery, and connect your bench power supply up to the ground of the USB-C connector and the VBAT pin of the BQ chip as shown below.

Set your bench power supply to 4.2V and 2A current limit. Any less than 2A and you will fail to get into second-stage boot.

Powering Switch from Bench Power
Powering Switch from Bench Power

Turning On Switch

In the spirit of bypassing as much as possible to keep potential issues like a bad ribbon cable or power button affecting our results, we can turn the Switch on with nothing more than a pair of tweezers.

Short out the top 2 pins of the power/volume ribbon cable to simulate pressing the power button.

Turn on Switch with tweezers
Turn on Switch with tweezers

Once you do this you should observe the bench power supply current draw increase.

Current Reading Diagnostic Table

The current will depend on the current operational state of the console, and if you have an LCD connected or not. We will base lots of our diagnostics on these specific current draw values.

For example a working console without an LCD connected would typically draw 200mA at first-stage boot, and jump to 400-600mA during second-stage full boot.

Here is a table of the power draws at the stages of booting. Starting with first-stage boot, then second, then sleep.

As we find more specific cases of failed components indicated by specific current draws we will update this table.



Setup

Indication of

First-Stage Boot

Second-Stage Boot

Sleep

4V at VBAT

Dead-short

Max current draw





4V at VBAT. No LCD

Working

200mA

400-500mA

8mA

4V at VBAT. LCD

Working

200-400mA

500-800mA

340mA then 13mA

4V at VBAT. LCD

Bad backlight IC or LCD

200mA

400-500mA

8mA

4V at VBAT

No/Bad eMMC Bad CPU (try reflow) Bad RAM (try reflow)

200mA (never goes second stage)

-

-

4V at VBAT

Current limited by supply or VBAT traces

0mA then 200mA (boot loop)

-

-

4V at VBAT

Bad MAX77621 below CPU

100mA

-

-















Updated 27 Jul 2022
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