I am going through some troubleshooting steps and need help figuring out what to check next. Thanks to Chris, G5CTH for these steps:
PCB #1 (8-pin)
1? Connect ground and V_IN, V_IN must be? +5V, 100mA max, no more than 5V. Leave these connections for all the tests
??? 1.1? +12V and VCC should show Zero V and the current should be almost zero. This is because the power has not been turned on using PWR_ON or PWR_HOLD
Result: +12v and VCC are both zero
2? Connect PWR_ON to ground, this should turn the power control FETs Q103 and Q105 on
??? 2.1? The +12V pin should show 5V, VCC should remain at 0V? Current should remain low but adding a load to +12V should give a current flow.
Result: +12v shows 5.01v, VCC shows 0v, adding 47k resistor as load to +12v shows a small current flow (0.10 mA)
3? Disconnect PWR_ON and pull PWR_HOLD high through a resistor, 47K should be plenty.
??? 3.1? The +12V pin should show 5V and VCC remain at 0V, current low but can be supplied from +12V.? This does the same as test 2 but using the MCU controlled power on switch.
Result: +12v shows 5.02v, VCC shows 0v
4? With PWR_ON low and IMPORTANT input volts less than 5.6V pull PWM_5V high. This simulates a 100% duty cycle PWM control.
??? 4.1? This should turn the SMPS FET Q108 on and VCC should show the input volts.? The reason to keep the voltage low is so the Zener D108 does not conduct.
??? 4.2? ADC_5V should show half VCC.
??? 4.3? Current will remain low unless current is drawn from VCC.
Result: VCC shows 5.02v, ADC_5V shows 2.50v
***PCB #1 passes all tests***
PCB #2 (6-pin)
1? Connect a 5.5V, 100mA max power supply to the GND and +12V pins.
??? 1.1? VDD should be 3.3V, supplied by the linear regulator IC101. Current should be low and supplying current to VDD should be possible. The SMPS section should be inactive.
Result: VDD shows 3.07v <-- Is this too low?
2? Connect LIN_REG_EN to ground
?? ?VDD should go low because the linear regulator is turned off.? Q111 will be on but the PWM isn't active so no power is supplied.
Result: VDD is low
3? REDUCE the input Volts to < 3.5V!!!? This is to protect the 3.6V Zener D109.? Pull LIN_REG_EN low and PWM_3V3 high, This will turn the SMPS on, simulated 100% duty cycle.
??? 3.1? VDD should be the same as the input volts and should deliver current.? ADC_3V3 should be half VDD. The current with no connection to VDD should be low.
Result: VDD shows 3.57v. ADC_3V3 shows 3.47v <-- This is too high!
***PCB #2 might have issues?***
Can someone take a look at the results here and let me know if there is something else I can check on PCB #2? I've done a close inspection under magnification of the board and I don't see any solder joint issues.??
