WRT54G v1.0 - No LEDs or Power - Page 2 - Electronic Circuits Projects Diagrams Free

OutToLunch · 24th June 2008, 06:49 PM

It is possible that the PWM chip is bad (it's a richtek part, which is garbage - at least imho). You said the input is around 6.9V - the maximum allowable input voltage on the RT9202 is 7V. It's never good to run a PWM controller IC near its max input level - especially if the same rail is being used as the input to the down coverter.

What you need to do is remove the output inductor (which you've already done) and place a voltage on the output of the PWM regulator that is the level that the regulator is supposed to be regulating to. If everything works like that, then you know you have a problem with the regulator and that can then be dealt with. If nothing works or excessive current is being drawn from your external power supply, then something downstream of the regulator is hosed.

What is the output level of the regulator? If you do not know, you can figure it out from the board. Pin 6 of the RT9202 is the feedback pin. There should be two resistors tied to this pin - one will have the other end tied to the regulated output (call this Rfb) and the other resistor will have its other end tied to ground (call this Rp). The regulated output voltage will be:
Vout = 0.8*(1+Rfb/Rp)
Its not easy to tell, but it looks like Rfb would be RF1, which is 330 ohms and Rp would be R3 which is 100 ohms. This would yield an output of 3.4V - which sounds about right for 3.3V logic, etc. Double check, though - the picture has shiny spots that make it hard to see the copper traces.

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24th June 2008, 06:49 PM	(permalink)
OutToLunch	It is possible that the PWM chip is bad (it's a richtek part, which is garbage - at least imho). You said the input is around 6.9V - the maximum allowable input voltage on the RT9202 is 7V. It's never good to run a PWM controller IC near its max input level - especially if the same rail is being used as the input to the down coverter. What you need to do is remove the output inductor (which you've already done) and place a voltage on the output of the PWM regulator that is the level that the regulator is supposed to be regulating to. If everything works like that, then you know you have a problem with the regulator and that can then be dealt with. If nothing works or excessive current is being drawn from your external power supply, then something downstream of the regulator is hosed. What is the output level of the regulator? If you do not know, you can figure it out from the board. Pin 6 of the RT9202 is the feedback pin. There should be two resistors tied to this pin - one will have the other end tied to the regulated output (call this Rfb) and the other resistor will have its other end tied to ground (call this Rp). The regulated output voltage will be: Vout = 0.8*(1+Rfb/Rp) Its not easy to tell, but it looks like Rfb would be RF1, which is 330 ohms and Rp would be R3 which is 100 ohms. This would yield an output of 3.4V - which sounds about right for 3.3V logic, etc. Double check, though - the picture has shiny spots that make it hard to see the copper traces.