Netgear DG834GT - bad Teapo SC causing catastrophic damage

[japlytic]

In a Netgear DG834GT wireless ADSL modem, there were some bulging Teapo SC units.
Replacing all of them did not fix the problem, but the diode at the DC-DC coverter near the 470uF 6.3V unit was shorted, along with the DC-DC converter.
So replace all of the Teapo units before it's too late!

[Agent24]

Re: Netgear DG834GT - bad Teapo SC causing catastrophic damage

Did replacing the diode and DC converter fix it?

[japlytic]

Re: Netgear DG834GT - bad Teapo SC causing catastrophic damage

The IC was a MP1410, which is hard to obtain in my country, so this unit was written off.

[Agent24]

Re: Netgear DG834GT - bad Teapo SC causing catastrophic damage

That's a pity. There's MP1410 on eBay but not SMD (for a decent price) which I assume is what the router uses.

[severach]

Re: Netgear DG834GT - bad Teapo SC causing catastrophic damage

Unless you tested the diode for shorts out of circuit, the diode, MP1410, and the P-MOSFET if equipped are likely to be fine. Those are the strong parts that can handle 25v or more, more than is available from the transformer. What is at risk when the ripple skyrockets from bad capacitors is the weak parts. Chips requiring the common low voltages: 3.3v, 2.5v, 1.8v, 1.5v, 1.25v, and many more are not going to be very resistant to over voltage so will burn out easily.

The diode near the SMPS chip is backwards across the supply rail through the inductor. If any part on that rail is shorted, that diode will show shorted to DC from the test probes. I've been testing a lot of routers and on occasion I mess up. Sometimes shorting the supply out makes the SMPS chip overshoot to recover. Sometimes I forget to discharge a test capacitor when moving from a higher to a lower voltage. Voltage goes up for a brief moment and shorts all the main chips out. The SMPS senses the short and locks out.

For small devices 3.3v is the most common voltage from the head SMPS. When the multi voltage chips short out, they can short 3.3v onto the lower rails shorting some of the chips that aren't directly hooked to 3.3v.