US Robotics ADSL router Recap problem

[pavithra_uk]

I have lightly used US Robotics USR 9112 ADSL modem/Router.

Used by my friend in last 2 years. not a heavy user. no problems at all.
when I got this router from him. like to mod it (recap and cooling mod)

1. I added heatsink for Router CPU (Its runnng very hot..)
2. Added another small heat sink for RAM chip
3. Replaced exiting 220uF 25V cap (this cap is placed output rail of 12V to 3.3V DC-DC convertor.) with 3300uF 6.3V cap
4. there is a 3300V 25V cap in 12V input line. I never replaced it.

I don't know why they put 25V cap in 3.3V rail.
DC-DC convertor is SC4519H IC

after I replace this cap. router dissconnects from ADSL link 10~15 times per day.
then I re solder previous cap, (220uF 25V) now router works fine.



all caps are 25V
even caps in 3.3V rails

Can SC4519H IC cause problem with large caps ? since its 600 KHz SMPS

[retiredcaps]

Re: US Robotics ADSL router Recap problem

3. Replaced exiting 220uF 25V cap (this cap is placed output rail of 12V to 3.3V DC-DC convertor.) with 3300uF 6.3V cap

after I replace this cap. router dissconnects from ADSL link 10~15 times per day.
then I re solder previous cap, (220uF 25V) now router works fine.

Unless there is a typo, replacing a 220uF with a 3300uF (something almost 15x more capacitance) will probably cause problems.

With capacitance, AFAIK, you can go slightly up, but 15x is sure to cause problems.

For voltage, you can go from a 25V cap to a 6.3V if you know for sure and confirmed with measurements using a multimeter.

[retiredcaps]

Re: US Robotics ADSL router Recap problem

PS. Topcat sells caps closer to the 220uF 25V specification

Rubycon 220uF 16v (if you are sure about the voltages - 16V is good)

https://www.badcaps.net/store/produc...products_id=53

[Krankshaft]

Re: US Robotics ADSL router Recap problem

You shouldn't increase capacitance unless you know what circuit it's in and if it that circuit will still operate properly with the added capacitance. Stay with the original value.

The only place where you can go up a bit without much worry is power supply filters.

Wow US Robotics there's a name I haven't heard in years.

The last USR product I had was a serial external 28.8 modem . Thought they were out of business.

[Agent24]

Re: US Robotics ADSL router Recap problem

Yeah...... they used 220uF for a reason. So you should put a 220uF in, not a 3300uF.

[Pyr0Beast]

Re: US Robotics ADSL router Recap problem

Can SC4519H IC cause problem with large caps ? since its 600 KHz SMPS
Yes.

Bigger is not always better.

[PCBONEZ]

Re: US Robotics ADSL router Recap problem

#1: 220uF to 3300uF is way WAY too much.

#2: They used 25v caps because the cans are bigger which makes the ESR lower and the Ripple capacity bigger.

Use a 220uF cap. That size is easy to find.
You can usually raise uF by 20% but there is usually no benefit in doing that.
[That is an option when you can't find the right uF cap but 220uF is easy to find.]
-
Voltage doesn't matter AS LONG AS you have low enough ESR and high enough Ripple -and- it is more than the circuits actual voltage. You will have to look up the specs on the old cap to know ESR and Ripple.
[And you didn't say what it is.]

A solid polymer 220uF might be an option.
They handle heat better.
.