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  • Author Author: koudelad
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ADSL modem repair: mission failed

koudelad

Hello,

 

Last time I wrote about a successful repair: Repair of a CNG boiler control board . This time, the repair didn't go well.

 

After about 12 years, our ADSL modem ASUS TI4631 stopped working. The ADSL connection didn't work and it was only possible to open the web management console, log in and see the home screen (with no useful information). All attempts to see the configuration, reset it (both software and hardware) didn't make the web interface to work.

 

So I opened the box and saw a few electrolytic capacitors inflated.

image

 

All capacitors were made by Teapo and were of SC series (low impedance, high ripple) and SY series (low impedance, long life series).The most inflated were the SC ones, used near a switching power supply, I guess.

 

Here is the complete list:

2x 470uF 35V 105C LI HR 10 * 20 mm

2x 100uF 35V 105C LL LI 8 * 11 mm

1x 1500uF 6.3V 105C LI HR 8 * 15 mm

4x 220uF 10V 105C LI HR 6,3 * 11 mm

1x 100uF 25V 105C LI HR 6,3 * 11 mm

 

LL = long life (6000 h)

LI = LOW impedance

HR = high ripple series

 

As you might notice, I wrote down everything I could see on the capacitors and also measured them physically.

 

Lesson nr. 1: Datasheets sometimes contain errors.

I just wanted to make sure I identified the capacitors correctly so I double checked some values with the datasheet. Surprise, two capacitor types have different physical values compared to the datasheet. Ordering a higher capacitor could result in a problem - it might not have been possible to close the box.

10 * 20 mm according to datasheet was in reality 10 * 15 mm.

8 * 11 mm according to datasheet was in reality 6,3 * 11 mm.

 

Lesson nr. 2: Catalogs of component distributors sometimes contain errors.

I love the possibility to filter products. There are 150 000 different capacitors. 2 000 with the same capacity, 50 with the same voltage and temperature, 10 with the same impedance and  5 with the same size etc.

BUT, the same errors as in the datasheets might happen. I completely understand it - no one (hopefully) adds and checks every single item manually. Instead, thousands of items are imported at once.

So I checked every single datasheet to check with the product parameters in e-shop.

 

Lesson nr. 3: Quality components cost more

I don't like people around me talking about how they bought something great for so low on some Chinese web market. The joy usually lasts the same period as the worst quality electronic component in it.

I am also sad that local electronic component stores (in my country) only offer cheap electrolytic capacitors, LEDs, IOs, because only a few people would probably buy better ones.

Quality components just cost 2-100x more than no name ones. It has reasons image

 

image

 

Lesson nr. 3: It is very hard to desolder the old capacitors

Industrially soldered products have only a little solder in the joints compared to joints made by amateurs. I couldn't even suck the solder from joints, so I had to pull all the capacitors legs one by one. Desoldering 2 legs at once was hard.

 

Lesson nr. 4: It is even harder to solder new capacitors back

I tried 3 soldering irons (1 temperature controlled SL30-CMC and two not), ruined a soldering tip and got angry. The solder doesn't want to attach to the original joints. This creates lots of awful joints. The longer time is spent trying to heat the solder and fix the situation, the more is the solder and the whole joint burnt.

 

image

 

I guess you will easily spot the original and new joints:

image

 

 

Lesson nr.5: It wasn't only the capacitors.

After assembling everything back together and powering the modem, I found out that the behavior is similar. It seems that something has improved, the web configuration can be accessed, but stops responding after a while.

 

So this repair is "mission: failed".

 

Do you have any tips for repairing commercial products and replacing components? Do you use any special equipment? Or are just my hands clumsy?

I would be grateful for your comments.

 

Thank you,

David

  • in reply to koudelad

    Hi David,

    Here is the iron that     was talking about. I have found it to be excellent and a lot of fun to use after fighting with unregulated irons for many years.

     

    https://www.element14.com/community/people/jw0752/blog/2017/06/14/tenma-21-10115-temperature-controlled-soldering-station

     

    John

  • in reply to koudelad

    I need a soldering iron that is capable of delivering a consistent amount of heat.

     

    John might be able to provide the answers ... and a link to the whole conversation.

    He recently got one from Newark, but whether it is availble at your element14 store is ??

     

     

    (Sorry I'm at work so it would be several hours before I can respond properly)

    Mark

  • in reply to mcb1

    Thank you very much, Mark.

     

    I am thinking about buying a new soldering iron. I have seen and read videos and articles about lead-free soldering and got to a conclusion that I need a soldering iron that is capable of delivering a consistent amount of heat. From a trustworthy manufacturer, no Chinese copy. I will probably also need a different soldering tip than the default round supplied with all soldering irons.

     

    Soldering new boards and custom protoboards with lead solder is so easy, it’s actually hard to get it wrong. I don’t remember repairing a single colder joint.

    But lead-free soldering and desoldering requires more skills and better equipment. I wish I knew someone near me to become a student for a few afternoons image

  • in reply to koudelad

    Most of these are flow soldered and using lead free solder.

    Best idea is add more solder, then try the sucking.

     

    The black is usually burnt flux, and will occur when it is overheated.

    edit .... You should be able to remove the black by using a metal sponge, rather than a wet one. Simple version is a stainless pot scourer.

     

    Since you're desoldering it isn't an issue.

     

     

     

    You'll also find the board is 4 layers, with a very large positive plane and a very large ground plane.

    This will definately suck heat from the soldering iron, and makes it nearly impossible using a soldering iron and sucker.

     

    You may wish to consider actually cutting the capacitor and then extract the leads.

     

    Mark

  • in reply to mcb1

    Good idea, Mark, probably the last thing to try (with my level of experience). I usually download and archive the latest available firmware for all devices, especially to those, that are not updated anymore.

    There were many problems in the era of portable MP3 players that somehow got corrupted their firmware after a few months of usage. Reflashing to get it back to work.