Help me understand what just happened

nowwhat?

Member
Joined
Jul 24, 2012
Messages
42
Points
18
Location
Namma Bengaluru
So I decided to try my hand today at soldering.

I have this Panasonic cordless phone that runs on a weird 5.5V DC voltage and comes with a strange jack. In the morning I tried the phone with a Sony 5V (actual voltage on multimeter was 5.2V) SMPS DC adapter after cutting the wire and then connecting the Panasonic jack. I had just braided the wires together. The phone worked fine all morning.

Satisfied after running it for a few hours, I decided to solder the joints. Admittedly , it was an amateurish job with a couple of blobs of solder deposited on to the joints after tinning the tips. When I checked the output voltage on the jack, it showed 5.2V DC. Exhilarated, I connected the adapter to the phone and to my shock and disappointment, the phone wouldn't power up!

I then tried to go back to what I did in the morning. I removed the section containing the solder joint and braided the ends as before. Still the same 5.2V DC, but the phone wouldn't power up!

I have tried this with one more adapter and I can't for the life in me figure out what is going wrong. I have checked the polarity of the DC voltage and there is no change when I braid or solder.

Could it be that the soldering process itself is somehow damaging the adapter? In that case, how come it still shows 5.2V DC?

Please someone help me before I go completely nuts! Thanks!
 
The DC adapter seems fine. The phone may have been damaged by using a non standard adapter during the whole morning.
In the case of adapters, it's not only a matter of output voltage but the output current matters too.
 
Last edited:
The DC adapter seems fine. The phone may have been damaged by using a non standard adapter during the whole morning.
In the case of adapters, it's not only a matter of output voltage but the output current matters too.

Phone worked fine when I tried on the second adapter.
 
Hi Koushik!

It's been a long time...

I carefully checked the polarity both when it was braided and soldered. They were consistent all along.
 
greenhorn makes sense. connect the adapter in question in the right polarity and measure the voltage. some adaptors may not have enough output to cater such device and the voltage will drop. another good idea is to connect four fully charged NiCds in series and measure the voltage. if the voltage drops drastically, there is something shorted in the phone. most probably, a zener or rectifier connected in reverse bias across the supply inside the phone.
 
koushik is correct
check polarity...wrong polarity can kill a board

No, its not the polarity. I checked and double checked.

the regulation on this SMPS may not be that great. can you measure the voltage with the phone connected?

Yes, This is exactly the information I was looking for! It never struck me to check the voltage with the phone connected. Shows how much of a greenhorn I am!

greenhorn makes sense. connect the adapter in question in the right polarity and measure the voltage. some adaptors may not have enough output to cater such device and the voltage will drop. another good idea is to connect four fully charged NiCds in series and measure the voltage. if the voltage drops drastically, there is something shorted in the phone. most probably, a zener or rectifier connected in reverse bias across the supply inside the phone.

Thank you, diesel engine and greenhorn!

I really wish I had got this information earlier as I wanted to try and figure it out on my own.

Out of frustration I gave the phone yesterday to a cell phone repair guy who is well-known to me. I will post the results once I get it back.
 
Order your Rega Turntables & Amplifiers from HiFiMART.com - India's reputed online dealer.
Back
Top