Batteries overheating in Cordless House Phone

[TheJay]

My cordless house phone recently stopped working. I tried to determine what was causing the problem so I charged the AAA batteries in a normal charger instead of the dock. The phone wouldn't turn on. I bought new rechargeable batteries with the same specs and tried those, still didn't turn on.

The only thing I have noticed is that once inserted, these batteries are getting extremely hot within 5 minutes to the point they can't be held on my hand for more than a few seconds.

Can anyone tell me what might cause this type of behaviour in a cordless house phone powered by two AAA rechargeable batteries? I have opened up the unit and can't see anything obvious.

 

[ZipZapOuch]

It means there is a failed component that is causing a short circuit to quickly discharge the battery which makes the battery hot, or, it means that a high-current load of the phone is supposed to happen for a short period of time is occurring for much longer periods of time (or continuously) - either because of a broken switch, broken wire or software glitch.

 

[TheJay]

Thanks for your reply. So what would be the easiest way to pinpoint the issue on the board?

 

[ZipZapOuch]

Thanks for your reply. So what would be the easiest way to pinpoint the issue on the board?

- Easiest but not answering your question - buy a new phone
- next Easiest, have a professional from the company that designed it examine and diagnose it.
- Alternatively (less easy) , get a schematic and/or a troubleshooting guide from the manufacturer.
- Even less easy, open up the device, locate the power supply and charging unit, identify the chips and components, take photos of both sides of the board and do a point-to-point continuity tests to recreate the schematic yourself, then use datasheets for the various components to understand how the circuit works and what voltages you should have at each node of the schematic when the battery is charged and discharged. If all areas of the power supply work, move on to HMI, audio amplifier, transmit, receive sections.

 

[TheJay]

Thanks for your reply. It looks like a fairly simple board with very few components, I can't see anything obvious.

Do you see any likely causes based on the design?

 

[vidalv]

Hello,
If you have a short-circuit on the battery it means a big problem on the power supply, if it is the power management circuit, it is not much to do, on such a device without technical documentation (This is the concern today, we throw everything in the trash, No Repair!). Another possibility, a short-circuited capacitor, you have to make a visual around the connection points of the battery and try to see if a capacitor is not in short circuit, at worst (and according to the type, not easy with SMD components) look at Electrolytic capacitors in the area. Not obvious that I recognize. Good luck!

 

[vidalv]

Try to remove this two caps :

We never know!

 

[TheJay]

Thanks for your replies, what do I do once I remove the capacitors?

I think this might be the problem:

Looks blown, right?

 

[vidalv]

Ok, if you have a multi meter, try to measure (Continuity test mode) between "+" and "-" on each capacitor, if you have a short-circuit? If yes, remove the caps and measure again if the short still alive or not ?
(If you are lucky, the short disappear, try to place battery and see if the phone work!)

Concerning the diode on snap, the black circle is normal that indicate de Cathode, to verify is the diode is Ok, again use multi-meter (Diode-Test mode) in both direction, if the diode is Ok, you measure 0.5 to 0.8V in one side and Over-Load on the other. If the diode is dead you measure OL in both direction.

Hope this help!

 

[vidalv]

You can check the voltage on the "+" line and look at involved components :

The A61 (dual diodes) then H5C (Regulator ?) 1AM (NPN transistor) all of this a involved in the supply ....

 

[Nigel Goodwin]

My cordless house phone recently stopped working. I tried to determine what was causing the problem so I charged the AAA batteries in a normal charger instead of the dock. The phone wouldn't turn on. I bought new rechargeable batteries with the same specs and tried those, still didn't turn on.

The only thing I have noticed is that once inserted, these batteries are getting extremely hot within 5 minutes to the point they can't be held on my hand for more than a few seconds.

Can anyone tell me what might cause this type of behaviour in a cordless house phone powered by two AAA rechargeable batteries? I have opened up the unit and can't see anything obvious.

Are you sure you put the batteries in the right way round?

Failing that, buy a Panasonic Cordless Phone set - the BT ones are rubbish - we used to sell both at work, but the Panasonic ones were absolutely bomb proof, and the BT ones were useless. We never had any Panasonic ones back under warranty (and most we sold were Panasonic), but loads of BT ones came back faulty.

 

[christinescoms]

My cordless house phone recently stopped working. I tried to determine what was causing the problem so I charged the AAA batteries in a normal charger instead of the dock. The phone wouldn't turn on. I bought new rechargeable batteries with the same specs and tried those, still didn't turn on.

The only thing I have noticed is that once inserted, these batteries are getting extremely hot within 5 minutes to the point they can't be held on my hand for more than a few seconds.

Can anyone tell me what might cause this type of behaviour in a cordless house phone powered by two AAA rechargeable batteries? I have opened up the unit and can't see anything obvious.

AC repair in Cedar Park

I have a cordless Panasonic phone (4-5years old) which has always given me
problems for charging. We let it charge over night and then keep it off
the charger until it dies (NiCd). With a new battery it last 3 days (only
1 hour talk time) and after 3 months of so it only lasts 1 day. Something
wrong with the phone or is it just cheap batteries

 

[gary350]

My hearing aid batteries over heat if I close the lid on the charger when it is charging. When lid is open batteries never over heat. Does that give you any ideas to check on your charger.

 

[ZipZapOuch]

I think this might be the problem:

I think that diode does look funky. The question is, what caused it? A power surge, reversed batteries, static, ...?

 

[vidalv]

This diode looks like a battery inversion protection ... given its size it would take several amps to destroy it. What do you measure with the ohmmeter between the + and the -? If you have a short circuit (which is probably the case) it is a component which is in short circuit, active device (transistor, regulator) or capacitor.

 

[TheJay]

Thanks for all your replies, I haven't had a chance to respond until now as I have been waiting for new probes for the multimeter. Just tested, I got a reading of OL on the diode regardless of polarity.

Checking the other components, I got these results:

 

[vidalv]

Hello, not sure to understand all, sorry.
1) "I got a reading of OL on the diode regardless of polarity." So, by placing the multimeter in Diode Test, one side should be 0.5 to 0.8V, and reverse OL, if you got OL on both the diode is distroyed ! Replace it.

What do you mean by 0.002V ? You put the 2 battery then you measure the voltage on caps ?
Same for the other, with both bats you got 1.495V on the other cap ?
Finally : "Continuity test pass" on what ? if you measure a wire that is normal, but if you measure a component this is wrong.
What did you measure when placing battery (at the battery connector) 3V or 0V ?
Give more details to understand please!

 

[TheJay]

I am very confused now. I have included photos to show you what I am getting. I haven't attached a battery at any point, I don't have a way to do that as the battery compartment is made up of two separated sections.

 

[vidalv]

Hello, thank you for the photos.
The diode test mode is generally used to check the diodes, to check continuity/short-circuit it is rather the ohmmeter.
- First snap, with 1.497V (diode mode) to measure the capacitor does not help, this indicate no short on this capacitor. (Ohmmeter mode should help more).
- Second, is more interesting, you got a short on this capacitor (This is probably relative to your problem). Again Ohmmeter value should be better.
- Next, it's seems the diode looks Ok with 0.728V.
- Next one, this is surprising, 0.609V but possible if somewhere another diode (IC input protection diode present in parallel).
- Fifth, same as 2 you are in beep mode you measure a short.
- Next, No short (this is good Over Load) this capacitor looks OK.
- Last, difficult to say ? Sorry.

You must proceed by elimination, the capacitor in short circuit, even if it is not him, must be carefully removed with a good welding iron.
Then redo the measurement, if the short circuit is always present the problem is somewhere on this line, you must follow the tracks (if possible) and measure the other components on it. I know easy to say but less to do it.

 

[TheJay]

Thanks for your reply.

How is a circuit tested if a component is removed? Surely then it's no longer a circuit?