GE 26920 Cordless Phone - Battery Does not charge

You didn't say whether there was voltage on the charging pins. You should start by tracing backward from the pins.

Also, it is not normal for a properly-specified resistor to be blackened (or even darkened) by heat. This resistor should be replaced by one of the correct value and wattage rating.

I realize English is not your first language, so I wanted to note that plurals do not have apostrophes. For example, pins, not pin's.

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Hi,

1. There is about 8V at the charging pins (not pin's) of the base unit. I have googled a ton of websites and one of them mention that this voltage at the base unit should be varying from 4V to 8V and when the handset is placed with battery connected, it should drop and stabilize at about 3.6v. In my case, the voltage is fixed at about

8V and does not vary.

1. I too wanted to replace the resistor. But its badly blackened with even the color coating layer cracked..... I do not have the schematic so I don't know what should be the value of the resistor. Any tips ?

1. There is about 8V at the charging pins (not pin's) of the base unit.

I have googled a ton of websites and one of them mention that this voltage at the base unit should be varying from 4V to 8V and when the handset is placed with battery connected, it should drop and stabilize at about 3.6v. In my case, the voltage is fixed at about

8V and does not vary.

Hmmm... Interesting.

If the battery is pulling current, then the voltage should drop. That it does not suggests that (QED) the battery is not connected. Have you checked all the wiring in the handset, to be certain the battery is properly connected?

ed

For last few hours , been working on this task. Here are some more findings.

1. The burnt resistor was showing 330Ohms on my DMM. I shunted it with another 140 Ohms resistor. Put a LED across the handset charge terminals of the base unit. Bingo !!! the base unit Charge/ In-use LED light's up......... so basically it may be that the original value of the resistance was around 150Ohms but due to heat, this got bumped to 330Ohms ( wild guess :-) ) The LED was drawing about 35mA of current
2. Now, instead of the LED, I wired the handset, connected the battery ( 3.6V, 300mAH) to the battery terminals on the handset PCB. The charge/in-use LED of the base unit lit up........ but after about a minute, the LED of the base unit is no more on... Removed the battery, measured the terminal voltage and it show's

3.6V but a little bit usage ( by pressing talk button on the handset) drops it to 2.2V The battery pack is brand new and not a old one so I cannot doubt the battery.

1. I repeated the step 1 and the LED of base unit is on again...

1. So basically, I still have not fixed this instrument. How can the battery voltage jump to 3.6V in just a minute ? Should it not be gradually increasing ( sorry, its been a while i have handled batteries so a bit rustic). why does the base unit LED turns off in a minute ? When this instrument was brand new, i remember this used to remain on as long as the handset was kept on the base unit.

2. I am going to buy one more brand new battery set and try the above steps again just to be sure that the battery is not the culprit.

Note: Yes, English is not my mother-tongue but its the language I have used in my profession for last 20 years. Any more grammar errors are welcome :-)

You need to know the proper current limiting resistor value. It sounds to me as though 150 ohms is still possibly too high. If you measure the voltage drop across that resistor, you can determine the charging current. Compare that to the suggested charge rate for the 3.6V battery pack and then adjust the resistor accordingly. I do not believe it is a defective battery pack, so would not purchase another replacement till you determine that it is receiving the correct charging current.

It is possible that the original resistor could have burned up over time if you had a dead shorted battery pack. I'd do with a higher calculated maximum wattage (assuming the full DC supply voltage gets dropped across that resistor) just to be sure this does not happen next time around.

Good luck. Your use of the English language is very good.

Bob

For last few hours , been working on this task. Here are some more findings.

1. The burnt resistor was showing 330Ohms on my DMM. I shunted it with another 140 Ohms resistor. Put a LED across the handset charge terminals of the base unit. Bingo !!! the base unit Charge/ In-use LED light's up......... so basically it may be that the original value of the resistance was around 150Ohms but due to heat, this got bumped to 330Ohms ( wild guess :-) ) The LED was drawing about 35mA of current

1. Now, instead of the LED, I wired the handset, connected the battery ( 3.6V, 300mAH) to the battery terminals on the handset PCB. The charge/in-use LED of the base unit lit up........ but after about a minute, the LED of the base unit is no more on... Removed the battery, measured the terminal voltage and it show's

3.6V but a little bit usage ( by pressing talk button on the handset) drops it to 2.2V The battery pack is brand new and not a old one so I cannot doubt the battery.

1. I repeated the step 1 and the LED of base unit is on again...

2. So basically, I still have not fixed this instrument. How can the battery voltage jump to 3.6V in just a minute ? Should it not be gradually increasing ( sorry, its been a while i have handled batteries so a bit rustic). why does the base unit LED turns off in a minute ? When this instrument was brand new, i remember this used to remain on as long as the handset was kept on the base unit.

1. I am going to buy one more brand new battery set and try the above steps again just to be sure that the battery is not the culprit.

Note: Yes, English is not my mother-tongue but its the language I have used in my profession for last 20 years. Any more grammar errors are welcome :-)

1. Now, instead of the LED, I wired the handset, connected the battery ( 3.6V, 300mAH) to the battery terminals on the handset PCB. The charge/in-use LED of the base unit lit up... but after about a minute, the LED of the base unit is no more on... Removed the battery, measured the terminal voltage and it shows 3.6V but a little bit usage ( by pressing talk button on the handset) drops it to 2.2V The battery pack is brand new and not a old one so I cannot doubt the battery.

You're assuming that the light going out means the battery has completely charging. This might not be true. Let it sit longer.

So basically, I still have not fixed this instrument. How can the battery voltage jump to 3.6V in just a minute ?

It's normal for nickel-cadmium batteries to return to "full" (or near-full) voltage after a short charge -- but the battery _isn't_ fully charged. Be patient.

the

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More updates.

1. Finally, I think I have managed to figure out the tentatively right value of the resistor. I have put a 82Ohms resistor and the voltages now appear correct. There is about 3.4V across the ni-cd battery terminals connector. There is zener diode across these terminals and using current meter, I have noticed that this zener diode is always conducting and there is about 25mA flowing through it I left the battery connected to the connector for more than 12hrs and it does not get charged. Using a current meter, I see that the meter oscillates between 0mA and 4mA continuously. Is this behaviour normal ? This time, I even tried with a BRAND NEW battery pack and there is no current flowing through it too..

1. There is a microcontroller chip on the handset too. To get 3.6V across the battery connector, I have isolated the microcontroller and the circuitry surrounding it by disconnecting one of the jumper providing supply. In fact this jumper is directly connected via the copper tracks to the cathode of the zener diode. Interestingly, I notice that everytime I connect back this jumper, the voltage across the zener ( and battery connector) falls to 1.5V

2. There are few SMD transistor like devices on the handset PCB. It has M6 written on it and a google search indicates that this can be a Jfet or a NPN transistor. I did following check on the terminals, and these are my results The M6 is a three terminal device and it has 1 pin on the right side and 2 pins on the left side. I guess this is SOT23 but not very sure ( a bit rustic on that now) Lets say we name the pin on the left bottom as 3, left top as 2 and right side as 1 and using a DMM in th diode testing mode/setting, below is the table of results

3 2 1 DMM Reading R B 1 R B 690 R B 1 B R 1 B R 680 B R 1650 Now, I am finding it difficult to decide on what exactly is this device ? There are 3 to 4 of them on the board and all of them show the same readings.

Any tips to find the faulty component causing the voltage to drop to

1.5v from 3.6v ?

If there is voltage at the charging terminals, but the battery doesn't charge, does that not suggest the battery is not making contact?

Depends on if the measured voltage at the battery charging terminals was while the phone was on the charging cradle or not. Also, if the phone was indeed on the cradle at the time, then I'd suspect the circuit inside the phone itself may be open circuit due to a number of possible causes.

Which was exactly my point. (I should have said "connection" rather than "contact", but...)

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Thanks for your response. Here are my inputs

1. The handset is not kept on the base cradle. I have physically wired them so that the contact issue is ruled out.

1. I am sure there is no issue with the contacts/connection with battery and the terminal connector on the PCB. Also if you note my description above, I have actually measured the current flowing into the battery and it oscillates between 0mA and 4mA. This shows there is no connection issue. Moreover, there is 22mA flowing through the zener all the times. In this situation, I am wondering if there would be any significant current flowing into the battery when the zener is conducting. Would the zener be not the least resistance path to the current instead of the battery directly in parallel ? Typically, as per design, should the zener be always be conducting across the battery ?

2. I am trying to find out the details of the SMD M6. Any clues ?

Its been more than a week and this instrument is still not fixed.....