Panasonic PNLC-1029 charging cradle repair
Panasonic PNLC1029 charging cradle
How to fix and repair by Avi
This post relates to Panasonic charging cradle, charger unit model PNLC-1029, PNLC1029 OR PNLC-1035, which charges the handset model KX-TGA470 or alike.
Those cradles were supplied with telephone set models:
KX-TG7731, KX-TG7732, KX-TG7733 and possibly with other models as well such as:
KX-TG7741, KX-TG7742, KX-TG7743, KX-TG7745, KX-TG8561E, KX-TG8562E, KX-TG8563E, KX-TG8564E, KX-TG254SK, KX-TG294SK etc.
The symptoms, the fault:
The Panasonic handset does not charge as expected. The battery charging indicator does not show any level increase after few hours of charging nor does it show “Fully charged” status on its display.
DISCLAIMER – Important!
A. Check first:
First to check is the voltage over the cradle’s charging points.
If you get a reading that is different from 5.5VDC (much less or high), check and /or replace the power adapter (*). Proper voltage is 5.5VDC measured both on the power adapter’s DC plug and over the cradle’s contact points.
(*) In case you need to replace the power adapter, get the Panasonic PNLV226XX.
XX stands for different models of plugs and mains voltage (input). Select one that is suitable to your local mains voltage and plug. If you pick a non-Panasonic adapter, beware that it might transmit interference to your system, especially if used in the base unit. For using it with the charging unit only it might be OK.
Voltage is not the only parameter that counts. It can be OK while still not charging.
The problem in this case is with the amperage draw.
When measuring the draw amperage of a non-charging faulty cradle, the result is much lower than the correct ~200mA draw and this is usually the cause for a non charging cradle.
B. The fix
1. Disconnect the power adapter from the mains and disconnect the cradle unit from the power adapter!
2. Remove the single screw on the cradle’s bottom part.
3. Open and separate the cradle’s housing parts in a rotational move.
4. The opened cradle reveals a small PCB model TH165B PNLB2081ZA-IG with 4 components:
A fuse marked F1, 2 resistors marked R1 and R2 and a diode marked D1
In most cases the cause for the charging malfunction is a bad D1 diode solder contacts or a faulty diode.
5. The D1 diode is an SMA/SMD type marked M2S with a package size of 4.0×2.7mm (the preceding numbers are manufacturing date).
According to Panasonic’s service manual of model KX-TG7731, the diode part number is B0ECKM000008. I couldn’t locate any official document of its specifications.
6. First try to fix it by re-solder the diode contacts.
7. Re-assemble the cradle’s parts and charge your handset for several hours to test if it works OK.
If it is charging OK and reached to 3-lines battery icon with “fully charged” display note, you have fixed the fault and this is all you need to do.
But if it does not charge, follow next steps:
8. Replace the diode.
You can use a replacement M2 SMA/SMD diode or use a through hole 1N4002 diode which you’ll need to bend and trim its legs in order to fit the existing PCB’s pads.
See this datasheet for the specs of SMA diodes by SYC for example.
See this datasheet for the specs of through hole diodes by Fairchild for example.
Remove / desolder the existing diode and solder the new diode to existing PCB’s pads.
Note: Pay attention to the diode polarity. It is clearly marked on the PCB.
Tip: If you can’t obtain the needed M2 or 1N4002 diode, you may use M1 or 1N4001 instead. That will work OK as well.
9. Re-assemble the cradle’s parts and charge the handset for several hours to test if it works OK and reaches 3-lines battery icon with “fully charged” display note.
If it did, you have fixed the fault.
If after ~7 hours of charging the charging level did not increase or increased but did not reach the 3-lines level nor the “fully charged” state is displayed, replace the batteries and try again to charge it.
Note: Use only 2x AAA Ni-MH rechargeable batteries.
A simple and very low cost fix which will allow your Panasonic charging cradle to work properly for years to come.
Enjoy your phone,
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