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Repairing a 24V NiCd charger

Thread starter #1
I'm trying to repair a 24V NiCd battery charger with my very, very limited electronic skills... The charger stopped working after using an old and dead battery pack, ie, battery with no charge at all. Probably making the charger drawn too much current.

The battery pack powers an impact drill, so it's a high current 24V battery pack which has 14 x 1.5v x 1300mAh cells inside.

Since the circuit looks relatively simple I decided to draw a schematic following the PCB and components. Attached here along with pictures front and back of the PCB.

Diagrama Cargador.jpg 20140622_190436.jpg 20140622_190454.jpg

Besides the basic components like diodes, resistors and capacitors, I found some info on the relay and IC:
Relay: MINI RELAY SPDT 5 PINS 5VDC 10A 120V CONTACT ( http://goo.gl/1FHGf5 )
IC: Texas Instruments; 8AH5V9K E4; CD4060BE ( http://goo.gl/SiYQk4 ) "Counter ICs 14-Bit Ripple"

There are a couple of components I couldn't find any info.
- One with 3 pins marked "BG" on the PCB, which looks like a transistor/triac. Top/Right of the diagram. It has the following labels K623 C8550 (or CB550) D. Couldn't find anything on Google.
- The one with a green arrow which looks like a inductor/filter or some sort. Top/Left of the diagram with the question mark inside. I'll call it X1, although I didn't label it on the diagram, nor it has any marking on itself. The PCB has a label of D00 or DOO under it, but not sure since it's not clear.

Here are the few test/results I did/got:
- Transformer and rectifier works. I get 26 VDC after the rectifier.
- All diodes test good, ie, no shorts, opens.
- I get +24V at the + side of the green LED. This LED should be ON as soon as the charger is powered.
- I don't get any continuity for X1 itself, and I only get +0.5V at the other end of X1 and +24V at the rectifier exit.

Based on this it might be X1 (D00), but since it doesn't have any markings, I cannot replace it at least to test the whole thing.

Any suggestions on what to test / look / do ??


Ian Rogers

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I don't understand..... The relay is a 12v relay not 24v or 5v..

The third battery contact is for the internal temperature sensor and is not connected to the negative side of the battery....

As there is no regulator for the IC, I think this is a 12v nicad charger circuit??? As for the component, Its either a fuse or a choke..
Thread starter #3
Yep, it's a T3 15A 250V fuse... For some reason it looked like an inductor to me instead of a plain fuse, which would have been obvious to change.

And yes, the relay is a 12V one, but the circuit battery is definitively a 24V one...

Did you ever work this out?
The board looks the same as the one out of my Machine Mart charger that has stopped just like your's, same burn marks on the board.
I replaced the 4 rectifier diode's and fuse, and it powers up just fine but blows as soon as you put in a battery.

I don't have enough knowledge to go forward from here. any and all help welcome.

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