Repairing a 24V NiCd charger

[evoiii90]

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.





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 ( https://goo.gl/1FHGf5 )
IC: Texas Instruments; 8AH5V9K E4; CD4060BE ( https://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 ??

Thanks...

 

[KeepItSimpleStupid]

Top of my head, the X1 may be a fuse covered in heat shrink. Remove the heat shrink.

Could also be a resistor or an inductor.

The k623 is a likely a 2sK623, a transistor.

 

[Allen6502]

2SK623 is in a TO247 package 20A mosfet. But the TO92 transistor looks more like a NPN transistor S8050 and the complement is S8550.

See datasheet here
https://pdf1.alldatasheet.com/datasheet-pdf/view/83743/ETC/C8550.html

I have redrawn the schematic as attached and it is clear that the 4060 acts as a timer and just charge the battery by a pre-determined time when the charging starts. The only protection during charging is a fuse to prevent over current.

Allen

 

[evoiii90]

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.

Interesting the charger doesn't account for the battery charge and just charges it for a determined amount of time. Although the circuit might do something else too since when the battery pack is fully charged, the charger doesn't stay on for long, just a couple of minutes max. Maybe there is something else on the circuit that measures actual battery charge and overrides the timer.

Either way, thanks for all the help and for redrawing the circuit.... This is why internet forums are great, and I just found another one very good one like edaboard.com