Trying to use existing 18v li-ion charging cradle

I decided to do that as the power supply did not work and not being able to test other components on the pcb I felt it was destined for the bin in any case. A last resort you might say. I will replace the diode as they are very cheap but don't hold much hope. Looks like it's the 24v power supply with 5 schottke diodes in series is the next option.

 

Some success. I purchased a couple of 'ordinary' silicone diodes and desoldered the 'dead' diode from the circuit board and replaced it. The red led on the power supply now is lit and the output voltage is 21.2V - it is rated at 21.0v
I connected it to the charging cradle and connected a battery. BOTH the green and red led came on immediately indicating that it is fully charged and it isn't.
A short time later the green led was not lit indicating it is charging.
Could someone please explain why these batteries have FOUR pins (2 for the charge current but what about the other 2)?
Also the 'dead' diode is a SB5150 (I couldn't read that until removed from the board).
I have found that it is a schottke diode. Would it matter that I used an ordinary diode in its place which has a higher forward voltage drop.

 

Its an OZITO brand mode; LCD5000 which is the marketed name for a hardware chain in Australia and probably not available anywhere else.

The only equivalents I can find are the 1N5822 (DO27) and the MBR735 (TO-220).
They are rated at 40V 3A and 35V 7A respectively. The SB5150 is rated at 150V 5A.
The power supply has on its label that it is rated at 21V 1.4A.
Would the 1N5822 be ok?

 

Strangely when I changed the diode to a 1N5822 schottke the red led started flashing slowly (usually remains steady) and then stopped. I checked the diode and it was shorted in both directions just like the original one. I put the ordinary diode back and it works again and it appears to charge the battery ok.
Could there be something else wrong which causes the schottke diodes to short out?
What could go wrong using a normal diode instead of a schottke?

 

Could the 470uF 35V electro cap next to the schottke diode be causing them to break down (short out in both directions) - note that ordinary diodes don't break down.
I have learned that this one is commonly used as filters in devices in various power supplies to reduce the voltage ripple as well as input and output smoothing as an LPF.
I know that they can leak etc but don't know if it could cause the schottke to break down. Sorry my knowledge of most devices is limited.

 

Thanks Harald

 

Something strange
If I measure the voltage of the 18v li-ion battery with no load my multimeter displays 5.38 volts DC YES just 5.38V.
When I place a small load across the battery terminals (680 ohm - wire wound resistor rated at 5 watts) the multimeter displays 17.16 volts DC.
Could someone tell me the reason for this?