Repair of Ryobi BCL14181H Li-Ion charger

[GraemeG]

Success! The charger is repaired and has charged a battery. Just one battery charged so far and time will tell how reliable the repair is, but I am fairly confident.

As I suspected in my last post, the final repair was just the replacement of D3/D9 and Q2. I used the MBR20200CT dual schottky diode to replace both D3 and D9. See the attached diagram but this device is a diode pair in a common cathode arrangement in a TO-220 package. Each diode has a current rating of 20A so much higher than the original 5A rating for each of the MBR5200 diodes. Just one half of the pair in the MBR20200CT should handle the job but the holes are in the board so why not make use of both. Yes I know it's not good practice to use diodes in parallel but there is no harm, there may be some current sharing because the two diodes are probably on the one silicon die and should have very similar characteristics, and the component is physically more stable using all 3 legs.

I also added a small piece of aluminium as a heatsink as it seems these diodes generate more heat that anything else on the board. The average current through these diodes is much less than the 5A rating of the original diodes but I suspect that the heat generated by the switching process is what tends to kill these diodes so anything we can do to keep them cool is probably a good idea.

This charger failed during the summer months in Australia. It was located in a garage, in the shade, but it may have been quite warm in there when it failed. I wonder whether this is a factor in the failure of these chargers?

A couple more suggestions before I finish:
 - Despite being careful, I somehow damaged the track between R12 and the gate of Q2 when I had unsoldered Q2. This track runs underneath Q2. Q2 was so cracked that it came off in 3 pieces and yet the track was broken. I am not usually heavy handed so be gentle when removing the dead MOSFET. I used a single stand of wire from some multi-strand hookup wire to bridge the gap.
- If you use a heatsink like this be careful of the ferrite bead FB1. Speaking from experience, it can short out against the heatsink which is connected to the tab of the diode package. Luckily no damage done!
- Not shown in these photos but I glued a small brace from the heatsink down to the board to make the whole thing more stable (and to make sure it never makes contact with FB1 again!!)

So in the end, once I had the replacement parts, this was quite a straight forward repair.

[Amir]

Used to do Electronics in last century. Some help needed.
I am getting close to 60V on charging leads.
When plugged in red light is blinking normally.
Resistor in photo looks burned and there was some oxidation in the area. Any suggestion is appreciated.

UPDATE
Light is steady red when no battery is inserted.
With battery charging it flashes intermittently, green - red

[GraemeG]

Hello Amir. 60V seems much too high! Looking at your photo it appears that some liquid has been on the board and caused the corrosion. I have seen this type of corrosion before, it looks like electrolysis. Perhaps some water found its way into the charger while power was on.

First, be careful of the high voltages on the circuit board! Depending on your fault there could still be a high voltage on the primary capacitor LC1 even after you have unplugged the charger.

If you are measuring a voltage on the output terminals then it seems likely that the switching transistor Q1 and its driver circuit are still working to some degree but 60V is too high. With no battery connected I measure 0V on the battery charge terminals and 4V on both the T1 and T2 terminals.

I would start by cleaning the corrosion as much as possible and remove and check any components that have corroded leads. I have seen electrolysis eat completely through component leads and circuit board tracks so each corroded component should be tested and the tracks carefully checked. The 4 pin IC in your photo is PC1 the LH1520 optocoupler that provides feedback from the low voltage secondary side of the transformer to the high voltage switch made up of IC1 (6853) and Q1 (NDF04N60). If the optocoupler is damaged then the output voltage will not be correct. Also check the components that feed the input to the optocoupler, ZD4 D5 R27 ZD3 R62 etc.

Can you take pictures of the whole board from both sides? I would also check the parallel diodes D3 & D9 and have a close look at the surface mount MOSFET Q2 on the track side of the board.

In case you haven't noticed it, check Greybeard's post #21 which has a link to a full circuit diagram for this charger.

[Greybeard]

There is no way I would repair a PSU in this miserable condition:



No one can guarantee your safety (insulation resistance, etc.).
I would throw this unit away and try to get a used one in better condition.

[GraemeG]

Good advice Greybeard

[Amir]

GraemeG - I got the diagram. Optocoupler I am ordering and more cleaning is coming prior to posting additional photos. (found 10 pack optocoupler for $5, and have no clue what to do with other 9 once this is replaced :-)
 Originally I was trying to post photos directly from the phone but they are too big.
Once it is vacuumed and images resized I will post other photos.
Rest of the board looks OK.
Eyes are not as they used to be so details are better through the camera.
Thanks everyone for input. (as for the throwing it in the trash - I would too. 220V units are expensive and wort thing is that I got it from flea market for a friend and now I feel bad for wasting his money -  hence trying to repair it)

[Amir]

As promised. Photos of the board before I start removing parts for verification. Will update this post with defective parts list. (Limited testing capabilities)
Nice to be getting back baby steps in electronics world

[fzabkar]

I would get red of that glue. It becomes corrosive and conductive with age.

Nice clean up job, BTW.

[GraemeG]

Yes clear the glue from around the optocoupler, ZD4 and the other corroded components. The bottom of the board looks clean and clear of any corrosion so that is promising.

You have a slightly different version to mine and others but I think the circuit diagram is probably still very close. If you compare yours with the photo in the very first post of this thread you can see that instead of a pair of separate diodes D3/D9 to rectify the secondary of the transformer, you have a single TO-220 package mounted with a small aluminium heatsink. This is a much better solution and this is how I set up mine when I repaired it.

The TO-220 package will almost certainly be a pair of diodes in a single package. You can check these 2 diodes using most multimeters using the diode test function. Fully testing ZD4 is a little harder but it is probably a 30V zener so should act like a normal diode as far as a multimeter is concerned.
You can test the optocoupler with a multimeter on diode test across the transistor (receiving side) and a second multimeter or even a battery and a resister to drive the photodiode on the transmitting side.

I just noticed in your first picture posted 3 days ago that the component beside ZD4 looks like a 3.15A fuse. On my version this is just a wire link but you should test it and replace it with the correct fuse if it is open circuit.

Also very carefully check CF1, RF1 and the link beside them. These are on the primary side of the transformer and look very corroded.

[GraemeG]

Amir can you read the part number of the TO220 package diode with the heatsink? I can see a date code of June 29, 2015 on the top of your board so this is a newer version than mine. My charger has a serial number  005624 and was made in week 4 of 2014 according to the label on the outside of the charger. What is the build date from the bottom of your unit?

It would seem that Ryobi has realised the weakness of the D3/D9 parallel diode pair that frequently fails. I am curious to hear what diode they have chosen to replace this pair.

[Amir]

At this time I removed primary side CF1 and RF1. Cleaned the board and will install new parts. Also replacing rusted link above them.

Removed ZD and fuse. Cleaned and will be getting new parts also. (ZD broke before removing so even if good it had to go :-) )

Optocouples for sure is gone. All connections cleaned for new one to be installed.

Charger was made in 44 week of 2015

Information from package diode is as follows
BYQ28E
200
PJA1524  B7
9863 (or 9663)
I will try measuring it and worst case scenario replace it too. No oxidation on that area.

[GraemeG]

Thanks Amir. The BYQ28E-200 is a 200V 10Amp dual common cathode diode. Definitely a better option than the two discrete 5A diodes that were originally in my version. And the heatsink is an improvement too.

Personally I still prefer the MBR20200CT as it is a schottky diode with a lower voltage drop and so a lower power dissipation but the BYQ28E-200 is still a good choice.

[GraemeG]

It has been pointed out to me that I had incorrectly listed the replacement I used for Q2 (P-Ch MOSFET 9565) as IRFR5303 when in fact it is IRFR5305. I have edited the 2 posts where the incorrect number was used.

There was also a question about the value of C4 (I assume used for transient suppression across the rectifier diodes). The print was quite faint on the two units I have looked at but I believe it is a 470pF 1KV ceramic capacitor. The marking is 471 which is code for 470pF. The attached photo is the best I can do without removing it but I'd be happy if anyone can confirm the markings.

[Amir]

Replaced oxidized parts. In electronic store they did not have 82kOhm resistor (installed 100k instead) and capacitor - they had ceramic)
Voltage on charging points is now 16 v and 3.9 with middle connector.
Charger now blinks red in stand by.
I will obtain correct replacement parts and verify again.
@GraemeG - when I get it back I will provide image of the capacitor in question.

[vanhien771354]

Hi all, i want to ask what is 6 pin IC ?? I dont recogize it

[GraemeG]

The surface mount 6 pin IC1 is a CR6853. I found the datasheet here https://datasheetspdf.com/pdf-file/789117/Chip-Rail/CR6853/1 but there are other sites that have it too.

[vanhien771354]

Hello all, I have some problem I replace IC1 CR6853  =  QWP36R
and I using VOM C3 just 14v, C25 same 14v . It working

[vanhien771354]

Hello all, I have some problem I replace IC1 CR6853  =  QWP36R
and I using VOM C3 just 14v, C25 same 14v . It working

thanks 

[p.larner]

so what goes here,started with waynes world them to graem them amir,so is this 3 threads rolled into one?,if so it needs to stop,gets hard to follow,why cant they post there own threads rather than hijack one?,who is with me on this??,merry xmas all.