Fixing a BC-900

[TomBrown]

I have a BC-900 with a bad slot. The voltage never rises above 1.28v in that slot. The other three slots work perfectly.

It looks like the film resistor has a chip out of one corner. I'm thinking about replacing it and see if that does anything.

Others have had bad slots. Has anyone managed a fix?

Also, does anyone know what value the film resistor right at the bottom of the positive charge connection is? ... or how to read a film resistor?

 

[dta116]

Here is the color code chart for resistors.http://www.pmel.org/Handbook/HBpage26.htm

It seems to me you should have seperate resistors for each channel?

Good luck!

 

[TomBrown]

Yes, seperate resistors for each channel.


Thank you for the link. :)

 

[tacoal]

There are three groups of resistors connected the positive terminal of battery.
one is 473, means 47K
the other is 5 1R00(1.00 ohm) in parallel for sampling charging current.
the final group is 4 7R50(7.50 ohm) in parallel for discharging load.

It seems the registers are good. The problem comes from the MOSFET or its control loop.

The reason will battery could go to 1.28V is due to the 47K resistor. It changes the battery even the MOSFET is off although the charging current is about 0.06mA and due to the small current, the battery can just go to 1.28V.

This means the real charging loop is not functional.

 

[TomBrown]

Thanks, tacoal. :)

I'll try to post a picture of the MOSFET later. I think it's a tiny device with numbers like 443J... but they're too small for my old eyes to read. That device has a piece missing from it's corner but I don't think the die is exposed... just the lead into the package. Still, I wouldn't mind replacing that item.

 

[tacoal]

The MOSFET is a NTGS3443T1 from ON semi. The datasheet is in http://www.onsemi.net/pub/Collateral/NTGS3443T1-D.PDF by google but the site seems dead for me. However, you could get it from http://pdf1.alldatasheet.com/datasheet-pdf/view/99877/ONSEMI/NTGS3441T1G.html