dewalt battery powered radio - no power at board

[geoff69]

Hi hoping you can point me in the right direction

Powerboard not outputing voltage to main board.

Looks like battery voltage comes in and runs through a battery discharge protection circuit triggering a P-Channel Mosfet NCE40P13S for output to main board.

Uses C3 pin on battery which I think is one of the cell voltages


Input from battery is 20V fully charged


Seems like there is full battery voltage at the gate of the mosfet, nothing on the drain and full battery again on the source which doesn't seem right.

The two diodes on the output of the mosfet seem to be ok.

Some of the solder points look balled - but compared to other boards ive seen this seems to be common or from factory?

Any tips on fault finding and understanding the way this circuit works please would be appreciated.

[stj]

Re: dewalt battery powered radio - no power at board

what are the 4 large center pads for?
i can see something was pressing onto them.

[geoff69]

Re: dewalt battery powered radio - no power at board

Nothing, test points?

Here are images of the reverse of the bird and also the board in situ showing no contact with anything else

what are the 4 large center pads for?
i can see something was pressing onto them.

[CapLeaker]

Re: dewalt battery powered radio - no power at board

Probably it’s not getting the command to turn on. Check things like the power button and that circuit going to the controller

[geoff69]

Re: dewalt battery powered radio - no power at board

Probably it's not getting the command to turn on. Check things like the power button and that circuit going to the controller

There's no comms going to the board, just a two pin output - no enable signal

The fet needs a differential between gate and source to turn on - spec says typical -2.5v

Tested it has battery voltage at both

[CapLeaker]

Re: dewalt battery powered radio - no power at board

Aaah! Gotcha! It’s just a plain battery low voltage cut off board. Well, with 20v on the gate of a p channel mosfet, yes, she will not switch. The gate drive Q5 and Q6 are mosfets too. They use the mosfet as a switch. Not sure if you looked at these resistors yet.

[geoff69]

Re: dewalt battery powered radio - no power at board

Aaah! Gotcha! It's just a plain battery low voltage cut off board. Well, with 20v on the gate of a p channel mosfet, yes, she will not switch. The gate drive Q5 and Q6 are mosfets too. They use the mosfet as a switch. Not sure if you looked at these resistors yet.

all resistors look sensible values

found short between two pins of the little (sop25?) 5 pin ic

re flowed and removed the short but still not joy

anyone know what this ic is and what its doing?

Marked B8PW but google isn't having any joy

[CapLeaker]

Re: dewalt battery powered radio - no power at board

maybe do some measurements on these pins

[R_J]

Re: dewalt battery powered radio - no power at board

It seems to be a S-80830CNMC voltage supervisor 3V , pin 2= Voltage input pin 3= ground

[geoff69]

Re: dewalt battery powered radio - no power at board

maybe do some measurements on these pins

Seem to be same as initial measurements

on a fully charged battery >

pin 1 - 18.67v
pin 2 - 20.5v
pin 3 - 16.42v

[geoff69]

Re: dewalt battery powered radio - no power at board

It seems to be a S-80830CNMC voltage supervisor 3V , pin 2= Voltage input pin 3= ground

ahh interesting

if thats correct it would make sense that it uses the differential between battery + and pin c3 on battery to detect single cell voltage and cut off if below 3v?

on a fully charged battery I have >

pin 1 - 18.67v
pin 2 - 20.5v
pin 3 - 16.42v

Vdet is essentially 4.1v in this case referenced to battery pin c3 rather than battery negative - and I'd expect VOut to follow Vdet which it isn't?

The short I had between pin 1 and pin 2 shouldn't have caused a problem other than turning it off - is that correct?

[petehall347]

Re: dewalt battery powered radio - no power at board

try measure voltages using pin 3 as reference .

[geoff69]

Re: dewalt battery powered radio - no power at board

try measure voltages using pin 3 as reference .

in which case we have

4.1v VDD Pin 2

3.7v OUT Pin 1

[geoff69]

Re: dewalt battery powered radio - no power at board

I've tried to draw out the circuit from the left hand side of the board

I've taken the values of the resistors as measured and they're close to the smd codes

transistors are two channel p and an n

Is it any help? I can't follow whats happening

[CapLeaker]

Re: dewalt battery powered radio - no power at board

I suggest you read that datascheet of the voltage detector very carefully. There is a theory on how this thing works, simple test circuits etc. what happens if you use a pull down resistor on the output?

[geoff69]

Re: dewalt battery powered radio - no power at board

I suggest you read that datascheet of the voltage detector very carefully. There is a theory on how this thing works, simple test circuits etc. what happens if you use a pull down resistor on the output?

From what I can tell >

If it is that particular voltage detector and not something else …

There is a voltage detect value in this case defined at 3v with upper and lower hysteresis values to prevent oscillation. Vdet being 3v with min -Vdet and max +Vdet

If vdd is below operating voltage the output is undefined

Otherwise output follows Vdd or Vss depending if Vdd is above or below Vdet - switching on the upper and lower bounds of +-Vdet values

Test circuit just seems to be a 100k resistor between output and Vss

I can't see a scenario where output is somewhere between Vdd and Vss as measured unless it's below operating voltage and therefore undefined or floating about?

There's a good chance I'm missing something obvious though so I am more than open to being corrected

[geoff69]

Re: dewalt battery powered radio - no power at board

SOLVED

Replaced output pmos NCE40P13S and now working

R5 looked suspect as measured only 674ohms vs expected 2M ohm and is across the gate and source

Thanks for all your help

[CapLeaker]

Re: dewalt battery powered radio - no power at board

Awesome!

[stj]

Re: dewalt battery powered radio - no power at board

now the only remaining problem is finding something worth listening to.
although if it's used in London you have all the R&B stations.

[geoff69]

Re: dewalt battery powered radio - no power at board

now the only remaining problem is finding something worth listening to.
although if it's used in London you have all the R&B stations.

Hah, I think it'll be getting a bluetooth board stuck in it now, its got an aux input I can commandeer - if I can find a 5v rail on the board I'll stash it inside somewhere