SOLVED : dewalt battery powered radio - no power at board

[geoffagain]

Hello, any clues on how to fault find this

Power board not outputting voltage to main board.

Seems 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


Measuring with a fully charged battery finds battery voltage at the gate of the mosfet, nothing on the drain and full battery again on the source which doesn't seem right. Data sheet suggests a differential of -2.5v needed between the gate and source to switch.

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.

[Jwillis]

Whats the model of that Dewalt radio. Might get lucky and find a circuit diagram for it.

[geoffagain]

Whats the model of that Dewalt radio. Might get lucky and find a circuit diagram for it.

DCR012 - haven't been able to find a schematic

looks to be battery discharge protection

[Jwillis]

More likely includes battery charge controller . The  DCR012 is also a charger for 7.2V to 18V DEWALT battery packs when connected to mains AC.

[geoffagain]

More likely includes battery charge controller . The  DCR012 is also a charger for 7.2V to 18V DEWALT battery packs when connected to mains AC.

I made a typo it’s dcr021

No ac on this device

This board handles battery input and outputs to main board via single connector

[nali]

The PMOS needs a Vgs to switch as you say so it's probably OK. Try looking at the other end, U1 looks like it is probably a comparator so try tracing the components and checking around there.

Mind you, a replacement board is only ~£20 including VAT & postage, so may not be worth spending too much time on it...
https://www.sparepartsworld.co.uk/product/1004694-54

[geoffagain]

The PMOS needs a Vgs to switch as you say so it's probably OK. Try looking at the other end, U1 looks like it is probably a comparator so try tracing the components and checking around there.

Mind you, a replacement board is only ~£20 including VAT & postage, so may not be worth spending too much time on it...
https://www.sparepartsworld.co.uk/product/1004694-54

You make a good point, its a cheap enough board to replace but if I can get this one working for free then all the better.

Found a short on U1 between pin 2 and 3

Cleared it and re flowed the joints but still no joy, doesn't seem to have made a difference

Seems to have single cell voltage between pin 2 and pin 3

Pin 3 16.42V - from battery c3 pin
Pin 2 20.5v - from battery + pin
Pin 1 is outputting 18.67v with reference to battery negative

U1 is marked B8PW

[geoffagain]

Ive had a go at drawing out the part of the circuit on the left hand side of the board

[geoffagain]

Triple posting here - but if anyone has any pointers for testing / fault finding this circuit be much appreciated

[nali]

Assuming it is a voltage detector, I would expect the output of U1 to be either at it's Vdd or Vss pins not some halfway value. It may well be an open-drain output. What happens if you put a lowish value resistor say 1k between pins 1&2 (it may help to remove it first)

Oh, if you did have a short between pins 2&3 that would permanantly load the top battery cell via R2/R10 which isn't ideal although hopefully the battery charger/BMS can cope with it.

[geoffagain]

Assuming it is a voltage detector, I would expect the output of U1 to be either at it's Vdd or Vss pins not some halfway value. It may well be an open-drain output. What happens if you put a lowish value resistor say 1k between pins 1&2 (it may help to remove it first)

Oh, if you did have a short between pins 2&3 that would permanantly load the top battery cell via R2/R10 which isn't ideal although hopefully the battery charger/BMS can cope with it.

Someone over on badcaps mentioned it looks like aS-80830CNMC a 3v voltage detector

looking up the datasheet

S-80830CNMC-B8P-T2   
Series Seiko Instruments
SOT-23-5
Voltage detector IC
3.0V±2%, -Reset ODO

Nch open-drain output (Active Low)

So should be passing battery voltage - like you say not some halfway value

I can try adding a high value resistor between pin 1 and 2 - I'll report back.

Correct on loading the top battery cell, thankfully I've only used my batteries for testing this briefly and as theres no output from this board through the pmos should be drawing minimal current

[geoffagain]

Tried a 1k resistor between pin1 and pin2

passes battery voltage onwards but pmos still not turning on

voltage differential at the gate of the pmos with resistor is about -200mV

[nali]

You'll need to be a bit more specific - what does "passes battery voltage onwards" mean?

[fzabkar]

Someone over on badcaps mentioned it looks like aS-80830CNMC a 3v voltage detector

Yes, that looks like it.

https://www.aliexpress.com/item/1005003238903647.html

https://ae01.alicdn.com/kf/Hb626592c16aa4522a51078f15211b2b3C/10pcs-lot-100-New-original-S-80830CNMC-B8PT2G-SOT23-5-Marking-B8PQ.jpg (photo)

[geoffagain]

You'll need to be a bit more specific - what does "passes battery voltage onwards" mean?

Sorry - yes essentially passes Vdd to output via 1k resistor - doesn’t seem to affect gate voltage at the pmos at the very end of the circuit, or at least not enough to turn it on and have an output at the output pins of the board. Measured differential at the gate of the pmos was about -200mV with the resistor added.

[fzabkar]

In your diagram you are showing R15 as 01E, 9Mohm. Should that be 01E, 1Mohm?

https://kiloohm.info/eia96-resistor/01E

Are the "205" resistors actually "20S", in which case they would be 15.8 ohms?

https://kiloohm.info/eia96-resistor/20X

"88D" is 806K.

https://kiloohm.info/eia96-resistor/88D

[geoffagain]

In your diagram you are showing R15 as 01E, 9Mohm. Should that be 01E, 1Mohm?

https://kiloohm.info/eia96-resistor/01E

Are the "205" resistors actually "20S", in which case they would be 15.8 ohms?

https://kiloohm.info/eia96-resistor/20X

"88D" is 806K.

https://kiloohm.info/eia96-resistor/88D

Well spotted! R15 is actually 0.986M ohm measured

Resistor values as measured in circuit >

J1 - 0 ohm
J2 - 0 ohm
J3 - 0 ohm
J4 - 0 ohm
J5 - 0 ohm

PCB number - SMD - value - measured

R2 - 101 - 100 ohms
R3 - 205 - 2M ohm - 1.953M ohm
R4 - 205 - 2M ohm - 1.875M ohm
R5 - 205 - 2M ohm - 0.674K ohm
R6 - 205 - 2M ohm - 1.958M ohm
R7 - 88D - 806K ohm -  0.77M ohm
R8 -  0 - 0 ohm - 0 ohm

R10 - 101 - 100 ohm - 100 ohms
R11 - 01E - 1M ohm - 0.988M ohm
R12 - 474 - 470K ohm - 0.470M ohm
R13 - 205 - 2M ohm - 1.98M ohm

R15 - 01E - 0.986M ohm
R16 - 01E - 0.987M ohm
R17 - 205 - 1.565M ohm
R18 - 01E -  0.985M ohm

R20 - 101 - 100 ohm - 100 ohm
R21 - 88D - 806K ohm - 0.805M ohm
R22 - 205 - 2M ohm - 1.829M ohm
R23 - 205 - 2M ohm - 1.563M ohm
R24 - 101 - 100 ohm - 100 ohm
R25 - 01E - 1M ohm - 1M ohm
R26 - 205 - 2M ohm - 1.951M ohm
R27 - 01E - 1M ohm - 0.984M ohm

[nali]

You'll need to be a bit more specific - what does "passes battery voltage onwards" mean?

Sorry - yes essentially passes Vdd to output via 1k resistor - doesn’t seem to affect gate voltage at the pmos at the very end of the circuit, or at least not enough to turn it on and have an output at the output pins of the board. Measured differential at the gate of the pmos was about -200mV with the resistor added.

Sorry, I messed up yesterday, I meant to say bridge pins 1&3 not 1&2 with the resistor (was feeling under the weather which is why I was on here instead of working!). The o/p of U1 doesn't "pass through" anything as it looks to be an open-drain output so should basically do the same - bridging OUT & VSS when it asserts its output.

That should provide the PMOS (Q3?) with a Vgs to turn on via R8. (I think that the source of that FET i.e. junction of R7/R4 should be at VBAT +20V?). Then hopefully Q3/R13 node goes to VBAT.

[geoffagain]

Sorry, I messed up yesterday, I meant to say bridge pins 1&3 not 1&2 with the resistor (was feeling under the weather which is why I was on here instead of working!). The o/p of U1 doesn't "pass through" anything as it looks to be an open-drain output so should basically do the same - bridging OUT & VSS when it asserts its output.

That should provide the PMOS (Q3?) with a Vgs to turn on via R8. (I think that the source of that FET i.e. junction of R7/R4 should be at VBAT +20V?). Then hopefully Q3/R13 node goes to VBAT.

Ok I think I was looking at the cmos implementation, thanks for explaining.

So output is floating below 3v detect voltage or pulled down to VSS when above 3v detected, with a hysteresis width?

bridging pin 1 and 3 with 1kohm does pull the output to vss

you're correct with resistor added Q3 has Vss via R8, and VBat at R7/R4 and again at Q3/R13

though still no output at output pins.

[nali]

Looking at the datasheet for the Seiko/Ablic device it lookls like the o/p is pulled low when the battery is low, so looks like that end of the circuit is working. I'd expect the gate signal to pull up to VBAT so not sure about your 18.67V reading, probably your meter's internal Z affecting the reading.

You could temporarily remove R8 I suppose to isolate U1 & get on with fault finding.

Then back to the schematic I guess... it would make a bit more sense if you can redraw it in a more conventional manner once you've sussed out the physical connections.

[geoffagain]

SOLVED

Replaced NCE40P13S and have cured the issue

R5 looked suspect measuring 674ohms vs expected 2M ohms

R5 is across the gate and source of NCE40P13S

Thank you to everyone who contributed to the thread and for your patience walking me through this one.