SOLVED : dewalt battery powered radio - no power at board - Page 1
Forum section: electronics / repair

author: geoffagain
author_rank: Contributor
timestamp: July 21, 2023, 09:00:04 am
content: Hello, any clues on how to fault find thisPower 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 voltagesInput from battery is 20V fully chargedMeasuring 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.

author: Jwillis
author_rank: Super Contributor
timestamp: July 22, 2023, 02:44:13 am
content: Whats the model of that Dewalt radio. Might get lucky and find a circuit diagram for it.

author: geoffagain
author_rank: Contributor
timestamp: July 22, 2023, 07:26:18 am
content: Quote from: Jwillis on July 22, 2023, 02:44:13 amDCR012 - haven't been able to find a schematiclooks to be battery discharge protection

author: Jwillis
author_rank: Super Contributor
timestamp: July 22, 2023, 02:43:50 pm
content: 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.

author: geoffagain
author_rank: Contributor
timestamp: July 22, 2023, 03:45:02 pm
content: Quote from: Jwillis on July 22, 2023, 02:43:50 pmI made a typo it’s dcr021No ac on this deviceThis board handles battery input and outputs to main board via single connector

author: nali
author_rank: Frequent Contributor
timestamp: July 22, 2023, 04:14:46 pm
content: 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

author: geoffagain
author_rank: Contributor
timestamp: July 22, 2023, 05:16:52 pm
content: Quote from: nali on July 22, 2023, 04:14:46 pmYou 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 3Cleared it and re flowed the joints but still no joy, doesn't seem to have made a differenceSeems to have single cell voltage between pin 2 and pin 3Pin 3 16.42V - from battery c3 pinPin 2 20.5v - from battery + pinPin 1 is outputting 18.67v with reference to battery negativeU1 is marked B8PW

author: geoffagain
author_rank: Contributor
timestamp: July 23, 2023, 11:52:16 am
content: Ive had a go at drawing out the part of the circuit on the left hand side of the board

author: geoffagain
author_rank: Contributor
timestamp: July 26, 2023, 01:59:28 pm
content: Triple posting here - but if anyone has any pointers for testing / fault finding this circuit be much appreciated

author: nali
author_rank: Frequent Contributor
timestamp: July 26, 2023, 04:13:03 pm
content: 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.

author: geoffagain
author_rank: Contributor
timestamp: July 26, 2023, 04:39:26 pm
content: Quote from: nali on July 26, 2023, 04:13:03 pmSomeone over on badcaps mentioned it looks like aS-80830CNMC a 3v voltage detectorlooking up the datasheetS-80830CNMC-B8P-T2Series Seiko InstrumentsSOT-23-5Voltage detector IC3.0V±2%, -Reset ODONch open-drain output (Active Low)So should be passing battery voltage - like you say not some halfway valueI 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

author: geoffagain
author_rank: Contributor
timestamp: July 26, 2023, 08:02:49 pm
content: Tried a 1k resistor between pin1 and pin2passes battery voltage onwards but pmos still not turning onvoltage differential at the gate of the pmos with resistor is about -200mV

author: nali
author_rank: Frequent Contributor
timestamp: July 26, 2023, 08:41:17 pm
content: You'll need to be a bit more specific - what does "passes battery voltage onwards" mean?

author: fzabkar
author_rank: Super Contributor
timestamp: July 26, 2023, 09:06:07 pm
content: Quote from: geoffagain on July 26, 2023, 04:39:26 pmYes, that looks like it.https://www.aliexpress.com/item/1005003238903647.htmlhttps://ae01.alicdn.com/kf/Hb626592c16aa4522a51078f15211b2b3C/10pcs-lot-100-New-original-S-80830CNMC-B8PT2G-SOT23-5-Marking-B8PQ.jpg(photo)

author: geoffagain
author_rank: Contributor
timestamp: July 26, 2023, 09:53:13 pm
content: Quote from: nali on July 26, 2023, 08:41:17 pmSorry - 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.

author: fzabkar
author_rank: Super Contributor
timestamp: July 26, 2023, 11:25:03 pm
content: In your diagram you are showing R15 as 01E, 9Mohm. Should that be 01E, 1Mohm?https://kiloohm.info/eia96-resistor/01EAre 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

author: geoffagain
author_rank: Contributor
timestamp: July 27, 2023, 08:14:44 am
content: Quote from: fzabkar on July 26, 2023, 11:25:03 pmWell spotted! R15 is actually 0.986M ohm measuredResistor values as measured in circuit >J1 - 0 ohmJ2 - 0 ohmJ3 - 0 ohmJ4 - 0 ohmJ5 - 0 ohmPCB number - SMD - value - measuredR2 - 101 - 100 ohmsR3 - 205 - 2M ohm - 1.953M ohmR4 - 205 - 2M ohm - 1.875M ohmR5 - 205 - 2M ohm - 0.674K ohmR6 - 205 - 2M ohm - 1.958M ohmR7 - 88D - 806K ohm - 0.77M ohmR8 - 0 - 0 ohm - 0 ohmR10 - 101 - 100 ohm - 100 ohmsR11 - 01E - 1M ohm - 0.988M ohmR12 - 474 - 470K ohm - 0.470M ohmR13 - 205 - 2M ohm - 1.98M ohmR15 - 01E - 0.986M ohmR16 - 01E - 0.987M ohmR17 - 205 - 1.565M ohmR18 - 01E - 0.985M ohmR20 - 101 - 100 ohm - 100 ohmR21 - 88D - 806K ohm - 0.805M ohmR22 - 205 - 2M ohm - 1.829M ohmR23 - 205 - 2M ohm - 1.563M ohmR24 - 101 - 100 ohm - 100 ohmR25 - 01E - 1M ohm - 1M ohmR26 - 205 - 2M ohm - 1.951M ohmR27 - 01E - 1M ohm - 0.984M ohm

author: nali
author_rank: Frequent Contributor
timestamp: July 27, 2023, 08:44:04 am
content: Quote from: geoffagain on July 26, 2023, 09:53:13 pmSorry, 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.

author: geoffagain
author_rank: Contributor
timestamp: July 27, 2023, 10:14:38 am
content: Quote from: nali on July 27, 2023, 08:44:04 amOk 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 vssyou're correct with resistor added Q3 has Vss via R8, and VBat at R7/R4 and again at Q3/R13though still no output at output pins.

author: nali
author_rank: Frequent Contributor
timestamp: July 27, 2023, 10:43:50 am
content: 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.

author: geoffagain
author_rank: Contributor
timestamp: July 27, 2023, 11:09:56 am
content: SOLVEDReplaced NCE40P13S and have cured the issueR5 looked suspect measuring 674ohms vs expected 2M ohmsR5 is across the gate and source of NCE40P13SThank you to everyone who contributed to the thread and for your patience walking me through this one.