Spectra S1+ Repair

Received one that wouldn’t turn on even with the adapter plugged in. Unit opens up with 4 screws removed from base.

Quick check found the main power rail shorted, initially I thought it was a shorted TVS on the input, removal of the input TVS didn’t fix that, so I started looking around, that’s when I found a small burnt area on the PCB.

Towards the left is the burnt out component, nearby is a NCP3063, as far as I can make out it’s a boost converter (I didn’t know initially what it does until later). I couldn’t de-solder the FET normally as it had fused itself to the PCB track when it failed. Applying heat and leveraging it off the board the copper it was soldered onto de-laminated from the PCB itself. Luckily the source and gate pins came off the PCB ok (just the drain pins were affected).

As far as I can tell, the SMD markings point to the FET being a NTGS4141N (S4 marking code, 7 date code).

With the FET removed (I cut the dangling bit of the PCB off with a scalpel), I could actually power up the unit with the adapter plugged in (yeah!).

I then decided to check if the FET driver and NCP3063 were at least still operational.

Hooked up some insulated magnet wire to the drive to my oscilloscope.

That verified it was still working, also during this time I saw the drive only come on for a couple secs during initial power up, my guess is it’s used only during battery charging (the pack is a 3S 11.1V nominal battery, so it needs ~12.5V to charge it fully when the adapter only outputs 12V, and charging is done through a MAX1873, which I guess needs a couple of volts headroom to charge to ~12.5V)

Scrounging around in my parts bin I found a NTP18N06, which is fairly similiar in terms of drive requirements, but a little higher Rdson (90mOhm vs 21.5), since I had lost part of the PCB I figured the exposed TO220 package would probably be best for heat dissipation and there was ample room on the PCB to mount it on.

Yeah, the size/packaging difference is huge.

A quick solder job and viewing the drive on the oscilloscope + output voltage measurement, verified nothing was wrong, no smoke and the boost circuitry output voltage was present (~14.5V or so for a couple of secs, I tried hooking up the original battery pack to see if it’ll start charging and let me test this section for longer but the pack was too far gone).

I scraped off a bit of PCB on the ground plane, flipped the TO220 package around and soldered the source pin directly to the FET, ran some insulated magnet wire to the inductor and gate pin on the PCB, held everything down with Dow Corning 3145 (electronics safe RTV).

Next I turned my attention to the battery pack, which had a bloated LiPo cell, I couldn’t source an exact replacement 3S battery pack (it uses a built in BMS to balance the charge, there are only 2 wires coming out of the pack, so non of the usual RC type LiPo packs with external balance connectors will work safely, at least not without wiring up a BMS on it). I removed the bad cell from the pack and clipped a random partially charged 18650 to it, attempting to charge it the battery came back to life (the BMS had stopped any voltage from coming out the pack with the 1 bad cell)

Got my hands on 3x new Molicel P26A 18650s and I decided to keep the original BMS.

A bunch of spot welding and soldering later, I’ve got a working battery pack with the original BMS.

Here it is in it’s original spot. I’ve elected to tape the original labels within the machine in case somebody/someone else needs to know what was in it originally. With these new cells, I’ve verified it’s able to charge and stop properly, (cut off at 12.5V) and it should last a bit longer given the capacity has now increased (original 2000mAH, now 2600mAH).

Finally, I re-soldered the input TVS diode and closed it all up. 😁