Monday, December 3, 2012

Fixing a Viewsonic Viewpad 7 with flashing red charging indicator

Had one of these land in my lap from my cousin, the unit would not power on. Hooking the adapter up to the unit will just cause the power LED next to the switch to just keep flashing red and no button inputs result in anything.
Tearing apart the unit was pretty simple. A stiff plastic card was used to carefully separate the back from the tablet. You wanna be careful doing this as the plastic is rather thin in some spots.

Viewsonic has helpfully left some voltage probe points right next to the battery connector for easy troubleshooting. In my case the battery read 2.5V, way under the nominal Lithium Ion/Polymer voltage of 3.7V. I suspect the unit might have been left to drain for a long time.
Hooking the charger/adapter to the tablet overnight didn’t charge the battery one bit, so I went hunting for a suitable replacement battery.

A shot of the new battery that I found locally (top's the old deadish battery). The original battery was 3250mAH. The new replacement was physically smaller in terms of width and length, but slightly thicker. I confirmed that it’ll fit in before purchasing it. The only drawback was that it had a capacity of 3000mAH, so I expect to have slightly less battery life compared to before. Oh well. The replacement battery costed me around USD$25. I’m sure with enough hunting around I might be able to find a better replacement, but for this price I think it can’t be beat.
The protection circuitry that resides on top of the old battery needed to be swapped over to the new cell, so I proceeded to cut the insulating tape and pull that off.

The new cell came with some circuitry as well, but since it won’t work with the Viewsonic tablet, it’ll have to go.

A picture of the protection PCB that’s going to be transplanted.

At this stage I had used a pair of pliers to carefully undo the battery tabs that were spot welded onto 2 metal plates soldered to the PCB. Then used a high power (about 60W) iron to remove the plates since I was going to solder the tabs to the PCB. I believe the plates are just there to let them spot weld the battery tabs onto the PCB.

Here’s a picture with one of the battery tabs soldered to the PCB. The tabs on the new cell are in a different position from the old, so I had to solder one end and jumper the other to the right pad on the PCB.

There’s the positive end that’s jumpered. I used 2 thin wires to try and increase the current carrying capability without compromising on the battery’s thickness too much.

Battery’s finally all done up and taped together. I just used some packing tape.

Installed and lying sideways inside the provisioned battery space. At this point even though the cell measured 3.8V, I didn’t measure the same voltage on the tablet’s test point. I tried plugging in the adapter and powering on the unit, lo and behold the screen came up and the test points measured 3.8V. I‘m guessing the electronics on the protection PCB can actually stop current from reaching the tablet (shutoff the battery totally) to prevent draining the battery too deep when it’s flat.

After confirming it works. I applied a little Dow Corning 3145 to the underside of the battery to secure it to the tablet. Wouldn’t want it shaking around inside.

Not forgetting the SIM+MicroSD protective cover, I re-assembled the tablet.

There it is, looks just like before.

Uhhh, not too sure what kinda wallpaper that is, but it works.

And it charges… Open-mouthed smile

Wednesday, July 25, 2012

Broken Logitech G25 Part II

Finally got the parts in the mail, I left the G25 disassembled the whole week and it was lying on my room floor, starting to get a little obnoxious. Here’s a shot of the broken FET.



I ordered 2x both N and P channel dual FETs, although only the IRF7103PBF was actually shorted on mine.



Proceeded to solder the replacement in.



I just held it on top of the pads and tacked on corner on. Then adjusted the whole IC until everything lined up and completed soldering it on. Not the cleanest job, because some of the pads on the board have no mask, so it looks like a couple of pins are shorting, but electrically it’s alright.

I then proceeded to re-assemble the motor and linear gear together.


I left the wheel installation out till I could see if the wheel would fire up and calibrate. During re-assembly I just put the linear rack gear somewhere in the middle and ta-da, it worked during power up and could calibrate properly.

There was a little bit of arcing and smell from the cleaned up motor though, I suspect the brushes haven’t bedded in properly yet. I then plugged and unplugged the wheel a couple of times to get it to cycle the calibration process more and that fixed itself. There was also some cogging present initially, that’s also fixed.

Proceeded to finally play some GT5. Open-mouthed smile

Tuesday, July 17, 2012

Broken Logitech G25 Part I

Wanted to play a little GT5 over the previous weekend. Hooked everything up and turned the PS3 on.

The G25 normally does a little calibration routine at the start, but this time it did a little quarter turn and sat there motionless. Power LED on the shifter just kept blinking, I thought WTH and decided to try rebooting the PS3. Nope, this time it wouldn’t even move and just kept blinking.

Plugged it into my PC, and everything works, except the wheel. I’m guessing without the calibration routing, the wheel axis will not work.

Measured the power coming out of the adapter and it was a stable 24V, as per the spec on it’s label.

Next I tore into the wheel itself to do a little poking around.

The 1st thing I suspected was the motor driving circuitry. Disconnecting both motors and probing around the vicinity confirmed that I was right, one of the dual MOSFETs in the IRF7103 was a dead short.

Proceeded to remove the FET and see if it’s really dead, or something else on the board had died.


Yes it was dead. Removed and re-probing with my trusty DMM confirmed that. I put both the FETs on order (IRF7342 and IRF7103) thru RS-Components (actually only the IRF7103 had fried, and it was a single FET in the dual FET package).

I then decided to find out what exactly killed the FETs, wouldn’t want my replacement to go up in smoke the second I powered it on, why did the wheel turn 1/4 way before coming to a stop?

Removed a couple of screws and disconnected a bunch of stuff to get the gearbox and motors out where they could be comfortably moved around. I then decided to probe the resistance of both motors.



Here you can see that one motor has an encoder (where I guess the wheel actually gets it’s axis signal).

A pic of the reading I got from the motor with the encoder on the back. This is the min resistance (I spun the motor slowly by hand and used the DMM’s min function).


One of the ‘other side’


I pulled the motor leads out of it’s connector and tried using the power adapter itself to power the motor with the encoder. Bad idea, a whole bunch of smoke came out of the commutator area and the motor just jerked a little and sat there pretty, whilst more smoke poured out. I quickly disconnected the wires.


Can’t really see the commutator in this pic, I then disassembled the whole motor so I could see what was going on inside, initially I suspected that maybe a winding was somehow shorted or the brushes were somehow shorting together.


Here’s what I saw after prying the back out. Look at the gaps in between the comm segments. A mixture of oil,grease and carbon has built up inside and I’m guessing is the cause of all the problems I’m having.

I dug through my drawer and found a little pin that was small enough to fit into the gaps and used that to clean it out. Together with some contact cleaner.


This is the amount of crap that flowed out.


All that black stuff came from the commutator. After cleaning I measured the resistance again.


Not too bad I’d say, pretty close to the other motor. For that motor I just sprayed a little cleaner into the comm through the side gap and called it good.

Piecing the thing back together. I had gouged the end ‘tabs’ a little during the disassembly, and ended up just using a small punch to wack 4 tabs back on afterwards, seems to be tight enough to me.


I also noticed a little crack on the encoder wheel and used a little bit of CA glue to stick her back together. The wheel just slides onto the shaft and is held there with friction.


Look forward to Part II where I replace the fried MOSFET and try powering her up! I have the parts on order right now and am waiting for them to arrive.

Sunday, July 8, 2012

Gigantic Hiberfil.sys in Windows 7

You’re reading this coz you have a tiny (40GB) SSD like me for the OS drive and there’s a gigantic (mine was up to 12GB before I had it removed) hiberfil.sys file and you want it gone to free up some much needed space? Fear not, this post is for you.

As far as I can tell, hiberfil.sys let’s your PC Hibernate, Windows will use hiberfil.sys to store it’s current state, and since windows is managing it, you can’t delete the file. Until you do the below steps of course.

Open up an administrator mode command prompt, and put this in.

powercfg -h off

You should immediately notice the Hibernate option gone from the shutdown menu, as well as, TADA, a bunch of free space on your C: drive (the file hiberfil.sys should also be gone from the root directory).

Note: I forgot to take screen captures of the process, sp yes you’d have to put up with a wordy post. Sorry.

Sunday, June 3, 2012

Cool Manga guide to SMT

Found this while surfing the net the other day. I think its really cool and a good idea. Should help those getting started into SMT soldering. Best of all, it’s free.

It kinda reminds me of this one.


Saturday, May 19, 2012

Quieting a whining inductor/SMPSU transformer.

I recently got a little Li-Ion charger that’s based of a SMPSU. It had the nasty habit of whining during charging though (it’s loud and annoying).

I decided to tear it apart and see if I can pot it in some epoxy. Of course best results would be if I could put the whole thing is some sorta vacuum to get rid of any voids and air bubbles. I didn’t have that handy, so I used some slow setting epoxy that’s very fluid.


Here’s the charger disassembled. The topside


And here’s the bottom, I then desoldered the little switching transformer that’s making all the noise.


Here’s that pesky transformer


I then used a little masking tape to form a crude sorta mold, keeping all the epoxy from flowing all over the place. Here I have poured in the epoxy


Here the epoxy has cured and I’ve taken the tape off. Seems to have covered everything.


I then assembled everything and tested the charger out. Glad to say a lot of the whining has been removed. I now need to put my ear up next to the charger to hear a perceptible whine.

Monday, April 30, 2012


I found these pictures on an old harddrive when I hooked it up today.


Enjoy Smile with tongue out