Monday, July 27, 2015

First Gen Moto X (2013) screen replacement notes

Sorry, no photos.  If you're reading this, you're probably deep inside the phone already and wondering how the screen/frame assembly on one side gets moved to the screen you purchased on the other side.

The iFixit Repair Guide is excellent, but fails to discuss the nature of moving the frame over.  They also separate the frame from the screen without removing the pins - you can do this to get things apart, but they won't go back together like this.

There are 7 very small (0.5mm x 1.5mm, maybe) pins that hold the frame into the screen assembly.

They all need to come out.  You can push them out from the inside with a SIM tool or similar.  BE CAREFUL.  They will disappear if you let them wander - they're genuinely tiny!  I found that pushing them partway out and then using tweezers to grab them is the best way to remove them.  Put them in a bowl or something so you don't lose them.

When all 7 are removed, the frame will come free of the broken screen.

Push the frame into the new screen assembly, being careful to route the cables properly (the display connector goes inside the frame, not between the frame and the plastic).  The spaces for the frame are beveled, so you have to do this before you put the pins in.

Once the frame is in place, drive the pins back in from the outside.  Again, be careful or you'll lose them - they really bounce.  Tweezers work well, and you can finish driving them in with the flat part of a Torx driver or something.

Let me know if you find this useful!

Bypassing the Schwinn Tailwind Battery Management System

You might recall one of my previous posts about the Schwinn Tailwind battery pack.  In a nutshell, it's a 24v, 4AH pack built of Toshiba SCiB lithium titanate cells.  It's really a weird pack - but that's fine, because it's on a really weird bike.  I did some analysis of it, but wasn't willing to hack it up as it wasn't my pack.  So I fixed the glitch and bought the bike.  It turns out, ebikes with bad battery packs aren't worth particularly much.  I knew this, though.


Bad BMS - Bummer!

The problem with the pack I now own is a bad BMS (or a bricked BMS that won't allow anything to happen, because the batteries drained too far - same result).  The pack won't charge, and it won't discharge.  The BMS controls the normal charge and discharge ports with a set of power semiconductors of some form or another, and it's stubbornly refusing to run them.

Except... it does charge.  The standard charge port for home use (8A charger - 2C rate... *blinks*) doesn't work, but the bulk charger (40A... 10C charge rate!!!) does, and I can charge the pack through that with an external power supply.

An inspection of the BMS shows that if I were to add a few wires to jumper current around, I could get pack voltage to the output - and get the normal charger port to charge the pack as well.

So, of course, this being an absolutely terrible idea, I set out to do it.

Lithium Titanate Chemistry

The only reason I'm considering this otherwise mostly idiotic idea is because the cells are lithium titanate.  An extensive amount of research indicates that they're a very well behaved, safe chemistry that can actually be discharged fully without damage (unlike a lot of the other lithium chemistries).  They're a low energy density chemistry as well, and I'm not too concerned about running them in light duty without a proper BMS.  I wouldn't do this with other chemistries, though.  Consider this a special case for a particularly exotic pack.

Don't Do This.  Seriously, don't do this.  And if you do, I'm not responsible.

This is a terrible idea, bypassing a BMS like I'm about to.  You shouldn't do this.  You definitely shouldn't get creative with my steps and do it better than I did.  And if you do, I'm not responsible.

Seriously.  This is battery hacking at a level that simply doesn't need to be done.  Buy a 24v battery of some other type and hook it up instead.  Don't do this.

... so read on to find out how to do this.

Friday, July 3, 2015

Schwinn Tailwind Service Manuals

If you have a Schwinn Tailwind, you might be interested in the manuals for it.

The following links are for the assorted manuals associated with this bike.  Feel free to download them - Schwinn support will send you them if you ask.

Schwinn Electric Bicycles Manual Supplement

Schwinn Electric Controller Replacement Procedure

Schwinn Ebike Tech Supplement - Fuse Replacement

Schwinn Hybrid Pedal / Electric Bicycle Dealer Service Manual

Hopefully you find this useful!  If there are any other manuals you have, please comment and let me know where to find them!