Archive for April 21st, 2010
The classic failure mode for a Palm Zire 71 is to stop charging. This might happen when the lithium-ion battery craps out and needs replacing, but the flex circuit between the cradle connector and the main board seem to go bad around that time, too. That’s what eventually killed my first Zire, so after I stuffed a new battery in the second, I tried fixing the first.
Here’s the flex circuit in its natural habitat (photo from the second Zire).
Here’s a picture looking down along the inside edge of the connector at the the flex circuit in the photo above. Notice the cracks at the junction of the soldered terminals and the copper flex traces. Click the pic for more detail…
I suspect some of those cracks came from my ham-fisted repairs over the years of owning the thing, but the fact of the matter is that many other owners who didn’t take their Zire apart have much the same charging / USB problems. I think the connector moves slightly when it’s jammed into the charging cradle and that’s enough to fracture those joints over the course of a few years.
Anyhow, cutting the flex just beyond the connector pins and scraping off the insulating layer with a sharp razor knife reveals the traces.
This end of the flex circuit has two additional ground traces bracketing the 16 traces leading to the exposed connector pins. As a result, the connector body is firmly grounded. The fat trace on the top is a paired ground conductor. The fat trace in the middle is another ground.
Here are some of the connections at the other end of the circuit, where it plugs into the Zire PCB. Note that the shutter button traces wind up in the midst of all the traces with numbers corresponding to the external connector pinout found there. The speaker traces lie outside the ground at the bottom edge of the picture above.
With that in hand, I untwisted a hunk of stranded hookup wire to get some fine copper wires and soldered them to the flex circuit traces. Note that the two outermost traces are soldered directly to the metal shell around the alignment / latch holes. The red stuff at the very end of the flex circuit is orange nail polish that will, in theory, keep the new wires from shorting to the copper shield layer in the flex. The silvery shape at the lower middle is the shutter button.
The wires turned out to be just slightly too long; were I to do it again, I’d pay more attention to getting the edge of the flex exactly where it was when I cut it off.
A layer of Kapton tape insulates and stabilizes the wires. A layer of copper foil tape atop the Kapton gets soldered to the connector shell for static dissipation, but I’m not convinced it was necessary. This view is from the other side of the flex, with more nail polish along the edge to glue things down.
A layer of Kapton on that side pretty well finished it off; I took some pains to press the two adhesive layers together around each of the wires.
Solder the speaker back in place and reinstall in reverse order, folding the new wires gently into position. That’s when I found out they were a few millimeters too long. I left ’em be.
Here’s the final result, minus the shutter button and bezel.
From this point, all the bits fit back together the way they used to.
While all this was going on, I won a pair of Zire 71s on eBay, plus a wireless keyboard (which solves a problem I don’t have), plus a known-bad Z22 (dead digitizer), plus a bunch of other odds and ends, for a whopping $25 delivered. I was so hot to get the pair that I even upped my bid to $45… there were no other bidders.
Now I have a cold backup for the hot backup for my PDA!
Amazingly enough, the (presumably OEM) batteries in the new-to-me Zires charged up and work fine, so I need not meddle with them for a year or two.