Repairing Merlin Membranes & Keys
The biggest problem with Merlin type phones that have a Membrane (Flat) faceplate is that they get locked up so that no buttons work after something is spilled in them. This also applies to other Merlin phones (like the BIS) that have real buttons, when something gets spilled into the dial, which is also mylar. The AT&T Spirit can also be repaired with these techniques.
We can fix about 70% of these phones at our shop, without putting on a new faceplate. After a few tries, you get good at peeling the membrane apart. It usually takes us about 15 to 20 minutes to do the whole repair in our shop. You don't even have to be a technician to do it, since we have the same guy that refurbishes the phone do this repair. If we can't get the phone to work after 10 to 15 minutes, we just send it in for repair or use it for parts.
There are three parts to the membrane. The top and bottom layers have the traces on them, and the middle section is a thicker piece of mylar that keeps the layers apart until you press a button. You do have to use caution when peeling it apart (do it slowly), to keep the adhesive from pulling up parts of the traces. If you do pick up part of a trace, just paint the missing part back on!
It is usually easier to unplug the two parts of the faceplate from the rest of the phone while you are working on them. I often unplug the dial and check inside the dial to make sure the liquid didn't get down there (it does quite often). If you see some green gook or something, it's the result of a chemical reaction between the traces and the electricity and the stuff that got spilled into the phone. Just wipe the gook off with a slightly wet towel (don't damage more traces while you're wiping it off!).
You will usually see that the trace that has been hit by liquid has turned very dark. If you take an Ohm meter to that area, it won't conduct. All you need to do is paint the trace back on, right over the old one, by using a toothpick or the end of a spudger (we sell the spudgers for about a dollar each). It doesn't have to be really thick. Don't use the huge brush that comes with the bottle! It takes about 10 or 15 minutes to dry. It is NOT conductive enough for the Merlin keys to work until it's dry! If you make the trace too wide (which happens quite often), just scratch off a little after it dries with the spudger or a little knife. It's not easy to try to wipe a little bit off when it's wet. We usually put the phone off to the side and work on another one while it's drying. Try not to bend the area where you have painted the traces back on very much, as you could crack the painted-on trace. I've never had a problem since it seems to be a little flexible when it dries.
I use an Ohm meter (with a beeper) a lot when fixing these, since it's hard to trace these traces by eye. Just put one lead of the Ohm meter on the trace at the button that's not working and keep moving the other lead farther and farther from the button until the continuity stops. That's where you have to paint the trace back on.
Use the same techniques on the mylar circuit board in the dial, and the button in non-membrane sets. After taking the dial apart the wrong way and dumping all of the buttons out on the table a couple of times, you begin to get good at dials also. It really pays to check the dial even if you don't think there's a problem with it, since it seems to be a perfect place for liquid to pool up. Use our very thin double stick tape to stick the halves of the faceplate back together, if the original adhesive doesn't hold. We find quite a few Merlin phones of all types that have a problem with the hookswitch (static or won't go on or off hook). After a few times, it's pretty easy to slide the little plastic cover off of the hookswitch and use our burnishing tool on the contacts. It's probably better not to spray the contacts with tuner cleaner since it usually tends to attract more gook.
If a customer calls you and says that he just spilled something in his phone (or computer etc.), tell him to unplug it RIGHT THIS SECOND! You can pretty much hose phones down with a fire hose and they won't be damaged electronically if they're not plugged in and stay unplugged until totally dry. It's the resistance changes and the chemical reaction between the electricity and the water that does the damage.
On Spirit phones, the LEDs tend to pop off the mylar sheet when it's flexed. To put them back on, use a 2-part epoxy to hold them to the mylar sheet. Then, paint over the ends of the LED with the Merlin Membrane Repair stuff, which will make a good electrical connection. Nothing except epoxy (not super-glue) will hold the LEDs to the mylar sheet!