dssf@ihlpa.UUCP (d s sand) (04/05/86)
This note is in response to the parent article of: > Subject: Re: quick repair/replacement of 800XL for tax time... > >From: jackson@TTIDCB.UUCP > Organization: Transaction Technology, Inc. (CitiCorp), Santa Monica > Sender: daemon@ucbvax.BERKELEY.EDU The original note referred to an 800XL keyboard with one (or more) non-functioning keys. The only suggestion posted that I saw said: a) buy a new one (they're inexpensive), or b) clean the keyboard plug/jack inside the cabinet. From my experience, the problem might be elsewhere, and easily repaired (without opening the cabinet). I purchased two 800XLs about a year ago (both were manufactured in the summer and fall of '84), and each had one or more non-functioning keys. In each case, adjusting the springs inside the bad keys fixed the problem. If you open the cabinet and disassemble the keyboard, you will see that it is really a membrane pad with individual key-contacts activated by springs depressed by the full-travel keycap. The force applied by the spring must be enough to compress the contact pad, but not too much so the key doesn't feel too stiff. The springs probably are correct at time of manufacture, but weaken with age. The fix is to "stretch" the spring a little, so that its rest-length is somewhat longer, resulting in more force when the key is depressed. The keyboard membrane assembly seems to be well protected from internal contamination such as dirt or dust (but probably not liquids), although several years of normal aging might corrode the contacts. Problems with key spring tension are common, and likely if one or more isolated keys don't function. (However, if several keys adjacent in a row or column are all bad, then it might be the plug/jack, since the keys are sensed by a matrix of contacts.) Assuming the key spring is at fault, the fix is roughly as follows: 0. !Don't! disassemble the cabinet. 1. Power up the 800XL (with display, but without peripherals or cartridge), with the 'option' key depressed (or in Basic, enter 'bye') -- this should give the self-diagnostic menu. 2. Select the keyboard-test option, and manually test each key, noting which keys don't respond. 3. Turn power off. 4. Remove the keycap* and assembly from one of the bad keys. There are several parts (the keycap, the spring, and one or two more). If you have strong fingers, the keycap can be lifted off directly by holding it. Otherwise, try to gently pry it loose using some sort of tool hooked under the keycap edge, preferably with two hooks on opposite sides of the cap. An IC extractor will work. Don't squeeze the keycap very hard - it is soft plastic. The other parts may come out with the keycap, or you may need tweezers for them. If you look in the hole where the keycap was, you will see the membrane pad at the bottom. 5. Power up and enter the keyboard-test routine again. 6. Insert a Q-tip (or other soft but stiff probe) into the key hole, so it touches the plastic membrane pad. Press the Q-tip with moderate force - about the same pressure you would use to depress a normal key. The screen should indicate key contact. (If not, the problem is elsewhere.) 7. Measure the length of the spring, and stretch it enough so that its new length at rest is about 1/8" longer (do it in small increments - springs like this are easy to permanently stretch, but very difficult to "unstretch"). 8. Reassemble the keycap and parts - this can be done with power on - the key should now register correctly. If not, the spring may need more stretching, so repeat steps 4 - 8 on this key. (Also, the keycap and other parts might be sticking somewhat, and a very small amount of lubrication (eg, vaseline) might help - but try to avoid this.) 9. Do steps 4 - 8 on each remaining key. Steps 3 and 5 (power down and up) are not really necessary if you are careful - removing the keycaps should have no affect other than multiple key strokes. However, you might want to have power off the first time you try to remove a keycap. * Most of the keycaps are plastic, but the 'reset', .. .'help' keys are flimsy metal. These keys are are easy to bend, but this can be avoided if the cabinet is disassembled first, which gives plenty of room to push the key tops out from below. It is better to reassemble the cabinet before powering up again. Opening the cabinet doesn't help with the plastic keys because they are all packed together, so don't go to the trouble of cabinet disassembly for them unless you really need to.