Take around three bristles from a small wire brush and chuck them in a pin vise or razor knife holder. Trim their ends even. Place a drop of 91% isopropyl alcohol in the hole behind the offending key and gently "scritch" around in the hole with the wire brush. Be careful not to break a bristle off in the hole. This also works for HP41 keys. If possible, avoid breaking the posts. If you need to cut them, try to do it in a manner that allows for subsequent glueing or otherwise sealing them when you are finished.
On the 22 I found that the 175Khz-clock signal was coming through the unused pins on RAM/ROM chip (the one closest to the battery compartment and did the following fix: I simply connected one of the unused pins on the RAM chip to ground. (At least some of the unused pins appear to be connected to the substrate of the chip.) In particular, I connected a jumper between pin 7 (ground) and pin 10.
On the 25 this repair did not work, although it too had clock noise coming through on the same unused pins. However, I found that the data signal line was quite noisy too. The fix here was to install a 20K resistor between the data line and ground. The data line is pin 11 of the ACT chip (the ACT chip is the one at the bottom of the circuit board.) and there is a convenient ground just across the chip on pin 12. One fellow collector has reported that this same fix worked as well on the 25C.
On the 25 this repair did not work, although it too had clock noise coming through on the same unused pins. However, I found that the data signal line was quite noisy too. The fix here was to install a 20K resistor between the data line and ground. The data line is pin 11 of the ACT chip (the ACT chip is the one at the bottom of the circuit board.) and there is a convenient ground just across the chip on pin 12. One fellow collector has reported that this same fix worked as well on the 25C.
