I've a problem that should be simple to solve, but I must be missing the
glaringly obvious, as the solution eludes me.

This is a discrete monostable divide by 5 countdown circuit being driven by
pulses every 1mS on the input, and should drive a pulse every 5mS at the
output.

I've checked the transistors (and subbed them just in case), the diode, and
the resistors, and replaced the 0.1uF timing capacitor, but still the darn
thing triggers almost randomly (though there is some preference for 5mS).

Here's the circuit (resistors using : characters) - use a monospace font to
view.

+12V
|
:
:3K6
:
|
------------------------o
| |
| |
| |
| +12V +12V |
| | | |
| : : o--||--o--o-- Output
| : 2K2 : 61K9 | .2uF | |
: : : | : |
39K0 : | | |/ 9K1 : --|--
: o--||--o-o--|--o--| : |
| | 0.1uF | | |\- | ___
| |/ --||-- | ___ .
-|-:::::-o-| 22pF ___ .
10K0 |\- .
|
___