I've spoken before about the trials and tribulations of diagnosing
the dreaded 'intermittent fault' - and I never ceased to be amazed
at the sheer variety of ways in which sod's law wreaks havoc.
Whenever a client who's suffering an excess of sod's law turns up
in the workshop the opening gambit is always the same - the client
has a problem, evidently, but as soon as they start to look for
it, it disappears. The moment they think that all is well again
- it reappears.
It's a safe bet that when they eventually get around to showing
the problem to someone who might be able to find it and fix it,
it cannot be found.
The latest example was almost breathtaking in its mechanical deviousness.
The problem, as described by the player, was that every now and
then the horn, a vintage Martin tenor, would lose everything. One
moment it would be fine - but a trip up to the top notes would sometimes
result in an awful howl. More curiously, it would sometimes suddenly
recover in mid squeal.
Clearly this was not a tenable situation for a horn player on a
gig - but there appeared to be no apparent fault with the instrument.
It seemed most likely that the problem lay around the top end of
the horn, perhaps with the octave key mechanism...a sticky or bent
key perhaps - although this wouldn't stop the horn dead, you'd at
least be able to get a few notes out of it.
I could see nothing wrong, so I contemplated a loose crook socket.
A leak here could be significant, and it could also open and close
as the horn was moved to and fro...but then it would have to be
a very significant leak to completely stop the horn, and by significant
I mean that the socket would have to be practically falling off.
I found no such problem, so I began an examination of the tone
holes. On a Martin these are soldered on, and there's a curious
malady that can affect the integrity of the soldered joint (known
as Selective Galvanic
Corrosion) whereby the solder oxidises and the joint fails.
A decent sized gap under a tone hole might be prone to opening and
closing as a key is pressed - but again it would have to be quite
a fair old gap to have such a drastic effect.
I couldn't spot any problems, and a general inspection of the action's
regulation revealing nothing untoward.
It was time to blow the horn to see if I could duplicate the problem.
So, I blew...and I blew....and I blew. All I got out of the horn
was that typically rich, vintage Martin sound.
I concentrated on the top notes, running chromatic licks over the
palm keys - still no problems.
And then it happened. Halfway through a lick the horn simply stopped
dead in its tracks and emitted a most awful noise.
I carefully moved the horn out of my mouth and swung it so that
I could peer at the action. I couldn't see a thing wrong with it.
I put the horn back in my mouth and, as expected, it blew fine.
Back to blowing then.
It took me a good few minutes before I was able to reproduce the
problem, and as soon as it occurred I stopped blowing and very,
very carefully moved the horn out of my mouth - keeping my fingers
in the exact positions they were in when I'd stopped blowing.
As I slowly moved the horn I felt a slight knock. Something had
moved! But what?
This narrowed down the field of possibilities. What I was looking
for now was a mechanism that was sticking, but one that was capable
of unsticking itself...which hinted at it being sprung. A stiff
Well, I waggled keys this way and that. I poked, I prodded, I wiggled
- but nothing stuck.
Casting my eyes over the top key stack I now noticed that the stack
rod screw was protruding from the top pillar.
My first thought was that this meant it had come unscrewed from
the lower pillar, and that the end of whatever key was positioned
there would be flapping about in the breeze. It hadn't come unscrewed
though, not fully at least, and the key that sat there seemed quite
snug up against the pillar.
'Self extracting' rod screws are a common problem. You often find
them, surprisingly enough, on brand new horns. The action is new,
and therefore unworn and relatively tight - and if a grease has
been used to lubricate the action it's often the case that the friction
of the tight action and the grease combined is enough to work the
rod screw loose over a period of time.
There could be other factors too - vibration, dirt in the key barrel,
or even a screw that simply wasn't done up tight in the first place.
On older instruments the reason for friction is far more likely
to be down to worn key barrels being able to twist, and thus rub
on the screw, or slightly bent key barrels.
Either way, this appeared to be a simple problem to fix (just tighten
the screw back up) and not really related to the problem - so I
reached for a screwdriver.
I found my access to the screw head blocked though, by the arm of
the side F key. In order to get to the screw head I'd have to first
remove the F key - and the screw head was really rather close to
the key arm. In fact...almost touching??
I love a good Eureka moment!
Nothing beats that wonderful feeling of visualisation. Just as thrilling
is the subsequent examination of the circumstances that have to
come together in unison to create 'the problem'.
In this particular case there were several factors in play.
The first was that the top stack rod screw had worked its way out
and that it was touching against the side F key arm.
This wasn't the nub of the problem though; had that been all it
was then the F key would have stuck once and stayed put, until such
times as the stack screw was tightened up. No, it was much more
complicated than that.
The head of the screw was somewhat chewed up. Years of use and abuse
had left the head rather uneven, with a distinct rough burr on it.
The screw had worked itself out until it had touched the F key arm,
and then stopped - or almost stopped. As I pressed various keys
down on the stack I could see the head of the screw turning....but
every so often, as I released keys, it would turn the other way...as
though re-tightening itself.
The chewed up tip of the screw was sharp enough to catch the F key
arm and hold it open, but the moment you pressed and released certain
keys at random the screw moved backwards, released the grip the
and the F key could fall home.
Even more dastardly, when the screw had locked the F key open the
slightest stress on the horn's body was enough to give the F arm
just enough space to free itself, and close...which was why the
problem could suddenly disappear halfway through the awful howl
created by an unexpectedly open side key - and I doubt you can get
any more intermittent than that!