Intermittent fault finding

[Welsh_sparky_21]

Is there anything more frustrating than an intermittent fault

 

[Lucien Nunes]

A theatre lighting dimmer rack that we installed would occasionally blow one or more of its three 2A control fuses (the control module takes all three phases to get a mains timing reference and will power itself from any or all of them.) There was nothing apparently wrong with the SMPSU so it seemed likely that there were transients on the supply that were being clamped by the control module's VDRs. After a few visits to replace fuses, Richard twigged that there was 4-pole isolation in the 3-phase supply. He tested the isolator and found that the neutral was breaking first and making last, causing a momentary neutral loss and hence overvoltage impulse on a random phase at each switching cycle. Replacing the isolator stopped the fuses blowing.

 

[Lucien Nunes]

The action of the Compton organ at Southampton Guildhall generates a good selection of intermittents. This mammoth instrument contains about 7,000 electromagnets, over 50,000 sets of contacts and over 100 miles of 26SWG cotton-covered wiring joining it all up. All of the electrical gear, much of which is installed in a dedicated relay room, is original 1937 equipment, almost unique today. The main problem is that it doesn't get used enough, so all those contacts sit there from one month to the next, gathering dust and tarnish (they are mostly silver) and take a few cycles of use to get cleaned and back to reliable operation.

When we attend for a service visit, it takes me the best part of half an hour to exercise everything and take notes of what is not coming back to life. I'll make a list of a few dozen problems that are all likely within a particular location - console, relay room etc - and usually find half of them unrepeatable or genuinely cleared by the time I get there. Once I've dealt with those, I'll return to the console for another round to find half of the half that had cleared are back. We never actually get them all, but on an instrument of that size, they tend to go unnoticed in normal use.

What does not go unnoticed is any failure of the setter action that stores and recalls stop combinations on the thumb pistons. This is a fully electromechanical binary memory of some 4-5 kilobits, that works using around 700 solenoids to manipulate grids of spring contacts into the correct slots in busbars. It is remarkably reliable but if you get one loud stop that fails to go off when a quiet registration is recalled, it is a real problem.

Typical problems that need dealing with on the electrical side are:
Dirty contacts
Dirty contacts
Inadequate tension of contact springs
Dirty contacts
Mechanically sticky parts associated with electromagnets and contacts
Flux corrosion to lead-out wires of solenoids
Dirty contacts
etc.

Later when I am on the other computer I will post some pics of two of the most challenging sources of intermittents in this instrument, which are the console main cable connectors. When you see them, you will understand!

FWIW I am posting all this stuff to amuse myself while sitting in hospital connected to the chemo infusion pumps. I must do some proper work.

 

[timhoward]

The action of the Compton organ at Southampton Guildhall generates a good selection of intermittents. This mammoth instrument contains about 7,000 electromagnets, over 50,000 sets of contacts and over 100 miles of 26SWG cotton-covered wiring joining it all up. All of the electrical gear, much of which is installed in a dedicated relay room, is original 1937 equipment, almost unique today. The main problem is that it doesn't get used enough, so all those contacts sit there from one month to the next, gathering dust and tarnish (they are mostly silver) and take a few cycles of use to get cleaned and back to reliable operation.

I hear you. (I'm an organist btw). I get called in to play for carol services on instruments that barely get played the rest of the year, and real ingenuity can be called for to work around the faults. Tracker (mechanical) action instruments are normally ok, but there's a couple of electro-pneumatics that are long running adversaries of mine. Each year I write a polite essay in the tuning book, and the following year I read the witty responses to last years faults. One year I had to avoid about 6 notes for the whole evening, substituting with right foot and octave coupler.
There's one considerably smaller EP action in a church near me has contacts that have been hopelessly bent out of shape by someone dropping the keyboard stack of the manual above on them. I've recently spent most of a morning gently re-shaping them. About 3 have snapped off leading to a fun session lying on my back on the pedalboard soldering in mid-air directly above my face!
I think these ones are phosphor bronze and I need to find a source of contact wire sometime...

BTW I too have been on the receiving end of those infusion pumps. Are they the Siemens ones, and have you learnt to silence the 5 minute remaining alert yourself yet?

 

[timhoward]

Just for @Lucien Nunes benefit - favourite quotes from the tuning book:
Organist: "Evidence of pedal felt falling off".
Organ tuner: "Evidence removed"

Organist: "Oboe Tenor C almost out of tune".
Organ tuner: "Oboe Tenor C almost tuned"

 

[littlespark]

One year I had to avoid about 6 notes for the whole evening,

That would have sounded like Les Dawson at his best

 

[Lucien Nunes]

Only a couple of weeks ago I had an intermittent on a Tenor C, on the Compton Electrone at a church in Ealing. This was John Compton's local church and there is some circumstantial evidence that one of their first electronic church organs was installed there, possibly as a field test of the new product. The console dates from 1938 or so, making it possibly the oldest British-made electronic church organ in use today in its original location. The tone-generator cabinet has been replaced once or possibly twice, with the 347-type unit now present dating from the late 1940s.

Inside the cabinet is the key relay, which consists of 154 relays (2x 61-note manuals + 32 note pedal) with either 6- or 10-poles each, that switch the DC voicing control signals to the correct generator pitches. Each individual contact controls one generator pitch of one rank on one key. This instrument had sat more or less unused for a long time but at the routine service visit I was pleased to find most of it working straight off. I last gave it a thorough pull-through about ten years ago. The only real problem I found was an intermittent fundamental on Gt. Tenor C, due to low pre-tension in the A-rank contact wire. I have made a special tool to reach inside amongst the 1,412 contact wires of the relay and re-tension them without dismantling, which is a day's work as the whole thing has to come apart before you can get inside any part of it. A quick tweak cleared the intermittent. Pics follow.

BTW Braun Infusomat, no 5-minute warning. I am done with the Oxaliplatin and Calcium Fluorinate now, time for the Fluorouracil bolus.

 

[brianmoooore]

Which make of scan I'm looking for a good car one.

Foxwell seem to be the manufacturer of choice at the moment. Various models, depending on how much sophistication you want, and how deep your pockets are.