Tuesday, 6 January 2015

Fuel gauge amplifiers part 2

Following on from overhauling the amplifiers with new spec capacitors I decided to give them a try on the Victor, using the fuselage gauging circuit to test them out, each one was plugged in one by one to test their operation and accuracy. Unfortunately (for me) I was alone and that meant I had to clamber up and down the wing at least seven times in order to trip the AC power supply in the cockpit in order to safely swap the amplifiers over.  After much effort and feeling like a 'One man band' I concluded the repairs had gone well and 6 out of 7 repaired amplifiers tested and indicated fuel contents. However due to slightly different spec capacitors the expected levels were not quite correct so, trimming of the circuits was required. I was however satisfied that I had got somewhere, if this repair had not worked then, there were no further options to go for... Further encouraged I carried out similar repairs to 4 more amplifiers. There are more to do so we should end up with around 6 spare units.

Ollie 'volunteered' to come in on Sunday to operate the fuel gauge test set and we set up internal intercom so that we could liaise without problems. Ably assisted by Rick Gill, Ian Finch, Rich Spaven and John Hawkridge we got into the task.
The 5 fuel tank groupings, Port wing, Fuselage, Stb'd wing, Fwd bombay, Aft bombay
Amplifier, Type LA15 with cover removed and plugged into the test set 
 Smiths fuel gauge test set Type QC32 on the plenum chamber floor
Ollie tested each amplifier on the test set for voltage & power consumption and then using the two capacitance trimmers within the amplifiers he set the low level and high level readings with myself tripping power on and off in the cockpit as required. Once a full set of 8 trimmed amplifiers had been achieved Ollie installed them one by one and I followed by installing the associated fuse and then observing the fuel gauge movement. On power up, the gauge is driven to zero and then is driven to the fuel level within the tank or tank grouping, depending on the circuit. We concluded that the port wing grouping is serviceable as is the port underwing tank, the fuselage tanks circuit is serviceable, the Starboard wing grouping appears to be out of trim or has a signal cable snag so that requires working on and the Stb'd underwing tank circuit is serviceable. The forward Bombay tank gauge has a fault that appears to be within the gauge and this will require replacing and the Aft Bombay gauge is working but requires trimming to the correct level on the Bombay cable box trimmer. The Port and Starboard underwing tank level repeaters situated on the Navigators panel are serviceable, as is the total contents Totaliser gauge.
The dedicated team members closing the jet up in the twilight after a satisfying and succesful Sunday

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