The place for technical discussions about GA and flying.
Forum rules: Technical discussions about GA only, please.
User avatar
By mikehallam
#1809194
Now that's most enlightening re the hole at the back. I saw a small paper patch and didn't disturb it, thinking it was an air pressure equalisation breather with anti dust filter ?

I didn't put any resistor on as generally in or out the instrument is a pig to plug on the leads. In the end it was done almost entirely by feel and a mirror to ensure the correct pins.
Squeezing the lead brass slip on connectors in pliers though risky did make them stay on and until the recent creeping lower readings I was stupid but happy with it.

Clearly now in receipt of your latest intelligence I will remove the gauge and peel off the rear aperture paper and see if I can adjust it.
Might not need a new one now & saves me over £100 !
Though as you comment it really needs to be compared with something else reasonably trustworthy. If it can be adjusted it's back to borrowing the plug triggered tacho.

Many thanks and I hope you too resolve the errors.
By MikeW
#1809226
I guess it will function as a breather too, hadn't thought of that, but the cal trim is definitely in there!
Needs a small jeweller's screwdriver AFAIR. Or do I mean a jeweller's small screwdriver? :clown:
By cockney steve
#1809312
^^^^^^^^^ NO! there are special non-conductive trimming-tools available. Using a pigmy's screwdriver will usually let the magic smoke out of the electrickery-driven device,-or, in the case of higher voltages the operator comes to a sudden end as well.
By MikeW
#1809354
He's way OTT. Shoving a bare screwdriver into the heart of HV electronics would be rather silly but to twiddle a trimpot (and I think it was a moulded plastic end not metal) through an access hole provided for the purpose in a plastic case with no access to anything else? :roll:
By cockney steve
#1809367
If it's saved even one reader from frying something expensive, it was a worthwhile post. Just because the item in question was fully -insulated, does not mean this is the norm for any electronic trim-pots/cores.
Nick liked this
By patowalker
#1810082
MikeW wrote:
MikeW wrote:Ah do you have the Aviasport one? I believe that has a 4th pin, I think it's to switch a Hobbs, not sure.


Sorry that's cobblers. See http://www.aviasport.com/Pagina_1682.aspx for the truth.
It gives you the wiring dia too - and a hint to try swapping over the two trigger wires if the reading is erratic.
It and the Rotax one bear a remarkably close resemblance to each other!


Not cobblers at all. It does have a four terminals. Number 4 is shown in the centre. It is for factory calibration input. http://www.aviasport.com/pdf/Instrument ... IM_105.pdf
User avatar
By mikehallam
#1810117
Looked at mine today. "N0. 4" is indeed a hole at the bottom of which is a screwdriver-able "pot".
It does alter the rpm reading.
What it then needs is a separate reference tacho or plug lead pulse counter to check/adjust it to cover from 1600 to 5,000 ish.
By MikeW
#1810283
patowalker wrote:
MikeW wrote:
MikeW wrote:Ah do you have the Aviasport one? I believe that has a 4th pin, I think it's to switch a Hobbs, not sure.


Sorry that's cobblers. See http://www.aviasport.com/Pagina_1682.aspx for the truth.
It gives you the wiring dia too - and a hint to try swapping over the two trigger wires if the reading is erratic.
It and the Rotax one bear a remarkably close resemblance to each other!


Not cobblers at all. It does have a four terminals. Number 4 is shown in the centre. It is for factory calibration input. http://www.aviasport.com/pdf/Instrument ... IM_105.pdf


No that is misleading as written in the datasheet - it is a calibration trimpot not a terminal. Then there are 3 terminals.
PS It was only myself I was being rude to if you noticed!
User avatar
By mikehallam
#1810709
Surprises all round to report !
My brand new Aviasport arrived today & sports four pins sprouting from the back. Otherwise except for the pretty red/yellow/green markings on the face it should be a shoe in for the 20 year old "lost its calibration" one - which as you'll recall has an adjustable pot down a hole at pos'n 4.
Setting that up on rpm guesses alone was a dead loss and spurious signals to the "tinytach" equivalent digital rpm device I hooked in wasted an afternoon trying to get reference figures. In the end it cost less on journeys, petrol and earlier wasted days to simply give in & spend. I now have a perfectly good spare gauge that only needs calibrating.
By MikeW
#1810752
Well b***** me! Confusion reins! No adjustment provision then?
Do you think it's a recent(ish) change or do you think the Rotax badged one is in fact not an Aviasport after all?
The Aviasport data sheet is dated 2013 and says initial issue. All 3 of the Rotax badged tachos I've handled are substantially older than that as is yours.
User avatar
By mikehallam
#1810774
The label on the new tacho still says the centre pin (was a hole with potentiometer) is for calibration, so I assume they have a better method now.

Aviasport is a Spanish maker from whom I had a quotation last week of identical spec. to the one offered from Eccleston (UK stockist) who told me that was where theirs come from. [FWIW the prices to me were almost equal, so I bought within the UK who provided a super fast delivery].
Hope to get to the Rans this week to fit & and give it a run.