Tachometer / Hobbs combination gauge

[dan tonner]

The Hobbs readout window on my Tach/Hoibbs gauge began flickering and became unreadale (partial numbers) during a flight yesterday. Because the Hobbs gives a readout as soon as my battery master is "on" and the key is in the "run" position, it appears to be simply a real-time clock using active 12v power. The pink wire  that comes from the Voltage regulator's "L" position provides the signal to both the Hobbs and the red "charge" lamp on the panel.    The Tach, of course gets its signal from the RPM pick-up coil on the flywheel.  There are no issues with the Tachometer or any of the other gauges or electrics. The red ":charge" lamp works as it should and shuts off as soon as the engine is running.The Tachometer ground wire and the signal wire (pink) from the regulator each show continuity from end to end.

 

Is there a way to reset the readout on the Hobbs window?   The gauge itself cannoity be opened - it has a crimped bezel holding the glass front to the plastic body.   Could this be an issue with the voltage regilator?    Anyting else?

 

Rather than replacing the gauge, I would probably just be more vigilant with my watch and start-up and shut-down times.  Or install a simple 12v digital clock that resets to zero on shutdown.

 

Suggestions welcomed,

CanadaDan

[Farmpilot]

G’day Dan, I prised the front open on my tachometer and put a new LCD screen in from eBay and it’s working perfectly again. My tachometer is a VDO brand and I googled ‘how to change VDO LCD’ and followed the instructions, it’s very easy. 
Cheers 

[dan tonner]

Thanks for the reply Farmpilot.

The front bezel of my Tachometer is crimped over a lip on the front edge of the case; if this was the situation with your tach, how did you manage to un-bend (then re-bend) the bezel without seriously damaging it?     (Photos attached)

CanadaDan  

[kgwilson]

The hour meter on a VDO tacho only activates when the engine is running, not when power is attached only. Just having the power on will not increment the time.

Edited September 6, 2022 by kgwilson

[Farmpilot]

My VDO was still working but the LCD gradually stopped displaying. For a while it worked intermittently then stopped altogether. When I put a new LCD in the hours were correct so the timer worked but just would not display the hours. I used a small flat head screw driver and gently prised the bezel off and the used pliers to press it back again. It did scratch it but I’m ok with that. 

[Farmpilot]

This is a link to what I purchased off eBay. https://www.ebay.com.au/itm/VDO-KENWORTH-SPEEDO-TACHOURMETER-NEW-LCD-DISPLAY-FIX-YOUR-OWN-KEEP-ODO-READING/223255942918?hash=item33fb175706:g:LkwAAOSwh39cB1pM&frcectupt=true

Pry the bezel open from the back like this video shows.  https://www.youtube.com/watch?v=aIGVe96yzN4

This video explains what causes the LCD to fail and I did try replacing the grease and it worked for a while but failed again so I recommend just replacing the LCD. https://www.youtube.com/watch?v=eldRUU7qc2Y

 

[dan tonner]

KGWilson and Farmpilot;

     Thanks for your replies.    The replacement LCD screen is due to arrive today (along with Hurricane Fiona).  Assuming my hangar and airplane withstand the meteorological assault, I'll let you know the results of the repair. I have already removed the tach, carefully prised open the case and removed the original screen.  (Before ordering the replacement, I also snipped 1/8" off the end of the ribbon connector and reinstalled it - a trick I learned from repairing microwave oven keypads.  However, this time it didn't fix the problem - the display was still as spotty and unreadable as before.)

      Farmpilot; I loved the video - that is one fellow I'd let work on my airplane anytime!    I'll let you know how I make out with the fix.

All the best; fly safely, 

      CanadaDan

 

[Farmpilot]

G'day Dan,

 

How did you get on with the repair? Hope it worked for you as well as it did for me.

 

Cheers

[dan tonner]

Thanks for the followup reminder, Farmpilot.

The repair was a complete success. The main issue was getting enough of the crimp relaxed around the plastic case to free the faceplate. Patience and proceeding in very small steps was a key. The Hobbs/Tach is reinstalled (the Hobbs remembered the last reading) and I had a few flights since where all worked well.

Thanks again so much for the advice and encouragement.

CanadaDan