Author Topic: Fenlow 705 nixie tube multimeter  (Read 855 times)

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Offline PureZXTopic starter

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Fenlow 705 nixie tube multimeter
« on: November 18, 2023, 06:36:30 pm »
Hello

I recently got hold of a nixie tube multimeter manufactured by Fenlow Electronics Ltd of Jessamy Road, Weybridge, Surrey. It works, and is surprisingly accurate, however, the polarity nixie is not working. Before investigating the problem I attempted to find some data on the meter, but I can't find anything. Has anyone got any data on the Fenlow 705, user manual, schematics and/or calibration data would be a great help.

Thanks
 
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Offline factory

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Re: Fenlow 705 nixie tube multimeter
« Reply #1 on: November 20, 2023, 09:27:45 pm »
Does the symbol bulb have the sine-wave & ohms symbols, as well as the polarity +/-? and are they connected? If yes, do they work with the function switch in AC & ohms?

David
 

Offline PureZXTopic starter

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Re: Fenlow 705 nixie tube multimeter
« Reply #2 on: November 20, 2023, 11:35:57 pm »
Hello David,

No, it can only display + or -.

Mike
 

Offline factory

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Re: Fenlow 705 multimeter
« Reply #3 on: December 05, 2024, 10:10:58 pm »
Could this be the same one, that I acquired recently?

First things were to work out why the symbol bulb was not displaying anything, this wasn't too hard, it was very dead, voltage was present on two of the pins. Removing the bulb & checking it with a Megger confirmed it was dead, no signs of life, not even at higher voltages.

Thankfully I had one of these, bought unknowingly from a TE murderer in Penkridge, fitting this I now had a minus symbol and an AC symbol. Next problem was the minus symbol was stuck on in all modes, even with a positive input.



I've worked out some of the circuit, 3 transistors near the bulb deal with switching the +/- symbols and the AC symbol is switched by another transistor found near the mode switch.
Eventually I traced the +/ toggle back to some Nand gates, one was stuck high on both inputs & outputs.
Replacing that 7400 got the symbols lighting one at a time, but with another fault where + or - was staying on in ohms mode.





I believe two more transistors near the range switch, should turn off the +/- symbols when in ohms mode, this is where I've got to with the repair ATM.

David

« Last Edit: December 05, 2024, 10:13:47 pm by factory »
 


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