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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders. |
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19th Jul 2017, 9:24 pm | #1 |
Heptode
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 693
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Evershed and Vignoles Series 2 Megger problem
I recently acquired the above at a BVWS auction. It was described as working but, although the meter moved on turning the handle, no difference was seen between open and short circuit on the terminals. How are you supposed to get into this thing? I removed the base screws which allowed a glimpse of the inards but it looks like it needs keyhole surgery to go any further. Eventually I resorted to unsoldering some of the wiring and releasing the nuts on the "springs" connecting to the meter movement. One of these is broken but getting in to solder it is going to be tricky. Why did they use this complicated connection scheme? Can I replace the "springs" with flexible insulated wire? Any advice would be appreciated.
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Keith Yates - G3XGW VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm |
20th Jul 2017, 2:01 am | #2 |
Dekatron
Join Date: Apr 2012
Location: Worksop, Nottinghamshire, UK.
Posts: 5,554
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Re: Evershed and Vignoles Series 2 Megger problem
Those springs look like resistors so their values will be important.
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20th Jul 2017, 9:19 am | #3 |
Heptode
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 693
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Re: Evershed and Vignoles Series 2 Megger problem
Thanks for the the suggestion. I did wonder if they were resistors but they measure zero ohms as far as I can tell. Also they are loosely supported on brass rods so their resistance would be rather indeterminate. I really can't see the reason for them but I'm sure someone out there will know.
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Keith Yates - G3XGW VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm |
21st Jul 2017, 10:12 am | #4 |
Heptode
Join Date: Jun 2010
Location: Zurich, Switzerland
Posts: 538
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Re: Evershed and Vignoles Series 2 Megger problem
Hi Keith,
I think you can see an answer on page 4(36)... Regards, Karl |
21st Jul 2017, 10:32 am | #5 |
Heptode
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 693
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Re: Evershed and Vignoles Series 2 Megger problem
Thanks Karl,
I had seen a diagram like this before so I think I understand the 2 coil measurement principle. I think the "springs" are what are referred to as "ligaments" in the diagram and I assume that they are simply a way of connecting to the meter movement so that the base plate is easier to remove without putting any strain on the delicate connections. I'll attempt to repair the broken one and see if that restores operation.
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Keith Yates - G3XGW VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm |
21st Jul 2017, 2:30 pm | #6 |
Heptode
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 693
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Re: Evershed and Vignoles Series 2 Megger problem
Well, I managed to re-connect the broken "spring" but this didn't fix the problem. Does anyone know what the resistances of the meter coils should be. One of mine measures about 60 ohms but the other (the one with the detached connection) measures about 800 ohms. This particular instrument has selectable 250/500/1000V outputs so is somewhat more complicated than the circuit shown in post 4.
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Keith Yates - G3XGW VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm |
21st Jul 2017, 4:43 pm | #7 |
Heptode
Join Date: Jan 2003
Location: Tewkesbury, Gloucestershire, UK.
Posts: 693
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Re: Evershed and Vignoles Series 2 Megger problem
Success! I'm pleased to say that the Megger is now working. The problem turned out to be an o/c control circuit resistance. This was a wirewound 100K component (hand wound and marked) which I replaced with a close tolerance metal film type. Calibration is pretty well spot on at 10, 20 and 30MOhm. I must say that the instrument is an absolute pig to work on and was not designed with servicing in mind! The "springs" were literally just that. long phosphor-bronze (?) jobs which helped (a bit) with the disassembly. It was still necessary to unsolder four wires to get access to the internals. The only remaining problem is the switch linkage rod which has a habit of disengaging from the switch rotor arm when changing voltages. I shall leave it at 1000V for testing HV transformers. Thanks for your replies.
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Keith Yates - G3XGW VMARS & BVWS member http://www.tibblestone.com/oldradios/Old_Radios.htm |
21st Jul 2017, 5:16 pm | #8 |
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Re: Evershed and Vignoles Series 2 Megger problem
I have one of the flat type, a very useful instrument. Not used very often but I know it works with a mere twist of the handle, no batteries(cells) to leak. Always ready for action.
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