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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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22nd Feb 2018, 11:23 am | #1 |
Octode
Join Date: Nov 2003
Location: Bath, Somerset, UK.
Posts: 1,805
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AVO8 MK3 reading high
AVO8 MK3 reading high on AC/DC volts and resistance ranges by 30%, current ranges severe overload of movement causing the cut out to operate. This is the sixties version with the diode and thermistor in the shunt circuit. Any pointers as to where to look?
Neil
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22nd Feb 2018, 11:45 am | #2 |
Octode
Join Date: Oct 2007
Location: Exeter, Devon, UK.
Posts: 1,554
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Re: AVO8 MK3 reading high
Sounds as though the universal shunt chain in parallel with the movement has gone open circuit. So the moving coil movement has reverted from 50 ua FSD to its native 37.5ua, which is why everything is reading high.
The thermistor is across the swamp resistor, in series with the movement. The diode is across the movement. As the movement responds, neither of these can be failing. Trace out the panel with the shunt resistors and check continuity - 8k+1.2k+300+450+43+ to total 10kohms. wme_bill Last edited by WME_bill; 22nd Feb 2018 at 11:56 am. |
22nd Feb 2018, 12:48 pm | #3 |
Octode
Join Date: Nov 2003
Location: Bath, Somerset, UK.
Posts: 1,805
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Re: AVO8 MK3 reading high
Thanks Bill, that has given me a head start as to what to look for,
Neil
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22nd Feb 2018, 3:26 pm | #4 |
Octode
Join Date: Nov 2003
Location: Bath, Somerset, UK.
Posts: 1,805
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Re: AVO8 MK3 reading high
Brilliant, just checked over lunch, 0.45ohm O/C as if the resistance wire had snapped in half, will select 0.45ohm this afternoon using the low ohm meter. Thanks Bill,
Neil
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preserving the recent past, for the distant future. |
24th Feb 2018, 6:34 pm | #5 |
Dekatron
Join Date: Aug 2016
Location: Colchester, Essex, UK.
Posts: 4,107
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Re: AVO8 MK3 reading high
So that was the 1.0A (5 turns) shunt that had failed then? Rather unusual.
Dave |
25th Feb 2018, 8:46 am | #6 |
Dekatron
Join Date: Jan 2004
Location: Newcastle upon Tyne, Tyne & Wear, UK.
Posts: 8,194
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Re: AVO8 MK3 reading high
Hi Neil, I may have some resistance wire if you need it.
Ed |