AVO8 mk5 mechanical problem - UK Vintage Radio Repair and Restoration Discussion Forum

hugozair · 23rd Jul 2021, 7:16 pm

I have just acquired another Avo8 Mk5 which has a problem with the 37.5 uA movement. If I "twist&turn the whole thing or apply a voltage the pointer stops dead abrupty at 1/10th FSD. I've opened it but in this "modern" version the movement is buried.. I wondered if anyone could suggest what could be the obstruction.. and whether it's worth what looks like a nightmare de-construct.. Thanks for opinions.. Roger

newlite4 · 23rd Jul 2021, 8:57 pm

I have had this problem before. I discovered that the magnet was slightly off-centre as described in this site:

https://www.petervis.com/avo-meters/...-movement.html

The magnet is not particularly well secured within the movement housing and is prone to shifting. Once the transparent cover is peeled off, access to the magnet is fiddly but do-able.
Neil

Jon_G4MDC · 24th Jul 2021, 10:05 am

Whiskers of iron filings in the coil gap are also common if the glass has worked loose.

hugozair · 24th Jul 2021, 7:40 pm

Thank you both.. I've nothing to loose by trying.. Roger

hugozair · 8th Aug 2021, 7:34 pm

Looking closely at the top end of the movement I can see a pin lying across the magnet. This pin looks remarkably like the one that sticks out at right angles to the needle on the other side.(pic) if it's that thats come off how was it fixed and do I have any chance of fixing it ?

23rd Jul 2021, 7:16 pm	#1
hugozair Triode Join Date: Jan 2010 Location: Penzance, Cornwall, UK. Posts: 34	AVO8 mk5 mechanical problem I have just acquired another Avo8 Mk5 which has a problem with the 37.5 uA movement. If I "twist&turn the whole thing or apply a voltage the pointer stops dead abrupty at 1/10th FSD. I've opened it but in this "modern" version the movement is buried.. I wondered if anyone could suggest what could be the obstruction.. and whether it's worth what looks like a nightmare de-construct.. Thanks for opinions.. Roger Last edited by hugozair; 23rd Jul 2021 at 7:17 pm. Reason: added Mk5

23rd Jul 2021, 8:57 pm	#2
newlite4 Octode Join Date: Nov 2003 Location: Bath, Somerset, UK. Posts: 1,805	Re: AVO8 mk5 mechanical problem I have had this problem before. I discovered that the magnet was slightly off-centre as described in this site: https://www.petervis.com/avo-meters/...-movement.html The magnet is not particularly well secured within the movement housing and is prone to shifting. Once the transparent cover is peeled off, access to the magnet is fiddly but do-able. Neil __________________ preserving the recent past, for the distant future.

24th Jul 2021, 10:05 am	#3
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: AVO8 mk5 mechanical problem Whiskers of iron filings in the coil gap are also common if the glass has worked loose.

24th Jul 2021, 7:40 pm	#4
hugozair Triode Join Date: Jan 2010 Location: Penzance, Cornwall, UK. Posts: 34	Re: AVO8 mk5 mechanical problem Thank you both.. I've nothing to loose by trying.. Roger

8th Aug 2021, 7:34 pm	#5
hugozair Triode Join Date: Jan 2010 Location: Penzance, Cornwall, UK. Posts: 34	Re: AVO8 mk5 mechanical problem Looking closely at the top end of the movement I can see a pin lying across the magnet. This pin looks remarkably like the one that sticks out at right angles to the needle on the other side.(pic) if it's that thats come off how was it fixed and do I have any chance of fixing it ? Attached Thumbnails