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Old 27th May 2019, 8:18 am   #6
Join Date: Sep 2007
Location: Ranfurly, New Zealand
Posts: 134
Default Re: AVO VCM MkIII repair

It's all go around here. I got my second wind and got back to the VCM late this afternoon. I pulled the relay out again as I had virtually convinced myself that it was the main offender. And it was. Before re-installing it I hadn't adjusted anything which in retrospect was a mistake. As you can see from this photo I took before I rewound the coil shows that lower arm which tensions the spring was bent as a result, no doubt, of a previous repairer winding down the adjustment screw to try & stop the relay chattering. Sigh!
Anyway I straightened it up and unwound the adjustment so that there was a good gap between pole piece & rocker arm. Then I adjusted the points for good contact pressure (resistance measured .6 ohm) and refitted the relay.
On power up it behaved, phew!..... and I waited....and waited for the valve diodes to warm up and for the meter to respond . Nothing! Damn...what now? So I swapped V1 and V2 around and hey presto the meter moved to the set mark . That means I need a new DH77 for V2 and hopefully the machine will then work . Obviously I'll have to check calibration and reset the relay later but it looks like I might yet have a long-winded win - assuming there aren't any more hidden bodges I have yet to discover.
I'll wrap it up in a day or two. Mike
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