AVO 8 Mk.III A.C. voltage not functioning. - UK Vintage Radio Repair and Restoration Discussion Forum

brunel · 14th Apr 2012, 7:10 pm

All other ranges are ok. It appears to be one of the switches on the AC switch cam/range switch.

On any of the voltage positions, I can see the leaf moving up, but not quite making contact with the leaf above, it is only a minute fraction out.

On any of the AC current ranges, the same switch moves slightly more and does make contact.

What is the correct and easiest way of solving this?

pmmunro · 14th Apr 2012, 7:16 pm

If the switch leaves concerned are making on some ranges but not on others it could be worth checking that the face cam has not come slightly loose and turned on the end of the knob spindle.

PMM.

brunel · 14th Apr 2012, 7:21 pm

Thanks for the info. PMM.

Is it fairly easy to detect this problem?

And what do I do to fix it?

brunel · 14th Apr 2012, 10:04 pm

I checked the face cam, it was secure, I did tighten the securing screws another quarter turn.

One thing I did notice, the lobe that actuates the voltage switch appeared to be
lower than the lobe that actuates the current switch by approx 1mm.

I took what I believe to be the only course left, a slight adjustment of the lower leaf switch towards the face cam, only just enough room to grip it with a small pair of long nose pliers.

The switch now makes contact on all AC volt ranges, and this old AVO now reads correctly on AC volts.

MrElectronicman · 14th Apr 2012, 10:50 pm

I had exactly the same problem with my AVO, and I used the same technique.

If that have not worked I was prepared to remove the leaf switch, disassemble it and adjust the springs. Shades of the old GPO when I was a youth-in-training in the local telephone exchange.

pmmunro · 15th Apr 2012, 8:16 am

As you will see from previous posts, it is very likely that the Avo leaf switches are directly related to PO 3000 style relay contacts.

Good to know another Avometer has been restored to full health.

PMM

14th Apr 2012, 7:10 pm	#1
brunel Hexode Join Date: Sep 2005 Location: LEEDS.......north of the River Aire. Posts: 429	AVO 8 Mk.III A.C. voltage not functioning. All other ranges are ok. It appears to be one of the switches on the AC switch cam/range switch. On any of the voltage positions, I can see the leaf moving up, but not quite making contact with the leaf above, it is only a minute fraction out. On any of the AC current ranges, the same switch moves slightly more and does make contact. What is the correct and easiest way of solving this?

14th Apr 2012, 7:16 pm	#2
pmmunro Heptode Join Date: Jul 2004 Location: Dundee Posts: 620	Re: AVO 8 Mk.III A.C. voltage not functioning. If the switch leaves concerned are making on some ranges but not on others it could be worth checking that the face cam has not come slightly loose and turned on the end of the knob spindle. PMM.

14th Apr 2012, 7:21 pm	#3
brunel Hexode Join Date: Sep 2005 Location: LEEDS.......north of the River Aire. Posts: 429	Re: AVO 8 Mk.III A.C. voltage not functioning. Thanks for the info. PMM. Is it fairly easy to detect this problem? And what do I do to fix it?

14th Apr 2012, 10:04 pm	#4
brunel Hexode Join Date: Sep 2005 Location: LEEDS.......north of the River Aire. Posts: 429	Re: AVO 8 Mk.III A.C. voltage not functioning. I checked the face cam, it was secure, I did tighten the securing screws another quarter turn. One thing I did notice, the lobe that actuates the voltage switch appeared to be lower than the lobe that actuates the current switch by approx 1mm. I took what I believe to be the only course left, a slight adjustment of the lower leaf switch towards the face cam, only just enough room to grip it with a small pair of long nose pliers. The switch now makes contact on all AC volt ranges, and this old AVO now reads correctly on AC volts.

14th Apr 2012, 10:50 pm	#5
MrElectronicman Hexode Join Date: Feb 2011 Location: Washington DC, USA Posts: 416	Re: AVO 8 Mk.III A.C. voltage not functioning. I had exactly the same problem with my AVO, and I used the same technique. If that have not worked I was prepared to remove the leaf switch, disassemble it and adjust the springs. Shades of the old GPO when I was a youth-in-training in the local telephone exchange. __________________ David

15th Apr 2012, 8:16 am	#6
pmmunro Heptode Join Date: Jul 2004 Location: Dundee Posts: 620	Re: AVO 8 Mk.III A.C. voltage not functioning. As you will see from previous posts, it is very likely that the Avo leaf switches are directly related to PO 3000 style relay contacts. Good to know another Avometer has been restored to full health. PMM