AVO 8 MKV Resistance range problem - UK Vintage Radio Repair and Restoration Discussion Forum

unixmanuk · 10th Sep 2013, 1:56 pm

Yet more AVO 8 problems....a MK V this time.

This example works fine on all ranges, except the x1 resistance range.

Seems that whatever the value of test resistance is applied, it always shows full scale deflection (i.e., zero Ohms), even with quite high test resistance values.

The other resistance ranges seem to be accurate, and both the batteries check out OK.

Appreciate any ideas on this one

Thanks,

Oldtestgear · 10th Sep 2013, 2:04 pm

I recently had one of these through my workshop with the same fault. Turned out to be the 22K pot used to adjust the X1 range. These are no longer available from Megger (hardly surprising but had to check) and the shaft is longer than any pot I could find with a quick search. Should be possible to extend a shaft with a bit of fettling though to get it working again.

Hope this helps.

Phil

unixmanuk · 10th Sep 2013, 2:10 pm

Hi Phil,

Thanks for that - I'll certainly give that the once over.

Was it o/c, or had it changed significantly in value? (my guess is o/c?)

Oldtestgear · 10th Sep 2013, 8:52 pm

Hi,
It was o/c or rather very intermittent!

Goodm luck.

Phil

unixmanuk · 17th Oct 2013, 1:27 pm

Hi,

Just for the record, this turned out to be the printed resistor (R1, 18R4) o/c.

This had obviously caused problems in the past, since it seems to have been "overwound" with what I'm presuming is very fine resistance wire. This wire had fractured in a (fortunately) accessible position, and I was able to effect a bridge repair.

The meter now reads accurately on its x1 low resistance range.

Cheers,

10th Sep 2013, 1:56 pm	#1
unixmanuk Pentode Join Date: Jan 2012 Location: Worcester, Worcs. UK. Posts: 112	AVO 8 MKV Resistance range problem Yet more AVO 8 problems....a MK V this time. This example works fine on all ranges, except the x1 resistance range. Seems that whatever the value of test resistance is applied, it always shows full scale deflection (i.e., zero Ohms), even with quite high test resistance values. The other resistance ranges seem to be accurate, and both the batteries check out OK. Appreciate any ideas on this one Thanks, __________________ John

10th Sep 2013, 2:04 pm	#2
Oldtestgear Hexode Join Date: May 2008 Location: Devon, UK. Posts: 307	Re: AVO 8 MKV Resistance range problem I recently had one of these through my workshop with the same fault. Turned out to be the 22K pot used to adjust the X1 range. These are no longer available from Megger (hardly surprising but had to check) and the shaft is longer than any pot I could find with a quick search. Should be possible to extend a shaft with a bit of fettling though to get it working again. Hope this helps. Phil

10th Sep 2013, 2:10 pm	#3
unixmanuk Pentode Join Date: Jan 2012 Location: Worcester, Worcs. UK. Posts: 112	Re: AVO 8 MKV Resistance range problem Hi Phil, Thanks for that - I'll certainly give that the once over. Was it o/c, or had it changed significantly in value? (my guess is o/c?) __________________ John

10th Sep 2013, 8:52 pm	#4
Oldtestgear Hexode Join Date: May 2008 Location: Devon, UK. Posts: 307	Re: AVO 8 MKV Resistance range problem Hi, It was o/c or rather very intermittent! Goodm luck. Phil

17th Oct 2013, 1:27 pm	#5
unixmanuk Pentode Join Date: Jan 2012 Location: Worcester, Worcs. UK. Posts: 112	Re: AVO 8 MKV Resistance range problem Hi, Just for the record, this turned out to be the printed resistor (R1, 18R4) o/c. This had obviously caused problems in the past, since it seems to have been "overwound" with what I'm presuming is very fine resistance wire. This wire had fractured in a (fortunately) accessible position, and I was able to effect a bridge repair. The meter now reads accurately on its x1 low resistance range. Cheers, __________________ John