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Old 27th Apr 2021, 5:12 pm   #1
technotel
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Default AVO 8 mk5

Can anyone help with an issue I have with this AVO 8 mk5 I picked up cheap on a famous auction site.
The x100 & x10k ohms ranges do not work at all. No needle movement. low ohms range is fine. I have fitted new batteries and checked values of R2 =2k16ohms. R3=51k which apparently can cause this problem. Values are fine.
However. R5 should read 1.8mohm. and it measure nearly 2meg. I am wandering if this maybe the culprit but do not have a 1.8meg resistor at the moment to try. See screen capture of that part of circuit. I am having problems tracking down a 1.8m ohm resistor. does not seem to be a preferred value anymore??
Any ideas ??
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Old 27th Apr 2021, 5:50 pm   #2
Sinewave
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Default Re: AVO 8 mk5

The value of that resistor won't make those ranges not work. Likely culprit are the printed ribbon cables and their connections if the battery is fine.
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Old 27th Apr 2021, 6:05 pm   #3
technotel
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Default Re: AVO 8 mk5

Hi Sinewave
Yes I have belled out the ribbon cable and appears to be fine although it looks battered and I see one route has had a wire put in to replace it as it was o/c. Do you think there is any mileage in changing the ribbon cable for a wire loom? would this effect the resistance, totally mess up the calibration??
many thanks
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Old 27th Apr 2021, 6:09 pm   #4
Sinewave
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Default Re: AVO 8 mk5

If it was totally ruined then cable would be ok, but calibration checks would need to be made. Whilst the ribbon may be ok, the terminations can be dodgy if its been got at before.
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Old 27th Apr 2021, 6:24 pm   #5
technotel
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Default Re: AVO 8 mk5

Thanks for the advise. I think I will rewire it to be sure.
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Old 27th Apr 2021, 7:27 pm   #6
vosperd
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Default Re: AVO 8 mk5

PM sent re mkV for spares.
Don m5aky
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Old 3rd May 2021, 3:03 pm   #7
technotel
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Default Re: AVO 8 mk5

Hi all
quick update on this AVO 8 MK5 repair. I found the x100 22kohm pot was the culprit. I have added a couple of images. The pot was broken but oddly enough still giving a resistance!! Thanks to Don who donated an old AVO mk5 to me. I was able to use a pot from it. The x10 and x100 sprang into life. Many thanks Don. Going to go through set up now with manual. Happy days. I rewired the battered ribbon cable first but this wasn't the problem.
Terry
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