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Old 18th Sep 2019, 2:55 pm   #1
mikeymouse
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Smile Avo 8 mk V high resist ranges u/s

Hi. I'd be very grateful if I could be pointed in the right direction with my issue. I recently purchased an Avo8 Mkv meter fitted with a miniature voltage converter (part no 6220-126). The meter was described as "appears to be working". More fool me!
On the lowest resist range, the meter zeros and works fine, however on the next two ranges, 100 and 10k, the meter needle stays at the extreme lhs and the zero pots have no effect whatsover. I have replaced the original D cell, cleaned the cell contacts and checked the fuse, all good.
Many thanks for any pointers ...
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Old 18th Sep 2019, 4:18 pm   #2
Sinewave
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Default Re: Avo 8 mk V high resist ranges u/s

Hello and welcome.

Perhaps dirty switch contacts or, more likely the printed ribbon cable has a fault, which connects to the switch terminals. The Mk5 is not difficult to work on, so if the particular circuit in the ribbon is damaged, you can make point to point wiring and solder to each connection.

Here's a link to the manual which contacts schematics.

https://www.vintage-radio.net/forum/...2&d=1421628490
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Old 18th Sep 2019, 6:55 pm   #3
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Default Re: Avo 8 mk V high resist ranges u/s

I replaced the voltage converter module in mine with a battery this restored normal operation
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Old 18th Sep 2019, 6:59 pm   #4
The Philpott
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Default Re: Avo 8 mk V high resist ranges u/s

Testing the output of the VC1 is done using as sensitive a voltmeter as possible, since it's designated current output is very low (90uA i think.)

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Old 18th Sep 2019, 10:14 pm   #5
Sinewave
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Default Re: Avo 8 mk V high resist ranges u/s

Yes, but he's missing one of the ranges covered by the 1.5v battery.
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Old 19th Sep 2019, 8:09 am   #6
mikeymouse
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Thumbs up Re: Avo 8 mk V high resist ranges u/s

Many thanks to all for the responses. Anyone know where I can source spares for this model?
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Old 19th Sep 2019, 10:12 am   #7
Sinewave
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Default Re: Avo 8 mk V high resist ranges u/s

Quote:
Originally Posted by mikeymouse View Post
Many thanks to all for the responses. Anyone know where I can source spares for this model?
Parts now are only available if you're lucky enough to find someone selling parts, second hand or new old stock.

However, you probably don't need any parts. Have you looked at the printed ribbon cables?
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Old 19th Sep 2019, 10:59 am   #8
mikeymouse
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Default Re: Avo 8 mk V high resist ranges u/s

Will do. Many thanks
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Old 22nd Sep 2019, 6:31 pm   #9
mikeymouse
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Default Re: Avo 8 mk V high resist ranges u/s

Hi. Looking for more clues, if you guys can help. My Avo8 mkV is working on the lowest range. The other ranges have no response to their respective zero pots. On the 100 range, the needle goes hard rhs and stays there. On 10k the needle goes hard lhs and stays there. Full travel cw and ccw of their respective pots does absolutely nowt. I have replaced the D cell and used shorting pieces of cables soldered directly to the D cell posts and the corresponding ends are connected to VC1. The output of VC1 measured across the VC1 terminals is approx 14.8V.
Be obliged for any further suggestions.
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Old 22nd Sep 2019, 9:13 pm   #10
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Default Re: Avo 8 mk V high resist ranges u/s

I can only refer you back to previous suggestions unless you've already tried - the printed ribbon cable connecting the range selection switches...
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Old 23rd Sep 2019, 4:37 pm   #11
mikeymouse
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Default Re: Avo 8 mk V high resist ranges u/s

Many thanks for your responses, Sinewave. I was hoping not to open up the box. From your images, as you say, dosen't look too bad to work on. That's my next step. Cheers for the assistance
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