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Old 7th Jan 2019, 9:39 pm   #1
Cathode Ray
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Default Avo 8 faulty- movement bad?

Hi folks,
I have an Avo 8 which dosent read anything on any range.

The movement swings wildly whenever the case is moved.

And when I measure the resistance between + and - terminals in DC current mode I can measure the following resistances:
8k ohms in 0.05 A range
1.3k ohms in 0.3 A range
390 ohms in 1 amp range
40 ohms 10A range
etc...

Can someone confirm this can only be a bad moverment?
Thanks
Ray
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Old 7th Jan 2019, 9:54 pm   #2
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Default Re: Avo 8 faulty- movement bad?

Hi Ray,
It could be less disastrous than that;
1) A wire to the movement has come loose or has a dry solder joint
2) The ('swamp') bobbin which is in series with the movement could have gone open circuit (Refer to the circuit diagram but i think it is an odd amount like 3,333 ohms..?)

What resistance do you get across + and - with meter set to 2.5v DC? Should be 50,000ohms.

(We should have known summat would be wrong with it- it's an ohmen..)

Dave
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Old 7th Jan 2019, 10:13 pm   #3
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Default Re: Avo 8 faulty- movement bad?

Hi Dave,
I get 66.00k ohms in the 3V DC range (its a MK5).


Ray
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Old 7th Jan 2019, 10:19 pm   #4
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Default Re: Avo 8 faulty- movement bad?

And the Reverse MC button is a little sticky, sometimed it dosent want to pop-up.
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Old 7th Jan 2019, 10:27 pm   #5
The Philpott
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Default Re: Avo 8 faulty- movement bad?

I'll get me coat- i thought it was a MkIII- i know nothing about the later ones i'm afraid!
D
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Old 7th Jan 2019, 10:35 pm   #6
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Default Re: Avo 8 faulty- movement bad?

Do you have a source able to provide current as low as 37.5 micro amps? At this point it may be best to try the movement on its own.

The mark 5 can appear daunting at first to work on, but it won't take you long to find your way around. If you can post photos I can help. I may be able to open one of mine and point out where you need to be.

At this point, it could well be an open movement, but we'll need to make some tests first.
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Old 7th Jan 2019, 11:12 pm   #7
Cathode Ray
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Default Re: Avo 8 faulty- movement bad?

Hi Sinewave,
the news is bad im afraid.

I've been watching a video over on YT which helped a lot to dismantle the meter.
I established that the meter coil is open circuit.

Before measuring it, I traced all the wires to the meter and made sure there wasnt an open in the meter feed.
I eventually accessed the meter itself and traced the red and black wires to the movement and continunity was good , so I measured the coil which is open.

So al thats remains is to source a doner meter for the movement.
Now what version would have a compatable meter ? mine is Mk5



Ray

Last edited by Cathode Ray; 7th Jan 2019 at 11:22 pm.
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Old 7th Jan 2019, 11:34 pm   #8
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Default Re: Avo 8 faulty- movement bad?

A mark 6 and 7 movement would fit but wait until you find another mark 5 with poor casing. Check out the radio rallies in the spring/summer, you'll find one.

I've got a good working Mk5 which has a cut out switch which was broken off in the past, I'm probably going to put that movement into another Mk5 which is otherwise good but had an open movement.
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Old 8th Jan 2019, 12:21 am   #9
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Default Re: Avo 8 faulty- movement bad?

Thanks Sinewave,
I'll keep my eyes open for one.

Ray
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Old 8th Jan 2019, 4:05 am   #10
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Default Re: Avo 8 faulty- movement bad?

You could always turn it into a steampunk table lamp and make a lump of cash. Then you could buy another working one.

I'm going to hide now and change my name before the hate mail and life threats pour in.
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Old 8th Jan 2019, 4:11 am   #11
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Default Re: Avo 8 faulty- movement bad?

The trouble is that the case gets wrecked unless you can find one with the bottom of the case smashed.
If not then we will just have to result to hate mail.
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Old 8th Jan 2019, 5:30 am   #12
Boater Sam
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Default Re: Avo 8 faulty- movement bad?

Is this the downside to upcycling? It was only a suggestion, it was my New Years resolution to be helpful and pleasant, difficult when you are a hated miserable old curmudgeon.
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Old 8th Jan 2019, 4:51 pm   #13
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Default Re: Avo 8 faulty- movement bad?

Thanks Sam,
Personally I detest the steampunk era, it's destroying many fine peices and increasing the market price of antique electronic equipment.

I'd rather keep it as what it is, an old Avo waiting to be restored.

Ray
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Old 8th Jan 2019, 5:10 pm   #14
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Default Re: Avo 8 faulty- movement bad?

Quote:
I'd rather keep it as what it is, an old Avo waiting to be restored.
And used as well, they are a joy. I keep my MK8 at work, no one nicks it.
 
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