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Old 20th Oct 2018, 11:32 am   #1
Superscope
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Default Heavy Duty AVO meter Mk 5

Hi Group,

Can somebody help me with a Heavy Duty Avo meter, Mk 5 I think (1965).
I've never actually seen a Heavy Duty Model before in the Flesh until this one.

Somebody has been inside, as expected with equipment this old and I can see some repairs which do not look particularly good.
I think the Cutout has been bypassed which is surprising as it appeared to work fine when I tested it.

Anyway, I can't find a Service Manual for this Model, and the Schematics on line are very poor quality. Can anybody point me in the right direction for
any of those?

Alternatively, and actually preferred, would anybody have any good Quality
Photo's of inside the meter?

I am particularly interested in how many Wires should be going to the
Meter Movement Module.
Where they come from and where they go too?

There are 4 on the one I have, and I think at least one shouldn't be there.

Thanks in advance for any help

Ian
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Old 20th Oct 2018, 12:12 pm   #2
John M0GLN
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Default Re: Heavy Duty AVO meter Mk 5

I've got a copy of the Avo instruction manual with circuit etc and will send it to you if you PM me with your email, attached is a screenshot of the circuit, is it any better than yours? If not then both of us will have to wait and see if a better one turns up.

John
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Old 20th Oct 2018, 12:19 pm   #3
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Default Re: Heavy Duty AVO meter Mk 5

Hi John,

Thanks for the Screen-shot, but that looks like the same
one I have.

I never had need for a HD Manual until now, and didn't
realize there was no Service Manual or good quality User
Manual (with Schematic) available. At least none that I
could find.

Even if I can't find a good Manual, a good Photo would
help me out.
Would like to see how an original should look before I
start stripping out some ugly repairs.

Ian
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Old 20th Oct 2018, 2:07 pm   #4
John M0GLN
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Default Re: Heavy Duty AVO meter Mk 5

The actual manual I have is easily readable, the circuit itself is the worst but even on this it's only about 8 resistors whose numbers are totally blurred, nevertheless it would be nice to have a better copy, have you any photos of the areas in question? This would give me an idea of what you want so I could take the same views.
I find my meter is excellent, accurate and I use it quite often.

John
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Old 20th Oct 2018, 2:43 pm   #5
Alf
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Default Re: Heavy Duty AVO meter Mk 5

Check this site, some info.
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Old 20th Oct 2018, 3:48 pm   #6
Alistair D
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Default Re: Heavy Duty AVO meter Mk 5

I have a heavy duty here. Not sure if it is a Mk5 but it looks the same as the one in the Bama manual.

PM me an email address and I will send you some Hi-Res pictures of the innards.

Al
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Old 20th Oct 2018, 5:05 pm   #7
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Default Re: Heavy Duty AVO meter Mk 5

Thanks Alf,

I have that one too already.

I have attached a pdf with Photo's on, and labeled the Area's
I'm trying to work out. I hope it makes sense.

It looks like the Positive Movement supply has been cut and a Preset Pot
has been placed in line.
Although, I haven't seen inside an HD before, so it could be replacing R17
which I assume is some kind of Swamp resister.
What I can read of the Schematic would support this.

The Pink wire, I think has been used to bypass the Cut Out all together, so
I think this shouldn't normally be there.

Also, is that a Magnetic Shunt I have labeled on the last Photo?
If so, it doesn't seem to do anything, although I haven't got the Movement
set up yet for calibration. I believe it is 600uA FSD


Ian
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File Type: pdf HD5 Photo's & Wiring Questions.pdf (711.5 KB, 112 views)
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Old 20th Oct 2018, 6:06 pm   #8
chriswood1900
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Default Re: Heavy Duty AVO meter Mk 5

There is also a reasonable copy of the manual here along with some other info http://www.richardsradios.co.uk/AVO/HDmk5.pdf
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Old 21st Oct 2018, 9:17 am   #9
John M0GLN
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Default Re: Heavy Duty AVO meter Mk 5

I can't answer all your specific questions except the obvious, like that preset isn't an original, but I have attached 3 general views which may help, my camera isn't the best but someone else may be able to provide higher def' ones if required.

John
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Old 22nd Oct 2018, 2:59 pm   #10
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Default Re: Heavy Duty AVO meter Mk 5

John, Al,

Thanks for the Photo's, they were actually quite helpful.

I made a couple of assumptions which were wrong.
The Meter Movement does indeed have Four connections.

Because the Cut Out is physically located on the Movement
Chassis, there are two connections for it.
One going to the Negative Terminal, and one going to the
Resistance Board.
The Schematic would suggest the Cut Out connects directly
to the Meter Movement, but it doesn't, it connects to the
Resistance Board and then a Pink Wire comes back from that
point to the Movement.
Then the Fourth Wire is the Movement Positive connection.

The HD is now all back together and working of a fashion.
The Meter Pointer was bent and Twisted when I got it, I have
straightened this, but the Meter is still a little bit Sticky.

The Ohms x1 doesn't work, the meter just pegs on a Short
regardless of where the Adjustment is set.
The x 100 works fine.


Ian
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