My latest additions - AVO8 & RF Sig Gen

[Yorkie]

Got some time to check out the sig gen and the AVO. Alas the AVO does not work on the x10k ohms range. The needle moves slightly when I short the leads but does not deflect across to zero like on the other two ranges. Before I go opening it up I'd be glad for any advice on things to check out. Its a MKV so I'm reluctant to move those plastic flat cables around too much.
John

Hi John,

If you can get full scale deflection and can zero the needle on the other two ranges, (x1 & x100) that suggests that the problem is the 15V battery, because the other two ranges rely only on the 1.5V cell. Worth testing the voltage on the 15V battery, which you can do on the AVO as the batteries only come into use on the Ohms ranges - not the voltage ranges. (Just a point if ever you fail to get a movement on the x1 and x2 ranges: check the 1Amp fuse as well as the 1.5V cell, which is in series with the fuse).

The flat B154 15V battery is, I think, unobtainable now, but it's claimed that the circular replacement will fit, though you'd need to check that. They're 34.9mm long, and 15.1mm diam, and you can get them from the Small Battery Company here:

http://www.smallbattery.company.org.uk/s...rious,B154

Do you have the 29 page manual? If not, I can e-mail it to you if you PM me with your e-mail address.

If you do have the manual, you'll see that if the fault doesn't lie with the 15V battery, you can narrow it down to switch contacts and to two resistors - one, a printed resistor 'R2', the other, the 15k preset pot 'RV2' which is in series with R2. Of course, the circuit looks a lot simpler than does the instrument when you open it up!

The fact that you are getting any deflection at all seems to exonerate the switch contacts, and I think it unlikely that the resistors are duff, so a replacement battery is my best guess. I think it unlikely that the calibration of RV2 is out, unless there are signs of tampering.

Hope that helps a bit.

(I'm not an Avo afficanado by the way - I don't own one, and the above comments are based on studdying the dircuit - not from personal experience).

Best of luck with it!

David

[Geaney]

I will check the battery right away - been in there since 1990 so entirely possible that its the culprit. Thanks for the pointer Alan......

John

[Bushbaby]

Hi John,
I've just noticed this thread, 2 good bits of kit there.

Regards

Rob

[Joe]

There are three dealers on e-Bay selling BLR121 batteries.

- Joe

[tiv48]

i have some BLR121 batteries if you need one just pm me your address and i will send you one
rob t

[Jamie-Skinner]

Maplin also sell them but they don't have maplin where you are.

[Bushbaby]

Hi All,
Am I correct in thinking that the only benefit in using the 15v battery is that it allows higher voltage measurements to the Avometers max range?

Regards

Rob

[Yorkie]

Hi All,
Am I correct in thinking that the only benefit in using the 15v battery is that it allows higher voltage measurements to the Avometers max range?

Regards

Rob

Yes Rob, a glance at the circuit will show that the 15V battery only comes into play on the x 10k Ohms range - the x1 and x10 Ohms ranges are powered from the 1.5V cell.

As I said earlier, if anyone needs the 29-page AVO8 MKIV manual (1.7mB PDF), I'll happily e-mail it if they PM me with their e-mail.

David

[Geaney]

Thanks Guys,
I have the manual David so I've no excuses - I'll get to it hopefully at the weekend. Maplin did ship stuff to me a while back so I might be able to use them again.
Many thanks for the offer of the battery Rob - I'll be in touch once I verify that's what I need.
I'll be jumping in the car and heading off to Ireland again in a few weeks - a few more radios to pick up and rescue from the dump - some projects to keep me going through the winter!
John.

[tiv48]

hi john
battery sent today,i think i can explane why some companys wont send to your country it not being in the eu, i had to fill in a custums form may be too time consuming (expensive) for them to get involved
rob t