AVO 8 mk5 problems

[ORAWA01]

Yes, it would be great help. Not sure if I will have quiet time for working on the AVO8 tonight, but will be good reference before opening the meter, because I have never had this meter before. Thanks.

[ORAWA01]

Checked again with the other DMM, but on the terminal of the AVO8, OC on every settings on both dials.

Same on the 3KV terminals too. Will open it, and see the meter and also PCB, Switches for OC.

[ORAWA01]

Managed to open the meter, and it seems it is a topicalised version. It has a strong rubber frame washer all around the seam, and was tough to open. Used a pry bar from mobile phone tool set, and it almost bent the bar.

When opened, inside was very clean. There was continuity from the lead terminal to PCB where the wires were soldered. But from that point, not sure where to check for the continuity.

The movement was fine. Moved nicely when checked with 0.5V DC from my DMM ohm settings.

[ORAWA01]

Looking at the youtube video on AVO8 mk5, it looks like my AVO8 has same problem as the one in the video, something is broken on the CUT-OUT switch I was wondering.

https://www.youtube.com/watch?v=Ew_HrAxTPvk

[Sinewave]

If your cut out it open, the meter dampening would not be present, so instead of the pointer moving about softly it would very wildly and loosely move around. That's a quick test you could perform before getting to the cut out.

[stuarth]

Unless I've mis-read the circuit, the AVO cut-out is in series with the black input (-) input terminal, so if the cut-out were open circuit, the damping would still be connected across the movement.

An earlier post (#3?) seemed to show damping changing as the meter was switched between off and an actual range.

An open-circuit movement would not cause the meter to be open circuit at the input terminals when switched to a DC or AC current ranges, but an open-circuit cut-out would.

Stuart

[ORAWA01]

I connected a pp9 battery to the leads and probed the points of the copper rail on the two dials. The meter shot up to the end with fast and powerful speed, and as the needle hit the end of the meter, it returned swiftly with the same fashion. There was no sign of soft damping in this movement.

[Sinewave]

Originally Posted by stuarth

Unless I've mis-read the circuit, the AVO cut-out is in series with the black input (-) input terminal, so if the cut-out were open circuit, the damping would still be connected across the movement.

An earlier post (#3?) seemed to show damping changing as the meter was switched between off and an actual range.

An open-circuit movement would not cause the meter to be open circuit at the input terminals when switched to a DC or AC current ranges, but an open-circuit cut-out would.

Stuart

Yes, the cut out opens the common terminal. Memory may not serve me well, but I seemed to recall loss of dampening with an open cut out. I'll have to go and check, I've got one around here somewhere.

[stuarth]

I’m not sure what you meant when you said you probed inside the meter.

What you should do is set the AVO to its 10V DC range, connect the 9V battery to the AVO terminals, then probe inside the AVO with your DVM on its voltage range.

If you probe inside the AVO with the battery, or with the DVM on its resistance ranges, you risk damaging the movement.

Stuart

[ORAWA01]

Originally Posted by stuarth

I’m not sure what you meant when you said you probed inside the meter.

What you should do is set the AVO to its 10V DC range, connect the 9V battery to the AVO terminals, then probe inside the AVO with your DVM on its voltage range.

If you probe inside the AVO with the battery, or with the DVM on its resistance ranges, you risk damaging the movement.

Stuart

Yes, that was my mistake. I shouldn't have connected the pp9 directly to the lead, and probed the AVO8 dials. The movement shot to the end with such a speed, and returns to the 0.
The reason I did that was, I thought the movement might be locked up or dead, because before that it really wasn't moving, and not moving very much.

I will connect the pp9 to the terminal with the cable, and follow the instruction.
I might have to open further, and take off the pcbs and boards to troubleshoot the AVO8, which I am not too keen to do. But if that is the last option and has to be done, then will go for it.