Sifam VU Meter AL29W

[timtom]

I have this SIFAM VU METER that isn't really working. I tried to put a signal with the 3,9k resistor in series but nothing moves. Is it possible that the rectifiers are damaged ?

 

[JohnRoberts]

A low range ac voltmeter suitable for connecting across a 600 ohm line and self contained except for requiring an external 3.6k ohm resistor. Calibrated for use with a 3.6k ohm resistor 4vu above the scale marking so that the reference deflection (0vu) is produced by a signal 4vu above 1mW in 600 ohms (1.228v).

The performance of the meter is based upon the requirements of BS 6840: Part 17:1991, IEC 268 - 17: 1990. The dynamic characteristics quoted, which requires the response time to 99% of reference deflection (0vu) to be 0.3 seconds +/-10% with an overswing of at least 1.0% but not more than 1.5% are not fully met.

The overswing, because damping is not so tightly controlled but allowed to spread within normal design restraints, can vary between deadbeat to 5%. To specify the dynamic characteristics in terms of time to 99% of 0vu under such circumstances would give an unrepresentative measure of the speed of response. For this reason the time to reach -3vu with a steady reading of reference deflection (0vu) has been taken as a more realistic measure.

The following comparison can be made based on a rise time to -3vu with steady deflection of 0vu:

Conventional vu meter 0.13 - 0.15 seconds

AL19 0.14 - 0.18 seconds

Did the meter stop working or have you never seen it work?

Perhaps troubleshoot for broken wire or worse. Do you measure anything with a VOM?

JR

 

[timtom]

I have never seen it work. How can I measure it?

 

[JohnRoberts]

If it has a broken wire it will read open circuit... otherwise there is a diode in series with a meter winding.

JR

 

[moamps]

I have this SIFAM VU METER that isn't really working. I tried to put a signal with the 3,9k resistor in series but nothing moves. Is it possible that the rectifiers are damaged ?

The needle of the instrument is in a very unnatural position, it is probably mechanically blocked or even the movable system is damaged. Newer instruments have a very sensitive suspension system and I have already had several cases of damage that could not be repaired.
Open the instrument and check if the needle can move freely or is stuck somewhere.

 

[timtom]

I checked everything and I looks like its somehow mechanically broken....

 

[Script]

Those sure were not cheap. Before opening it up...

Did you buy and receive it in that condition ? If so, maybe contact them first.
Otherwise, can it be somehow mechanically fixed ?

 

[Rob Flinn]

Those sure were not cheap. Before opening it up...

Did you buy and receive it in that condition ? If so, maybe contact them first.
Otherwise, can it be somehow mechanically fixed ?

I think the AL29 was the cheap model in the Sifam range. Used to cost about £30 U.K. The expensive ones were like the ones in this pic I ,with a much bigger motor unit on the back.