AVO VCM163 Relay testing/Operation.

[dawaterfall]

Can anybody here outline exactly how to test the relay protection circuit on these testers ? I think I have followed the service manual correctly but the relay does not operate under test conditions. It does work and remains latched on if I push the metal end plate on it until the secondary contacts make.
Thanks.

[Bazz4CQJ]

There does not appear to be any info in the manual to say what the nominal operating voltage of the relay is, though the capacitor across is it only rated at 30 volts, so the relay might well be 12 volts. I would replace the capacitor as a matter of course and then explore activating the relay by connecting it to an external 0-24V PSU.

B

[Dekatron]

I was asked by David in a private message here on the forum about the relay, my answer and his answer to the question can be seen below - I didn't spot the question here before today.

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Hi, I wonder if you could help me on testing my recently aquired 163 ? I don't appear to be able to get the relay to operate. It will latch correctly if the end plate is pressed until the secondary contacts supply the power to the coil. The manual is quite simplistic on how to test it, so I may have misinterpreted where to make the connections with the 960 ohm resistor etc.
Thanks, David.

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Hi David,

At what voltage does the relay trip if you set it up like in the service manual?

The relay should have an internal resistance of 1.2 Ohm. If it has been damaged due to prolonged time in the on position, or if it has "chattered" due to over current that didn't quite trip it fully it could be damaged due to overheating.

You should also check the relay contacts to see if they are burned due to arcing and also check the contact resistance.

The only ways of adjusting this relay is by either bending the contact fingers or by bending the L-shaped bracket that moves the contact finger, the one that is drawn to the coil when the relay is energized. This should only be done with the proper tools as it might otherwise upset the fine balance between the contact fingers and the moving arm which means that the relay won't trip properly. If you are going to change anything I suggest that you leave the fingers alone and just bend the L-shaped bracket. Before you bend this bracket put it on a piece of paper and use a pencil to draw lines which shows what angle it had to begin with so you can get it back in shape if necessary. Bending it might be easy or hard depending on what your bracket looks like, some are solid metal and some have a cut which eases the bending. Just bend it a few tenths of a millimeter as that is usually enough to compensate for the possibly worn down pieces that move the contact fingers.

If the relay doesn't have the correct internal resistance you will probably have to have it rewound. If it needs to be rewound it would be kind of you if you could tell me how many turns it needs and of what diameter the copper wire is.

I've had to bend the bracket on two relays to get them to perform properly.

The test procedure is quite straightforward to me, just hook the 960 Ohm / 30W resistor up between anode and cathode on the valve panel, set anode volts to 12.6 and Ia to 100mA test circuit selector to "Test", then turn Anode volts up step by step, the relay should trip somewhere between 175V and 350V but never at 150V. The relay usually trips closer to 350V than 175V.

Cheers,

Martin

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Hi, thanks for the reply. The relay does actually work, I needed to be a bit more brutal with it to get it to operate. I was concerned that the meters were going fsd during the time I was switching the anode volts upward. Setting the anode switch at 275/300 or above then switching the tester on, relay operates OK. I have now followed all tests (except the one's needing a standardised valve) in the service manual and apart from from minor pot resetting the unit measures within spec on all but one of the tests. DC current on a fluke 189 figures are -5% - this I can live with (could be instrumentation error using the modern uncalibrated fluke). I don't suppose you have a scanned copy of the vcm163 only data manual do you? It's easier to read than the others available.Thanks, David.

[Bazz4CQJ]

Thanks for sharing that info Martin; always useful to know.

B

[Dekatron]

I forgot to write that corrosion on the metal parts has also been a cause for the relay not actuating correctly, the corrosion blocks the L-shaped bracket to move properly.

You will find this corrosion on the pivot point where the bracket rests on the relay body, this is a thin edge that the bracket rests on and if too much corrosion builds up there the bracket either sticks or the layer of corrosion blocks it from moving the full swing.