Schaub Lorenz Music Center 5001

[Joe_Lorenz]

Hello,
judging from your accurate description I would start to investigate as follows:

1. If the voltage across the coil drops so hard, there may be a short in the coil windings. If you do not have any data of the coil I would try a different 12V relay. Car relays are not the best choice as they often need very high current to operate. They are build to serve extreme rattling and shaking conditions.

2. The other possible problem could be in the supply branch for that 12V source: A resistor having risen its value, a diode having become blind or similar faults.

I would try to operate that original relay using an external 12V source. So you can decide easily where to look next.

Regards, Joe

[ms660]

Does the replacement relay have a similar coil resistance as the original relay?

Lawrence.

[Termorilis]

The mercury relay coil measures 26 ohms. The replacement relay coil is approximately 128 ohms. I tried to replace with another relay always mounted in the same alarm but the result is the same: it does not trip. The coil of the latter relay is 94 ohms. Isn't it risky to power the original 12v mercury relay with an external power supply? Doesn't it hurt? The relay is mounted in a circuit with a 390 Ohm resistor and a series diode. I also checked the diode and resistor - they are ok.

[ms660]

Based on the voltages in the schematic, with the original relay the current flowing through its coil and the 390 Ohm resistor will be approx. 40mA.

To get 12 volts across your 12 volt relay from the same supply you would have to replace the 390 Ohm resistor with a 53 Ohm resistor and the current flowing through its coil will then be approx. 94mA, more than twice that than with the original relay, that might stress the 18 volt regulator transistor.

An alternative would be to use a relay that passes 40mA or less through its coil and change the 390 ohm resistor to a value that suits.

Lawrence.

[Termorilis]

Thanks so much for the info Lawrence. Could I find alternatively a mercury relay with similar characteristics to the original one? On the net there are for sale but I can not understand the characteristics.

[ms660]

I don't know, I've never seen that type before, a single pole double throw reed relay might be suitable as long as the coil current is 40mA or less.

Lawrence.

[Termorilis]

I have found a suitable relay for 9V. Bought in the electronics store. I connected to the circuit without changing the 390 ohm resistor. Shoot! Now you need to mount it and remove the mercury one. I will keep it. It is part of the history of the Music Center. I have to find a suitable box to prevent it from getting damaged.

[Termorilis]

I assembled everything.
I isolated the relay from the rest of the circuit. I avoided making extra holes and soldering in the printed circuit in order not to upset the original structure. After adjusting the erase voltage based on the discussion of the previous Music Center, it now records fine.

[Termorilis]

Another problem: at the end of the recording I hear a loud buzz in the loudspeaker instead of the pilot tone. Automatic return does not trigger. In addition to the pilot tone relay contacts, if I make a jumper the automatic return does not trigger. I have to find out why.