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Testing the voltage of the 2032 coin-cell battery

Lithium coin-cells have a smaller electrical capacity and greater chance of electrolyte evaporation or leakage

than cylindrical cells. It would not be surprising if a coin-cell was still working fine after 20 or 30 years, but

I suggest opening the machine, as described above, and checking the voltage after 10 years, and then every 5

years after this.

Once the back has been removed from the machine, as described above, the voltage can be measured with a

digital volt meter at the metal contacts of the socket, which are visible at either side of the holder in the first

picture above. As long as the voltage is above 3.0 volts, and there is no sign of leakage and corrosion, the

battery should be fine for another five years or so. Since 2032 cells are inexpensive, a better approach

would be to install a fresh one every 10 years. Check the old battery and the battery holder for any signs

of corrosion.

Testing the VRAM voltage

VRAM is the voltage which drives the memory chips. In machines with Option B or C, this is directly

connected to a large electrolytic capacitor – 6,800uF – which is located in the lower part of the case, to the

left of the battery compartment. This voltage will be driven high, such as to 5 to 5.5 volts, when the machine

is powered on. After that, the voltage will drop slowly. If there are no C-cell or coin-cell batteries installed,

then over time (days to months, depending on the internal leakage current of the capacitor, the current drawn

by the memory chips and any other sources of leakage) the voltage will fall. The chips will probably retain

their data down to 2.5 or 2.0 volts.

If you are interested in the rate at which the voltage falls, you can measure the voltage without dismantling

the machine. Making two measurements hours, days or weeks apart will enable you to estimate how long

the memory contents would be retained in the absence of both the C-cell and the coin-cell batteries.

As shown in the following image, the positive wire of the capacitor is extended so it can be contacted

through the gap just to the left of the positive C-cell battery contact, once the battery compartment door is

removed.

To do this, use a digital multimeter (DMM), set to its 20 volt or similar scale, and connect the positive lead

to this wire, with the negative lead going to ground, such as the metal outer part of the CV Out or Gate Out

TB-303 sockets on the rear panel. Assuming the DMM presents a 10M ohm load to the circuit (it may be

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Cyclone Analogic Bass Bot Manual do Utilizador Página 12