Is your Digitimer DS3 or DS2A failing and need to be repaired? Or is it something simple……
It might surprise you to learn that many stimulators that our service department have received for repair only need a new set of batteries.
Both the Digitimer DS3 Constant Current Stimulator and the DS2A Constant Voltage Stimulator are powered by batteries. In fact, 11 of them to be exactly. One 9V (PP3) control battery which is used to power the stimulator control circuitry and ten more 9V batteries located in the battery compartment. These provide the compliance voltage source for the stimulator. (Digitimer does NOT recommend rechargeable batteries). Failure of these batteries will result in a weakening of the output, which will be demonstrated by a smaller or absent stimulus artefact and response. And you wouldn’t want to discover that you have failing batteries in the middle of an experiment. Therefore, it’s wise to regularly check them. We’ll show you how.
A battery powered stimulator makes sense due to its inherent low noise (but high voltage power). But, those who are familiar with the DS3 or DS2A know very well that at some point the batteries will need to be replaced….as once they begin to fail their stimuli will become weak or and/or unreliable. It’s a good idea to regularly check the batteries given your specific work flow so that you get a sense as to how often you’ll need to replace them. This way you can make sure your experiments will always have satisfactory stimulation and you can stay ahead of their eventual failure.
Check those batteries!
You can find instructions for battery checking and replacement in the DS3 and DS2A operator’s manuals. However, since you’re here we would like to take this opportunity to describe the process in detail.
Are my batteries failing?
DS3 and DS2A (and even DS4) users will have noticed the battery test sockets on one side of the case (pictured above). These sockets provide access to the battery voltages within the stimulator, allowing to check status of all batteries without having to open up the device. Voltages are most easily measured using the probes of a digital multi-meter set to measure a DC voltage in the expected range. However, it is important to ensure that the voltages are checked while the internal batteries are being stressed. The best way to do this is to set the stimulator to deliver a long (2s) output pulse, trigger the delivery of a stimulus via your usual stimulation electrodes immersed in saline or aCSF and measure the test socket voltages using the multi-meter. Quite often, the stimulator battery pack will show a normal voltages when the batteries are at rest, but as soon as a stimulus is being delivered, the voltage drops significantly, indicating failing batteries.
How do I know that it’s too low?
If the control battery voltage is below 6.5V, then the control circuit within the stimulator will start to fail soon and battery replacement is recommended. The appropriate time to replace the compliance batteries is determined by the voltage that is required to pass the required stimulus. In the case of our constant voltage DS2A, if the battery voltage has declined to the extent that it is below the voltage setting normally used, then the batteries clearly need replacing.
For constant current devices like the DS3 (or DS4), it is important that the battery voltage is enough to pass the requested current through the stimulation electrode(s). For example, if you typically stimulate with 10mA through a 5kohm stimulating electrode, Ohm’s law predicts that the voltage required to do this would be 50V. Therefore it is important to ensure that the battery voltage never falls to this level. If you don’t know the typical impedance of your stimulation pathway, then you can use a multi-meter to measure it, giving you some idea of the lowest voltage you can allow the stimulator battery pack to drop to.
How to replace the batteries.
In the case of the DS2A and DS3, it is necessary to remove all four of the case screws on the bottom (picture below) and slide the two halves of the stimulators apart, taking good care not to strain the interconnecting cable between the stimulator motherboard and the battery pack.
Once separated, the two halves can be completely disconnected from each other by unclipping the small white plug next to the control battery housing.
At this point the control battery can be removed and replaced.
Access to the remaining 10 batteries is achieved with the removal of the four screws holding the black battery pack in place. Once these are removed, the battery pack can be lifted away and inverted, revealing the ten individual batteries and associated wiring harness.
Each battery should be removed from its battery clips and replaced with a new good quality alkaline equivalents. Note that Digitimer does not recommend use of rechargeable batteries as their voltages can decline significantly without any warning, making them less reliable than disposable batteries.
The stimulator can then be reassembled by reversing the process, taking care to re-attach the battery pack cable and ensuring it is not pinched by the case halves when they are brought back together.
If, after all of this and with fresh batteries, you find that your stimulator still doesn’t work then please contact us so that we can discuss arranging having the stimulator repaired.