Technical Information
117
CVA 4062/CVA 4066/CVA 4068 Coffee Systems
temperature (steam = 160°C; coffee = 116°C). As a final layer of protection, the
temperature fuses are calibrated to open at 216°C. Once this fuse opens, the heater
will no longer operate.
“Runaway Heater” Scenario:
In some cases, a TRIAC can fail. This device can fail open or shorted. If it fails open,
AC power can no longer be sent to the heater. If it fails shorted, it will continuously
deliver AC to the heater, regardless of the NTC feedback. At this point, the heater will
cycle based on its bimetal self-resetting thermostat. Since this is a mechanical device
being stressed in this scenario, it also can possibly fail. Once this happens, the heater
can ‘run away’ and possibly damage other components or the entire appliance. This is
where the temperature fuse will activate and shut the heater down permanently. This is
not the only scenario that can cause runaway heat. Other causes could be a faulty
NTC or an internally shorted heater.
If you find a heater with an open temperature fuse:
During the diagnosis process, if you find that a temperature fuse has opened, all of the
other parts in this circuit should be suspect.
1. Ohm out the heater element (steam = 12.5 and coffee = 12.7) and be sure to
check both ends of the element against the heater case (ground). This should read
infinity (∞). If either of these tests fail, the heater is bad. The heater may have
caused the electronic to fail.
2. Disconnect the heater and see if voltage is present (with the machine turned off via
the electronic, not the mains switch). If voltage is present, the electronic is bad.
3. Ohm out the NTC sensor (approx 130k at room temp.) and make sure its
resistance decreases as you warm it up. If in doubt, replace it.
4. Once the determination has been made, the parts should be replaced, and in all
cases, replace the appropriate bimetal self-resetting thermostat. To replace the
temperature fuse, the part designated for the CVA 2650 will work. Currently, the
temperature fuses are not listed under the CVA 40xx models in the parts CD. We
expect that to change in the near future.
10 CVA 406x & MDU Updates
When accessing a CVA coffee system with the MDU, you may see an indication that a
software update is available (or required). Before attempting an update, check the
serial number, because some earlier electronics will not accept this update. Any serial
below 81441919 must have the EPX (control electronic) replaced first. Use part
number 7541483 or later.
Remember, when preparing to apply an update with the MDU, double-click the update
to view the details page. There will also be a link on the details page with more specific
information.
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