Primus 2490 free download

File name Primus 2490 Unofficial Repair Guide v1.pdf

Primus 2490 Unofficial Repair Guide This is an unofficial picture based guide covering my own experience with repairing the Primus 2490 Central Heating System. The PCB Overlay picture (see the bookmarks) should give you a fair chance of repairing other parts of the circuit that are not mentioned here. The circuits are simple designs realised with the bare minimum of components necessary. They are fully serviceable by the average DIYer. The control unit for the boiler should not be powered up without some kind of spark plug connected. Doing this could damage the ionic flame sensing circuit. The ignition is a dual spark type, with the second spark occurring across a gap in the PCB inside the box. The unit must be sealed tight to prevent gas from entering the box. Please see the official manuals for general system wiring and system checking. The Control Panel is mentioned later in this guide. The lid is fastened by hooks and a sealant. It can be carefully pried off using a flat screwdriver. Do not pry against the PCB itself, as it is very fragile. The connector terminals and the ignition coil are a part of the casing. De-soldering these completely will allow you to lift out the PCB. You may want to test the complete unit first before doing any further disassembling. The power source should supply 12V DC at minimum 1A and current limited to max. 2A. Wires can be soldered directly to the board according to the connection overview picture below. Connection Overview Boiler Thermostat Vcc Pump Gnd Solenoid Hold Solenoid Pull Solenoid Gnd Internal Spark Gap Ignition Coil Secondary #1 & Ionic Flame Sensor Input Winding Low V. Output Winding Ignition Coil Primary High V. Output Winding Bridge the boiler-thermostat terminals during testing. If the ignition coil is connected, remember to connect an ordinary automotive spark plug. With the spark plug gap wide open, the spark should be able to fly to the ring of the plug. If the PCB is tested bare, a 10ohm wire-wound resistor can be used in place of the ignition coil primary winding. The current pulses are short but very high. Basic Function Ignition Capacitor Q4 and VZ1 form a 7.5V regulator with a 470uF cap at the input and a 220uF cap at the output. This voltage is very noisy as it also feeds the switching high voltage converter. Q5 and Q6 are parts of an oscillator feeding Q7 followed by Q8 which drives the input winding on the transformer. The low voltage output from the transformer is rectified by D5, and used to charge (via a resistor) the 47uF/63V cap close to Q12/Q14 during the first few seconds (set by C14) of each power cycle. This charge is used to energize the 12V hold-relay (to the right) when its driver transistor opens. Once energized the relay is held by 7.5V via one of its contacts and a resistor. The hold-relay feeds the 5V pull-relay (to the left), which is turned off after successful ignition. This way the gas-solenoid cannot open unless the voltage converter is running