NATIONAL NNN -C 2000P LOW VOLTAGE PRIMARY GETS FREQUENTLY OPENED
I replaced low voltage transformer on PCB of display board , and when i started for a while all was ok but next day when i started microven once again this transformer got opened and my oven stopped working, on transformer there are 2 terminal marked P1 and P2, can some one explain why this is happening , is it correct to loop P1 AND P2 externally(as i believe this are looped inside transfomer,and due to some reason gets opened)
Please guide on possible cause and rectification
Re: NATIONAL NNN -C 2000P LOW VOLTAGE PRIMARY GETS...
I had looped externally P1 and P2 and now it is working , to assure myself I also checked current in primary of transformer it was measured to be from 300 mA to 600 mA when I started to use microoven.
For safety I had now fixed 2 Amp fuse between P1 and P2.
Is that all ok. To add I checked all voltages mentioned on PCB viz. 30volt, 5 volt etc which on measuring were found almost ok.
Any comments please
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Did you have any power surges in the house? Any thunder storms?? even if you are not using a microwave, but it is plugged in , you see the clock?? That means it is getting power and running the clock so while you may not be cooking in it, it is actually using power to run the clock functions. So, if there was a power surge, it damages a part on the main board called the Low voltage transformer. It takes the 120 volts from the wall and drops it down to the voltages the board needs to operate, sometimes 5,12 24 or maybe 30 volts. If the primnary winding gets damaged from a surge of some sort. it will no longer light up if that small transformer was damaged. That can happen without even blowing the fuse as the small wires in the transformer were never meant to carry the 15 or 20 amps the fuse is rated at. So the transformer goes bad and the unit is dead but no blown fuse. Have to check the primary winding of the low volt transformer to see if it has continuity. If not, will need new main circuit board. Sorry But $$$$$
Would need to check power to main board. A lot of times it is the small low voltage transformer on the main board. If the primary winding goes bad it cant get power to the rest of the board to function. So to start, is there power getting to the low voltage transformer on the main board??Have you had any thunder storms or power surges at your home where it is plugged in? If a home loses its Neutral power line it can mess up a lot of electrical devices in the home. do you notice your lights browning at times. If so you may need to get your power company out to do a load test on you system. But the transformer is a very low amp device and will not blow the main fuse if it goes bad. So you could bhave aburnt trace on the back of the main board or a bad transformer. Best guess. Good luck
If the fuse were blown, You wouldn't even get a display. If you're handy with a multi-meter, and feel somewhat comfortable making electrical tests, the first thing to check is whether the problem is coming from the low voltage (control) side of the oven, or the high voltage side (transformer, magnetron, capacitor and diode).
Unplug the oven and remove the cabinet cover. Before reaching into the chassis, discharge the capacitor by shorting between the two sides with a screwdriver or similar tool. It can store up to about 2000 volts, and can hurt you badly. A brief touch with your shorting tool is all that's necessary.
Disconnect the wire lead that goes from the power transformer (the largest component on your oven's right side (as you face the door), to the capacitor. Insulate it against any metal contact by wrapping electrical tape around the connector.
Set your meter to test for house voltage (the 200VAC range). Plug the machine in and select a cooking cycle. While it's trying to cook, place your meter's leads on the wires coming from the control board to the primary terminals on the transformer. You're looking for a reading that's reasonably close to 120VAC. If you don't get enough voltage, the problem is with the control board. If you do get the required voltage, the problem is in one of the high voltage components.
Write back with your results for further diagnosis.
Disconnect the connector to the primary winding of the high
voltage transformer. Put a new fuse . If the fuse is not
blowing the problem may be in the secondary side of the high voltage
transformer. Chek the highvoltage diode, capacitor,
magnetron respectively. you can also check the primary winding of the
low voltage transformer.
ok i just opened mine up on counter and found that the white wire on the high voltage transformer had been loose and melted so i put a new female spade connector on and it works fine. i suspect that from a year of use and humm from transformer had loosen it and gotten hot thus loosing connection and getting dirty causing it to overheat and burn off plastic sheilding. easy fix!!!
Is your line voltage correct?
That needs to be measured, perhaps even monitored.
Is it possible you have installed 120 volt replacements into a 220 volt model?
Otherwise, there is a component shorted on the control board, such as a rectifier diode, zener diode, filter capacitor, or transistor. This would call for old-style troublehsooting.
It's possible you have a bad sensor, but I doubt it. They could be disconnected or bypassed for test purposes.
Not sure about the Neff brand, but in general you'd want to check for 110VAC power on the primary side of the low voltage transformer on the control panel / board.
If that is present, check the secondary for voltage, about 12-30VAC. If the unit has a VFD type display, there will be a heater filament supply, usually around 2.5-6VAC. Also look for bad connecitons on the VFD.
If those voltages are present, check connections on the board, look for bloated / bulging capacitors, shorted diodes, breaks in the board, etc.
Also look for thermal cutouts and thermostats.
If this doesn't fix it, can you take several photos of the inner parts and circuit boards?