10 replies to this topic

[skintdigit]

Query for the all-knowing:
Said kitchen appliance device blows main fuse, but only when HV components are energized. Magnetron and transformer check within parameters for resistance tests. Capacitor appears to be shorted(reads 1.7 ohms terminal to terminal). Diode forward voltage drop is about 2.8 volts with a 9 volt battery in series, so I believe it's OK.

Specs call for RepairClinic part #828490, but it's out of stock.

Will this one do, instead? http://www.repaircli...s?s=t-832483-==

Capacitance and voltage are a match, but can't tell about terminals...anyone know if this'll work out of the box?


SD

[Budget Appliance Repair]

It mentions that is has 1/4" terminals which are normally the standard terminal size on microwave capacitors.

Large microwave capacitors almost always have at least 2 terminals on each connector, some have 3 or 4, you usually shouldn't need more than 2 terminals so that one should work with no problems if the volts and MFD are correct.

[skintdigit]

Thanks, Willie. Have ordered the part, will follow up. Is a shorted capacitor a symptom of another problem with the HV workings, or do they usually just fry on their own? I'll use the "Willie method" to check the mag once I can get voltage to it.

On a related note: in looking for a reliable way to test a microwave oven HV rectifier/diode, I came across this.....




I'm not an electrical engineer, does this method work....or is something wrong with the theory?


SD

[RegUS_PatOff]

that test seems OK,
maybe not the best test

[skintdigit]

I tested the rectifier/diode a couple of days ago using the 9 volt battery method found here:

http://fixitnow.com/...microwave-oven/


Then did the same test with a 12v. automotive battery. Next, (microwave is in pieces on kitchen table, so I have to at least APPEAR to be doing something to it), I tested the rectumflyer using the method described in the above video. Here are the results:

Test #1 with a 9 volt battery (battery voltage measured at 8.8 volts DC): forward voltage drop just shy of 3 volts, that is, the meter reads 5.9 volts DC with the diode one way, and 0 volts DC when the polarity is reversed.

Test #2 with a 12 volt auto battery( batt. voltage at 12.9 vdc): forward voltage drop at around 3 volts again(9.8vdc on meter), with no voltage recorded when diode polarity is reversed.

Test #3: Just for fun, I tried the 120 volt AC test described in the video posted by Js2060. With the meter set to AC and using a wall receptacle with metered voltage at 123vac, I get a reading of 119vac in one direction and 0vac when the diode is reversed.

So, according to the first two tests, the diode is functional. Test #3, however, indicates that it is not. Can't test it live in the microwave until the new capacitor arrives, so I don't know whether the diode is good or not. The diode does not appear to be burned cracked, discolored, folded, spindled or mutilated in any way.

I have either a bad diode or a bad testing method...not sure which.

Would anyone care to shed some light on this, maybe testing a known good diode with the 120vac method?


SD

[RegUS_PatOff]

... I tried the 120 volt AC test described in the video posted by Js2060.
... With the meter set to AC and using a wall receptacle with metered voltage at 123vac,
.... I get a reading of 119vac in one direction and 0vac when the diode is reversed.

you should get the same reading no matter which way the Diode is connected ...
UNLESS you have 120v DC at your wall outlet.

[skintdigit]

That's what had me scratching my head, too. No DC at the wall here, residential single phase three wire service.
Just tested the rectifier with my newer Klein meter and get 66 volts, so I guess the old Sperry cheapie that I've had for 10 years is not up to the task. Sorry for the confusion.......


SD

[skintdigit]

Capacitor arrived from RepairClinic today...very pleased that the part got here so quickly. Installed capacitor and new 20amp. ABC main fuse, unplugged magnetron and fired it up. All good. Discharged capacitor, connected mag. leads and hit the go button....all good again.

Thanks to RepairClinic for getting the part to me so quickly and to RegUS and Willie for their assistance.


SD

[kdog]

Nicely Done !

[Samurai Appliance Repair Man]

Mighty fine fixin' there, Master skint!

[skintdigit]

Thank you, kdog and Samurai. Wouldn'a been possible without the generous and entertaining help here at appliantology.org.

And thank you for the upgrade!

SD