Microwave oven diode testing - Page 1
Forum section: electronics / beginners

author: JHNC
author_rank: Newbie
timestamp: January 19, 2024, 02:15:21 pm
content: Testing a CL04-12 diode from a microwave oven. Tested using a Peak DCA55 & a Fluke 87 DMM. Tests as bad / open on both devices. Then I read on a post that these type high voltage diodes will read as shorted on a DMM, such as my fluke and that you need to test them with a 9 volt battery [not sure what they meant as my meter uses a 9V battery]. While peak lists no exception for HV diode testing and many DMMs have a built in diode test function setting, I want to know:1. Can you accurately test a12 kV0.45 Amp diode on a DMM using either theOhms scale or the diode test setting?2. If not, how do I correctly test it for open or short on an HV diode?

author: coromonadalix
author_rank: Super Contributor
timestamp: January 19, 2024, 02:24:01 pm
content: nonormally an microwave diode need many volts to test it, i think around 7 -8 volts should be sufficientsearch google for microwave diode testing ...

author: Andy Watson
author_rank: Super Contributor
timestamp: January 19, 2024, 02:35:03 pm
content: Quote from: JHNC on January 19, 2024, 02:15:21 pmI think you mean open-circuit. If the diode tests as shorted on DMM then it is definitely dead.QuoteThe datasheet shows that the forward voltage could be as high as 10V - you will need a meter with at least this voltage source to be able to test these diodes. Perhaps you could find a 12V battery and use a small (<3W) lamp a a load.https://supcache.miancp.com/data/hvgtsemi.com/upfile/pdf/2018050711530586978.pdf

author: JHNC
author_rank: Newbie
timestamp: January 20, 2024, 07:33:04 pm
content: Fluke Instruments web page makes no mention of using an external battery or different procedure [or device] when testing an HV diode:https://www.fluke.com/en-us/learn/blog/digital-multimeters/how-to-test-diodesThere is a slight difference between using a Fluke with adiode test settingand a Fluke with no specific diode test setting but instead using the resistance  test setting. I am assuming that this will apply to all meters in general.I have ordered a replacement HV diode & will test it the same way I did the old one and advise on the results when completed.

author: Zero999
author_rank: Super Contributor
timestamp: January 20, 2024, 07:41:51 pm
content: Quote from: JHNC on January 20, 2024, 07:33:04 pmThat applies to single diodes. A microwave diode, is not a single diode, but a module containing many diodes in series.

author: wasedadoc
author_rank: Super Contributor
timestamp: January 20, 2024, 07:59:01 pm
content: Quote from: JHNC on January 20, 2024, 07:33:04 pmDo NOT use an external voltage source (battery, wall wart etc) in combination with a multimeter set to resistance or diode ranges. You risk damaging the multimeter.

author: bdunham7
author_rank: Super Contributor
timestamp: January 20, 2024, 08:17:42 pm
content: Quote from: JHNC on January 20, 2024, 07:33:04 pmThat's a very basic and generic explanation of how to test 'typical' diodes which have a forward voltage of about 0.6V or so using typical multimeters which may have an open circuit test voltage of 2 volts or so. It doesn't apply to your case.I have a couple of similar HV diodes here that I just checked--they have a forward voltage of about 7.5V. Most meters, even newer ones that work with white LEDs, will show that as an open circuit. Out of all the meters I have, only three were able to test that HV diode and none of the three are very common. Well, maybe the Simpson 270 is common enough.I doubt your diode is bad as rectifiers have two common failure modes--shortedanddisintegrated. I'm fairly certain your new diode won't test any differently.

author: Zero999
author_rank: Super Contributor
timestamp: January 20, 2024, 08:27:12 pm
content: Quote from: wasedadoc on January 20, 2024, 07:59:01 pmTrue, but a Fluke meter won't be damaged by connecting it to a battery. The correct way to test a microwave diode is with a couple of 9V batteries in series a 10k resistor.The voltage across it should be about 5 to 10V when forward biased and the full battery voltage when reversed.

author: JHNC
author_rank: Newbie
timestamp: January 20, 2024, 09:02:13 pm
content: As I stated above, I ran the 2 tests on the new diode. The results are as follows:The new diode tests as no component / bad using the Peak tester. The new diode tests bad using the Fluke ondiode test setting. Both results are the same as with the old diode. I did get a reading of ~ 230 Meg Ohms using theFluke's resistance settingin one direction and OL  in the other.I then tried testing both diodes using a 9 Volt battery in series with each diode using the Fluke's 40 Volt DC setting, first in forward bias, then reversing the leads to reverse bias the diodes.Forward biasing showed 4 VDC, reverse biasing showed 0 VDC.I thinkbdunham7explained the mystery: the standard DMM diode test function is designed to test diodes with an ~ .6 V forward voltage drop, whereas this diode has a specified maximum forward voltage drop of 10 Volts [see attachment].https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwiFguLu7eyDAxWlOkQIHW6xCZ0QFnoECBMQAQ&url=https%3A%2%2Fsupcache.miancp.com%2Fdata%2Fwww.hvgtsemi.com%2Fupfile%2Fpdf%2F2018050711530586978.pdf&usg=AOvVaw34Rod-SvIiqyMZwuBg51WX&opi=89978449This explains why inserting a 9V battery in series with the diode and making a DC Voltage measurement accurately tested this diode. Lesson learned.Now, the question becomes: other than HV diodes such as found in this case, what other types do we need to be aware of that will require the insertion of a voltage source - or other alternative procedure - to check accurately?

author: Andy Chee
author_rank: Super Contributor
timestamp: January 20, 2024, 09:11:19 pm
content: Testing zener diodes will require an external voltage source.

author: MarkT
author_rank: Frequent Contributor
timestamp: January 20, 2024, 10:48:19 pm
content: Does a diac count?

author: BILLPOD
author_rank: Frequent Contributor
timestamp: January 21, 2024, 02:21:23 pm
content: EEVBLOG 121GW meter ha a 15 volt diode test setting.

author: JHNC
author_rank: Newbie
timestamp: January 21, 2024, 05:08:53 pm
content: BILLPOD: Thanks for the heads up!Here is a link to the EEV Blog DMM. Looks to be one fine piece of equipment.https://eevblog.store/products/121gw-multimeter

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: January 23, 2024, 07:44:37 pm
content: You can use a circuit like this:

author: JHNC
author_rank: Newbie
timestamp: January 23, 2024, 09:07:52 pm
content: Thanks to all for the suggestions!