Sharp R-990K Microwave started making rapid clicking sound and smoke - Page 2

**redwire** · 03-06-2022, 08:50 PM

Relays typically must operate given 70-75% of their rated coil voltage, so 13.5V minimum spec. If you hear it click with 12VDC, that's good enough, we just want to see if the contacts are pooched and that is where the arcing occurs.
It's low current the coil, 20mA so even two 9V batteries could be used.
Careful not to remove a fan relay and then operate the oven, it needs airflow.

Widget · 03-06-2022, 10:40 PM

Hey Red, thanks for the info

I did a rough wiring to the relay, connecting 12v from my PC psu ans 12v car bulb. Seems ok. There was a little crackling but I think that was due to poor contact with the power-in in the leg of the relay.

I thought about swapping relays with the fan, just to see if the fan still works, but maybe I don't have to if the relay seems to be working?

Everything on the board seems dry. The only other testing I can think of doing is,

1. Testing with a incandescent bulb sam_sam suggested,
2. Plugging it all in, power on, and start checking voltages

I don't know what to do about the buttons not working correctly though. Heck, for all I know it's a completely unrelated issue and became like that long ago (I rarely used those numbers, usually just hit start or preheat at lower temps).

Here's a video of the relay test. Sorry about the hand and background chatter.

https://youtu.be/zAG3H-k7hQA

Widget · 03-11-2022, 05:54 AM

update: Microwave is working. I put it back together, and buttons seem ok. Convection oven preheats ok too. Not sure what when wrong with the keypad, perhaps ribbon cable wasn't aligned or had some dirty contacts.

I tried connecting the bulb to the transformer wires as suggested (to check relay) but nothing happened. As of writing this, it came to mind perhaps it would have only engaged the bulb if the convection was activated ?

Other than that, all seems ok for now.

Thanks again for all the suggestions, much appreciated

**sam_sam_sam** · 03-11-2022, 03:05 PM

You have to set an amount of time like you would if you did not have the incandescent light bulb instead of the transformer

03-06-2022, 08:50 PM	#21
redwire Badcaps Veteran Join Date: Dec 2010 City & State: Alberta My Country: Canada Posts: 2,983	Re: Microwave started making rapid clicking sound and smoke Relays typically must operate given 70-75% of their rated coil voltage, so 13.5V minimum spec. If you hear it click with 12VDC, that's good enough, we just want to see if the contacts are pooched and that is where the arcing occurs. It's low current the coil, 20mA so even two 9V batteries could be used. Careful not to remove a fan relay and then operate the oven, it needs airflow.

03-06-2022, 10:40 PM	#22
Widget Member Join Date: Aug 2015 City & State: New South Wales My Country: Australia I'm a: Knowledge Seeker Posts: 22	Re: Microwave started making rapid clicking sound and smoke Hey Red, thanks for the info I did a rough wiring to the relay, connecting 12v from my PC psu ans 12v car bulb. Seems ok. There was a little crackling but I think that was due to poor contact with the power-in in the leg of the relay. I thought about swapping relays with the fan, just to see if the fan still works, but maybe I don't have to if the relay seems to be working? Everything on the board seems dry. The only other testing I can think of doing is, 1. Testing with a incandescent bulb sam_sam suggested, 2. Plugging it all in, power on, and start checking voltages I don't know what to do about the buttons not working correctly though. Heck, for all I know it's a completely unrelated issue and became like that long ago (I rarely used those numbers, usually just hit start or preheat at lower temps). Here's a video of the relay test. Sorry about the hand and background chatter. https://youtu.be/zAG3H-k7hQA Last edited by Widget; 03-06-2022 at 10:43 PM..

03-11-2022, 05:54 AM	#23
Widget Member Join Date: Aug 2015 City & State: New South Wales My Country: Australia I'm a: Knowledge Seeker Posts: 22	Re: Microwave started making rapid clicking sound and smoke update: Microwave is working. I put it back together, and buttons seem ok. Convection oven preheats ok too. Not sure what when wrong with the keypad, perhaps ribbon cable wasn't aligned or had some dirty contacts. I tried connecting the bulb to the transformer wires as suggested (to check relay) but nothing happened. As of writing this, it came to mind perhaps it would have only engaged the bulb if the convection was activated ? Other than that, all seems ok for now. Thanks again for all the suggestions, much appreciated

03-11-2022, 03:05 PM	#24
sam_sam_sam Badcaps Veteran Join Date: Jul 2011 City & State: Some times Sunny Jacksonville FL My Country: USA Line Voltage: 120 Volts 60 HZ I'm a: Knowledge Seeker Posts: 4,009	Re: Sharp R-990K Microwave started making rapid clicking sound and smoke You have to set an amount of time like you would if you did not have the incandescent light bulb instead of the transformer __________________ 9 PC LCD Monitor 6 LCD Flat Screen TV 30 Desk Top Switching Power Supply 10 Battery Charger Switching Power Supply for Power Tool 6 18v Lithium Battery Power Boards for Tool Battery Packs 1 XBox 360 Switching Power Supply and M Board 25 Servo Drives 220/460 3 Phase 6 De-soldering Station Switching Power Supply 1 Power Supply 1 Dell Mother Board 15 Computer Power Supply 1 HP Printer Supply & Control Board * lighting finished it * These two repairs where found with a ESR meter...> Temp at 50F then at 90F the ESR reading more than 10% 1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later ) 2 Hem Saw Computer Stack Board All of these had CAPs POOF All of the mosfet that are taken out by bad caps

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