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Repair guides for the Quasar microwave oven, released in 1984 and identifiable by model number MQ7774XW.

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I have an old microwave from the 1980's from quasar. I want to fix it.

I have an old microwave from Quasar from the 1980's, it's been super dependable and I'd like to fix any failing internal components but don't see detailed enough guides so far.

Any suggestions?

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Please tell us what is wrong with your microwave

It's been weakening in power over the years but works well enough, but recently as of three weeks ago, sometimes you'd plug in the amount of time you want it to reheat something, and you press start, and the timer starts to go, but the rest of the machine doesn't.

Eric, I was wondering if you were able to fix your start button. My one and 10 second and minute buttons aren’t working but the cancel and start not responding. I’d love to know how you fixed it...

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Hi @packratfixer90 ,

What is the model number of the microwave oven?

If there is nothing wrong with it, leave it alone.

If there are definite problems with its’ operation that is a different matter.

What criteria are you going to use to determine which components are “failing”?

Just because a component looks “old” or ”faded” doesn’t mean there is anything wrong with it, e.g. a bulging or leaking capacitor is an obvious problem but then you could have a faulty capacitor which shows no external indications of a problem at all, and to test them you’d have to remove them from the circuit board.

You could cause more problems than what you started with (if any) when trying to conduct preventative maintenance on electronic components.

Mechanical components are a different story. e.g. if the turntable motor sounds as though it’s struggling or grinding etc then by all means replace the motor or if the microwave has mechanical timers or switches that are becoming unpredictable in their operation then again look to fix them, but as to the purely electronic components, (resistors, capacitors, diodes etc) wait until they actually fail or start to cause a problem before looking to replace them.

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There isn't a turntable on this model of microwave. I will try to find the exact model number but the backplate (whatever ink they used for that information) has faded as it is from the 1980's.

I suspect it might be an electrical component, and it doesn't always fail. The device worked tonight just fine, it's just I'm prepping for when I need to crack it open and see if there needs to be a fix.

I definitely need to diagnose what's wrong with it though or where the point of failure is; that I haven't worked out yet and I am here partly to procure troubleshooting advice should the microwave continue to fail more frequently and with more reproducibility.

Hi @packratfixer90 ,

Reading your comment "press start, and the timer starts to go, but the rest of the machine doesn't.", it may be that the start button might be failing or operate a relay perhaps etc.

Without a circuit you'd be only guessing unless you want to trace the wiring by doing point to point testing and drawing it out and then work out how it operates.

I think it's two problems, and I'm conflating them. I think the start button is wearing out or failing, so far as long as I press it a certain way it's fine. But I also think it's weakening in microwave intensity and that would suggest to me circuits on the motherboard are wearing down or the emitters are going out. I'll figure it out.

I have the Pro Tech Tool kit, and a multimeter already, is that enough equipment to crack it open and begin testing?

Hi @packratfixer90 ,

Have you worked on microwave ovens before? If not then you can kill yourself if you are not careful.

Are you aware of its' inherent danger even if it is unplugged?

You need to correctly discharge the HV capacitor (potentially lethal voltage) before doing any static testing of anything.

It is better if you can find the model number and get a schematic. If a component's value markings have faded over the years due to heat etc, then without the schematic you would have no idea what value the component has (or even what type it is) to know whether it was OK or not, except perhaps if it were open circuit or short circuit but what would you replace it with?

Simple things like switches, buttons and relays etc can be tested for correct operation and continuity .

Wondering, Eric, if you were able to fix the start button. Mine isn’t working either, nor the clear. Only the 1 & 10 min and sec buttons are working. I’d love to fix mine.

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