Hi, I’m trying to resurrect my unresponsive microwave from the dead and need some guidance from those smarter than I.

Here is info on the patient
Make: Audiovox
Model: ACM 1200
Issue: It’s completely dead. No display, no beeping, no nothin!

Here is what I’ve done to troubleshoot this far:

Tested power outlet with multimeter to confirm current is flowing.
Removed cover and tested internal fuse.
Tested thermal both thermal fuses.
Tested both interlock door switches.

The patient passed all of these initial tests. On to the circuit board. I removed the circuit board and found visual evidence of a blown...something:

Any ideas on what happened here and how to go about diagnosing/fixing it?

Thanks for any help!!
Glenn

 

Can't really tell whats blown in your picture the zener diode (zd1) or the what I am guessing is a MOV (the green disc thingy)
I think both but hard to tell.
You'll need to supply better pictures. If you can capture any markings that is a plus.

 

Here are move pics. Hope this helps!

 

So its definitely both VS1 and ZD1.
Its a tight fit you may be better off to remove them and inspect for any markings.

 

Looks like a simple transformer and bridge rectifier psu with zeners and capacitors. Test the voltage from the transformer and output from the bridge rectifier across the capacitors.

 

So its definitely both VS1 and ZD1.
Its a tight fit you may be better off to remove them and inspect for any markings.

Thanks for that Narkeleptk! I Think I will test first to confirm those are the blown parts, but it certainly seems that way.

Looks like a simple transformer and bridge rectifier psu with zeners and capacitors. Test the voltage from the transformer and output from the bridge rectifier across the capacitors.

Thanks Dodgydave! I'm a newbie at this - could you provide any further guidance on what exactly to test? I have a multimeter but couldn't find the schematics of this circuit online since it's quite old. Happy to provide more pics if that would help. It would be awesome if I could just replace a couple of circuits and have this baby good as new!

 

Check on AC the mains on the Transformer primary side, and Secondary side.
If it's giving out voltages on the Secondary then check the input and output of the 5V regulator, if there's no Secondary voltages , unplug from the mains, and check on Ohms the mov, and the primary windings of the Transformer and any fuses.

 

safety first. Disconnect the wires going to the big transformer before making any testings. The display should come on all the time to show the time etc. And do not run the microwave when the cavers are removed.

 

I don't see any evidence that the zener is damaged but VS1 is certainly blown and ZD1 just got some some of the mess blown out of VS1.
VS1 could be either a MOV in parallel with the power, or a NTC in series with the input. A blown MOV wouldn't stop it working unless it took the fuse with it but all fuses are OK.
A blown NTC, as it is in series with the input, would stop it working.

Does that connector with the orange, black and white connector connect to the supply power input?
If so can you trace the tracks on the back to see if VS1 is indded in series with one of them?
If so you should also check the bridge rectifier for shorts.