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Son of Samurai's Blog

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How to Troubleshoot a GE Cooktop like a Real Tech vs. like a PCM

Son of Samurai

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What we call Parts-Changing Monkeys (PCMs) around here at Appliantology are techs who rely on pattern recognition, tech myths, and blind luck to make their repairs. Case in point with this example of a GE ZGU385 gas cooktop, where said PCM figured he would get lucky by replacing a couple of components that seemed related to the problem, apparently without any troubleshooting beforehand.

Spoiler: he didn't get lucky.

Real technicians don't rely on luck to get things fixed. We rely on knowledge and the skillful application of that knowledge to troubleshoot and identify the problem.  As the Samurai shows in this video, a professional technician can solve this problem using a systematic troubleshooting approach. All it requires is a basic understanding of electricity and the willingness to take the time to study the circuits and technology you're dealing with.

Watch and learn...

 

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Given the schematic, what did the problem end up being?

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splinterexpert

Posted

Maybe it was not properly grounded. It may have been fine in the past, but something happened to make the connection unsatisfactory. I've had to run extension cords through houses in south Texas to get a correct power supply to a unit for various reasons. 

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Son of Samurai

Posted

2 hours ago, jhonrath said:

Given the schematic, what did the problem end up being?

This was based on a problem posted at Appliantology, and the OP hasn't yet posted the solution, if he's found it.

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Son of Samurai

Posted

1 hour ago, splinterexpert said:

Maybe it was not properly grounded. It may have been fine in the past, but something happened to make the connection unsatisfactory. I've had to run extension cords through houses in south Texas to get a correct power supply to a unit for various reasons. 

Improper ground to the appliance would not affect the reignition module. Only if the module itself were not grounded (meaning it doesn't have a path to the chassis) would there be an issue, since in that case the spark would have no return path to the module. 

However, this would not cause a no-spark problem. Rather, it would cause an issue where the burner would never stop sparking, because the module would have no way to sense that the burner was lit.

We cover reignition modules in depth (and much more) in our Oven and Range course -- check it out if you're interested in learning more: https://mastersamuraitech.com/appliance-repair-courses/oven-range-repair/

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splinterexpert

Posted (edited)

Funny. I've seen problems with these that were mysteriously resolved when a poorly grounded outlet is circumvented. They tend to be intermittent. What was the solution for this one?  Maybe its those spark ignition systems for bake and broil ignitors I'm remembering. They are particular about earth ground. 

Edited by splinterexpert

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Son of Samurai

Posted

33 minutes ago, splinterexpert said:

I've seen problems with these that were mysteriously resolved when a poorly grounded outlet is circumvented.

There's actually no ground connection at the power supply shown on this schematic -- the two ground connections you see are just signifying chassis ground. In addition, the reignition module is isolated from the power supply by that transformer. So in this particular case, a bad or missing ground at the power supply would not be the cause. 

Again, we are dealing with a reignition module. These modules work by detecting the return spark current through the cooktop chassis as modified by flame rectification

GE-ZGU385NSM1SS-Cooktop-Schematic.jpeg

33 minutes ago, splinterexpert said:

What was the solution for this one?

 

On 1/21/2020 at 1:57 PM, Son of Samurai said:

This was based on a problem posted at Appliantology, and the OP hasn't yet posted the solution, if he's found it.

 

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mdappliancerepair

Posted

I'm working on this exact model with a no spark, no lights problem. Tested the transformer and it was getting 120V input but the output was nothing. No 12V AC from Red to White, and no 240V AC from Red to Brown. I replaced the transformer and am getting the same results.  I did have continuity when testing the outputs. Is there anything other than a bad transformer that can cause the lack of voltage output?

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splinterexpert

Posted

36 minutes ago, mdappliancerepair said:

I'm working on this exact model with a no spark, no lights problem. Tested the transformer and it was getting 120V input but the output was nothing. No 12V AC from Red to White, and no 240V AC from Red to Brown. I replaced the transformer and am getting the same results.  I did have continuity when testing the outputs. Is there anything other than a bad transformer that can cause the lack of voltage output?

What happens to your 120 input when you close a switch?

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Son of Samurai

Posted

48 minutes ago, mdappliancerepair said:

I'm working on this exact model with a no spark, no lights problem. Tested the transformer and it was getting 120V input but the output was nothing. No 12V AC from Red to White, and no 240V AC from Red to Brown. I replaced the transformer and am getting the same results.  I did have continuity when testing the outputs. Is there anything other than a bad transformer that can cause the lack of voltage output?

I don't see how this could be anything but an open transformer winding. Try disconnecting the Molex connector on the transformer secondary wires and then repeat the voltage test on both windings. Check the resistance of both windings too, just in case there really is an open.

Make sure to use a loading meter/LoZ function to do those voltage measurements! That will ensure that you're not getting faked out by ghost voltage.

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Son of Samurai

Posted

One more thought on your problem, @mdappliancerepair: if one of those vertically-oriented LED indicators has shorted, that would create a short between both ends of the secondary, which could in turn lead to one of the transformer windings going open. Another good reason to disconnect the molex from the secondary winding when doing your voltage testing.

If the new transformer that you put in does have an open, that should prompt you to check those LEDs. You'll want to test their resistance, both forward and reverse bias. If one of them reads low resistance both ways, you know you've found your short.

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mdappliancerepair

Posted

I tested the transformer with the input 120V connected and the secondary disconnected. Ordering a new transformer tomorrow. Will update when it arrives. Thanks.

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Son of Samurai

Posted

57 minutes ago, mdappliancerepair said:

I tested the transformer with the input 120V connected and the secondary disconnected. Ordering a new transformer tomorrow. Will update when it arrives. Thanks.

Did you check the resistance of the primary and secondary windings to confirm an open? 

When you put in the new transformer do not connect the molex for the secondary right away. First test your voltages across the coils. If it's in spec, then you should check those LEDs I mentioned earlier. If one of those is shorted, it could take out the transformer again.

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