[FalconEddy]

First post here.

I've spent nearly 30 hours taking this unit apart, measuring key H.V. components (diode, magnetron, capacitor), door switches, thermostats, and flame sensors.

Checked for loose wiring/connectors, bad fuses, and broken wires inside their PVC or cloth insulation jackets.

Performed Key Panel, Smart Board, and Sensor tests; but I still cannot locate the reason(s) why it's not heating. Both the H.V. cap and diode have been replaced even though the originals tested out ok.

Utility supply was measured at 119.3VAC


The H.V. tranny tested out with the following results:

Primary winding: .4Ω

Secondary winding: 68.5Ω (schematic shows nominal as 79Ω) This was measured from the white wire on the tranny to ground.

Filament winding: 0Ω

Primary winding to ground: Infinite

Filament winding to ground: Infinite


The Magnetron tested out with the following results:

Resistance between the two filament terminals: .1Ω

Resistance from filament to Magnetron chassis: Infinite


Now, I don't have a meter that will accurately measure resistance (milli-ohms) in the windings; but the schematic lists them as 430mΩ on the primary and 100mΩ on one of the secondary legs.

Anyone have some ideas??? I'm completely stumped on this one.

Thanks,
FalconEddy

[glen65]

Try a voltage test,
“Carefully” check to see if
you are getting 120 Volts AC to the primary
winding of the transformer when the unit is running.

[FalconEddy]

Originally Posted by glen65

Try a voltage test,
“Carefully” check to see if
you are getting 120 Volts AC to the primary
winding of the transformer when the unit is running.

Already did that. Getting 119.3VAC from the utility to the H.V. primary. I tested it off the big switching relay on the Smartboard. It went from a few millivolts right up to 119.3VAC right after engaging the start button.

I also measured amperage during operation. No surprise that it was only between 3.5A to 4.5A.

Next step(s)?

At this point I'm tempted to change out the magnetron (I have a replacement here) just to see if I was getting false 'good' readings when I tested it. But, that still doesn't explain the low current draw. . . does it?

. . Falcon

[glen65]

Originally Posted by FalconEddy

Already did that. Getting 119.3VAC from the utility to the H.V. primary. I tested it off the big switching relay on the Smartboard. It went from a few millivolts right up to 119.3VAC right after engaging the start button.

I also measured amperage during operation. No surprise that it was only between 3.5A to 4.5A.

Next step(s)?

At this point I'm tempted to change out the magnetron (I have a replacement here) just to see if I was getting false 'good' readings when I tested it. But, that still doesn't explain the low current draw. . . does it?

. . Falcon

Ok youre getting 120VAC off of the smart board relay but are you getting it at the transformer primary terminals themselves?

[FalconEddy]

Originally Posted by glen65

Ok youre getting 120VAC off of the smart board relay but are you getting it at the transformer primary terminals themselves?

Yes.

Sorry if I wasn't clear enough about that in my first reply.

Voltage was measured both on the wiring at the smartboard relay, and the primary terminals where the wires make the connection.

I've already measured all pertinent wiring from end to end without being connected to ensure there were no open conditions.

. . Falcon

[glen65]

When you checked the diode did you get
a reading with the probes connected in one
direction and nothing when you reversed them?

[FalconEddy]

Originally Posted by glen65

When you checked the diode did you get
a reading with the probes connected in one
direction and nothing when you reversed them?

Although the original diode appears to be open, two other diodes I have (right out of the factory sealed package) both also test open (in both directions). Since my meters will see the forward voltage higher than 2 volts, this HV diode cannot be checked on them. My three meters will all check smaller diodes and bridge rectifiers (1N4004, 1N4007, Vishay GBPC606-E4) with no problem (which does me absolutely no good in this case), and I've verified all three meters are working accurately.

I've also got a vintage Simpson meter (non-digital) around here somewhere, but haven't been able to locate it. Hopefully, my wife didn't take it to the Goodwill store with my o-scope that only needed a new probe.

As I initially mentioned, note that I have used one of the new replacement HV diodes with the same results; as well as a new HV cap.

. . Falcon

[glen65]

Although the original diode appears to be open, two other diodes I have (right out of the factory sealed package) both also test open (in both directions). Since my meters will see the forward voltage higher than 2 volts, this HV diode cannot be checked on them. My three meters will all check smaller diodes and bridge rectifiers (1N4004, 1N4007, Vishay GBPC606-E4) with no problem (which does me absolutely no good in this case), and I've verified all three meters are working accurately.

You can check those 4000 series diodes with
just about anything. You need a meter that’s running
at least a 9 volt battery to get anything out those HV diodes.

I've also got a vintage Simpson meter (non-digital) around here somewhere, but haven't been able to locate it. Hopefully, my wife didn't take it to the Goodwill store with my o-scope that only needed a new probe.

It’s probably a Simpson 260, just hope that one didn’t walk
away from you. A new one is about 250 -300 bucks.
You would be able to check the HV diodes with that one.
you would just need to set it on R times 10,000.
If you locate it -hang on to it. I still have mine
and I still use it quite a bit.

As I initially mentioned, note that I have used one of the new replacement HV diodes with the same results; as well as a new HV cap.

Ok.. provided everything is wired correctly and you are
getting 120VAC at the primary of the transformer, about
the only two things left would be 1. the transformer
is not putting out HV (bad secondary) or 2. the mag is bad.
Based on youre earlier post I suspect the latter of the two.

[Gene]

According to all tests performed and their results it looks to me that the first failure suspect is the magnetron.

Gene.

[FalconEddy]

Originally Posted by glen65

You can check those 4000 series diodes with
just about anything. You need a meter that’s running
at least a 9 volt battery to get anything out those HV diodes.


It’s probably a Simpson 260, just hope that one didn’t walk
away from you. A new one is about 250 -300 bucks.
You would be able to check the HV diodes with that one.
you would just need to set it on R times 10,000.
If you locate it -hang on to it. I still have mine
and I still use it quite a bit.


Ok.. provided everything is wired correctly and you are
getting 120VAC at the primary of the transformer, about
the only two things left would be 1. the transformer
is not putting out HV (bad secondary) or 2. the mag is bad.
Based on youre earlier post I suspect the latter of the two.

Yup. That's why I've been trying to find it (Simpson).

If not, I could whip up a 15v HV diode analyzer early next week with my variac and a couple of other component parts.

But, seeing as how I've already got the mag, I may as well just install it (and reuse the t-stat on the original). The worst that could happen is that it still won't heat.

It may actually be the HV tranny since there's not really a loud noise coming from it. It has that 'bad transformer hum' sound during operation. But, the mag is the most likely candidate.

Mother's day tomorrow, so I won't get around to it until Monday at this point. I'll let you know after I change out the mag.

Thanks,
. . Falcon