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Mep 803a no AC

G

gelane

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Location
Florida
Long time reader, first post.
I have owned my 803 for 2 years with little to no problems.
This unit shows 4k hours and is in good condition. I run it every so often
with a 7.5 kw load for usually an hour or so. Haven't needed it yet as a backup.

It didn't have the "fuse mod" so I did add the 3 amp slow blow fuse to the quad
winding. Not the varistor (?) though.

I went to start it yesterday and it starts and the engine runs fine but no AC.
It had run for a minute or so when I noticed the no AC state. (I usually let it
warm up for a few minutes before applying a load).

I stopped it and checked the fuse and sure enough it was blown. (The unit
has 10 or more hours with the mod, so the install there is not the problem)

I replaced the fuse and watched close on start up to notice the voltage start to
build the fall to zero after a second or 2. Yep, blown fuse again.

I have checked the quad winding and it appears to be a direct short with the wires
removed from the voltage regulator. Not to ground but no resistance.

I have the manuals downloaded and would appreciate direction for the next tests.
I am hoping the experts here would chime in with "look here because the problem is
almost here" rather than me spending hours chasing my tail.

The unit has been in my shop for the time I have owned it so weather isn't a factor.

Thank for looking,
Gary
 
K

kloppk

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Gary,

The resistance spec for the MEP-803A Quad winding is only 0.9053 to 1.224 ohms. When measured with a common DMM it's will appear to be be shorted. Common DMM's don't measure really low resistances well.

Based on your description of the "Fuse Mod" fuse repeatedly blowing generally points to a blown A1 Voltage Regulator.
Fortunately you had the Fuse Mod installed BEFORE the Voltage Regulator died! Otherwise the Quad Winding could have been damaged.
 
G

gelane

Member
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Location
Florida
kloppk said:
Gary,

The resistance spec for the MEP-803A Quad winding is only 0.9053 to 1.224 ohms. When measured with a common DMM it's will appear to be be shorted. Common DMM's don't measure really low resistances well.

Based on your description of the "Fuse Mod" fuse repeatedly blowing generally points to a blown A1 Voltage Regulator.
Fortunately you had the Fuse Mod installed BEFORE the Voltage Regulator died! Otherwise the Quad Winding could have been damaged.
Click to expand...

Thanks for the reply,
I believe you are the gentleman that offers the replacement VR and
your input is greatly appreciated.

I think it probibly is the A1 but I want to be sure before ordering one.

I have 2 meters that will read .000 so I'm pretty certain I'm correct.
I will reasearch the diagnosis further and see what I come up with.

I believe I read that your A1 will also run without the quad winding.
Am I correct in that thought ?

The thing I don't get is how it would go bad just sitting there.

One thing I forgot to mention is that when I did my first start
the other day was that I hit the GFI test button on start up.
Don't know why, I never tried it before.
I don't think that would have caused the problem ??

Should I remove the A1 and look for burned parts or just move
ahead to checking the other windings and diodes ?

Thanks again.
Gary
 
K

kloppk

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Correct, I do offer a replacement for the A1 Voltage Regulator. Yes it works even if the Quad Winding is bad.

Failure of the Voltage Regulator due to its internal diode bridge shorting out is linked to when the set is started. So it may have failed just as you started it recently. Voltage spikes on the output of the Quad Winding in excess of the PRV voltage rating of the diodes in the bridge can cause them to fail and short out. There can be other failures of the Voltage Regulator too.

If the diode bridge shorted out you likely won't see any burned diodes inside the A1. Doesn't hurt to look around in there for other visible issues.

The Quad Winding is responsible for powering the Voltage Regulator (VR). You can test to see if the Quad Winding is generating AC power by doing the following AC voltage test. Can be done with the Fuse Mod fuse blown.
With the set running connect your meter leads to A1 terminal 7 and try both ends of the Fuse Mod Fuse with the other lead. The AC voltage there should be in the neighborhood of 69 VAC. You may need to bump S1 to the START position while doing the reading.
 
Last edited:
G

gelane

Member
12
29
13
Location
Florida
kloppk said:
Correct, I do offer a replacement for the A1 Voltage Regulator. Yes it works even if the Quad Winding is bad.

Failure of the Voltage Regulator due to its internal diode bridge shorting out is linked to when the set is started. So it may have failed just as you started it recently. Voltage spikes on the output of the Quad Winding in excess of the PRV voltage rating of the diodes in the bridge can cause them to fail and short out. There can be other failures of the Voltage Regulator too.

If the diode bridge shorted out you likely won't see any burned diodes inside the A1. Doesn't hurt to look around in there for other visible issues.

The Quad Winding is responsible for powering the Voltage Regulator (VR). You can test to see if the Quad Winding is generating AC power by doing the following AC voltage test. Can be done with the Fuse Mod fuse blown.
With the set running connect your meter leads to A1 terminal 7 and try both ends of the Fuse Mod Fuse with the other lead. The AC voltage there should be in the neighborhood of 69 VAC. You may need to bump S1 to the START position while doing the reading.
Click to expand...

OK.....I did as you directed and with the engine running and holding in
"start" mode my multimeter shows upper 70's ac voltage when connected
to the quad winding.

I am a little surprised my meter wouldn't read the quad winding.

So......at this point I'm pretty well convinced it is as you said the A1.


Can you PM me with purchasing info ?

Thanks for your time,
Gary
 
Guyfang

Guyfang

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One thing I forgot to mention is that when I did my first start
the other day was that I hit the GFI test button on start up.
Don't know why, I never tried it before.
I don't think that would have caused the problem ??

Not even. The A1 is, was, and always be a weak spot for the whole line of TQG's.
 
Light in the Dark

Light in the Dark

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They are very high quality items, and a very fair price considering what the OEM unit goes for (and is not as good as Kurt's solution, in my opinion).
 
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