My Zenith 9S367 is just dead. I have 136 v DC at the input to the FC coil and nothing at the output. From the output of the FC to ground measures 280 ohms.

Sounds like your field coil is open.

:Sounds like your field coil is open.

I know. Why does it ohmmeter OK?
John
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Disconnect one end of the coil from the circuit and ohm across it (the field coil). Ohming the "downstream" node to ground just gives the resistance of the circuit elements that are hanging on the node- won't tell you anything about the state of the field coil itself.

:Disconnect one end of the coil from the circuit and ohm across it (the field coil). Ohming the "downstream" node to ground just gives the resistance of the circuit elements that are hanging on the node- won't tell you anything about the state of the field coil itself.
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I measured the FC when the speaker was unplugged from the radio and the FC measured 1050 ohms. If the FC was open wouldn't the voltage come up to source and be much greater than 135v DC?
John

The print indicates 1250 ohms for the FC so your measurement seems close enough.
The voltage chart shows 280vDC of the cathode of the rectifier feeding the FC... and the SC of the output shows 229vDC and 210 on the plate.
That means the FC is dropping 65v.
65v divided by 1250 ohms means the B+ is drawing about 52-60ma
If you have continuity ( as you stated 1050 ohms) with the FC there is no reason that the B+ of +285v on the FC input side should not appear on the output side at about +220v under load.

plse excuse my typos:
That was supposed to read B+ of 220vDC on the SG of the output tube.

:
:plse excuse my typos:
:That was supposed to read B+ of 220vDC on the SG of the output tube.

If I measure only 280 ohms or so at the output of the FC to ground doesn't that seem like a huge load and thus something is drawing the voltage down?
But what puzzles me is that I also get no voltage on the output of the FC.
John
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Yes 250 ohm is too much load.

But if you can measure continuity of 1050 ohms on the FC ... is that with one end lifted?

If so.. and if you lift up the LOAD end of the FC... you should be able to read the same +285vdc that is going in .. on the other end too, as long as the loads are removed... right?

Then..if that works ok.. then at least you can feel you've verified to FC continuity as ok.

At that point you can try temporarily clipping about a 4k load to the FC output side.

(+220vdc divided by 4,000 ohms is equal to 55ma.)

So that 4k temp resistor will simulate a normal load on the FC.
If that works and the FC drops about 65vDC then you have proven that the FC is good.

Remove the temp 4k resistor.

So then it's time to start looking at and measuring the other radio loads.
Start by lifting off all the leads that feed into all the loads.
Then start adding back sections at a time to see where the excess loads are.

:

:Yes 250 ohm is too much load.
:
:But if you can measure continuity of 1050 ohms on the FC ... is that with one end lifted?
:
:If so.. and if you lift up the LOAD end of the FC... you should be able to read the same +285vdc that is going in .. on the other end too, as long as the loads are removed... right?
:
:Then..if that works ok.. then at least you can feel you've verified to FC continuity as ok.
:
:At that point you can try temporarily clipping about a 4k load to the FC output side.
:
:(+220vdc divided by 4,000 ohms is equal to 55ma.)
:
:So that 4k temp resistor will simulate a normal load on the FC.
:If that works and the FC drops about 65vDC then you have proven that the FC is good.
:
:Remove the temp 4k resistor.
:
:So then it's time to start looking at and measuring the other radio loads.
:Start by lifting off all the leads that feed into all the loads.
:Then start adding back sections at a time to see where the excess loads are.
:

Yes, thanks Peter. I was thinking that would be my next approach. Late now and will start tomorrow.
John
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