Old Muntz TV for sale Locally to me, Should I pick it up?

[Electronic M]

Originally Posted by vortalexfan

OK So testing pins 2 and 8 of the 5U4G tube socket I'm only getting 25.5 Ohms on those pins, and not the 22,000 Ohms I should be getting.

I'm guessing that means that the issues I'm having with the excessive (4.5 Amps, 520 Watts) current draw lies there somewhere?

Or is that a sign that something else further down the line is causing that excessively low filament resistance reading on my 5U4G tube socket?

Are you measuring 2 to ground and 8 to ground, or measuring 2 to 8 ( 2 to 8 ain't helpful)?

Either 2 or 8 should have a choke(in series with B+) or B+ line connected to it... unsolder the B+ line or choke and check 2 and or 8 to ground resistance. If the resistance is much higher than before then you have confirmed the rect and transformer are good. You'll then have to disconnect splits on the B+ line from the main line and check b+ to ground resistance till you find the point that has the short.

Most B+ shorts happen in ways that make visually identifying the issue impossible. You gotta rely on instruments, logic guided by the schematic.

It is not impossible for paper caps to dead short and for that to effect the B+... usually there is a power resistor in series that smokes out first, but not all sets are wired the same.

If I had it on my bench I could probably isolate the short in 30 min.

[old_coot88]

Originally Posted by Electronic M

...If I had it on my bench I could probably isolate the short in 30 min.

I could do in less than 1 min. Just kidding! Make it 2 minutes tops.

[vortalexfan]

Originally Posted by Electronic M

Are you measuring 2 to ground and 8 to ground, or measuring 2 to 8 ( 2 to 8 ain't helpful)?

Either 2 or 8 should have a choke(in series with B+) or B+ line connected to it... unsolder the B+ line or choke and check 2 and or 8 to ground resistance. If the resistance is much higher than before then you have confirmed the rect and transformer are good. You'll then have to disconnect splits on the B+ line from the main line and check b+ to ground resistance till you find the point that has the short.

Most B+ shorts happen in ways that make visually identifying the issue impossible. You gotta rely on instruments, logic guided by the schematic.

It is not impossible for paper caps to dead short and for that to effect the B+... usually there is a power resistor in series that smokes out first, but not all sets are wired the same.

If I had it on my bench I could probably isolate the short in 30 min.

I was measuring pin two to ground and pin 8 to ground, and those were the measurements I got, 26 ohms on pin 2 measuring to ground and pin 8 measuring to ground.

And as far as a paper cap being responsible for this goes, there are over 50 capacitors in there I'll have to check individually which will take me a while to test each and every capacitor with an ohm meter to see if the capacitor is still "good" or if it's open.

[Electronic M]

Originally Posted by vortalexfan

I was measuring pin two to ground and pin 8 to ground, and those were the measurements I got, 26 ohms on pin 2 measuring to ground and pin 8 measuring to ground.

And as far as a paper cap being responsible for this goes, there are over 50 capacitors in there I'll have to check individually which will take me a while to test each and every capacitor with an ohm meter to see if the capacitor is still "good" or if it's open.

If you are testing capacitance, don't bother. If the cap is open that is better. What you want to do do if you are hell bent on checking the paper caps is check the resistance across the cap and make sure it is too high for the meter to measure, and even that is a waste of time for two reasons. 1 some caps won't show leakage at the low 9V a DMM puts out (though that 25 ohms is registering on a meter so you might find it that way). 2 there is no guarantee it is a capacitor (could be almost anything on the B+ line) and it is far simpler (less, possibly MUCH less than half the work of checking all the caps) to start at the rectifier and split the B+circuit into segments by cutting it at nodes then measuring resistance to ground and splitting the lowest resistance section into smaller parts till you find the short.
Can you post a schematic of the power supply in your set?... I can write you a simple procedure to isolate the short if I can see the circuit.

[vortalexfan]

Originally Posted by Electronic M

If you are testing capacitance, don't bother. If the cap is open that is better. What you want to do do if you are hell bent on checking the paper caps is check the resistance across the cap and make sure it is too high for the meter to measure, and even that is a waste of time for two reasons. 1 some caps won't show leakage at the low 9V a DMM puts out (though that 25 ohms is registering on a meter so you might find it that way). 2 there is no guarantee it is a capacitor (could be almost anything on the B+ line) and it is far simpler (less, possibly MUCH less than half the work of checking all the caps) to start at the rectifier and split the B+circuit into segments by cutting it at nodes then measuring resistance to ground and splitting the lowest resistance section into smaller parts till you find the short.
Can you post a schematic of the power supply in your set?... I can write you a simple procedure to isolate the short if I can see the circuit.

I've got a schematic for the power supply circuit, I'll upload it when I get a chance.

[dieseljeep]

Originally Posted by vortalexfan

I was measuring pin two to ground and pin 8 to ground, and those were the measurements I got, 26 ohms on pin 2 measuring to ground and pin 8 measuring to ground.

And as far as a paper cap being responsible for this goes, there are over 50 capacitors in there I'll have to check individually which will take me a while to test each and every capacitor with an ohm meter to see if the capacitor is still "good" or if it's open.

Disconnect the lead going to the 5U4 socket from the B+ circuitry. It has to be in the B+ feeds, electrolytics, grounded filter choke, even the vertical output transformer.
As stated before, the smaller circuit capacitors throughout the circuitry of the set wouldn't cause a dead short in the B+ rail.
IIRC, the B- isn't going to the chassis but is forming a low bias source.

[init4fun]

With how many times now the poor 5U4 has been the purple guy here

it stands to reason that when the short circuit is finally found and fixed that the 5U4 may be too far gone to properly run the set .

[vortalexfan]

Originally Posted by init4fun

With how many times now the poor 5U4 has been the purple guy here

it stands to reason that when the short circuit is finally found and fixed that the 5U4 may be too far gone to properly run the set .

Don't worry I have several 5U4s to work with, the one I'm using right now is one that wasn't in very good shape to begin with, I haven't been using the original one.

[jr_tech]

Originally Posted by dieseljeep

Disconnect the lead going to the 5U4 socket from the B+ circuitry. It has to be in the B+ feeds, electrolytics, grounded filter choke, even the vertical output transformer.
As stated before, the smaller circuit capacitors throughout the circuitry of the set wouldn't cause a dead short in the B+ rail.
IIRC, the B- isn't going to the chassis but is forming a low bias source.

I would also disconnect the focus coil and measure the resistance to ground of both leads. Also do the same for the 5U4 5 volt heater winding of the power transformer.

jr

[dieseljeep]

Originally Posted by jr_tech

I would also disconnect the focus coil and measure the resistance to ground of both leads. Also do the same for the 5U4 5 volt heater winding of the power transformer.

jr

I forgot about the focus coil circuit!
The last three sets I restored had PM focus units or electrostatic focusing.