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

[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

[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.

[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.

[Tube TV]

Yes, looking forward to seeing a schematic!
I would disconnect all connection off the 5U4 that were suppling and voltages and see if it was arcing after that.
Beyond that I would avoid any more power ups with that much load put on the transformer otherwise it's going to cook out a winding in short order, if that is not already a issue.
Look for defective 5U4 tube socket, also a filter choke with a short to chassis. I can't imagine the 5 volt cap would not cause that much of a problem.
As someone else mention the focus, check that the focus control is not shorting to chassis.
What is the current draw on the input of the transformer with all the tubes out?

[vortalexfan]

Posted below for everyone's information is the power supply section of the Schematic for this TV.

Hope this helps everyone help me figure out why my TV's power supply is drawing over 8 Amps of current and causing my 5U4 tube to arc and nearly redplate.

[Electronic M]

Disclaimer: the component designators in the attachment are fuzzy and I may not have read them correctly.

Procedure: disconnect C1a positive and L1 from pin 2 of 5U4. Measure resistance to ground at pin 2 if the resistance is that specified in the service literature or higher then the shot is not in the tube or power transformer (but if it meaures well below spec resistance spec the tube socket and or power transformer are prime suspects).

If you cleared the power transformer of suspicion next disconnect L1, R95, C2b, focus control, and focus coil from each other. Check resistance of C1a, C1b, and both wires of L1 to ground...if any of them measures less than 1M to ground replace the part that has low resistance.

Check R95, focus pot, and focus coil to ground. If R95 checks lower than 100k to ground you may need to check the circus it feeds off the image you attached. If focus coil checks under 100k to ground unhook the other focus coil lead and measure each lead to ground if still low replace focus coil. If focus pot tests under 100k to ground disconnect it's terminals from circuit and measure from each to ground. If still too low pot is defective.
Also disconnect the positive of C1c and measure it's resistance to ground. Do the same for R94...if you still haven't found the short check the items off the attached image that the B+ drives.

Methodically divide and conquer...er um I mean measure till you find your shorted part(s). Replace culprit part(s) remeasure, reconnect all disconnected connections, remeasure to be sure the short is gone, and then power up if all now checks good (use a variac and or dim bulb tester if you have one just in case something is still wrong).

[vortalexfan]

Originally Posted by Electronic M

Disclaimer: the component designators in the attachment are fuzzy and I may not have read them correctly.

Procedure: disconnect C1a positive and L1 from pin 2 of 5U4. Measure resistance to ground at pin 2 if the resistance is that specified in the service literature or higher then the shot is not in the tube or power transformer (but if it meaures well below spec resistance spec the tube socket and or power transformer are prime suspects).

If you cleared the power transformer of suspicion next disconnect L1, R95, C2b, focus control, and focus coil from each other. Check resistance of C1a, C1b, and both wires of L1 to ground...if any of them measures less than 1M to ground replace the part that has low resistance.

Check R95, focus pot, and focus coil to ground. If R95 checks lower than 100k to ground you may need to check the circus it feeds off the image you attached. If focus coil checks under 100k to ground unhook the other focus coil lead and measure each lead to ground if still low replace focus coil. If focus pot tests under 100k to ground disconnect it's terminals from circuit and measure from each to ground. If still too low pot is defective.
Also disconnect the positive of C1c and measure it's resistance to ground. Do the same for R94...if you still haven't found the short check the items off the attached image that the B+ drives.

Methodically divide and conquer...er um I mean measure till you find your shorted part(s). Replace culprit part(s) remeasure, reconnect all disconnected connections, remeasure to be sure the short is gone, and then power up if all now checks good (use a variac and or dim bulb tester if you have one just in case something is still wrong).

Sorry about the fuzzy diagram the Sam's Folder came to me that way when I downloaded it from the Sam's website.

I'll definitely check those things out for sure.

[old_coot88]

Originally Posted by vortalexfan

I'll definitely check those things out for sure.

But by all means start with this from Electronic M:

Procedure: disconnect C1a positive and L1 from pin 2 of 5U4. Measure resistance to ground at pin 2 if the resistance is that specified in the service literature or higher then the shot is not in the tube or power transformer (but if it meaures well below spec resistance spec the tube socket and or power transformer are prime suspects).

With C1a+ and L1 disconnected from pin 2, you should read infinite resistance (open circuit) from pin 2 to ground. If so, that eliminates 5U4 socket and xfmr as suspects. Then proceed 'downstream' per Electronic M's directions.

[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.

[edison64]

Wow there are more posts about this set than there are Parts in it LOL

[Kevin Kuehn]

Originally Posted by edison64

Wow there are more posts about this set than there are Parts in it LOL

Whomever said it was easy to teach troubleshooting skills via the internet was mistaken.

[vortalexfan]

Originally Posted by Kevin Kuehn

Whomever said it was easy to teach troubleshooting skills via the internet was mistaken.

Yeah, I wish there was someone nearby that could help me with this but unfortunately none of you here live nearby where I live.

I really do want to get this set going because it is such a rare set and also this would be the oldest tv I've ever owned.

[Tube TV]

Vortalexfan, how are you doing with this, are you making any headway?

[vortalexfan]

Originally Posted by Tube TV

Vortalexfan, how are you doing with this, are you making any headway?

Unfortunately no, I'm no closer to figuring out what's causing my 5U4 tube to arc and red plate than I was a couple of weeks ago.

I've been testing various components and replacing suspect capacitors in the power supply and I'm not getting anywhere.

[Kevin Kuehn]

Originally Posted by vortalexfan

Unfortunately no, I'm no closer to figuring out what's causing my 5U4 tube to arc and red plate than I was a couple of weeks ago.

I've been testing various components and replacing suspect capacitors in the power supply and I'm not getting anywhere.

So what did you find out when you followed Electronic M's below procedure?

Originally Posted by Electronic M

Procedure: disconnect C1a positive and L1 from pin 2 of 5U4. Measure resistance to ground at pin 2 if the resistance is that specified in the service literature or higher then the short is not in the tube or power transformer (but if it meaures well below spec resistance spec the tube socket and or power transformer are prime suspects).