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

[Kevin Kuehn]

If you haven't replaced it already, there's likely a 1 meg resistor in series with high voltage lead heading off to the anode button. The resistor is likely mounted under the 1B3 socket. They often go high in resistance or open.

[Electronic M]

Originally Posted by vortalexfan

I was able to confirm High Voltage, I was able to draw a 1/4" arc off the 1B3 tube's anode, however there is no high voltage at the picture tube's anode button.

Your HV rectifier tube is probably bad.

Edit: check that resistor Kevin mentioned first.

[jr_tech]

How did you test for HV at the CRT anode?

jr

[vortalexfan]

Originally Posted by Kevin Kuehn

If you haven't replaced it already, there's likely a 1 meg resistor in series with high voltage lead heading off to the anode button. The resistor is likely mounted under the 1B3 socket. They often go high in resistance or open.

Actually the resistor was mounted on the top of the 5kV Doorknob capacitor and it measured 50 ohms shy of 1 Meg Ohm, so it drifted down a little bit over the years but its still within tolerance suprisingly enough.

which means that it could be the 5kV doorknob capacitor we'll have to look at next...

[vortalexfan]

Originally Posted by jr_tech

How did you test for HV at the CRT anode?

jr

I lifted the rubber insulator off the anode of the CRT tube and touched it with the tip of a plastic handled screwdriver to see if I could get it to draw an arc and I couldn't get it to develop an arc like I did at the anode of the 1B3 tube.

[jr_tech]

The voltage on the 1B3 anode is high frequency AC and will arc to an insulated screwdriver. After passing through the 1B3 rectifier, you have DC voltage outputted to the CRT anode, so you may need to ground the screwdriver blade to the chassis to draw an arc.

jr

[vortalexfan]

Originally Posted by jr_tech

The voltage on the 1B3 anode is high frequency AC and will arc to an insulated screwdriver. After passing through the 1B3 rectifier, you have DC voltage outputted to the CRT anode, so you may need to ground the screwdriver blade to the chassis to draw an arc.

jr

Ok, thanks, I'll try that.

[vortalexfan]

OK so I do have high voltage to the picture tube anode cap, but still no raster, although I've noticed that when I turn the brightness control I get a raster for a split second before it goes away again, so I'm guessing it's like what what Kevin was saying earlier, I may have to adjust the ion trap to get a raster on this thing.

But it seems that everything is good to go as far as everything running goes, except that I still don't have audio except for the sound of the HV section coming through on the speaker, which means the Sound IF may be out of alignment, I'm not sure about the Video IF sections or the Tuner and whether or not those are in need of alignment or not, I won't know until I can get the picture tube to produce a picture.

[Kevin Kuehn]

Originally Posted by vortalexfan

OK so I do have high voltage to the picture tube anode cap, but still no raster, although I've noticed that when I turn the brightness control I get a raster for a split second before it goes away again, so I'm guessing it's like what what Kevin was saying earlier, I may have to adjust the ion trap to get a raster on this thing.

But it seems that everything is good to go as far as everything running goes, except that I still don't have audio except for the sound of the HV section coming through on the speaker, which means the Sound IF may be out of alignment, I'm not sure about the Video IF sections or the Tuner and whether or not those are in need of alignment or not, I won't know until I can get the picture tube to produce a picture.

OK, one step at a time here. How about you measure the voltage on the center terminal of the brightness control(alternately pin 11 on the CRT socket) to verify you have an adjustment range with a minimum of around 140vdc. This is referenced from chassis ground.

You should also see if you have 380vdc on pin 10 of the CRT socket, or if it's easier you can measure under the chassis on the end of R44 which connects to a wire leading up to pin 10 of the CRT socket. This one is also referenced to chassis ground.

If those two voltages look good you can proceed to adjusting the location of the ion trap, first try it with the brightness control all the way up. You'll need to move it around the neck as well as fore and aft. Once you get a raster you'll want to turn the brightness down so it's just visible and then find the ion trap's sweet spot that provides the brightest raster.

[vortalexfan]

Originally Posted by Kevin Kuehn

OK, one step at a time here. How about you measure the voltage on the center terminal of the brightness control(alternately pin 11 on the CRT socket) to verify you have an adjustment range with a minimum of around 140vdc. This is referenced from chassis ground.

You should also see if you have 380vdc on pin 10 of the CRT socket, or if it's easier you can measure under the chassis on the end of R44 which connects to a wire leading up to pin 10 of the CRT socket. This one is also referenced to chassis ground.

If those two voltages look good you can proceed to adjusting the location of the ion trap, first try it with the brightness control all the way up. You'll need to move it around the neck as well as fore and aft. Once you get a raster you'll want to turn the brightness down so it's just visible and then find the ion trap's sweet spot that provides the brightest raster.

OK, so how the heck do I measure the voltages of the pins of the CRT's tube socket? There's a plastic cover over it that's riveted on and I don't want to break the CRT Socket.

Secondly which center terminal is the one for the brightness control? the inner or the outer?

[Kevin Kuehn]

Originally Posted by vortalexfan

OK, so how the heck do I measure the voltages of the pins of the CRT's tube socket? There's a plastic cover over it that's riveted on and I don't want to break the CRT Socket.

Secondly which center terminal is the one for the brightness control? the inner or the outer?

There's 3 terminals on the brightness control. You want to measure on the center one, between the 2 outer ones.

Yes it's tough to measure on the CRT connector, which is why I suggested to find the end of R44 which is under the chassis and connected to a wire going up to the CRT socket.

[vortalexfan]

Originally Posted by Kevin Kuehn

There's 3 terminals on the brightness control. You want to measure on the center one, between the 2 outer ones.

Yes it's tough to measure on the CRT connector, which is why I suggested to find the end of R44 which is under the chassis and connected to a wire going up to the CRT socket.

I was referring to which set of terminals is for the brightness control, because the brightness and contrast pot is double-ganged pot an inner pot and an outer pot, and both have three terminals.

Although it makes no difference as I got the measurements I needed, and everything is measuring as it should except for pin 10 of the CRT Socket which is measuring at 404 VDC rather than 380 VDC, but Pin 11 of the CRT Socket (the center tap of the brightness control) is measuring between 15VDC and 140VDC like you said it should when the knob was rotated.

So the 404 VDC on pin 10 of the CRT Socket, does that mean something is wrong with that part of the circuit, or is that just because of the higher line voltages?

[Kevin Kuehn]

I should have told you to also measure the voltage which goes to pin 2 of the CRT socket referenced to chassis ground, should be 1.3vdc. You can get to that under the chassis on the end R35 that should be connected to another wire going up to pin 2 of the CRT socket. Use the resistor identification on page 17 of your sams to find the actual physical location of the resistors.

[Kevin Kuehn]

Originally Posted by vortalexfan

So the 404 VDC on pin 10 of the CRT Socket, does that mean something is wrong with that part of the circuit, or is that just because of the higher line voltages?

I think it's close enough. See my previous post about measuring voltage on pin 2 on the CRT socket. If these 3 voltages are in the ball park you should be good to see if you can get a raster by adjusting the ion trap.

[vortalexfan]

Originally Posted by Kevin Kuehn

I should have told you to also measure the voltage which goes to pin 2 of the CRT socket referenced to chassis ground, should be 1.3vdc. You can get to that under the chassis on the end R35 that should be connected to another wire going up to pin 2 of the CRT socket. Use the resistor identification on page 17 of your sams to find the actual physical location of the resistors.

OK, Pin 2 of the CRT is about 1.6 VDC which is only .3 volts higher than the reading given in the Sam's Voltage Chart, so I would say those 3 voltages are in the ballpark of where they should be.

So now how do I go about adjusting the Ion Trap on this TV?