Muntz tv - Page 2 - Videokarma.org TV - Video

radio nut · #16 09-17-2012, 11:07 AM

Well I took the last tube and put it in and so far the set is picking up a fan and sending noise to the speaker and I can hear the horizontal noise from the flyback but the screen is dark.I went through most of the resistors with my ohmeter and most are way off. and the video detector diode reads 4,000 ohms both ways so I still have more work ahead of me.

radio nut · #17 09-23-2012, 12:18 PM

So now My rectifier tube is lighting up like it is shorted. I tried other 5u4's and same problem. I think one of the electrolyitics went out. They were new but I tried to form them on a cap checker I was not used too. If there is anything else that would cause this tube issue please let me know.

Also the screen did light up before this tube issue. The magnet on the back of the crt was missing and I put one on and did get a horizontal line on the screen. the vertical is out and i am not sure why. I did get a diagram and found a bad resistor in the vertical circuit. Plus I need a 4,000 pf cap in the vertical circuit and the closest I had was 5,000. So maybe it is not letting the circuit osc. at the right frequency.

So far this tv seems to be one step forward and one step back.

So my biggest concern is the shorting out rectifier tube. I have three good ones and all start to light blue. But not in my capehart radio which uses them. So it is the tv.

I do not know what else could be the problem besides electro's. I checked the filter choke and audio, vertical and other transformers as far as resistance and they check fine. the main transformer does not have resistances listed but this set did put up a horizontal line on the screen for about 3 hours before the shorting rectifier tube started. It started on fire up last time I tried the set.

Any ideas please post them!

***Eric H*** · #18 09-23-2012, 12:46 PM

It sounds like one of your Electrolytics has shorted, you certainly have a short on the B+ line somewhere.

If they are new then double check to make sure you put them in correctly (Polarity).

This is really one of those times you need a Variac to keep from blowing your Rectifier tube.
You can rig up a Solid State replacement for testing purposes but it will increase the B+ so you don't want to run it at full voltage lest you explode a shorted Cap.

If you can run it on a Variac you can feel the Caps and see which one is getting warm, or disconnect them one at a time until the short goes away.

jr_tech · #19 09-23-2012, 01:09 PM

Another possibility would be that the focus coil could have shorted to ground.

jr

radio nut · #20 09-23-2012, 03:01 PM

Quote:

Originally Posted by Eric H

It sounds like one of your Electrolytics has shorted, you certainly have a short on the B+ line somewhere.

If they are new then double check to make sure you put them in correctly (Polarity).

This is really one of those times you need a Variac to keep from blowing your Rectifier tube.
You can rig up a Solid State replacement for testing purposes but it will increase the B+ so you don't want to run it at full voltage lest you explode a shorted Cap.

If you can run it on a Variac you can feel the Caps and see which one is getting warm, or disconnect them one at a time until the short goes away.

I have run it for about 3 hours before this short so I pull electro's and am going to test them this week. hopefully it is not the focus coil.

radio nut · #21 09-25-2012, 04:53 PM

Quote:

Originally Posted by jr_tech

Another possibility would be that the focus coil could have shorted to ground.

jr

I don't remember seeing any wires for the focus coil seperate from the yoke. Should I?

Also I am curious. one of two things was happening. Either the rectifier tube was getting shorted or a ten watt 2500 ohm resistor was arcing to the chassis. It is one of those long metal resistors that is mounted onto the chassis and has a flat piece of metal that is folded over to cover it. If the rectifier tube did not short the resistor started arcing to the chassis itself from the wires inside of it. It had two leads so it was not grounded per se. Could this be the culprit?

I did take my electolytic caps out and test them at fair radio. I could not find a heathkit cap checker which I am used to. I had to use a sprague but I am not sure if it is functioning perfectly. That being said two of the 100mf caps seemed to not form right. On the 6ma. setting they held 150 volts instead of dropping to zero as they charged up. I grabbed 2 more and they did the same. I went to the bin and opened a new bag and they dropped down to about 5 volts or so. Plus after they were charged they had a loud snap if I shorted them on some metal and the first set really did not snap very loud. I am hoping this is the problem ......Really wish I had the heathkit checker because I know how to "read"it.

jr_tech · #22 09-25-2012, 05:14 PM

It is possible that your model does not have a focus coil. Perhaps a permanent magnet focus assembly is used. The only sams that I could dig up for a Muntz of that period was for models M-31, M-32, M-33, and the focus coil is clearly shown.

I don't trust those chassis mount resistors at all... I have seen several that have shorted to ground, so that indeed may be the problem... That can get exciting!

jr

radio nut · #23 09-25-2012, 06:10 PM

I think this is a m-31. I do have the diagram but it is at my friends house along with the set.

Fair Radio does have a heathkit cap checker.... it was hidden in the back(where I was at earlier). I will go back in tomorrow and use it to double check my caps so I am confident about their condition before I put them back in. The Sam's should be 108-8. if my memory serves me correctly

jr_tech · #24 09-25-2012, 06:56 PM

The Sams that I am looking at is 116-10, so perhaps it is a different set... I don't see a chassis mount resistor in the pictures, but the wires for the focus coil are clearly visible, behind the yoke.
Must be nice being close to Fair Radio !

jr

radio nut · #25 09-25-2012, 07:40 PM

My set has a chassis mount resistor in the high voltage cage. Yeah having Fair in the neighborhood is cool. I worked there as a second job and liked it but quit due too being tired as my first job had overtime a lot. But going in early monday morning and being the first to go through their auction purchases was the best!.

I did check just now and my set is Sam's 108-8.

I just got to thinking that maybe the wires for the focus coil run through a different hole in the chassis so I will have to check for them sunday on my next day off.

radio nut · #26 09-26-2012, 02:36 PM

Well I retested the caps on a heathkit cap checker that I went through and recapped, replaced out of tolerance resistors and calibrated.
They all check good...... that being said 2 of the 100mf caps that I originally used did form very slowly. The newer ones formed quick.

So I guess I will replace the chassis mount resistor and check the focus coil although I am not sure how to check it right now. The tv itself is in another town at my friends house and I called him and he stated that there are only 4 wires going to the yoke and not 6. So I am unsure how the focus coil is hooked up.
If my memory serves me correctly the diagram showed a coil and(or) a permanent magnet assembly for focus but did not show routing of wires but when I look at the yoke it appears to have a narrow coil in front of the deflection coils.
Oh well if this hobby was easy more people would do it....right?

radio nut · #27 10-01-2012, 12:41 PM

Well I got this set running. Yeah! The 2,500 ohm chassis mount resistor was shorted to ground. The picture tube did check like it is alive but was not strong...

What's funny is there is a burn in the screen....took me a while to figure out what it was but it appears to be a tv station test pattern . A circle in each corner and a dark spot in the middle! So now I need a 16rp4 crt. Wish me luck!

Oh, One last question; Does a crt lose its contrast capabilities as it gets weaker?
The picture did not impress me as far as how white the whites were.