motorola 19k2 - Page 2 - Videokarma.org TV - Video

radio nut · #16 02-11-2015, 12:57 PM

I found another issue that is going on.... the blus has 3 different voltages all coming from the same main line , 3oo, 265 and 115.
My set is running 315,278 , and 185.
The high wattage voltage droppers check ok with ohm meter.
I disconnect the 115 line from the voltage dropper and it goes to 115....should be dead!
my diagram does not show another 115 source.
well the If tubes were running 140 for b plus instead of 100, ok so they are probably working harder and are over driving the signal.
I did have a small portable years ago that had an adjustable agc and turned to either extreme did end up with the same crappy image on the screen.
Idid look for sloppy work ....solder dripped onto other items or just stuff touching things they shouldn't and so far nothing.
I will try to pull tubes in case one shorted under voltage and causing the voltage bleed into the b plus line.

Electronic M · #17 02-11-2015, 02:19 PM

If you are getting 300, 265 and 115 volts on three points that are directly connected together with wire, then look for bad solder joints connecting them, and open or high resistance interconnect wire.

Look for heater to cathode shorts in tubes as well. Some sets float the cathodes at a variety of voltages, and if the heater line shorts to two cathodes, or is resistively pulled to a certain voltage and a cathode shorts to it, then all manner of havoc can occur....If you find a tube with a H-K short be sure to look up the max heater to cathode voltage in the tube data sheet, and check that voltage in set set to ensure it is not exceeded.

I wish I had enough sam's to be able to pull the one for any given set and follow along, but I don't.

radio nut · #18 02-11-2015, 02:22 PM

Well, I pulled most of the tubes and with the 5u8 still in place the 115 is zero volts.
I started putting tubes back on and found that the once the 12au7 is installed the 115 line jumps to 50 volts, the 6au6 and the line jumps to 115.
Ok, I took them to fair radio and tested them on a TV-7 tube tester and they show good.
I sub in other tubes and I get the same results....
each tube has both 115 and 265 being fed to them but there isn't a path to each other I can find unless both have ceramics to ground that are shorted but wouldn't the chassis be live then?

radio nut · #19 02-11-2015, 11:58 PM

I found 1 area between the 12au7 and the 6au6 that has 115 on one wire and 265 on another with a 5 mmf cap going to both, replaced that and I still have the same power bleed.
The only thing I can think of now is maybe I miss wired the electro's and have a wire going to the wrong source or a part that I may have moved around that is touching something and needs moved.

EdKozk2 · #20 02-12-2015, 12:16 AM

Make sure you have your focus control in the fully ccw position when you take your voltage readings on the 12au7 and 6au6 sound I.F tubes.Your cathode supply voltage
on both those tubes is +115vdc and the plate supply voltage is +265. Your cathode resistors of 220 ohms only drop about 1.5 to 2 volts. Check R-60 the 22k resistor connected to pin 5 of V12 and ground, that forms the final leg of your power supply bleeder, 115 volt to ground. An open or way off spec 22k resistor could through the readings off. The sync clipper is a DC coupled to the sync amp. The sam's also notes that the pin voltage readings are between various supply voltage points, e.i. 115 and pin 6 of the 12au7. A shorted capacitor would tend to burn a resistor ,a transformer,and blow itself up even.
Ed

radio nut · #21 02-12-2015, 08:53 AM

Quote:

Originally Posted by Electronic M

If you are getting 300, 265 and 115 volts on three points that are directly connected together with wire, then look for bad solder joints connecting them, and open or high resistance interconnect wire.

Look for heater to cathode shorts in tubes as well. Some sets float the cathodes at a variety of voltages, and if the heater line shorts to two cathodes, or is resistively pulled to a certain voltage and a cathode shorts to it, then all manner of havoc can occur....If you find a tube with a H-K short be sure to look up the max heater to cathode voltage in the tube data sheet, and check that voltage in set set to ensure it is not exceeded.

I wish I had enough sam's to be able to pull the one for any given set and follow along, but I don't.

Maybe you misunderstood my point or I am not understanding yours, but just to make sure...
This set uses 300, 265, and 115 as high voltage supplies in this set.
They all originate from the same line dropped by resistors.
When I cut the 115 leg from its' voltage dropping resistor and had 0 tubes in the set the 115 line read 0 volts with only the 5u4 installed . reinstalling tubes one at a time it stayed 0 until I got to the 12au7, it hit 50v and then went higher with the 6au6, up to 115v.
I am not showing any cathode to heater shorts and even took my tubes to Fair and used there tv-7 as a back up incase my tester broke.
I have poked and tugged on my solder connections in the voltage supply section and looked for a poor solder job on resistors/caps I have installed.
Took a break yesterday and will check suggestions posted here and hopefully looking at this set fresh today will help.

EdKozk2 · #22 02-13-2015, 01:49 AM

If your 115 volt line is still disconnected from the 115 B+ source, and you insert the 12au7 and get a 50 volt reading on the disconnected 115v bus line, that's because the 265 volts at the plate (pin 6) is being dropped through the plate resistors and cathode resistor. Then when you also insert the 6au6 it drops the same 265 volts through its
plate (pin 5) resistor and cathode (pin 7) resistor. Remember the current in those tubes starts to flow because you connected a voltmeter to an open circuit, the disconnected 115 volt B+ line. If you tested the 115 line after replacing the 6au6
first you'd get a different reading.
Did you recap the entire set. I would also make sure C36 in the 6ah6 (pin 1) is
not leaking. An easy test is to remove the 6ah6 and read the voltage on pin (1).
If you still get a positive voltage reading then C36 is defective, most likely.
Ed

radio nut · #23 02-13-2015, 08:50 AM

Yes this set is recapped, electro's, paper and the 3 domino (mica). the rest of the caps and almost all resistors original.
I started checking the 115 line cause the 115 line was running 185 and had the b plus to the IF's at 140 and should be 100.
I did recheck the sync resistor mentioned earlier and it was fine.
I am taking all tubes to Fair radio today and using their tv-7 for testing.
When the problem with this set kicked in I did perform with my new digital volt/ohm meter the voltage and resistance tests on all tubes and it led to a couple of resistor replacements.

radio nut · #24 02-13-2015, 08:55 AM

On the c36 to be checked there is one problem with that. my set has r31 hooked to the contrast control (not used on all sets). I guess I could try to adjust that control for zero volts and then pull the tube.
If all tubes test ok , then I will rehook the 115 line and rerun the volt/resistance checks and re read this entire thread and make sure I did not miss any ideas posted.

radio nut · #25 02-13-2015, 08:59 AM

I did find 2 caps on the 6al5 horizontal phasing that were completely backwards as far as the spots in the vertical sync where they go. I made them match the diagram and now the set performs worse.
Before I switched them I had good sound and strong lock in the vert. and horiz. with washed out picture.
Now sound is weaker and picture weaker and will not hold lock.
It is jumpy in the vert. and horiz.
This is of course right now with 115 line still disconnected.

radio nut · #26 02-13-2015, 09:02 AM

I have one question, could the tuner inductor that I put in being higher value cause some of this or is it not the issue since I have signal ?

radio nut · #27 02-13-2015, 09:04 AM

Since the inductor was in the Osc. tuner circuit could the osc need calibrated now?
It was L9, going from pin 8 Osc. section of the 12at7 to ground.

radio nut · #28 02-13-2015, 09:10 AM

Also, I have tube shields but during testing I am not using any and the tuner is uncovered, the bottom cover is not on. Could not having any shields be causing some of this problem?
the set is in the basement and I am using plain light bulbs.

This set is not near a running microwave or flor. light bulbs.

radio nut · #29 02-13-2015, 09:37 AM

Also tomorrow I will re hook the 115 line and go from there. I might just go ahead and check all new paper replacement caps (yellow ones) to make sure I do not have DC voltage on both sides unless they should.

Electronic M · #30 02-13-2015, 09:52 AM

Lack of shields could be causing problems. TVs emit RF interference, and if the shielding is off things can feedback and cause problems.
As for the osc possibly being off...Adjust the fine tuning and try adjacent channels and fine tuning adjustment on those channels. If you can't get a better signal within 1 channel of the number of what it should be then I'd assume the osc is close enough.