motorola 19k2
 

I am currently working on a 1950 Motorola set for my boss's wife....seems she loves antiques and Turner classic!
I heard she is excited to have an old tv playing old shows...ok cool!
This set has been difficult and so far I have avoided posting any questions in an attempt to force myself to learn diagnostic tools.
So far so good?
Yes ..the question is there on purpose!
really so far I am fine, I have raster and hiss from the speaker but hooked to a vcr no picture or sound from the show
I did find a cathode choke that shows open from pin 8 of the 12at7 to ground in the tuner.
Being that it is the Osc. side of that tube I feel that this is at least part of the problem.
I realize I may have other issues once the signal actually makes it through the set!
I have a spare tuner for parts but it's chokes are .2 ohm's per diagram.
The Motorola cathode choke is 2 ohm's . Is that close enough?
Fair radio has a selection of wire wound chokes and I believe they have 2 ohm chokes......But are they universal or designed to "choke" certain frequencies?

Inductance is likely more important than resistance in this application.

One thing that has made this interesting is the fact that some resistors are going to the right place( ex. pin 8 to ground) but are not where the Sam's shows them at.
had it happen a couple of times, or the looks original cap having a different value then the diagram, but there isn't a note on the sam's about it.

If the parts list does not show inductance in microhenries then what should I do?
Use spare tuner piece or go to Fair and grab one of theirs?

Sam's did not document a good portion of production changes, and sometimes has blatant errors to boot. If something don't jibe with sam's keep it the way you found it unless it looks like someone's hack repair work. If the circuit containing the change don't work properly after repair, and every part in the circuit tests good, then changing it to match the sam's may be worth a try.

A sam's is just a manual someone that bought 2 TVs of a given model made based on reverse engineering them....It is not like some of the other older schematic sources that built a relationship with the makers and got the factory to send them production schematics and changes.

If they list part numbers for a replacement look into availability of that part, and if not available look for specifications of that replacement.

I don't have the schematic for it in front of me so I don't know the exact purpose of that coil. If it is part of a tuned circuit inductance is critical, but if it is just a filter choke you may be able to use something that ain't very close, but is still in the right zip code so to speak.

Ok, this may be interesting since The parts list only has Cathode choke and 2 ohm and a Motorola part #.
I will try to see if Moyer's can get a replacement for me or has the specs.
Other then that I have no idea how to get the specs unless the part itself has it written on it.
If you have a set of Sam's it is set 122 folder 5.

Is there another company other then Moyer's that sells the old tv/radio parts anymore?

well I have picture and sound now, Fair Radio gave me a couple of chokes to try and they were the smallest values they had. I put a 4 micro henry in . the picture is not right yet. It almost looks like a negative but if you turn the contrast up or down the image goes great for a second and then to a washed out look.

The voltages on the new 6ah6 tested video amp are good except. pin 1 should be 1 and is 4, pin 5 which goes to the crt is about 50 and should be 175.

The other pins are within 2 volts of the diagram . I have checked the volt dropping resistor and it is good, b plus is 8 volts 8 high, there are 3 coils between b plus drop resistor and pin 5 and they show correct resistance.
I am thinking it is a signal issue.
Since the B plus is good and the tubes output voltage is low then it is a bias/signal issue.
Am I right?

could the 4.0 micro henry choke be "choking" part of the tv signal ? The sound is clean and loud. the picture does lock in the horiz and vertical although it does get jumpy when I mess with contrast.

I'd try cleaning the contrast control first.

Does your set have AGC? If so try adjusting that. Negative picture could be a symptom of AGC misadjustment.

Did you replace the .1 mfd cap in the plate circuit of the 6AH6 video amp. If it's
old and leaking it will load down the plate circuit. Does your brightness control
affect Pin 5's voltage reading. A bad cap in that video plate circuit can also cause trouble picture/ video image polarity.
Ed

Will try cleaning the contrast control, and I have put a new .1 in the plate circuit.
I have more so maybe I will sub another cap in.
This set does have an agc line although not adjustable, so I will investigate it.
Thanks

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.

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.

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?

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.

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

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.

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

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.

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.

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.

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 ?

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.

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.

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.

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.

Without the 115 volt B+ line connected , your sync pulses can't lock-in
the vertical or horizontal oscillators, nor would the sound work well.
Ed

More of the Motorola 19K2

ok, I put on tube shields, put the b plus wire back on, replaced a cap that I was told to test and here is what I have. The vertical is locking, the horizontal is jittery, and the image on the screen is a negative image...
At least it appears that way to me and still is washed out like the signal too strong or too weak.

It was mentioned to check the cap in b plus line to pin 5 of the video amp, which I replaced again to be safe. There is a ceramic cap in parallel with a coil in that line that might also be an issue so i did grab a replacement for it and will try it tonight...hopefully!

i put in a new cap.....it is in parallel with a 4.5 min coil coming off of the video amp.
the picture is better,but retested the crt and it is shorted............and i do not have a replacement. so this project is on hold for now.

Is it a heater-cathode short? If so just get an isolation transformer for the heater (some 'brighteners' were not brighteners, but rather isolation transformers) or add a separate heater transformer for the CRT.