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