RCA Victor portable TV from the 1950s

[Electronic M]

Originally Posted by Dubis7

My understanding is that thermistors are a sort of heat-responsive resistor. It starts out with high resistance to prevent current inrush on power up, and quickly drops to basically 0 as the set warms up. It's a protection thing, but you should be safe to eliminate it for now.

You could literally use alligator clips on either side or solder a wire to bypass it for the time being. I'd recommend replacing it if it's bad, though.

Feel free to correct me if I'm wrong. I'm not nearly as experienced as some people here.

A common repair mans trick was to just twist the leads together... replacement is better but not strictly necessary in most sets.

[vortalexfan]

Originally Posted by Dubis7

My understanding is that thermistors are a sort of heat-responsive resistor. It starts out with high resistance to prevent current inrush on power up, and quickly drops to basically 0 as the set warms up. It's a protection thing, but you should be safe to eliminate it for now.

You could literally use alligator clips on either side or solder a wire to bypass it for the time being. I'd recommend replacing it if it's bad, though.

Feel free to correct me if I'm wrong. I'm not nearly as experienced as some people here.

Ok, thanks, that might be why it's refusing to power up because that thermistor thingy is burned to a crisp and broken in half.

[vortalexfan]

Originally Posted by Electronic M

A common repair mans trick was to just twist the leads together... replacement is better but not strictly necessary in most sets.

ok, I'll give it a shot.

[vortalexfan]

Good News, it was just a failed Thermistor, as soon as I bypassed it using the method Electronic M suggested, the TV powered up and the TV was working perfectly, no distortions in the screen or anything, nice full screened raster with snow and white noise to go with it, all while working with its original RCA branded tubes.

See Picture Below.

[vortalexfan]

Here's some even better news, I think this TV is a low hours set because after I left the tv sit powered on for 5 minutes the picture became nice and bright!

I have a feeling that what happened with this TV is that it got struck by lightning at some point in time and the lightning strike fried the thermistor which saved everything else in the TV thankfully and so the owners of the TV just put it away and bought a new TV to replace it because they thought the TV was toast and didn't want to pay to have a repairman out to look at the set.

unfortunately the brightness control don't work right and on the ride home the the vertical hold knob broke.

[Electronic M]

CRT probably woke up from sleeping sickness.

Those thermistors were designed to get hot and often would unsolder at the point the leads joined the resistive puck... Sometimes the pucks would crack too. These were high failure parts in color TVs (which was the main application for them).

Check the brightness pot and if it is good change any caps in it's circuit that might be leaky and dragging it's output.

[vortalexfan]

Originally Posted by Electronic M

CRT probably woke up from sleeping sickness.

Those thermistors were designed to get hot and often would unsolder at the point the leads joined the resistive puck... Sometimes the pucks would crack too. These were high failure parts in color TVs (which was the main application for them).

Check the brightness pot and if it is good change any caps in it's circuit that might be leaky and dragging it's output.

Ok, thanks, I'll check into it.

Although this set has mostly Mylar caps in it except for about 4 paper caps that I saw on the back of the set so it seems that there shouldn't be too many caps needing changed in this set.

[Electronic M]

The early mylars are not completely above failure, but are very low failure....I've found 2-3 genuine bad ones out of many dozzens encountered.

[Kevin Kuehn]

By the looks of how nice that sets plastic is I'll agree it may have been a closet queen most it's life.
Post a couple close up's of the broken knob and possibly someone will have one in their stash.

[vortalexfan]

Originally Posted by Kevin Kuehn

By the looks of how nice that sets plastic is I'll agree it may have been a closet queen most it's life.
Post a couple close up's of the broken knob and possibly someone will have one in their stash.

Here's a few photos of the broken knob on my TV.

[dieseljeep]

Originally Posted by michaelz

check filament of all the tubes.

IIRC, the set is considered to be a 1961 model.
RCA made about three years of that model. The 1959 model used a 5U4 rectifier, where the newer ones used the voltage doubler circuit.
A member of my family had a 1960 model that was the TOTL. It had a two-tone charcoal and white cabinet with all chromed metal knobs and a better looking front bezel.
The one you show is a lower priced version of basically the same set.
The TOTL 1961 models had a new-vistor tuner.

[vortalexfan]

Originally Posted by dieseljeep

IIRC, the set is considered to be a 1961 model.
RCA made about three years of that model. The 1959 model used a 5U4 rectifier, where the newer ones used the voltage doubler circuit.
A member of my family had a 1960 model that was the TOTL. It had a two-tone charcoal and white cabinet with all chromed metal knobs and a better looking front bezel.
The one you show is a lower priced version of basically the same set.
The TOTL 1961 models had a new-vistor tuner.

Yes, and apparently it also came with a remote in the Top of the line models...

My tv seems to have developed a vertical problem where the top of the screen isn't going all the way up to the top and it bounces around, and the vertical output/oscillator tube is still good yet, any ideas as to what could be causing the unstable vertical?

One theory I have is that the vertical section has about 3 paper caps in it which may have become leaky, but not sure if that's the problem or not.

[vortalexfan]

OK so I was looking in the Sam's Photofact for this TV and found that the specs given in the manual for the thermistor for this TV is 120 Ohms Cold, with that in mind what kind of thermistor should I get?

I know there are two different types of thermistors, ones start off high resistance when Cold then as they warm up they kick in at zero ohms and then there's ones that start off at zero ohms cold and as they warm up they get higher in resistance.

I'm assuming I'm going to need one that starts off high resistance cold and then goes to zero when its warm, if so would any of the thermistors in the Mouser link below work in this application?

https://www.mouser.com/Circuit-Prote...z0x6xbZ1z0z5h6

Thanks for your help!

[JohnCT]

Yes, but choose one based on amperage. See what your TV draws for nominal running current as the resistance of the thermister will be based on what percentage of its rated current is being used.

If the TV normally draws an amp, pick a 2A thermister. Running at half the current, the resistance will be an ohm or two.

If you pick one too high in current rating, the thermister will have a higher run resistance which may or may not be an issue.

Also, if it's not mounted in the board, make sure to get one with leads!

John

[mr_rye89]

I did a '56 RCA KCS 94 a month or so ago in this thread

I used this to replace my crispy inrush limiter thermistor:

https://www.mouser.com/ProductDetail...3uJp0Cqw%3D%3D

Works great!