a real challange?

[Yamamaya42]

for example,
https://imgur.com/gBixele
i find it quite hard to believe that a resistor this far out of tolerance would not cause many problems.
and as I mentioned, almost half of them are this bad.


edit

another example..
https://imgur.com/XZsIK7W

that SHOULD BE 39 :O

[Yamamaya42]

Changing the resistors did make a marginal improvement, but there is still a snowy picture.
I am guessing the RF amp is still weak. When checking voltage there it was still too low.
Should have 130v and was 107v
I then looked at the main 130v line, it TOO was low.
109v
that comes via the bleeder resistor (1.36k) from the 275v which is ay about 265v once things warm up.( close enough.
That bleeder is still getting quite warm :/
IT checks OK resistance wise, but that does not mean anything :/
gonna have to replace it.

It calls for a 17w part
closest I could find was 1.3 kOhms at 25 w

Hopefully this will get the voltage in the right area
anyway, here is how it looks with direct video input
https://www.youtube.com/watch?v=YIMi...ature=youtu.be

[JohnCT]

That's not coming from the picture tube, so cross that off your list.

But it could be a bad peaking coil.

John

[Yamamaya42]

Originally Posted by JohnCT

That's not coming from the picture tube, so cross that off your list.

But it could be a bad peaking coil.

John

i have no way to test them, yet...
I do have one of those ultra cheap LCR meters coming from , china that should be able to test them, out of circuit, but if any are bad, they will be very hard to find any replacements.
this tester
https://www.ebay.com/itm/283562838501


keep in mind that right now my 130v bias id about 25v or more low, i don't know what that effect that has on everything, but once the resistor is changed, i will see what happens.

[jr_tech]

“I do have one of those ultra cheap LCR meters coming from , china that should be able to test them, out of circuit, but if any are bad, they will be very hard to find any replacements.”

Mouser and others stock tons of small iinductors, are these not suitable?

https://www.mouser.com/Passive-Compo...ctors/_/N-wpcz

jr

[Yamamaya42]

Originally Posted by jr_tech

“I do have one of those ultra cheap LCR meters coming from , china that should be able to test them, out of circuit, but if any are bad, they will be very hard to find any replacements.”

Mouser and others stock tons of small iinductors, are these not suitable?

https://www.mouser.com/Passive-Compo...ctors/_/N-wpcz

jr

i'm not sure if they work the same in this situation or not, no idea if they do the same thing as a " peaking coil " in a video amp circuit.

[Electronic M]

Originally Posted by Yamamaya42

i'm not sure if they work the same in this situation or not, no idea if they do the same thing as a " peaking coil " in a video amp circuit.

Search this site for posts by miniman82 on replacement peaking coils for CT100 or 21CT55 the family the recommended inductors are in contains a good variety of leeded inductors of various values. After replacing the peaking coils in my 21CT55 if I need coils for any other set I usually check that family for something with the correct inductance.

[Yamamaya42]

https://imgur.com/UnvD4ps

I'm gonna replace both of those resistors, i guess the 6.75k is checking a 5.43, that's prob dragging down the 130v :/

[Kevin Kuehn]

Originally Posted by Yamamaya42

Changing the resistors did make a marginal improvement, but there is still a snowy picture.
I am guessing the RF amp is still weak. When checking voltage there it was still too low.
Should have 130v and was 107v
I then looked at the main 130v line, it TOO was low.
109v
that comes via the bleeder resistor (1.36k) from the 275v which is ay about 265v once things warm up.( close enough.
That bleeder is still getting quite warm :/
IT checks OK resistance wise, but that does not mean anything :/
gonna have to replace it.

It calls for a 17w part
closest I could find was 1.3 kOhms at 25 w

Hopefully this will get the voltage in the right area
anyway, here is how it looks with direct video input
https://www.youtube.com/watch?v=YIMi...ature=youtu.be

In an attempt to narrow things down you could try pulling rf and if tubes one at a time to see if your 135v supply increases significantly with any of them removed. When something is drawing too much current and pulling the supply down, you're not going to fix anything by changing resistors that are high or normal in value.

[Kevin Kuehn]

Another thought is the tuner and IF sections have a whole slug of 1500pf power supply bypass caps between B+ to ground. If pulling those RF and IF tubes doesn't give results, it's possible you have one or more bypass caps that are leaky. Also if you disconnect one end of R39(Sams 150 ohm) you would free up that 135v supply from the 4th IF stage forward. Something needs to give and it's simply a matter of sniffing it out. The key here is you need to divide and concur to find out what circuit is pulling the voltage down. Forget worrying about your picture quality until you find what is pulling that B+ down.

[Yamamaya42]

Originally Posted by Kevin Kuehn

Another thought is the tuner and IF sections have a whole slug of 1500pf power supply bypass caps between B+ to ground. If pulling those RF and IF tubes doesn't give results, it's possible you have one or more bypass caps that are leaky. Also if you disconnect one end of R39(Sams 150 ohm) you would free up that 135v supply from the 4th IF stage forward. Something needs to give and it's simply a matter of sniffing it out. The key here is you need to divide and concur to find out what circuit is pulling the voltage down. Forget worrying about your picture quality until you find what is pulling that B+ down.

well. the 6.75k resistor is definitely testing too low, by almost 1 k out of circuit, it's a 3 resistor thingy stuck in 1 pack, the other 2 check fine 12 & 93 ohms.
i got new ones coming Tue, and will replace the 6.75k first and see what happens.

[Kevin Kuehn]

Originally Posted by Yamamaya42

well. the 6.75k resistor is definitely testing too low, by almost 1 k out of circuit, it's a 3 resistor thingy stuck in 1 pack, the other 2 check fine 12 & 93 ohms.
i got new ones coming Tue, and will replace the 6.75k first and see what happens.

Changing that one first is fine.

It's easier for me to follow these power supply voltages using the Riders schematic I posted here. https://www.flickr.com/photos/152661...7713086856613/

[edit] So if your 6.75k is part of a candohm, it's possible that part of it's winding is shorting to ground by insulation breakdown. If that's the case you'll be much further ahead by replacing all three sections. Otherwise it would be unusual for a resistor to drift down in value.

[Yamamaya42]

Originally Posted by Kevin Kuehn

Another thought is the tuner and IF sections have a whole slug of 1500pf power supply bypass caps between B+ to ground. If pulling those RF and IF tubes doesn't give results, it's possible you have one or more bypass caps that are leaky. Also if you disconnect one end of R39(Sams 150 ohm) you would free up that 135v supply from the 4th IF stage forward. Something needs to give and it's simply a matter of sniffing it out. The key here is you need to divide and concur to find out what circuit is pulling the voltage down. Forget worrying about your picture quality until you find what is pulling that B+ down.

there are 21 of those little bastards in there.
all still orig, I was hoping they would not be a problem, but if the new 6.750 k bleeder does not bring up the 135v to around where it should be, they are next on the list, might as well get them all, they are cheap enough.
I just hope that the resistors IN the tuner are OK, for I really don't want to go in there or have to take it out to get to them, but with the way that I have found some resistors that were almost 2x over what they should be, I DO wonder...
But finding resistors that far off does not surprise me, given that this thing spent 2/3s of it's life neglected in a dark, dank musty basement in Pennsylvania.
And I know that carbon resistors HATE THAT!

[JohnCT]

Originally Posted by JohnCT

Yes, but if one turn shorts out to an adjacent turn, it will have no measurable effect on the resistance you read with a meter. But what happens with a shorted turn is that one single shorted turn kills the Q of the coil. At that point, an 8 ohm peaking coil becomes an 8 ohm resistor.

Again, unlikely that's your problem, but I was just pointing out that a single shorted turn can't be read with an ohmmeter.

That's why ringers were so popular with TV techs. A shorted turn in a flyback, yoke, vertical output transformer, etc. won't show up in a resistance check, but will in a ringing test.

I bought an LC75 Sencore Z Meter brand new back in 1985 and still use the crap out of it. It will perform both ringing tests and test the value of any inductor as well. Smaller inductors that don't ring well on ringers can be tested for their value.

I paid $1000 for the Z-Meter back in '85, but today, we can buy these handy multi-testers for pocket change:



I know these are toys, but I couldn't resist and bought one. Just put any two or three lead part into the socket in any direction, and this toy will identify what it is, what the lead configuration is, and give you things like transistor gain, resistance in ohms, capacitance and ESR, and inductor values. These will check inductors for value but no ring test. But a shorted turn in an inductor will throw off the value. If your TV has more than one of the same part, you can compare them if the schematic doesn't identify the value of the inductor.


John

Update: I took an NOS RCA peaking coil from my parts supply and measured it. On my Z-Meter, it reads 5.8uh (marked 5.6 on the bag).

On my cheapo mega328 tester, it reads as a 0.2 ohm resistor... I tried several times and did the calibration procedure, but it won't read inductors - it sees them as resistors. Now, this tester is at least three years old and it's possible that this early version didn't read inductors while the later ones (which still look identical) purportedly do.

Incidentally, on the Sencore Z-Meter this 5.6uh peaking coil shows 5 rings.

Lastly, this is an RCA part number 119590. Judging by the part number, I'd say this is an early 60s to mid 60s coil for a color TV, but it likely covered many years.

If anyone wants this, it's theirs for the asking. Email me at delstv@aol.com

John

[Yamamaya42]

Well the thing I got ( when ever it gets here ) was only about $6.50, and they say it does coils, and 5.6uh is kinda small
the ones in the set are 93-120-250 , just have to see what happens when ever it gets here, on the slow boat from China...