Flyback don’t get hot at all and when I injected the video at test point B the screen was focused and the focus voltage is good and variable. Just all of a sudden the coil fell out of the housing that it was in and it gets so hot you cannot touch it at all and because of this heating the ohms are going up from 35 ohms now to 53 ohms I’m sure it gets warm but not this hot.

It is still hot after putting in the right size C99?

Well in a previous post I made a mistake it does have the right cap but I’m Going to try the original cap.

Is that a permanent change of resistance or does the coil return to 35 ohms when it cools down to room temperature? :scratch2:

jr

It’s permanent and when it was at 35 ohms it started getting hot and went up from there.

In the past, did you ACTUALLY measure the coil to be 35 ohms, or are you relying on the SAMS measurement for your baseline “before” number?

jr

When it first started getting hot I measured it and it was 35 ohms.

I agree with adding this resistor, you should also stick on the ceramic heat sink using thermal conductive epoxy as I mentioned, save the coil as best as you can.

With injecting video point b would the agc affect that video since it follows to the video amp.

I do remember when agc is maxed it has a blank screen like I have now so if that’s the case then I have to find out if it’s maxed with the pot at minimum. There one wire that goes to v1 from the v6 area maybe I should disconnect it and see what happens at this point.

Ok so I have a theory the high voltage across L42 my theory is that the voltage on the path of the 470pf cap which goes to v6 as well as the 2.2 cap coming off the agc pot both those voltages come from the flyback so if infact there is still a problem with v6 then I think it’s safe to say the tube is not conducting correctly if any at all because if it were conducting then I think it would relieve excessive voltage at L42 because right now it appears to be solid standing voltage on both sides of L42 780v. That may explain why removing one lead from each cap having no change and still heating L42. Which in turn possibly shutting down v1 having no snow on screen and no video.

That is not how it works.
The AGC circuit does not take any voltage away from there via C59, it does take filtered horizontal pulses from the FBT, any DC is blocked by C59.

That lower winding on the FBT serves more than one function, one of them is generating +/- 500v AC horizontal pulses AND the boost voltages, pin 9 being the pin where power is fed in.

ALL PINS are at DC boost potential in the focus circuit, this is normal.
As there is no diode used in this boost setup, no matter where you measure, you will see boost level voltage in this area.

So there is no “excessive voltage on both sides of L42” the entire area is at 780v DC and this is normal.

What is causing it to heat is the AC pulses it's getting and nothing with any DC voltage in the circuit.

Yes and no.

If the video fed in was up to the level needed at that point, 5v ptp, it would start to fool the AGC into thinking that there is good video coming in and start to do it's thing, but since it is low at 1v, it is still like a weak/ no signal from the tuner.

Well here is another theory is it possible that being there is no video for the focus to work that is the possible reason why it’s getting hot. The focus coil gets hot also. So just because the resistance check on v6 was good don’t mean there is no problem there.

If the agc was at max what at v6 could create this with the pot at minimum

Its still suggested to do as SB said, get a 10 or 20 ohm resistor, stick it in series with L42.
https://www.amazon.com/HONJIE-Power-...7771596&sr=8-1

Get IF working.

add a small ceramic heat sink 15mm.

Ok I got an 18 ohm 10 watt resistor so if I put this in and the catch is if this focus L42 issue has anything to do with v1 and not having video then I’ll be waisting even move time looking for something I may never find.

Just some evening AMC Rambler-ings,,,, If you want to see if the AGC is doing something
you might want to feed that tuner subber back to V2 where you had a pretty good
picture, and make some before & After voltage measurements on the AGC line.
You might also want to play around with the AGC control while there is a nice
picture on the screen, and see if there is a voltage change on the AGC line,
it's not so important to see a change on the screen at this point.

As for L42, you can do one of 2 things... Cut it out and throw it into the pond, or
you can try to protect it as best you can. Coils are made of 2 things, An Ideal
inductor, and some resistance - from the copper. If this coil really really did
change it's resistance, and increase, then it's already burned. If it's getting
Hot, it's because Current is heating up the resistive part of the coil.
So the current is either coming from a AC, or Pulsed DC signal
causing a field change in the coil sufficient to cause large
enough current to make it hot! The other possibility
is there is large current flowing through it and
making it hot...... That's really the only
2 possibilities...... Unless, it's within
distance to be inductively coupled
to another coil causing current
to flow in the coil...... So, is
this tv too close to your
Warp Coils ?


.

This L42 is just a roll of very fine wire no ferret on it just wire.

.

I'm wondering about the path of current through L42, I think the thinking that C96
could have been shorted to send high voltage & a current path through L42 is not
correct. But the regular current path of from Pin 5 to Pin 1. Since the flyback
windings are low ohms, that's a lower voltage, & high current source.
Much higher current than the HV winding... Transformer Basics....

How is that 10 Ohm resistor R136, I know you probably
checked it 4 times already....

So do you have control of the HV adjust?
Does it work?



.

This I believe is a definite NO - Mostly because the voltage of the signal is
too small as Yamama said, but mostly because the sync pulse is not
"syncing" anything.... In your screen shot it looks a lot like a Whometco
home theater image after they turned on the late night pay service.
In this pay service they use to suppress the sync pulse and the
picture locked on any semi-dark part of any image.....
What you got was a pretty scrambled image if
you were not a paid subscriber....

You had a better lock with the tuner subber on V2. That might have
done a little for your AGC, and well worth checking.... If you had
nothing else to do......

DAMM another freaking page!!!!!


.

This thread needs s sticky, or its own forum. Its pushed a few other interestingnposts down a bit…

. Hv adjust works ok 10pm resistor is 11 ohms

Unless someone knows this Motorola chassis and how certain things work being they are different then most other chassis there is a reason why L42 is overheating and until I can find out why then this project will probably hang in the balance with lots of guessing and assuming I can only hope I nail it soon.

I think once I get the snow on the screen then I can say I got it. The 470pf cap I think has something to this whole puzzle because something has to conduct with this cap it cannot just be there to look good so the question is what happens at this junction with the cap and the tube I do believe both are related in some way here. Ac or dc on whatever end of the cap something supposed to happen here that I don’t think is happening.

First and foremost, the loss of L42 is not going to mean a catastrophic end of this set, YES, there is no replacements to be found on the market, but this is nothing new to people who restore vintage electronics, and as I recall there is at least one person (if not more) out there who has the equipment to wind their own replacement coils, who I no doubt would be more than happy to help you out in replacing this coil.

Also, as been stated several times, you have yourself severely hamstrung, there is only so much you can do with the limited tools you have on hand, digital multimeters, soldering irons, a schematic, a handful of parts can get you only so far, complex issues like you are having need an oscilloscope and the general know how to use it, otherwise you will keep hitting walls, over and over and over.

You have been given tips by Squirrel boy and myself to try and protect L42, it's your choice to use them or not, it would be in your best interest to do so and turn your attention to the tuning / IF problem first.
Even if putting in this protection degrades the ability to focus a bit.

Things I have been wondering.
What prompted the replacement of the FBT in the first place when the original seemed OK?
This is an extreme measure, and only done when you are VERY sure it's bad.

What caps were replaced in the set?
In this era there are only 2 known that will be problematic.
Electrolytic capacitors and any obvious paper capacitors.
ALL ELSE should be left alone unless you can show that they have failed.
These include all ceramic disc capacitors and sealed film types (drop caps).
To arbitrarily replace the above w/o reason (proof of fault or fail) is asking for a major headache.

The way choose to go on from here is yours, but your best choice is to protect l42 as mentioned.

I do plan on putting in the resistor for L42 and the reason I originally changed the flyback was the low hv and the caps I changed were in and around the horizontal oscillator and the sync circuits the rest I left in the set then with the new flyback it kept red plating the hot that don’t happen anymore since putting the old one back in. The power supply caps I checked for mistakes like a 190v on a 275v tap but all is good by checking tube sockets where power goes to make sure the right voltage is there.

You can think of the AGC as sort of a comparator circuit.
The reference is the pulses from the FBT via C59 there is boost potential on the far side of C59, thus it is a 2kv part, the pulses are 450v ptp.

It gets compared to matching pulses from the video amp that is being fed in via the tuner/IF, if this is too low, it will raise the gain of the IF and tuner stages, if too high, it will lower it.
The matching pulses from the video amp can be enhanced / adjusted with pulses from the FBT via C60 & R14, but if there is no incoming video, or if the video at the video output stage is too low, then AGC will be stuck thinking that levels are too low, and lock the gain at the highest level, and R14 will have no effect no matter how you set it.

Again, there is 700+ dc boost potential on the far sides of C59/C60, but should only be passing AC pulses to V6, if they are passing DC, then they are leaking and bad.

Those 2 caps you mention are the 470pf and 2.2pf I guess it wouldn’t be a bad idea to change them both I do have them or I should lift one leg on each cap and check for ac or dc. At this point I don’t know the next step to take with the video.

whats the voltage rating on this new 2.2pf cap you have? is it a NPO?

The 2.2pf is 1kv and it is supposed to be a npo it’s old new stock.

This one, most likely.
https://talonelectronics.com/shop/item.aspx?itemid=9535

you could replace them, but it would most likely not change anything function wise. :(

It is supposed to be npo but does not show it on the cap all it shows is n750 2.2 +25 1 kv

if it has a black mark on the top then its NPO.

No black mark just RMO

that is NPO then! :)

Ok short history of this set with me, I got it changed the power supply caps didn’t change any other caps put the chassis in tried it , it had low hv and no video so what I have done to date didn’t affect its operation in a positive way except for the hv. I really expected it to work as all of my other sets in worse condition then this one. And I put the 18 ohm 10 watt resistor in series with L42 still getting hot. And it does appear that on dc scale I’m getting 7.5 vdc on the tube side of the 470pf if it was ac my meter jumps back and forth to indicate it’s on wrong setting.

That cap had ac on it with leg off the 7.5 vdc is on the tube side with leg off

The 7.5 vdc on pin 3 of V6 (far side C59) is perfectly understandable, as there is no video for the circuit to compare to and thus no pulses on pin 6, the gain is being turned up to the max, if you were to hook up the subber to the grid of V2 like you did before, as Squirrel boy mentioned, using a decent video source, and adjusting R14, you should see that 7.5 vdc come down as the AGC tries to bring down the gain.

So now I’m checking L1 L2 L3 so far they are looking ok. I do remember having the video put tag pin 2 of v2 getting video I turned the agc made no difference in the Video I got. I did check the agc it does vary not much.