Motorola 17T21 Flyback & Schematic
 

Hello,
I am in need of the schematic for a Motorola 17T21/TS-418.
it is in Sams 269-9
I also need the flyback transformer cross reference as the one that is in it I suspect is bad.
Someone at a old time tv shop told me it is a Thoardarson FLY-33.
Thanks

I have Sams 269-9 here. I can scan it for you, but the fold out pages will be scanned in sections, which makes it kind of a pain to read. PM me your email if you can deal with that.

The OEM flyback number is 24K733106, which according to Sams crosses to:

Thordarison Fly-64
Merit HVO-28
Ram X106
Stancor A-8224

PM sent
My set does not have that flyback.
it has a 24K733646
Production change?

Hard to say. At any rate I just looked up 24K733646 in my Thordarson cross reference and it also crosses to Fly 64. What about your flyback makes you think it's bad? I'm in the process of scanning the Sams, should have it about an hour.

All the wax is melted off the coil and onto the phenolic board.
There is the remnants of a tube keyway stuck in the 1B3 socket.
It looks to me that someone had probably plugged it in and the filter caps shorted (one has black ooze on the bottom) as well as cracked bumblebee caps.
I can provide a picture if needed.

A picture might help. I wouldn't write if off just because of the melted wax, alone. Sometimes an old TV gets stored in a hot enough environment that the wax simply drips off without the set even being operational.

If I had a dollar for every melty or burned fly I've had or seen that still worked, I could buy a pretty snazzy TV. If your concerned you could try giving it a ring test.

People snap the locator pins off tubes a lot I never let that bother me...Unless I need to plug such a tube in.

Here are some pics of the flyback.
Looks to me like it had a literal meltdown.

That fly looks familiar....I think I have a parts chassis similar to that.

Hard to tell what was going on there. I see signs that at least some of that wax cracked and fell off. The wire winding's sure don't appear burnt.

Should I replace it?
The main primary coil is intact measures 233ohms schematic says 236.
I cannot test the other coils as the terminals are covered in the wax from the flyback.
How would i go about removing the keyway.

That fly is probably fine. It is not uncommon for them to molt their wax with age. You may need to clean the fly and coat it with sensor safe RTV silicone to prevent arcing/corona.

I can't see the top or bottom of your socket well enough to say for sure how to get the old key way out. If the bottom is open you could try to push it through, if the top is all you can access you may need to reach in and grab it with pliers, if it is trapped in a hollow you may need to remove the socket or partially dismantle the assembly to get at it.

Put a dab of super glue on the end of a wood dowel or something similar that would reach into the stub. Let it harden and then tug it out.

.

You might also be able to snag the key way by inserting something like a screw or tap thread into the center of key way(possibly drill a pilot hole), then carefully wiggle it out. Of course be careful not to jam something too big in there and destroy the socket.

I used a larger sheet metal screw. It shouldn't be hard to remove.
The Motorola flybacks were made to be disassembled and only the bad coil replaced. Try re-coating it first.

By the way would anyone have any knobs for this set?
All knobs are missing with the exception of the power/volume.

How would I go about adding a dropping resistor to bring the B+ back to the spec 250v after replacing the selenium rectifiers. Should I just add in a 100 ohm 5w resistor or similar after the diodes?
Something like this?

You only need one resistor and probably less than 100 ohms. An easy way to do it is replace the 7.5 ohm R97 with a bigger resistor.

No, you want only one resistor on the line with the arrow pointing to "w". Value of resistor will depend on the voltage you need to drop, the current of the circuit, and the way the load reacts to the change...

Should the resistor be before or after the field coil? The field is 83 ohms.

I don't think it matters

I have placed a order at Mouser for some capacitors for the set.
The transformer has been recoated with the silicone.
I will solve the dropper resistor problem after the set is recapped and working using Ohms law.

Is this yoke salvageable?
It will have to have a new cover made for the back at the very least.
The rotted portion goes deep inside between the coils and 4 pieces of metal, which when I removed the clamp to remove most of the rust they all fell off of the degraded plastic core.
Two of them now have small chips from when they fell out (i have the pieces) because the edge of the plastic is warped.
Attachment 193800

Attachment 193801

Attachment 193802

If you still have the centering rings you could make a new back cover to hold them. Most aftermarket yokes won't include those rings or the correct cover to hold them.

Unless a yoke in that state is electrically malfunctioning I'd say it is best not to try and dismantle it. Rust normally hurts nothing (except maybe your eyes).

I will just be making a new rear cover to hold the centering rings.
Do the centering rings have a direction they must face?

I don't think it matters, but experiment it you can before permanently mounting them. You should be able to get the set working before bothering to make a new yoke cover.

Also it will work fine without the rings at all. You only need them to tweak the image so it's centered in the screen.

I show one way to fabricate a yoke cover with centering rings in this video: https://youtu.be/UXyra3vNYuQ

I finished recapping the set.
So I tried powering it up. No luck.
No picture, no HV static in speaker when you turn the volume control.
after about a minute and a half I noticed the horizontal output tube was glowing blue so I shut it off.
The output, damper and HV rectifier tubes are all good. Horiz, osc tube tested weak so I swapped it around with the other 6SN7 in the set (I do not have spares).
I have moved all the controls on the back including the horiz hold potentiometer before powerup.
Should I try to mess around with that?

P.S Can a moderator please change the name of this thread to Motorola 17T21 Restoration (I don't see a way to do it myself)

Blue glow doesn't necessarily mean anything bad. A blow glow on the inside of the glass is common for power output tubes. Now if it's move of a purple and between tube elements then you've got a gassy tube.

Most common cause of no HV is the horizontal oscillator isn't running.

Odd that you don't hear any crackle from the speaker, It's field coil is a critical part of the power supply. But it must have continuity otherwise you wouldn't have any power going to that output tube,

I will be testing all the voltages on the horiz, output and osc tubes.
I will use my Fluke 87 DMM or my Eico VTVM with the set plugged into a isolation transformer.

Also, check the voltages on the audio output tube. It's used as a voltage divider, known as stacked B+. Try substituting the 25L6 tube. :scratch2:

The audio is working fine I hear static when the volume is turned up ( I made a mistake in my other post)
Voltage measurements: ( taken with Fluke 87, horiz, out plate cap off)
25L6
pin 8 159v Sams 150v
25BQ6
pin 4 136v Sams 135v
pin 5 -37v Sams -32
pin 8 0v Sams 0v (gnd)
6SN7
pin 1 -9 Sams -13 (varies with horiz, hold potentiometer could not get it any lower)
pin 2 182v Sams 135v
pin 5 197v Sams 175v
pin 6 6v Sams 6v
pin4 -.034v Sams -.3
Boost (measured at terminal 1 on flyback)
265v Sams 435v The plate cap is off of the output tube so that could affect that.

The plate voltage for the 6SN7 is way off. Is this related to the dropping resistor?

High plate voltage is usually indicative of tube not conducting as much as it should.

Should I try and adjust the horizontal osc coil?
Could that affect anything.

That would change the free running frequency but it's not going to have all that much of an effect. Test it for continuity and check the associated resistors, caps and wiring.

I would not touch it without a raster on the screen, an oscilloscope, or an ear that can hear H-Osc. whistle in TV's and accurately tune for the right pitch.

With the scope you can adjust the osc accurately, by looking at a composite video source, getting ~2-5 H sync pulses on screen, counting divisions between them, then connecting the scope to the H osc in the TV and adjusting the H coil in the TV till the peaks of the wave form are at or close to the same distance you measured earlier...If it is a synchroguide based osc you should adjust for roughly equal peak and hump height too while your at it.

I decided to once again try the set with the cap on the tube.
After about 30 seconds or so I heard the 15kHz sound of the oscillator and my neon bulb lit up near the flyback. No picture. When I turned the set off, there was the typical vanishing raster that you see when set is turned off. No raster when set is turned on.
Ion trap? Low HV? Bad flyback?

Check the ion trap (try adjusting for max brightness in dark or nearly dark room), and compare the gun bias voltages to the schematic....May also want to evaluate how the controls effect those voltage versus what the schematic voltages and resistances indicate those controls should be capable of.

If you have a WELL INSULATED plastic handle screw driver then you may want to see how long of an arc you can draw with it off of the HV.

I got a raster!
I had to crank up the brightness all the way but I got one.
I will be borrowing a HV probe sometime from a friend.

Great!

I'd tweak the Ion tap for max brightness rotate either way a bit then move forward/back a bit...You never know if the last setting was best (it often ain't).