View Full Version : Motorola 17T21 Flyback & Schematic


Mre12ax7
02-06-2017, 01:22 PM
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

Kevin Kuehn
02-06-2017, 04:51 PM
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

Mre12ax7
02-06-2017, 05:35 PM
PM sent
My set does not have that flyback.
it has a 24K733646
Production change?

Kevin Kuehn
02-06-2017, 09:17 PM
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.

Mre12ax7
02-06-2017, 10:09 PM
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.

Kevin Kuehn
02-06-2017, 10:22 PM
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.

Electronic M
02-06-2017, 10:34 PM
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.

Mre12ax7
02-06-2017, 10:57 PM
Here are some pics of the flyback.
Looks to me like it had a literal meltdown.

Electronic M
02-06-2017, 11:06 PM
That fly looks familiar....I think I have a parts chassis similar to that.

Kevin Kuehn
02-06-2017, 11:08 PM
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.

Mre12ax7
02-07-2017, 10:00 AM
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.

Electronic M
02-07-2017, 10:10 AM
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.

WISCOJIM
02-07-2017, 10:35 AM
How would i go about removing the keyway.
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.

.

Kevin Kuehn
02-07-2017, 10:36 AM
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.

dieseljeep
02-07-2017, 12:29 PM
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.

Mre12ax7
02-08-2017, 12:25 AM
By the way would anyone have any knobs for this set?
All knobs are missing with the exception of the power/volume.

Mre12ax7
02-08-2017, 04:58 PM
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?

bandersen
02-08-2017, 05:12 PM
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.

Electronic M
02-08-2017, 05:14 PM
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...

Mre12ax7
02-08-2017, 05:39 PM
Should the resistor be before or after the field coil? The field is 83 ohms.

bandersen
02-08-2017, 06:05 PM
I don't think it matters

Mre12ax7
02-09-2017, 05:27 PM
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.

Mre12ax7
02-09-2017, 08:33 PM
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.
193800

193801

193802

Kevin Kuehn
02-10-2017, 12:45 AM
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.

Electronic M
02-10-2017, 09:31 AM
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).

Mre12ax7
02-10-2017, 11:04 AM
I will just be making a new rear cover to hold the centering rings.
Do the centering rings have a direction they must face?

bandersen
02-10-2017, 11:18 AM
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

Mre12ax7
02-15-2017, 07:53 PM
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)

bandersen
02-16-2017, 09:52 AM
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,

Mre12ax7
02-16-2017, 10:58 AM
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.

dieseljeep
02-16-2017, 11:47 AM
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:

Mre12ax7
02-16-2017, 03:14 PM
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?

Electronic M
02-16-2017, 03:18 PM
High plate voltage is usually indicative of tube not conducting as much as it should.

Mre12ax7
02-16-2017, 03:24 PM
Should I try and adjust the horizontal osc coil?
Could that affect anything.

bandersen
02-16-2017, 04:42 PM
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.

Electronic M
02-16-2017, 04:48 PM
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.

Mre12ax7
02-16-2017, 05:15 PM
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?

Electronic M
02-16-2017, 05:25 PM
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.

Mre12ax7
02-16-2017, 05:47 PM
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.

Electronic M
02-16-2017, 05:54 PM
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).

Mre12ax7
02-16-2017, 06:52 PM
I notice that there is some vertical foldover at the top of the raster.
The Sams says check 12BH7 VOT.
One side checks ok and the other is in the yellow ? range. Could this be the cause.
The ion trap was right where it should be which means low HV or weak CRT (maybe it needs to "cook" for awhile)



BTW I think I figured out why the tube was glowing blue. I had swapped the 6SN7 osc tube with another one from the set. Maybe the oscillator is picky?.

Mre12ax7
02-17-2017, 08:35 AM
Status of the set.
I replaced the 12BH7 vert, output tube to no effect. Still has foldover.
There is sound getting trough and I presume video but there is no sync.
Horizontal hold is at the one extreme there is maybe 10-15 horizontal lines.
Turn it too far the other way and HV cuts out and it makes unhappy noises.
Vertical hold appears to keep rolling as well. I have replaced the sync separator tube with another one with no effect.
I am guessing that I should check the voltages on the 12SN7 sync separator?

Mre12ax7
02-17-2017, 03:29 PM
I have gotten the set to display a picture.
The only thing is that it will not lock on powerup, you have to adjust the horiz, hold.
It seems there is some component that will not allow the set to lock when cold until it warms up after about 2 minutes.

Electronic M
02-17-2017, 04:12 PM
Is it just the horizontal that is unstable? If so shotgun the resistors and mica caps in the horizontal oscillator, Horiz. AFC and any feedback from the fly. If not do the same for the sync section.
It may be a good idea to adjust the AGC (if present first).
If you rather troubleshoot than shotgun, I recommend getting a can of freeze spray letting it warm up and stabilize then start spraying things with it running. The part that makes it flake out when you cool it is the problem.

Mre12ax7
02-19-2017, 06:55 PM
The set seems to have quite poor horizontal lock.
I have borrowed a HV probe from a friend and it seems to measure a little over 10kV maybe 11kV. The top half inch or so of the picture when locked seems to pull to the right gradually getting worse, eventually the horizontal lock is lost. Vertical is rock solid. Should I go on a witch hunt in the horizontal oscillator section.

Electronic M
02-19-2017, 08:13 PM
The set seems to have quite poor horizontal lock.
I have borrowed a HV probe from a friend and it seems to measure a little over 10kV maybe 11kV. The top half inch or so of the picture when locked seems to pull to the right gradually getting worse, eventually the horizontal lock is lost. Vertical is rock solid. Should I go on a witch hunt in the horizontal oscillator section.

Probably. Your not using a VCR as your signal source correct?...VCRs often will cause bad horizontal tearing at the top of the screen on tube era TVs.

Mre12ax7
02-19-2017, 08:49 PM
Actually, I am using a vcr.

mrjukebox160
02-19-2017, 09:29 PM
I bet the VCR is at least part of your issue. Try a DVD player. It's OK to use the VCR with the DVD as the problem only happens when you play a tape.

Mre12ax7
02-19-2017, 09:54 PM
I tried hooking the TV up to a Super Nintendo game system via the composite out and the horizontal lock was solid. No tearing. Now there is a new problem I just noticed. there is a "flag waving" effect in the picture. The left and right edges seem to ever so slightly wave back and forth like a flag.

Electronic M
02-19-2017, 10:52 PM
So the width narrows and widens differently as you look up or down the screen, and the whole effect rolls up or down the screen right? On rect color sets that is called pincushion...On monochrome sets that is called bad electrolytic caps or insufficient filtering.

Mre12ax7
02-20-2017, 08:32 AM
The left and right sides are straight.
The effect is very subtle, you only see if if you look for it. All electrolytic capacitors are brand new from nichicon. Could I try moving the video wire of the crt away from the rest.

Mre12ax7
02-20-2017, 08:59 AM
Well I spoke too soon.
The dreaded horizontal issue is not fixed by not using a VCR.
It would seem that the horizontal oscillator is running off frequency, being that the spot where it locks is at one extreme of the control. I switched out the horizontal osc tube for another one and it just made it worse (new tube checks good), there was different sounds and it was so off frequency that the high voltage died when you turned the hold control.
Should I try and get a hold of a oscilliscope?

Electronic M
02-20-2017, 09:24 AM
What I would do is put back the good tube, get the hold as close to center as you can then adjust the H osc transformer/coil to re-sync...If you can't get the front control to center you may have to alternately walk the pair. There is often two adjustments on the osc. can one is for stability. If the service lit lacks a non-scope method of adjusting the osc. then it may be a good idea to get a scope on it.

Mre12ax7
02-20-2017, 10:08 AM
What I would do is put back the good tube, get the hold as close to center as you can then adjust the H osc transformer/coil to re-sync...If you can't get the front control to center you may have to alternately walk the pair. There is often two adjustments on the osc. can one is for stability. If the service lit lacks a non-scope method of adjusting the osc. then it may be a good idea to get a scope on it.
I tried what you suggested. I think that made it worse, there is now no point where it will lock the picture.

dieseljeep
02-20-2017, 12:35 PM
I tried what you suggested. I think that made it worse, there is now no point where it will lock the picture.
You have to follow the horizontal osc coil proceedure, per the schematic. The set also uses the horiz phase detector circuit, another 6SN7 next to the 25L6. Check around that area. :scratch2:

Mre12ax7
02-24-2017, 08:04 AM
I feel really mad.
I managed to break the fine tuning shaft.
The shaft is broken where it connects to the little plate in the back.
Does anyone have a spare tuner or a way to fix it?

Mre12ax7
03-08-2017, 05:44 PM
I fixed the fine tuning shaft.
I also replaced the two 150k feedback resistors from the flyback.
They had drifted up to 195k each.
No change.
Should I check more resistors.

Mre12ax7
03-13-2017, 09:42 PM
I have purchased a Eico 460 oscilloscope. I have restored it and built a 10x probe.
Can I connect the ground lead of the scope to the chassis? The chassis is connected to a isolation transformer.

dieseljeep
03-14-2017, 11:19 AM
I have purchased a Eico 460 oscilloscope. I have restored it and built a 10x probe.
Can I connect the ground lead of the scope to the chassis? The chassis is connected to a isolation transformer.

Fine, as long as it's connected to an isolation transformer.

Mre12ax7
03-14-2017, 11:28 AM
I have scoped out several waveforms in the horiz, osc section and they don't really match the schematic.
The waveform on pin 1 of the 6SN7 multivibrator looked squished vertically and the general
shape did not look right. Is it better to start at the sync separator and go towards the oscillator or vice versa?

Mre12ax7
03-14-2017, 01:53 PM
Here are some of the waveforms I got with the picture locked.
Sync phase inverter (12SN7, pin 4)
194193
Horiz, AFC (6SN7, pin )
194194
Horiz, multivibrator (6SN7, pin 6)
194195
After I got these I tried to check the waveform on pin 1 of the oscillator tube.
When I connected the scope probe to that point the lock just disappeared completely.
Is that a clue?
Ignore the 2 dots in the pictures, its a reflection from the ceiling light.

Mre12ax7
03-22-2017, 07:54 AM
I think I have found the root cause of the problem.
Video noise on the sync signal. When you turn up the contrast there are various points on the right side of the screen that pull to the right. But when the screen is black, it goes away.
I will be doing some more probing with the scope to find where it is coming from.

Mre12ax7
03-29-2017, 11:36 AM
The video noise appears on the power supply.
It goes away when the video output tube is removed from circuit and connect to the filament string with clip leads.