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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Apr Wed 05, 2017 1:10 am 
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Ok I see what I am doing wrong.
I am saying one thing in one post then another thing in another.
R49 is the part that was circle with "R49"
It had a greyish black coating with the motorola part number and the resistance on it.
I think I am going to take a break until I can get ahold of the TV guy.

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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Apr Wed 05, 2017 1:18 am 
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I think I know what has stopped the oscillator. One of the resistors came undone from the terminal strip!
When I was checking all the resisoter the other day it must have not been soldered very well.
EDIT the resistors did not fix it. The arcing also came back. I am going to stop working on this for a while and take a break. I am in over my head here.

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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Nov Mon 20, 2017 11:12 pm 
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I have decided to come back to this set after a long break.
This time I want to be more methodical.
So far I have checked all the resistors associated with the AGC switch. They check ok or slight out of spec so no smoking gun there.
I have also checked most if not all the resistors associated with the video output tube. No smoking gun there.
If I intentionally unlock the vertical to see the blanking interval I am able to see it. I have some old TV service books from the 50s and 60s that say if you can see that its in the sync section.
Replacing the 12BY7A video output tube has a effect on the problem but does not remove it completely. I tried 4 tubes. I am thinking that the tube is not the issue. All the video out tubes tested good. I swapped the IF tubes with a entire other set of tubes.
Problem still persists. Those 3 tubes checked good. I am now starting to wonder if the horizontal oscillator is failing to properly use the sync signal. There are 2 domino mica caps in the osc circuit. (No they are not "Micamold" paper caps, they have a very low value) I could try replacing those and all the resistors there too along with all the resistors in the sync separator. However this problem does not seem like a problem caused by drifted resistors, although anything is possible. I also checked voltages on the sync sep tube and they seem normal. I have also though about directly injecting video into the video amp bypassing the front end. This would tell me if the problem was in the font end or in the sync somewhere. I am also looking for someone with one of these sets with the TS-418 chassis that would not mind taking a photo of the tuner connections under the chassis. At one point I had to repair the fine tuning shaft and I want to make sure my connections are correct.

I am going to try and not make the mistakes I made earlier in commenting on this thread when I had no access to the set or the schematic which caused a great deal of confusion for everyone.

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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Nov Mon 20, 2017 11:43 pm 
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For quite awhile It was thought that mica caps never went bad. But more recently people have been finding bad micas in circuits where there is a fair amount of voltage across the cap. Sync circuits and horizontal circuits are some such circuits. Mica caps across coils in the IF strip should be OK.

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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Nov Tue 21, 2017 12:52 am 
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Tom Schulz wrote:
For quite awhile It was thought that mica caps never went bad. But more recently people have been finding bad micas in circuits where there is a fair amount of voltage across the cap. Sync circuits and horizontal circuits are some such circuits. Mica caps across coils in the IF strip should be OK.

I am thinking that I will replace them. Never hurts to put new parts in the horizontal oscillator. Less potential problems down the road.

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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Nov Tue 21, 2017 2:19 am 
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MrE12AX7 wrote:
I have decided to come back to this set after a long break.
This time I want to be more methodical.

If I intentionally unlock the vertical to see the blanking interval I am able to see it. I have some old TV service books from the 50s and 60s that say if you can see that its in the sync section.

Problem still persists.

I have also though about directly injecting video into the video amp bypassing the front end.


Do those service books show a TV block diagram and explain the signal flow? The raw video signal, which is call Composite Video, contains the sync pulses. The horizontal sync and vertical sync pulses are separated and sent to the respective oscillators. The sync pulses, mostly the vertical, are used to generate a blanking pulse that is sent to the CRT, it turns the beam off while the sweep goes back to the start of the scan.
There are special pieces of equipment, like B&K 1075, 1076 and 1077, that provide substitute signals. I've got one but a oscilloscope is a more useful piece of equipment. The problem with another source is the signal level. Solid state TV don't have signals large enough usually.
Since it has been a while, just what is the problem now? I guess the sound is OK. Speaking of sound, when you say the sound of the horizontal goes away could it be that it actually is hard to hear because it should be above 15,000 Hz normally?

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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Nov Tue 21, 2017 3:22 am 
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Notimetolooz wrote:
MrE12AX7 wrote:
I have decided to come back to this set after a long break.
This time I want to be more methodical.

If I intentionally unlock the vertical to see the blanking interval I am able to see it. I have some old TV service books from the 50s and 60s that say if you can see that its in the sync section.

Problem still persists.

I have also though about directly injecting video into the video amp bypassing the front end.


Do those service books show a TV block diagram and explain the signal flow? The raw video signal, which is call Composite Video, contains the sync pulses. The horizontal sync and vertical sync pulses are separated and sent to the respective oscillators. The sync pulses, mostly the vertical, are used to generate a blanking pulse that is sent to the CRT, it turns the beam off while the sweep goes back to the start of the scan.
There are special pieces of equipment, like B&K 1075, 1076 and 1077, that provide substitute signals. I've got one but a oscilloscope is a more useful piece of equipment. The problem with another source is the signal level. Solid state TV don't have signals large enough usually.
Since it has been a while, just what is the problem now? I guess the sound is OK. Speaking of sound, when you say the sound of the horizontal goes away could it be that it actually is hard to hear because it should be above 15,000 Hz normally?

The problem is the same tearing that had us stumped and going off on a wild goose chase earlier. The horizontal makes the same high pitched sound all crt tv sets make. The set never looses sync entirely but it just tears the picture with the contrast turned up. I had thought about getting a B&K 1077 but you say a good scope is better. I want to learn to use it better and use that to fix the TV. I have the Riders Basic television 5 book set. Yes there are plenty of diagrams like you describe. I am thinking I am going to scope the detector output because its pretty distinctive in shape.

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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Nov Tue 21, 2017 6:56 pm 
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The main reason I said a scope would be better is that it is more general purpose, you can use a scope on a radio, computer, hi-fi, LCD TV, etc. You would want one no older that about 1980, so you probably wouldn't need to re-cap it first. Early scopes didn't have a well calibrated sweep (horizontal time display), with a calibrated triggered sweep you can get a very good idea of frequency. A scope is very useful on a TV because the shapes of the waveforms are important. You can use it to trace the signal path also.

The sweep oscillators in the TV should free run without a sync signal, the free run frequency should be a little lower than the proper frequency when the oscillators are lock with a sync signal. If the horizontal oscillator is far off in frequency the flyback circuit won't generate the proper high voltage. As a matter of fact with no signal to the horizontal output tube, the tube can draw excessive current and be damaged and the flyback can over heat.
If the contrast control effects the horizontal sweep then that sounds like a clue.

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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Nov Tue 21, 2017 7:26 pm 
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I think I am getting somewhere.
I scoped the output of the video detector diode (Point 1). When doing this there was snow in the picture and snow sound in the speaker. It almost completely stopped the tearing!. it only tore a tiny bit with the contrast up at max. However when disconnecting the scope it came right back. I am thinking what is going on is that the scope is loading down the circuit and bringing down the signal level. I then tried another spot on the output of the detector(Point 2). No change in the problem.
Here is a diagram of that part of the set with where I connected the scope.
Image

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 Post subject: Re: Motorola 17T21 RF or IF Overloading LARGE IMAGES
PostPosted: Nov Tue 21, 2017 8:31 pm 
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I forgot you had a scope! Never mind the sales pitch before!
Yes I think the first spot killed too much of the signal. I take it you are sending in good video from a DVD player or convertor box. On a DVD player it helps some to have it paused on a simple image.
Look at point "B".
You should see about the same signal at the grid (pin 2) of V8, 12BY7. Then again with larger amplitude and flipped upside down at hthe junction of L30, L31 and R52. Check the grid (pin 1) of the Sync Sep V13, 12SN7GT , it should look about the same but without so much low frequency content.
It might help to change the contrast control and see what effect it has. It should change the amplitude of the signal at the junction of L30, L31 and R52, it probably change the DC level also.
How does the service info say to adjust the Horizontal Coil? Have you adjusted that?

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 Post subject: Re: Motorola 17T21 RF or IF Overloading LARGE IMAGES
PostPosted: Nov Wed 22, 2017 12:29 am 
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Notimetolooz wrote:
I forgot you had a scope! Never mind the sales pitch before!
Yes I think the first spot killed too much of the signal. I take it you are sending in good video from a DVD player or convertor box. On a DVD player it helps some to have it paused on a simple image.
Look at point "B".
You should see about the same signal at the grid (pin 2) of V8, 12BY7. Then again with larger amplitude and flipped upside down at hthe junction of L30, L31 and R52. Check the grid (pin 1) of the Sync Sep V13, 12SN7GT , it should look about the same but without so much low frequency content.
It might help to change the contrast control and see what effect it has. It should change the amplitude of the signal at the junction of L30, L31 and R52, it probably change the DC level also.
How does the service info say to adjust the Horizontal Coil? Have you adjusted that?

In trying to scope out the signal as described I unfortunately let the probe slip and it shorted out something. I say a big spark and a loud pop sound. I will fix whatever I blew out then I will get back to you with the results of the waveforms. I was able to look at point b and pin 2 before I did that and they looked mostly the same although point b was flatter.

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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Nov Wed 22, 2017 4:51 pm 
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MrE12AX7 wrote:
With contrast turned up.
Image
With it turned down.
Image

I want to be sure we are all on the same page now. The pictures above show "the problem".
Also it seems the horizontal hold control needs to be at it's counterclockwise extreme. Could you measure the resistance from pin 1 of V15, 6SN7GT, Horizontal Multivibrator. Should be about 200K.
I've re-read all the past posts to refresh my memory.
There are a couple of issues that I would like to bring up.
Did you adjust L35, B1, Horizontal Oscillator coil according to the service info? What was the procedure? That may very well solve the extreme setting problem. You only posted the schematic, and that has missing sections. Next time when you scan something like that, make sure to overlap the scams so nothing gets missed. While on that subject, it was requested that you scan and send the info to the Early Television Museum website. The RadioMuseum website would be another good place to send it and it would get you "points" with them.
Someone also suggested soldering all the chassis ground connections in the area. That's a good idea. You would need an iron or gun with at least 60 to 100 watts, up to about 200 watts.
I think you said you had a scope probe with a 33M resistor and a 35 pf capacitor across it. Your scope is a EICO 460 I think. That scope has a 3M plus 35pf input spec. A 10X probe would be a 27M resistor and something like a 3.5 pf capacitor. If you really do have a 35 pf in the probe then you will be seeing more high frequency detail than is really there.

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 Post subject: Re: Motorola 17T21 RF or IF Overloading LARGE IMAGES
PostPosted: Nov Wed 22, 2017 5:17 pm 
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I'm probably the guilty party that scanned Sams 269-9 for MrE12AX7. I only have a standard flat bed scanner and it generally picks up everything when I scan the schematic as folded in 3 sections. If more clarity is needed I can redo a section.


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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Nov Wed 22, 2017 5:42 pm 
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Notimetolooz wrote:
MrE12AX7 wrote:
With contrast turned up.
Image
With it turned down.
Image

I want to be sure we are all on the same page now. The pictures above show "the problem".
Also it seems the horizontal hold control needs to be at it's counterclockwise extreme. Could you measure the resistance from pin 1 of V15, 6SN7GT, Horizontal Multivibrator. Should be about 200K.
I've re-read all the past posts to refresh my memory.
There are a couple of issues that I would like to bring up.
Did you adjust L35, B1, Horizontal Oscillator coil according to the service info? What was the procedure? That may very well solve the extreme setting problem. You only posted the schematic, and that has missing sections. Next time when you scan something like that, make sure to overlap the scams so nothing gets missed. While on that subject, it was requested that you scan and send the info to the Early Television Museum website. The RadioMuseum website would be another good place to send it and it would get you "points" with them.
Someone also suggested soldering all the chassis ground connections in the area. That's a good idea. You would need an iron or gun with at least 60 to 100 watts, up to about 200 watts.
I think you said you had a scope probe with a 33M resistor and a 35 pf capacitor across it. Your scope is a EICO 460 I think. That scope has a 3M plus 35pf input spec. A 10X probe would be a 27M resistor and something like a 3.5 pf capacitor. If you really do have a 35 pf in the probe then you will be seeing more high frequency detail than is really there.

The horizontal hold issue has been solved a while ago. I replaced the tube and set the hold control like the manual says.
The issue is the tearing as seen in the photo. Its in either the video or the sync separator. I was able to make it go away by loading the detector with my scope.
I will have to look inside the probe I made to see the value of the cap and resistor. I think that I need to make sure that is working fine before trying to use it to fix the TV set as that can throw off the waveforms on the scope and that would not help.
The real probes for this scope have a variable cap of 3-30pf. I was not able to find such a part so I used a fixed cap I think a 15pf. I have several values to try.
I have found what got fried last night. I fried the video detector diode. I am going to get a new one today hopefully along with some new resistors.

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 Post subject: Re: Motorola 17T21 RF or IF Overloading LARGE IMAGES
PostPosted: Nov Wed 22, 2017 5:55 pm 
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There's even a chance that replacing that video detector diode will solve your problem. Some of those early diodes appear to get wonky with age, possibly developing internal resistance, but not necessarily in a linear fashion.


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 Post subject: Re: Motorola 17T21 Video noise on sync signal LARGE IMAGES
PostPosted: Nov Thu 23, 2017 1:17 am 
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MrE12AX7 wrote:

I have found what got fried last night. I fried the video detector diode. I am going to get a new one today hopefully along with some new resistors.

Well, that's rotten luck. Do be careful, there is 250V in some parts of the set. We wouldn't want you to get fried.
I really hope that it didn't zap the winding in L26, that would be hard to find a replacement for.

You said you replaced the Horizontal Hold pot. Did that have a plastic shaft? The metal of this chassis has a 50% chance, depending on the way the power cord is plugged in, of being connected directly to the hot side of the line power. So all the controls must be insulated somehow.
I've been researching the circuits and I have some good ideas on what to look at when you get the damage repaired. I noticed on the schematic that you are supposed to measure the voltages without a signal coming in.
The waveforms are to be looked at with a good video (RF) coming in.

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 Post subject: Re: Motorola 17T21 RF or IF Overloading LARGE IMAGES
PostPosted: Nov Thu 23, 2017 1:46 am 
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Kevin Kuehn wrote:
I'm probably the guilty party that scanned Sams 269-9 for MrE12AX7. I only have a standard flat bed scanner and it generally picks up everything when I scan the schematic as folded in 3 sections. If more clarity is needed I can redo a section.

Oh. I didn't know where MrE12AX7 got the schematic.
What might of been a solution, is that two more scans were done of the region between the three other scans.
Another thing that might have allowed just three scans, is arranging the two end scans to not include the blank borders.
One thing about sending the scans (the whole SAMS) to the Early Television Museum is I think they will convert them to pdf files that we could download.
Although I see there are online ways of generating a pdf from jpg images, I've never used them. I might try them sometime, I had thought you had to buy the whole Adobe program to do that.

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 Post subject: Re: Motorola 17T21 RF or IF Overloading LARGE IMAGES
PostPosted: Nov Thu 23, 2017 4:03 am 
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Based on advice from a few fellow collectors I have decided to replace all the resistors that have gone out of spec in the sync separator and the video amp I replaced of them tonight. R70, R69 (or 71 cannot remember which one exactly), R75, R76.
This is actually made it a little better! The picture will no longer pull the center of it at max contrast, although it still shifts the picture sideways. There is also only one spot of tearing that I can see. I will replace the rest of the resistors tomorrow and it should be even better. I replaced the detector diode once before when trying to fix this problem with a 1N34A. This is the one that went open from having B+ shorted to it. I replaced that one with a 1N60 as per the parts list. I think I am on the right track here with the resistors.

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 Post subject: Re: Motorola 17T21 RF or IF Overloading LARGE IMAGES
PostPosted: Nov Sun 26, 2017 7:01 am 
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What happens when you reduce the RF input?
I had the same issue with an early 50s German Saba just recently. It can't handle more than about 2mV without sync problems, just fine with the input attenuated. Similar problem with an old Philips, replacing 6BX6 3rd IF tube (low emission) fixed that . You might have a bad 6CB6 in the 3rd IF or maybe even a bad 1N34 vision demod.


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 Post subject: Re: Motorola 17T21 RF or IF Overloading LARGE IMAGES
PostPosted: Nov Sun 26, 2017 11:34 pm 
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i think a b&k television analyst would help you locate the trouble in short order. you can inject a video signal into the video output tube and work your way back till you find the stage with the problem. then voltage and resistance measurements will locate the bad component. that is if it is a problem in the video circuit. the same can be done with the sync circuits. this is the way i learned to troubleshoot a tv. personally i wouldnt attempt to troubleshoot a tv without one.

when making a probe for your oscope i would try to stick to the component values of the original probe as close as possible.

this tv is giving you a baptism by fire. once you fix this you should be able to fix anything. just remember just throwing new components in with no particular reason never was and never will be a substitute for proper troubleshooting procedure. the tv books you mentioned should explain the logical step by step procedure for troubleshooting.

i have never tried to use an oscope to troubleshoot so i can not advise about that. good luck and keep us posted as to progress.

does the tearing start right away or does the set have to warm up first? if the set has to warm up awhile before the tearing appears it could be some kind of thermal problem. spraying the resistors and condensers one at a time with freeze spray in the video and sync sections might help locate the problem.


Last edited by thomas13202 on Nov Sun 26, 2017 11:45 pm, edited 1 time in total.

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