Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Vintage TV & Radio Tech Forum

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #16  
Old 10-25-2018, 01:46 PM
Dubis7's Avatar
Dubis7 Dubis7 is offline
Alchemizes cash to tubes
 
Join Date: Nov 2014
Location: Leesburg, VA.
Posts: 397
Alright, I just checked the pins on the base of the CRT while it was turned on and everything was plugged in. I removed the connector enough to wiggle a multimeter probe in there while maintaining electrical connection.

Most of the pins seem to check normal, but pin 3, which is listed as 260V boost, is showing closer to 90V. Could low boost voltage be causing my problem? I'm not actually sure what it does, but it doesn't seem like there should be that much variance. It looks like that's coming off of a lug on my flyback, and going through resistor R79. I suppose my next step is to verify that R79 hasn't drifted above tolerance.

I remember hearing that, when testing a resistor, the correct procedure is to unsolder one of the leads and isolate it from the circuit. Would that be correct in this case?
__________________
To keep your tubes running smoothly, make sure to dust underneath the glass as well.
Reply With Quote
  #17  
Old 10-25-2018, 03:17 PM
zeno's Avatar
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 4,672
Time to back up a little...........
Remove the plate cap from the 1G3 & let it hang away from metal.
Take a well insulated screw driver & get it near the cap ( wire end).
You should get about a 1/2 inch arc, NOT just a spark if you touch
it or get very close.

Boost comes from the flyback. Its stacked on top of regular B+ voltage
( think of 2 batteries in series ) & filtered by C50 & C51. R79 must also
be good.
On your set if pin 3 of CRT goes to low it will kill the raster BUT not effect the HV.

Next is to get good HV ( that nice arc ) you need the following stages running.
1) horz osc
2) horz output
3) damper
Any defect will lower & or kill the HV & boost.

Bottom line it nice big arc = good till that point
Small arc = problem is before HV rect.

73 Zeno
LFOD !
Reply With Quote
  #18  
Old 10-25-2018, 03:57 PM
Dubis7's Avatar
Dubis7 Dubis7 is offline
Alchemizes cash to tubes
 
Join Date: Nov 2014
Location: Leesburg, VA.
Posts: 397
Gotcha. That's the first test I ran, so I can say with certainty that it was a very small spark. The screwdriver didn't have to quite touch the metal inside the cap, but it had to come very close to get a spark. I'd estimate a maybe 1/16" spark? Maybe less. So it sounds like my HV is low.

I keep thinking back to that Horizontal Hold control. It may be a red herring, but I was noticing some significant power supply defects when I adjusted that control before I recapped in. Specifically, a DTV converter box on the same outlet would actually reset itself as if the power were interrupted if I turned that control all the way up. Obviously I didn't repeat the test after I figured out what was happening, but I hope I didn't damage something doing it. A short somewhere, maybe? I checked the control, and it seemed to test fine, though I need to go back and make sure I'm testing the three leads correctly. I used to know how to do that, but it's been so long I've forgotten the specifics. I did notice that, at the extreme end, it drop from kohms down to ohms, which seemed extreme. I wonder if I've got a bad control, though that wouldn't explain the low voltage elsewhere.

I think I'll still give R79 a looksee. Worst case, I've practiced testing a resistor, and I might find a problem.
__________________
To keep your tubes running smoothly, make sure to dust underneath the glass as well.
Reply With Quote
  #19  
Old 10-26-2018, 02:57 PM
zeno's Avatar
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 4,672
Resistors should be check with one leg lifted IF they check
bad in circuit. After a while you get the hang of which to
do & speed things up.

For now check pin 2 of the horz out tube & be sure its about -20 VDC.
If not its a dead horz osc stage.
Also check voltages on the 8FQ7 & 22JU6 & post them.

73 Zeno
LFOD !
Reply With Quote
  #20  
Old 10-28-2018, 11:03 PM
Notimetolooz's Avatar
Notimetolooz Notimetolooz is offline
VideoKarma Member
 
Join Date: Mar 2014
Location: Dallas, TX
Posts: 547
Quote:
Originally Posted by Dubis7 View Post
I also went ahead and restested that 1K resistor under the rectifier socket. The results were mixed. An ohms test across the resistor with the tube removed is reading just about 1K, within tolerance, but a continuity test across the same resistor is showing no continuity. At the same time, doing another reading of the anode wire is showing stable continuity when I flex the cable, so I'm inclined to believe that's actually fine, but I'm also getting no continuity across that cable when I measure from the opposite side of the resistor. Is that normal, or is the resistor suspect?
Is that continuity test on your meter a GO/NO-Go kind of thing? Is the indication a tone or light going on? If the test is this sort, then you must realize that the meter has a threshold to determine the result. If the threshold is below 1K then when you measure something with a resistance of 1K the meter will call it an open.
If the boost voltage on the CRT is that low it probably would prevent the beam from lighting the screen. It also would suggest that your HV was low. If the horizontal frequency is far off it would decrease the HV.
Reply With Quote
Audiokarma
  #21  
Old 10-30-2018, 01:07 PM
Dubis7's Avatar
Dubis7 Dubis7 is offline
Alchemizes cash to tubes
 
Join Date: Nov 2014
Location: Leesburg, VA.
Posts: 397
Quote:
Originally Posted by Notimetolooz View Post
Is that continuity test on your meter a GO/NO-Go kind of thing? Is the indication a tone or light going on? If the test is this sort, then you must realize that the meter has a threshold to determine the result. If the threshold is below 1K then when you measure something with a resistance of 1K the meter will call it an open.
I looked this up after the fact, and yes it appears that my meter was probably responding to the functioning resistance of that resistor as if there was no continuity. That was my bad, but at least now I know that's how that works.

Sorry for the late response, all. I was out of town over the weekend, but I'll run those voltage checks sometime today or, if not, Thursday and see where I am.
__________________
To keep your tubes running smoothly, make sure to dust underneath the glass as well.
Reply With Quote
  #22  
Old 10-30-2018, 03:38 PM
zeno's Avatar
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 4,672
Quote:
Originally Posted by Dubis7 View Post
I looked this up after the fact, and yes it appears that my meter was probably responding to the functioning resistance of that resistor as if there was no continuity. That was my bad, but at least now I know that's how that works.

Sorry for the late response, all. I was out of town over the weekend, but I'll run those voltage checks sometime today or, if not, Thursday and see where I am.
Continuity is zero or near zero ohms. My fluke has a beep & a scratchy
tone. A beap is 0 ohms. If you wiggle something like a connector with
a rusty connector it will make the scratch sound.

Many meters have range select & auto range also so watch for that
when measuring,

73 Zeno
LFOD !
Reply With Quote
  #23  
Old 10-30-2018, 07:17 PM
Notimetolooz's Avatar
Notimetolooz Notimetolooz is offline
VideoKarma Member
 
Join Date: Mar 2014
Location: Dallas, TX
Posts: 547
Usually a continuity test is for things where you expect the resistance is very low, maybe no higher than 10 ohms. It is really for testing wire, contacts and switches. You can also use it on things like filaments and modern speakers. If it is a resistor use the ohms measurement, otherwise you will just confuse yourself.
Reply With Quote
  #24  
Old 11-01-2018, 03:00 PM
Dubis7's Avatar
Dubis7 Dubis7 is offline
Alchemizes cash to tubes
 
Join Date: Nov 2014
Location: Leesburg, VA.
Posts: 397
Okay, so I may have broken something, but it may not have been something I did.

I got the voltage measurements. For my 22JU6:

1: Unused
2: -20V
3: 0V
4: .3V
5: .15V
6: Unused
7: 120V
8: 37V
9: Unused

For the 8FQ7 (I checked then all because it's easier to access the pins above the chassis):

1: 0V
2: 5V
3: 8.6V
4: 109V
5: .04V
6: .06V
7: 5V
8:2.3V

Then, I measured Pin 9 on my 8FQ7, and the yoke started squealing and sparking. I see no indication that I shouldn't measure that pin on the schematic, and I fact, looking underneath, I don't even see anything hooked up to that pin, nor any mention of it at all on the schematic.

It looks like a wire may have broken on my yoke. I'm attempting to attach a picture, but I'm on mobile so I may have to do a separate reply for that.

So basically here's where I am: I don't think I should go any further without looking this yoke over. Is there a way to check if it's okay? If I do have a broken wire (it's accessible, but small) what are my repair options? If the yoke was having trouble, could that be causing my low high voltage problem? Also, from the schematic, should I be safe to measure pin 9 of my 8FQ7? How do my other voltages look? Some of them seemed off to me.
Attached Images
File Type: jpg 20181101_154928.jpg (64.4 KB, 13 views)
__________________
To keep your tubes running smoothly, make sure to dust underneath the glass as well.
Reply With Quote
  #25  
Old 11-01-2018, 07:59 PM
Notimetolooz's Avatar
Notimetolooz Notimetolooz is offline
VideoKarma Member
 
Join Date: Mar 2014
Location: Dallas, TX
Posts: 547
Your 22JU6 voltages are fine except pin 8, you got 37V but it should be 25V.
You should measure on the other side of R77, the voltage should be near 145V. Also check the value of R77, should measure 47K.

Your 8FQ7 are nearly all wrong! Did you measure the wrong tube?

Yes, check out the yoke. Perhaps there is a short or maybe is arced because the voltage got too high somewhere.

When you measure the filament pins you need to use the AC volt ranges.

Last edited by Notimetolooz; 11-01-2018 at 08:00 PM. Reason: Typos
Reply With Quote
Audiokarma
  #26  
Old 11-01-2018, 09:02 PM
Dubis7's Avatar
Dubis7 Dubis7 is offline
Alchemizes cash to tubes
 
Join Date: Nov 2014
Location: Leesburg, VA.
Posts: 397
Quote:
Originally Posted by Notimetolooz View Post
Your 8FQ7 are nearly all wrong! Did you measure the wrong tube?
I just double checked. Unless someone rewired this thing and moved one of the tubes, which I don't see any evidence of, it was definitely the right one. That being said...

Quote:
Originally Posted by Notimetolooz View Post
When you measure the filament pins you need to use the AC volt ranges.
I had my multimeter on DC. Maybe that's part of the problem? I'll rerun my tests, but I'd better check out that Yoke first. Looks like Moyer Electronics has a replacement, but I think I'll try and resolder that wire first. Assuming it's just the lead that's broken off, would splicing a new wire onto that lead and running an extension to the terminal be alright? I get the impression that the winding pattern on the yoke is fairly significant to its operation.

While I'm at it, I suppose it would be a good idea to measure the resistance on the yoke. I imagine I can do that from the plug, but I'm not sure how to tell which lead is which. Any ideas?
__________________
To keep your tubes running smoothly, make sure to dust underneath the glass as well.
Reply With Quote
  #27  
Old 11-01-2018, 09:23 PM
Notimetolooz's Avatar
Notimetolooz Notimetolooz is offline
VideoKarma Member
 
Join Date: Mar 2014
Location: Dallas, TX
Posts: 547
Maybe the arcing at the yoke when you were measuring pin 9 was a coincidence.
The yoke plug pin out and connection is shown on the schematic. The coil resistances also. Unplug the yoke to make the measurements. Make sure that the resistance between the horizontal and vertical coils is basically infinite.
From your picture it is hard to tell whether there is a strand out of place that is causing a short or close gap that may have arced, or maybe a wire has opened.
The filaments are fed AC, the rest of the tube pins should DC measurements.
The filament string voltages are shown in the lower left corner of the schematic but are seldom the problem.
Reply With Quote
  #28  
Old 11-01-2018, 10:07 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 14,758
If the yoke is open or shorted it will greatly reduce the HV and throw off everything else in the horizontal section...Ever pull the H yoke leads on a CTC-15 and power it up?..I have.
Check your yoke like tolooz sayz. That magnet wire is coated in lacquer or some such translucent insulator and you'll need to scrape, melt, or dissolve it off before you can solder it...A short jumper if a section burned off will be fine...Just don't make it longer than it needs to be and don't place it where it could arc to other things.

It could be that pin 9 was being used as a terminal/tie point for other things in the horizontal osc or that it shorted to another pin...Sometimes if the osc is tuned close to the point where it screams adding a small bit of load to the circuit from a meter can push it over the edge in to the scream zone.
__________________
Tom C.

Zenith: The quality stays in EVEN after the name falls off!
What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4
Reply With Quote
  #29  
Old 11-02-2018, 07:15 AM
ronl ronl is offline
VideoKarma Member
 
Join Date: Jun 2014
Location: Surrey (near Vancouver) BC Canada
Posts: 155
Looks like some carbon was created when the arc occured.make sure you scrape and or sand that black stuff off.its conductive.RonL
Reply With Quote
  #30  
Old 11-02-2018, 09:45 AM
zeno's Avatar
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 4,672
You have -20 volts on the G-1 of the output so the osc
is running. Testing around the osc will often throw it off
freq so that may be the scream you got.
If yoke wire broken you may be able to patch it if you can dig
out both ends. After that you are pretty much don to a bad
flyback, yoke or damper tube.

HINT ! When yokes get a shorted winding its usually on the
inside windings. Pull the yoke back off the bell. That will give
it air to burn better & you will see it often. Saves time !
If its not burning you may see on the CRT where it was burning.

73 Zeno
LFOD !
Reply With Quote
Audiokarma
Reply


Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 08:11 AM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
©Copyright 2012 VideoKarma.org, All rights reserved.