Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Oct Wed 27, 2021 11:21 pm


All times are UTC [ DST ]





Post New Topic Post Reply  [ 27 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: My Predicta went dark
PostPosted: Aug Fri 27, 2021 4:46 pm 
Member
User avatar

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1627
Location: Albion, CA, USA, 95410
Howdy All,

Well, tragedy struck last night. We were watching "What's My Line" on the Predicta Holiday and the picture was a little unstable. No adjustment helped. It was just jiggling, it didn't seem to be the horizontal lock. I have noticed a little occasional jiggle over the last few months, now that I think about it. The jiggling got worse and then *poof* we lost picture. I can't say if we lost sound because we have been running the sound through the stereo and I was on my feet and hitting the power off as fast as I could. This morning I tried turning it on. It has a picture, disturbed as it was last night. I am guessing if I left it on it would go dark again. Sounds like something is getting warm. The set smells fine, no hot smell.

Some background: I "restored" this set, finishing about 4.5 years ago. "restored" is in quotes since it was my first and only TV that I have worked on. "Got it working with the help of others" might be a better description. It has been recapped, new tube sockets installed on the PCB, new couplates, new diodes, replaced the fusible resistor. It has been working fine for years with hundreds of hours on it. I am hoping for some help with troubleshooting, I am not an expert and my theory is weak.

Many thanks in advance!


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Aug Fri 27, 2021 7:01 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 3519
Location: Dallas, TX
If you replaced all those things I don't think there would be much risk in turning it on again and trying to notice more details. Does it have sound when the picture goes out, odd noises, flashes of light, smells?
You may eventually have to remove the chassis, connect clip leads to important voltages like B+, run it until it goes dark again.
There were several Predicta chassis made, which one is this?
If you include a link to the old posts about it, that may fill in the blanks about the set.

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Aug Sat 28, 2021 3:41 pm 
Member
User avatar

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1627
Location: Albion, CA, USA, 95410
I did try it again. I pulled the chassis out so I could look. It ran for about 10 minutes before going dark. No noise or drama, just poof.

Unfortunately, my work bench and the TV live in different houses. I will bring some basics over here and see what I find. Not only would I have to pack the TV up but the RF modulator etc. to be able to work on it at the bench. I have been meaning to pick up a smaller test CRT, then I could just pull the chassis and take that.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Aug Sat 28, 2021 11:55 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 3519
Location: Dallas, TX
If both picture and sound suddenly went off it would point to a power supply problem.

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Aug Tue 31, 2021 4:53 pm 
Member
User avatar

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1627
Location: Albion, CA, USA, 95410
Yes, probably in the HV area. I am at work for a 72 hour shift but should be back to the set Thursday or Friday. I will be armed with some tools this time and so will do as suggested and report back.

And thanks, the help is much appreciated.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Thu 02, 2021 10:33 pm 
Member
User avatar

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1627
Location: Albion, CA, USA, 95410
Finally where the set it. Now when I power up I get nothing.

Swapped out V8, V10, V11, V12, V13. No change. The horizontal output tube looks like it might be red-plating a little but I am not sure. It is just a dim orange.

Voltage at the rectifiers is a little low, 247 instead of 290. I couldn't find my HV probe before I came over to where the set is. How did I misplace something 12" long with a cord on it? I dunno. Anyway, I measured the flyback resistances and all are exactly as they were when I restored the set.

What do do next? I guess start trying to track down the low B+ voltage. I think I have a test socket I can put on the horizontal output tube and do some looking at the voltages there.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Fri 03, 2021 12:08 am 
Member
User avatar

Joined: Nov Thu 11, 2010 6:03 pm
Posts: 1606
Location: Pewaukee, WI
If anything other than the heater/cathode glows a visible color then the tube is redplating.

Red, orange, white...All plate colors other than dark are VERY bad.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Fri 03, 2021 12:40 am 
Member
User avatar

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1627
Location: Albion, CA, USA, 95410
This is the first and only TV I have ever restored and as my daddy used to say, if brains were lard I couldn't grease too big a pan. Orange was wrong, very slight red. But as you say it shouldn't have any color at all and I don't recall it being that way in the past. Part of the problem is that it has been over four years since I did the set and I seem to forget things that happened more than about 10 minutes ago.

What are the most likely causes of the horizontal output tube red plating? Since the flyback tests ok, does that mean that the output of the tube is not the problem? Looking at the resistors and caps around the HOT I know the caps have been replaced but the resistors I am not sure. They are under the chassis and where I have the set right now I can't really flip it over to look. I see that it says "95 - 135 mA" but I don't see where that would be measured.

Thanks so much for the help.

edit: Drat. Just found out my my test socket is too tall as the output connection (the cap on top) won't quite reach.


Last edited by madlabs on Sep Fri 03, 2021 12:56 am, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Fri 03, 2021 12:48 am 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 3519
Location: Dallas, TX
If I read between the lines, I guess you have sound and the tube heaters light.
You still haven't said which chassis you have.
Many times the horizontal output tube will draw excessive current when it doesn't get the proper signal from the horizontal oscillator circuit.
A simple test to see if the flyback and/or output tube is getting a driving signal is to hold a compact fluorescent lamp near it.
That lamp does not have to be a good one, as long as the lamp tube is still sealed.
Attachment:
FluorHorzEE1.jpg
FluorHorzEE1.jpg [ 114.2 KiB | Viewed 787 times ]

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Fri 03, 2021 1:03 am 
Member
User avatar

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1627
Location: Albion, CA, USA, 95410
Yes, the filaments are all lit. Sound I am not sure because I have been running the sound through a stereo for better sound quality. I do still have a hum through the speaker. I can go digging through the cabling and try to send some sound through the set.

The CFL trick indicates no HV.

Oh and it is model G4242L, chassis 9L37


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Fri 03, 2021 1:37 am 
Member
User avatar

Joined: Mar Sun 01, 2009 10:27 pm
Posts: 5837
Location: Ann Arbor, MI
If the horizontal oscillator is not running, the horizontal output tube will draw too much current which will pull.down the B+.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Fri 03, 2021 2:16 am 
Member
User avatar

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1627
Location: Albion, CA, USA, 95410
So, the horizontal oscillator is the the 6CG7, called horizontal multiplier in the schematic? I do not have an oscilloscope here, so is there a way for me to determine if it is running? I do have a frequency counter in my DMM.

Edited to add: Here is the link to the Sam's: http://www.earlytelevision.org/pdf/phil ... _439-1.pdf


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Fri 03, 2021 2:56 am 
Member
User avatar

Joined: Mar Sun 01, 2009 10:27 pm
Posts: 5837
Location: Ann Arbor, MI
That would be horizontal multivibrator. Check the voltage at the grid of the horizontal output tube. If you don't get something like -45 volts then the multivibrator is either not running or the signal is not making it to the output tube. You could have a bad tube, a bad contact with the tube socket, a cracked solder joint or one of the couplets has failed. Making voltage readings around that circuit might help pinpoint the trouble.

_________________
Tom


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Fri 03, 2021 5:21 pm 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 896
Location: Rockaway , nj 07866
If the voltage off the rectifiers is low I would suspect one or both are failing , try reading the voltage and when the picture goes out see what the voltage is , I have a 64 zenith that runs ok then after ten to twenty minutes it starts getting darker and things start looking a bit squeezed , this is caused by the rectifiers


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Fri 03, 2021 5:48 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 3519
Location: Dallas, TX
madlabs wrote:
Edited to add: Here is the link to the Sam's: http://www.earlytelevision.org/pdf/phil ... _439-1.pdf

Ah, so that is one of the hot chassis sets. Unless you have an isolation transformers take extra care.

By the way, how do you take the sound signal off of the TV and send it to your hi-fi?

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Tue 07, 2021 2:08 am 
Member
User avatar

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1627
Location: Albion, CA, USA, 95410
Crazy week! Got a lot done but only had the on chance to work on the TV. At work on my 72 hour shift now. Later this week I will figure out a way to lay the chassis on the side to take some voltage readings. Really I should lug it over to where the work bench is but I am always scared of dropping it.

I don't pick the sound off from the set. Since I don't receive any OTA signals I am using DVD and streaming as my source. So I separate the audio before it goes into the RF modulator.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Tue 07, 2021 3:20 am 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 3519
Location: Dallas, TX
madlabs wrote:
I don't pick the sound off from the set. Since I don't receive any OTA signals I am using DVD and streaming as my source. So I separate the audio before it goes into the RF modulator.

OK. The reason I asked was that since this is a hot chassis set if you had added an audio jack to the TV, the ground of the audio connector might be hot (connected to the power line) and there might be a lot of current passing between the TV and the audio system. What would be the ground for the TV antenna terminals is isolated from the TV chassis, so no problem there.
So did the TV sound ever work?
The reason for my asking is that it may indicate another power supply problem.

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Tue 07, 2021 4:59 pm 
Member
User avatar

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1627
Location: Albion, CA, USA, 95410
Yes, the sound used to work. As the first set I ever worked on I never got the fine tuning/buzz pot/contrast adjustments right. While it was OK, after a while I decided to re-route the sound and then deal with trying to improve it next time I had it on the bench. Once I get the picture back I am going to try to improve the sound while I have it pulled apart.

I will also re-route the sound back to the set this week. I do think it is working as I heard the DVD faintly and distorted when I moved the local/distance switch on the back, must be some bleed through the mess of cables.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Wed 08, 2021 3:04 pm 
Member

Joined: May Thu 14, 2015 4:15 pm
Posts: 3519
Location: Dallas, TX
It might be a little early to jump to a conclusion, but if the CFL did not light it indicates that horizontal output and fly back are not switching the current to any extent. Could also be way off frequency.
Without the HO circuit switching current there will be do HV.

It could be a main power supply problem.
It could be that the horizontal oscillator isn't running or is way off frequency. I also could be that the oscillator signal is not making it to the HO.

This seems to as good a time to mention this, I know this guy and he does an excellent work. I think he is still making couplet kits. The couplets are the parts on the schematic in the dotted line boxes.
https://tvrestorerguy.com/

_________________
Tim
It's not the Destination, It's the Journey.


Top
 Profile  
 
 Post subject: Re: My Predicta went dark
PostPosted: Sep Wed 08, 2021 3:20 pm 
Member
User avatar

Joined: Aug Thu 20, 2015 3:09 pm
Posts: 1627
Location: Albion, CA, USA, 95410
Thanks notime. I will be back at the set in a couple of days. The couplates have been replaced with ones made by banderson when I did the set 4-5 years ago. There might be one original underneath the chassis, I think I was told that it never went bad.

I ordered a little sains-smart 'scope that will be easier to bring over to where the set is. I'm still hoping to avoid moving it back to where my bench is. I will get some voltage readings this week. Since the FBT tests the same as when I restored it and the HOT is red plating a little my guess is as you have suggested that the horizontal osc isn't running. I will take another dig looking for my HV probe to confirm the lack of HV.


Top
 Profile  
 
Post New Topic Post Reply  [ 27 posts ]  Moderators: Mr. Detrola, 7jp4-guy Go to page 1, 2  Next

All times are UTC [ DST ]


Who is online

Users browsing this forum: No registered users and 6 guests



Search for:
Jump to:  


































Privacy Policy :: Powered by phpBB