Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > Early Color Television

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 08-06-2012, 12:33 AM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 260
CTC-15 restoration

Starting a restore for a VK Member. This CTC-15 chassis is in rough shape. This is a high hours set and has signs of a lot of old and new work. It had a raster recently and CRT should be OK. I will be checking it.

There was no video however, then no nothin... there are some parts clipped, bad electrolytics and all but vaporized terminal strips under the square/ hots. some wires are not much better. A previous attempt by someone has a top-hat in place of a boost diode, glass diodes in place of the dual diode, resistors stacked to attain needed value, and a good number of those wooden looking resistors checking way high.
Are there any pitfalls I should know about the 15 chassis? The things we were used to seeing 35 years ago don't necessarily relate to the state of that equipment 45 years later.
This may well be a diamond in the rough and I'm excited for the owner. Its even a remote. I'll post some pictures next visit.
Reply With Quote
  #2  
Old 08-06-2012, 01:01 AM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,604
Ground stakes on all boards

power resistors on chroma board with crystalized solder pads, reflow

jumper wires on top of chroma board,green corrosion, breaks off. The CRT will turn a solid color like screen control turned up too high.

Grid coupling cap, .01 between the power resistor and a 6GU7 will be weak, the other .01 grid coupling caps for the difference amps will prob be ok.

a trace on the side of the PCB near the horz out tube may fracture, back this up with a buss wire. It connects to a 390k resistor at the horz blanker tube. this shows as a loss of HV due to the blanker tube supplying too much neg bias to the horz out.

Caps in the vert feed back .0082 1kv mainly. the vert out cathode bypass cap, 50uf I think, its on the sweep board. Often ok, but if you doing for someone else then prob should be replaced.

1k power resistor on term strip near vert out trans, ofter the term strip solder has crystalized due to heat.

focus stick, sometimes goes bad mounted to side of fly.

horz output tube coupling cap. I replace this just to be safe.

Filter caps, of course these can be bad, if someone else set then I would restuff the cans just to be safe.

thermistor is fragile often broken.

on off switch is gets a lot of abuse. I use a remote power switch (the kind that are often sold during Christmas time for remote turn on of light) to save wear and tear on all my old vintage stuff.

Check line voltage. PT may have a high line voltage jumper that can be used. Better to use if line voltage is high, which is often the case.

check and adj horz eff coil, often a minor tweak can save 10-15ma or more good for fly life.

Check shunt tube and HV setting per sams. there is a 1k 5% resistor that is used to check voltage drop across for checking current in shunt. Generally you want to see about .5 to 1.5v drop across this while watching normal programing. think you will see this with the HV set to about 23kv and the fly current around 200ma
Reply With Quote
  #3  
Old 08-06-2012, 09:25 AM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 260
Thanks DaveWM

Good info, esp. the .01 coupling caps in the driver ckt. The .0082 in the vert is rated at 2KV. and is one of the cut components. This seems a bit over kill. I'm thinking 1600v replacement. Thoughts?
There is a thick layer of sticky dust on almost everything. A blower doesn't do much and Deoxit and Q-Tips is an expensive way to cleanup but the results are good. I really need to see everything. Do you have a recommendation?
Reply With Quote
  #4  
Old 08-06-2012, 09:59 AM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,604
yea 2kv I would stick with that, large pulse from the transformer.

I generally just used compressed air to get the big dust bunnies out of the way, use care around any coils or wires. If it really bothers you I have found rubbing alcohol and q tips works fine.

to check those chroma jumper wires just give them a slight tug, they will break instantly if bad, when they do break they stay put so it looks like they are fine.

there is prob a tube cap on the bottom, connected across the primary of the vert out, think its a .001 2kv and prob one on the audio out as well. May as well replace those, mainly since I cant test them at rated voltage (spikes).

Of course there is the across the line tube cap that should be replaced as well.

What I generally do is scan the parts list for HV caps, and make up an order from that, making sure I have them covered. I get them from mouser, HV caps are found in the film cap section as "snubber" caps.
Reply With Quote
  #5  
Old 08-06-2012, 04:37 PM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 260
Pictures attached.

The bright camera flash makes it look better than reality. The cleaned up spots do look better.
I think I'm going to inject a composite video signal and eliminate the tuner and IFs . The display is so bad I can't tell where to begin. I will say that the CRT cathodes are sky high so my dark screen issue will start in the video section. I have re flowed the grounds on the chroma board and that cleared up some filament issues.
Attached Images
File Type: jpg DSCF0063.jpg (106.1 KB, 140 views)
File Type: jpg DSCF0064.jpg (115.6 KB, 118 views)
File Type: jpg DSCF0062.jpg (108.2 KB, 116 views)
Reply With Quote
Audiokarma
  #6  
Old 08-06-2012, 05:38 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,604
futz around with the AGC pot. check the control grid voltage on the video out and see if it varies with the brightness setting.

try subbing in a new video out.
Reply With Quote
  #7  
Old 08-06-2012, 06:29 PM
ctc17 ctc17 is offline
VideoKarma Member
 
Join Date: Jul 2009
Posts: 1,617
The flyback is the weakest point I would say.

Dave is dead on.

I would add color crystal.

If the crt is good try and lower the HV down to around 20kv, letting it run up to 25kv is just asking for the doughnut to arc out and burn up.
Reply With Quote
  #8  
Old 08-06-2012, 11:37 PM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 260
Being a shunt(load) regulator adjusting the HV down should add more current load to the HV rectifier and thus the fly-back. Output tube current is the operative here and if any thing would reduce fly-back current it would be the CRT brightness, screen grid volts at the HOTube and the circuit being at resonance. A screen grid method was used in later chassis designs in the square screen, tube, portables.
I have checked the AGC pot and it slightly lightens the dim raster, but not the answer yet. I'm going to check basic voltages at the Vid out and work back.
The CRT had intermittent green as the loose cap was touched. I re-flowed the green pins and then re-flowed them again with an added thin solid wire inserted in the socket pins and is now stable. The CRT checks really good otherwise but Im not comfortable with this turn of events especially when I could see someone previously soldered the pins before me, but its stable for now.
Forward boys, we march on.

Where would I find a schematic (RCA / PDF or such) with scope readings or more voltage details? I found a basic that I've been using but it's very basic at www.boxcarcabin.com/rcaschematics.html, but I need more info.
Right about now I wish I had a test jig and a million dollars
Reply With Quote
  #9  
Old 08-07-2012, 12:16 AM
ctc17 ctc17 is offline
VideoKarma Member
 
Join Date: Jul 2009
Posts: 1,617
Those are a bunch of scans of the schematics that came with the tvs I posted there.

You would think shunting the fly would cause more heat and it may, but keep in mind the failure mode of the flybacks. Its arcing from the top of the doughnut to the bottom and its caused by high voltage breakdown. I have disassembled and re waxed and repaired a few of these. Trust me when I say shunt it.
If you want to lower overall heat, use the high line voltage tap on the power transformer. That will lower the headroom on the high voltage and increase the life of everything in the set big time.

Ill look and see if I have the full service manual on the 15.
Reply With Quote
  #10  
Old 08-07-2012, 03:11 PM
ctc17 ctc17 is offline
VideoKarma Member
 
Join Date: Jul 2009
Posts: 1,617
PM me your email and what info you need (what areas you are having issues with). Ill get you a custom set together tonight.

I have tons of information on color stuff and cant scan it all with this crappy little scanner.
Reply With Quote
Audiokarma
  #11  
Old 08-10-2012, 02:49 PM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 260
Still dark

I'm thinking its a blanking issue. CRT checks VERY good. I have focus voltage, screens are up, but not much brightness. The bias sw has little to no affect even in the service mode.
My Sams shows there should be +90 v on the blanker grid, but there is not. The plate has 130 plus or minus. On the very left inch or less of the screen I can see noise, the rest is black.
What develops this +90 volts?

Last edited by 6GH8cowboy; 08-10-2012 at 04:46 PM. Reason: wrong plate volts
Reply With Quote
  #12  
Old 08-10-2012, 03:19 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,604
confused, you have HV correct?

what are the pin voltages on the CRT again?
Reply With Quote
  #13  
Old 08-10-2012, 03:34 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,604
whats the plate voltage of the 12BY7?
Reply With Quote
  #14  
Old 08-10-2012, 05:41 PM
6GH8cowboy 6GH8cowboy is offline
VideoKarma Member
 
Join Date: Mar 2011
Location: Palm Beach County Florida
Posts: 260
Plate 12BY7 210

CRT K 284 G1 147 G2 903 well into cutoff right?
Reply With Quote
  #15  
Old 08-10-2012, 08:21 PM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,604
hmmm

plate voltage is off, should be around 320v as should be the K G1 should be around 200v. You have about a 130v neg bias vers about 120v. which is not much. don't think that would cut it off.

I would check the brigtness control and make sure its working properly. as you need to get a handle on the odd plate voltage. Make sure you are reading with no signal. I like to use a VTVM for testing voltages, although a DMM would be fine, just not a VOM.

Pin 2 of the blanker should be -95v.

Make sure you have about 5kv of focus voltage. If the focus voltage is too the CRT will be dark.

Last edited by DaveWM; 08-10-2012 at 08:33 PM.
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 02:07 AM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
ęCopyright 2012 VideoKarma.org, All rights reserved.