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
  #1  
Old 10-13-2009, 01:33 AM
Tubejunke's Avatar
Tubejunke Tubejunke is offline
VideoKarma Member
 
Join Date: Apr 2003
Location: Martinsville, VA
Posts: 1,823
How to check voltages??

I moved this from my "Help ID Space Command parts" thread because it seems to have died a quick death. I know someone knows the ins and outs of doing simple voltage checks. Again this is a 1958 Zenith Space Command. That really doesent matter. A lot chassis are removed without the crt or sometimes the tuner coming out with it. I need to know the best and safest method of powering up a chassis with such components disconnected. Can it even be done this way?

Original: "This may sound stupid, but they say that there is no such thing as a stupid question. What is a good method of checking voltages on a chassis that has been disconnected from the tuner, speakers, and CRT. First, I fear that something could be damaged operating a chassis like this. It could be dangerous to ME if I don't disable the HV, or at least more dangerous. This all leads to my second fear that any measurements taken might be off with so many things disconnected. I already know that they made a universal test CRT that can still be found. Right now, I don't have this, as I'm sure many of us don't, but we still must check voltages. I know I could remove that large CRT and rig up a bench mount of some sort, including the tuner and speakers. That sounds pretty far fetched to perform a fairly simple procedure. Any ideas or advice would be great."
Reply With Quote
  #2  
Old 10-13-2009, 08:44 AM
DaveWM DaveWM is offline
VideoKarma Member
 
Join Date: Feb 2009
Location: Orlando FL
Posts: 5,607
a tube stand off is nice for checking tube pin voltages.

B+ can be located, on some PCB types the sams will indicate where various B+ voltages can be taken off the pcb at test points.


both of the above can be done with the chassis in and everything hooked up.

I have found I can get to the pic tube pins by just pulling the socked off enough to allow a clip on a pin but still have the crt connected. I dont like to be probing around, incase something slips so I make sure I have a clip and nothing is shorted, then power up take a reading and power down to remove clips.
Reply With Quote
  #3  
Old 10-13-2009, 03:14 PM
Tubejunke's Avatar
Tubejunke Tubejunke is offline
VideoKarma Member
 
Join Date: Apr 2003
Location: Martinsville, VA
Posts: 1,823
On this old Zenith chassis, there are strips made of PCB material where various components make their connection. These are definitly test points because they are accessable from the top of the chassis. My schematic does not map these out. I guess I could mark points that I want to measure voltage by looking underneath the chassis, marking, reassembling, then measuring. Thanks for the help. This forum must not be as active as it used to be. Seems like you don't get nearly as much reaction to questions these days.....
Reply With Quote
  #4  
Old 10-13-2009, 06:51 PM
edison64's Avatar
edison64 edison64 is offline
THE A-1 WIRELESS MAN
 
Join Date: Nov 2007
Location: NW INDIANA THE MAPLE CITY LA PORTE (GO SLICERS)
Posts: 334
Not to sound stupid, but what is the correct name given to the "tube standoffs" had a set years ago but now cant find any.
__________________
RCA VICTOR and its dealers bring you......
Reply With Quote
  #5  
Old 10-13-2009, 08:44 PM
bandersen's Avatar
bandersen bandersen is offline
RCA 741PCS
 
Join Date: Mar 2009
Location: Chicago, IL
Posts: 8,085
Quote:
Originally Posted by edison64 View Post
Not to sound stupid, but what is the correct name given to the "tube standoffs" had a set years ago but now cant find any.
I've seen them called "tube test socket adapters" and "tube extenders". They generally fetch a pretty good price - especially for a complete set.
__________________
Here are my Vintage Radio & TV YouTube Channel and Photo Gallery
Reply With Quote
Audiokarma
  #6  
Old 10-14-2009, 02:04 AM
Tubejunke's Avatar
Tubejunke Tubejunke is offline
VideoKarma Member
 
Join Date: Apr 2003
Location: Martinsville, VA
Posts: 1,823
I sure miss restoring my RCA TC-127. Everything pulled out together and you could flip it on its side and do whatever you need.
Reply With Quote
  #7  
Old 10-14-2009, 02:07 AM
Tubejunke's Avatar
Tubejunke Tubejunke is offline
VideoKarma Member
 
Join Date: Apr 2003
Location: Martinsville, VA
Posts: 1,823
Can you safely power up a chassis with the tuner and crt disconnected long enough to do voltage checks?
Reply With Quote
  #8  
Old 10-14-2009, 11:31 AM
Phil Nelson's Avatar
Phil Nelson Phil Nelson is offline
VideoKarma Member
 
Join Date: Jan 2006
Posts: 4,030
Re tube extenders, here's a photo from when I restored my Predicta. One is shown with a tube plugged into the chassis. The others are just strewn around to show different types. I got a whole sackful at a swap meet years ago.

They do come in handy. Before I knew there was such a thing, I hand-built one to test voltages in the RF deck of a Hallicrafters SX-28. The construction is such that you can't reach the underside of the tube base at all. Same deal on the PC board of this Predicta, as I recall. My handmade extender is the one with little white "socks" on its legs. Not as spiffy (or safe) as the factory extenders, but it got the job done.

Phil Nelson

Reply With Quote
  #9  
Old 10-15-2009, 10:55 PM
Tubejunke's Avatar
Tubejunke Tubejunke is offline
VideoKarma Member
 
Join Date: Apr 2003
Location: Martinsville, VA
Posts: 1,823
Looks like these extenders would help, if someone lucked up and found some. If I could find a connection for tube bases and sockets, I could make them myself. I know you can still buy the sockets new. It might be possible to create the bases out of dud tubes. For now I need to check some voltages on this Zenith. Perhaps I can remove the big 24" crt and build a side mount jig to hook everything up.

I know a man who has some kind of universal chassis test jig of some sort. He told me that it was from the 70's, or so, and you more or less take a chassis like I am dealing with and hook it up to this 'tester" and somehow dial in settings. Then supposedly you view the performance of the chassison the screen and through the speaker of the test unit. Sounds great, but I'm sure it's limited as to how many years or models can be tested on it.
Reply With Quote
  #10  
Old 10-16-2009, 02:37 PM
Phil Nelson's Avatar
Phil Nelson Phil Nelson is offline
VideoKarma Member
 
Join Date: Jan 2006
Posts: 4,030
Regarding test points on a chassis, some may be for things other than voltage. For example, an RCA CTC-11 has test points where you can clip a small resistor from there to the chassis to disable a CRT gun while making adjustments like convergence.

Is it possible to reconnect everything if you set the chassis on its side behind the cabinet? Here's one of my CTC-11s.



Years ago, I did the same thing by hoisting a cabinet onto the workbench and sliding the chassis partway back in. Every connector reached, except for speaker leads, which I extended with alligator clip leads.



May sound goofy, but it's easier than building a complete set of extension cables that you may never use again.

For a chassis that won't safely stand on edge, I have used heavy metal "L" braces screwed into the chassis mounting holes.



Just some ideas.

Phil Nelson
Reply With Quote
Audiokarma
  #11  
Old 10-16-2009, 03:42 PM
Tubejunke's Avatar
Tubejunke Tubejunke is offline
VideoKarma Member
 
Join Date: Apr 2003
Location: Martinsville, VA
Posts: 1,823
Quote:
Originally Posted by Phil Nelson View Post
Years ago, I did the same thing by hoisting a cabinet onto the workbench and sliding the chassis partway back in. Every connector reached, except for speaker leads, which I extended with alligator clip leads.

May sound goofy, but it's easier than building a complete set of extension cables that you may never use again.
Just like there is no such thing as a stupid question, there is also no such thing as a "goofy" idea. I never thought of several of the ideas that I have been given. I think turning the set on its side and pulling the chassis backward may work. Where there is a will there is a way. Although I would need a helper for getting the big lug up on the table. I could do it on the floor if no help is available.

Thanks everyone! I wasn't getting much feedback for a while. Any other general pointers with late 50's Zenith black and white sets are always appreciated.
__________________
"Face piles of trials with smiles, for it riles them to believe that you perceive the web they weave, and keep on thinking free"
Reply With Quote
  #12  
Old 11-01-2009, 04:44 AM
jshorva65's Avatar
jshorva65 jshorva65 is offline
VideoKarma Member
 
Join Date: Jun 2002
Location: Ohio
Posts: 358
Quote:
Originally Posted by Tubejunke View Post
Just like there is no such thing as a stupid question, there is also no such thing as a "goofy" idea. I never thought of several of the ideas that I have been given.
There's often no such thing as a simple "one size fits all" answer, either. For that reason, becoming familiar with several techniques which work well for the most-frequently-encountered situations makes a good strategy. From there, elements of one technique may be combined with those of another technique for a situation in which neither of the two (or more) component techniques alone would have worked.

When performing troubleshooting or alignment, I use a test CRT (one of three types, depending on set vintage) for most B/W sets. I also have "universal" Test Rig devices (two models which work well for most 1946-51 and 1952-57 models respectively) with B/W sets where the test CRT alone isn't adequate (no convenient means to set the tube in the set's own yoke, thus requiring clipping or plugging in a "universal" yoke to use with the test CRT). I also have a "universal" Color Test Rig which supports most tube-chassis Color models directly, although some custom Yoke plug and Convergence ballast adaptors are required for use with sets using the older 21AXP22 (metal cone) CRT. The rig was equipped "stock" with virtually all adaptors required for sets using all-glass "roundie" and rectangular picture tubes. I've also fabricated some extensions for frequently-encountered chassis cabling (octal plug to octal socket, etc.) and use a small selection of Tube Test Socket Adaptors (not as impressive as Phil's selection of them, but adequate for most situations). Custom stands for often-encountered chassis types, adaptor brackets for similar chassis, L-brackets, cushions, braces, etc. (and combinations of them) are another trick I use for supporting a chassis in "service position" on the bench.

Last edited by jshorva65; 11-01-2009 at 05:00 AM.
Reply With Quote
  #13  
Old 11-02-2009, 12:21 AM
Tubejunke's Avatar
Tubejunke Tubejunke is offline
VideoKarma Member
 
Join Date: Apr 2003
Location: Martinsville, VA
Posts: 1,823
Gosh, you have your own repair shop. That must be really cool. For now, I utilize my kitchen table area for a work bench. I have a rack that holds some component bins, Sams folders, a soldering station, and a DVOM. You can really do a lot with what little I have, but I would love to have more space and equipment. Until I get my electronics degree I am in the poor house anyway, so I'm not going to be doing any TV restoration this winter. I might throw some caps, that I have sitting around, in an old radio or maybe two, if I'm lucky.

Now this crazy Space Command I can work with because I have already replaced all of the caps in it. It may need a vertical output transformer. Can't afford that right now.
Reply With Quote
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 02:06 PM.



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