Videokarma.org

Go Back   Videokarma.org TV - Video - Vintage Television & Radio Forums > General Off Topic Forums

We appreciate your help

in keeping this site going.
Reply
 
Thread Tools Display Modes
  #1  
Old 01-17-2018, 08:50 PM
MIPS's Avatar
MIPS MIPS is offline
VideoKarma Member
 
Join Date: Jun 2014
Location: West Canadia
Posts: 462
CRT discharging: Ill effects?

I already know the answer to this from my own routine of doing this and don't need a lesson in how to discharge a CRT. I just need to ask the question with an audience who is a bit more seasoned and experienced with day to day television and video display maintenance.

I have a friend who says that when you discharge the anode and flyback system of any CRT, regardless of the tube size you must have a resistor inline with the path to ground or else the strong and instant grounding will negatively affect the inner properties of the CRT and how it can act as a capacitor. Furthermore the strong discharge with the flyback has the potential to damage the ultrafine windings of the flyback. The latter I can understand if the set was powered, but for this instance it is not plugged in, or turned on. It's being serviced.

How appropriate does this sound to you old salts who spent a large portion of their lives working on and discharging TV's? Have you ever come across an instance where an instant discharge damaged the unit?
Reply With Quote
  #2  
Old 01-17-2018, 09:06 PM
Electronic M's Avatar
Electronic M Electronic M is offline
M is for Memory
 
Join Date: Jan 2011
Location: Pewaukee/Delafield Wi
Posts: 9,196
It should not harm the flyback at all there is a diode there to block. I'd almost worry about SS diodes being damaged by transients, but HV diodes are usually multiple diodes with parallel capacitance and sometimes resistance to reduce and equalize strain on the diodes.

I've never seen damage from hard grounding the CRT (except for mistakes where technicians reflexes were triggered by discharge through the human body). Sets that are on and have repeated arcing for a few moments can implode...HV arcs get very hot in a concentrated area and glass does not like that...But It usually takes MUCH more than a simple discharge to get there.

The main advantage of the resistance method is that the charge will not bounce back and bite you 10 seconds later. (Had that happen enough to favor resistance strongly.)
__________________
Tom C.

What I want. --> http://www.videokarma.org/showpost.p...62&postcount=4

Reading between the scan lines since the mid 2000's.
Reply With Quote
  #3  
Old 01-18-2018, 08:07 AM
zeno zeno is offline
VideoKarma Member
 
Join Date: Mar 2013
Location: New Hampshire
Posts: 2,889
Never heard it can damage things in abt 40 yrs on the bench.
If you wish discharge it through a HV probe then short out the
last few KV in a few minutes.

73 Zeno
LFOD !
Reply With Quote
  #4  
Old 01-18-2018, 12:16 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 4,423
I wouldn't trust discharge through a resistor to prevent dielectric relaxation and a charge buildup after a while, unless you leave the resistor connected for several minutes (which you could also do with a plain wire).
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany
Reply With Quote
  #5  
Old 01-18-2018, 12:22 PM
dewickt's Avatar
dewickt dewickt is offline
Will fix about Anything
 
Join Date: Aug 2003
Location: Knoxville, TN
Posts: 93
Hard discharge is harmless, in my 12 years at Philips I discharged over a thousand CRTs with the only problem of not having a good tie to the DAG a few times.
__________________
Terry
DeWick Repairs
www.mcintoshaudio.com
Reply With Quote
Audiokarma
  #6  
Old 01-18-2018, 12:27 PM
old_tv_nut's Avatar
old_tv_nut old_tv_nut is offline
See yourself on Color TV!
 
Join Date: Jul 2004
Location: Rancho Sahuarita
Posts: 4,423
This brings to mind the fact that the early color CRTs needed resistors in the HV feed to prevent strong arcs from damaging the guns. Redesign of the CRT's internal discharge path fixed this, but later sets sometimes used limiting resistors to prevent arc damage to other components besides the CRT. If a set has such limiting resistors designed in, it should be able to withstand short circuit discharge when the set is off.

In my earliest job at Motorola, I did arc testing on a new chassis, which was done with the set running for maximum safety factor. The discharge path in a particular chassis can be very circuitous (no pun intended). One Motorola solid state B&W had a problem with CRT arcs killing the sound section. The arc was going into the B+ supply via [Edit: the CRT grid 1 vertical blanking coupling capacitor to:] the vertical sweep transformer, and then through the audio output transistor (no damage along the way) to the audio driver transistor, which it would kill. The initial fix was to use a beefier audio driver, and eventually a choke coil in the driver circuit to squelch the initial transient.
__________________
www.bretl.com
Old TV literature, New York World's Fair, and other miscellany

Last edited by old_tv_nut; 01-18-2018 at 10:08 PM.
Reply With Quote
  #7  
Old 01-18-2018, 08:28 PM
MIPS's Avatar
MIPS MIPS is offline
VideoKarma Member
 
Join Date: Jun 2014
Location: West Canadia
Posts: 462
Thank you for the answers you guys.
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 11:08 AM.



Powered by vBulletin® Version 3.8.4
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.
ęCopyright 2012 VideoKarma.org, All rights reserved.