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 03-23-2019, 08:18 PM
AlanInSitges's Avatar
AlanInSitges AlanInSitges is offline
VideoKarma Member
 
Join Date: Nov 2017
Location: Sitges, Catalonia, Spain
Posts: 446
I'm just going to add to this thread so I don't stink up the whole forum with dumb questions. Not talking about video anymore!

I am replacing a few of the capacitors in the vertical section while I have this thing's guts up on its chest.



One part in particular Mouser didn't have in stock, and I'm wondering how critical the capacitance is. I'm talking about C5 in the image above. As I understand it, the frequency of the vertical oscillator will depend on the rate at which that capacitor charges and so if I replace it with a substantially different value, I'm going to be way off frequency. The one in the set is .0015 at 1000V, the manual calls for .0015 at 1600V, and the closest I have on hand is .0068 at 1600V. Is a difference this great possible to compensate with vhold control? Or should I just order the right part?

The other doubt I'm having is about C13. I replaced it with the correct value but in the process realize that there is also a .1uf part tacked in parallel underneath the PCB that I'm certain was done at the factory - there are a slew of these in various places. That raises the capacitance an order of magnitude at the same place in the other half of the circuit. If that's the case, then my .0068 shouldn't be such a big deal, I guess?

If you're wondering why I don't just try it, well, it's going to be a big deal to get the PCB loose and change it, and I really would rather only do it once.

As always, thanks!
Reply With Quote
  #17  
Old 03-23-2019, 10:27 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
Got 3 .0047uF 600V caps?...If so and you wire them in series you'll get 1 .00156666uF 1800V cap...I used to do that from time to time before I started stocking 1600V caps. Caps in series (assuming all are the same value) the new capacitance is the face value divided by the number in series, and the rated voltage adds.

Caps in parallel the capacitance adds, and the voltage is that of the lowest rated part.

If C13 really has a .1 in parallel with it then it is a .133 cap. That may have been done to get a really precise value and or compensate for adapting an NTSC design to CCIR.

You don't want to monkey with sweep cap values unless it won't run on frequency with all the right parts...I know from experience it can be a messy proposition to deal with fudged values.
__________________
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
  #18  
Old 03-25-2019, 09:26 PM
Hugo barbedo Hugo barbedo is offline
VideoKarma Member
 
Join Date: Jul 2018
Posts: 24
hi
as said you could also put a 1nf and a 470pf in parallel that will give you .00147 wich is preety close. 1nf is easy to get...470pf maybe you need to order it or if you search locally maybe you will only find ceramic discs wich are not very good for that application because they drift with temperature changes

also if you search on mouser for 1500pf capacitors of 1600volts or higher you get about 400 parts
you have some nice orange drops and the usual rectangular plastic caps that are epoxy-dipped
you also have the wima mkp or fkp etc
i wonder if you serched for the wrong value because they have a bunch of them
https://pt.mouser.com/ProductDetail/...9irIy0rgpp4%3D

other important thing:
make sure you use mkp fkp or other AC pulse capacitor when you are recapping anything connected to the plate of the vertical output or when recapping next to the horizontal output or for the boost filter..regular caps may not last there and their DC voltage rating may not mean anything there.

Last edited by Hugo barbedo; 03-25-2019 at 09:52 PM.
Reply With Quote
  #19  
Old 04-12-2019, 09:31 AM
AlanInSitges's Avatar
AlanInSitges AlanInSitges is offline
VideoKarma Member
 
Join Date: Nov 2017
Location: Sitges, Catalonia, Spain
Posts: 446
Well a huge thank you to everyone that offered some help in this thread. This was the first TV repair I've attempted since around 1980. And I'm happy to say that we got it working great (I consider it a group effort).

In the end, I replaced X4 the video detector diode, replaced two capacitors in the vertical section, and cleaned and repaired the tuner. It had nearly 60 years' worth of tobacco juice that had made a thick, rich glaze on all the contacts. After like, 20 qtips I had it shining like new. Then I had to repair the contacts for the switch that turns on B+ to the UHF tuner when switched to the UHF position. I've just finished putting it back together, have all the knobs and body parts de-gunked and back in place, and have got my hands on a plastic screen bezel that was missing from my set.

The only thing remaining is to touch up some of the missing silver trim paint, and polish out some scratches on top of the cabinet.

I'm feeling super optimistic now that I was able to see this through to the end, and have already started on a Zenith from the same era. Once I get the cabinet all prettied up I'll do a blog post and put some photos here; I know it's a set that a few people are interested in.
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 03:18 AM.



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