shmups.system11.org

Shmups Forum
 
* FAQ    * Search
 * Register  * Login 
It is currently Sun Sep 19, 2021 8:47 pm View unanswered posts
View active topics



Post new topic Reply to topic  [ 6 posts ] 
Author Message
 Post subject: [SOLVED] Dark horizontal bars on 5" CRT TV
PostPosted: Sun Sep 12, 2021 8:58 pm 


User avatar

Joined: 11 Mar 2020
Posts: 9
Location: England
Hello folks,

I did post this somewhere else but without any success, so here goes.

The TV is a Samsung CI-125R; it has composite input and controls for brightness, contrast and saturation.

And this is this issue:
Image

Here it is with contrast turned all the way up:
Image

*Initially thought it was the saturation control, but the bars disappear completely if the contrast knob is down all the way.

I've already tested quite a few capacitors that seemed in a relevant part of the circuit with an ESR meter, and replaced those that seemed a bit "suspicious", but no joy.
Before I go any further, maybe some of you experts can give me a better clue? Appreciate any advice :cry:

P.S. I couldn't find a service manual or even a piece of schematic. Happy to post pictures of the board if it helps.


Last edited by Fox Cunning on Mon Sep 13, 2021 9:22 am, edited 3 times in total.

Top
 Offline Profile  
 
 Post subject: Re: Dark horizontal bars on 5" CRT TV
PostPosted: Sun Sep 12, 2021 9:28 pm 


User avatar

Joined: 16 Jan 2014
Posts: 1550
Just a complete guess, but something related to the chroma demuxing circuitry maybe?


Top
 Offline Profile  
 
 Post subject: Re: Dark horizontal bars on 5" CRT TV
PostPosted: Mon Sep 13, 2021 5:25 am 



Joined: 13 Sep 2021
Posts: 4
Honestly, I would probably recap everything just to be safe. The caps could be acting differently under a real load. I've had a similar issue with rolling black lines on my Saturn but recapping the psu in it fix the issue.


Top
 Offline Profile  
 
 Post subject: Re: Dark horizontal bars on 5" CRT TV
PostPosted: Mon Sep 13, 2021 7:23 am 


User avatar

Joined: 11 Mar 2020
Posts: 9
Location: England
Josh128 wrote:
Just a complete guess, but something related to the chroma demuxing circuitry maybe?

Thanks, that made me realise it's actually the Contrast control, not the Saturation one causing the problem! Sorry about the confusion.
I'll double-check that section of the circuit now; there should be one diode and one capacitor that I have not replaced there -- I've seen components that tested good out of circuit but still caused issues, in the past.

If all looks fine there, maybe the contrast control inside the PAL decoder chip (TDA3565 by the way) could be the culprit?
Replacing that chip would be a pain in the backside, I'd like to rule everything else out before I do that.


Top
 Offline Profile  
 
 Post subject: Re: [SOLVED] Dark horizontal bars on 5" CRT TV
PostPosted: Mon Sep 13, 2021 9:31 am 


User avatar

Joined: 11 Mar 2020
Posts: 9
Location: England
I can't believe I was looking at the wrong control the whole time! :oops:

It was indeed the contrast circuit, not the saturation one.
I traced the correct section now, and it looks like this:

Image
*TDA3565


The capacitor measured inconsistently between 2000pF and 180nF and sure enough it was that leaky bugger that caused the problem.

Image



Replaced with a new good one and voila, nice vibrant image!
Thanks again Josh, maybe a bit indirectly but you put me on the right track :)


Top
 Offline Profile  
 
 Post subject: Re: [SOLVED] Dark horizontal bars on 5" CRT TV
PostPosted: Mon Sep 13, 2021 2:30 pm 


User avatar

Joined: 16 Jan 2014
Posts: 1550
lol fantastic job man!


Top
 Offline Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC


Who is online

Users browsing this forum: bzn, Climhazard, Google [Bot], SavagePencil and 14 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
Space Pilot 3K template by Jakob Persson
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group