Featured
Latest
Frame transformer f...
 
Share:
Notifications
Clear all

Forum 141

Frame transformer for BRC 960

111 Posts
11 Users
6 Likes
14.2 K Views
Focus Diode
(@focus)
Posts: 729
Honorable Member Registered
Topic starter
 

With the set on the bench I removed the chassis and CRT connections rather than attempt any servicing partially in situ. I have visions the CRT neck could easily be knocked, no nice swing up panels in this version!

Took some photos with the chassis out. Note the French Mazda (no relation) PL504 courtesy of Til.

Another shot shows the very poor accessibility of some components close to the Lop stage holding and main electrolytic including the scan correction capacitors. The 1400s were a complete contrast!

With the set's unreliability in use I noticed more of those horrible rough textured resistors in the sound output stage, so I'll be replacing these too.

Could account for why the volume isn't as loud as it should be.

Cheers

Brian

IMG 20180520 144413
IMG 20180520 144521
IMG 20180520 143158
IMG 20180520 143735
IMG 20180520 143811
 
Posted : 20/05/2018 1:59 pm
crustytv
(@crustytv)
Posts: 11869
Vrat Founder Admin
 

Is this the new one Brian? If so we should split it off into its own thread.

CrustyTV Television Shop: Take a virtual tour
Crusty's TV/VCR Collection: View my collection
Crustys Youtube Channel: My stuff
Crusty's 70s Lounge: Take a peek

 
Posted : 20/05/2018 2:01 pm
Focus Diode
(@focus)
Posts: 729
Honorable Member Registered
Topic starter
 

Hi Chris,

No, it's the same 2633 I got from you many years ago. Originally the set had a red Jellypot Lopt of course.

I don't have the 2638, it belongs to another forum member who I'm hoping will do a post on it soon.

Cheers,

Brian

 
Posted : 20/05/2018 2:08 pm
Focus Diode
(@focus)
Posts: 729
Honorable Member Registered
Topic starter
 

Resistors at the sound output transformer were replaced. The 12K one read 27K when taken out of circuit. In view the originals were very close to the PCL 86 it was possible to mount them away from the valve. 

The result of my efforts was no sound at all. What had I done?

This version of the 960 has a unique warm up sequence which is the reverse of a conventional valved receiver. The sound is the last to appear, several seconds after a stable picture is on the screen.

Despite waiting a few minutes it was clear the sound wasn't going to appear.

Ponder for a moment then realised I'd forgotten to re-connect the speaker leads to the sound output transformer.....

Anyway, it didn't make much of a difference, the sound is certainly adequate but not to a level I would expect.  In contrast the Ferguson Personal 11" has a superb level of volume. If only they included VHF radio with that model as was fitted to some 900 sets.

Anyway, fully warmed up with sound present. Occasional frame disturbance which soon settled. Tapping the frame pre-sets resulted in disturbance to the picture similar, but not the same as the fault condition. The linearity controls really need to be replaced, but it's finding a source that's the problem.

I'd thought about using conventional potentiometers but space doesn't allow for this as it conflicts with the VHF aerial!

Now, to try disconnecting the VDR to the height control as suggested by Andrew.

Brian

IMG 20180520 165128
IMG 20180520 165037
 
Posted : 20/05/2018 4:17 pm
Focus Diode
(@focus)
Posts: 729
Honorable Member Registered
Topic starter
 

At last it's looking more hopeful!

The thermistor from the boost feed to the height control was disconnected resulting in grossly excessive frame scan which was not unexpected, yet it was  stable apart from the frame hold which, under the circumstances can be expected.

I then tried wiring in one of those black thermistors as used in later BRC/Thorn sets. The outcome was encouraging indeed with a stable image appearing!

So, Andrew, it appears you were right! 

Now to solder in the replacement properly then put it under test.

Fantastic!

Brian

IMG 20180520 174206
IMG 20180520 174013
IMG 20180520 173927
 
Posted : 20/05/2018 4:53 pm
PYE625
(@pye625)
Posts: 5121
Famed Member Registered
 

Well done Brian  ? 

Let's hope it solves the problem.

I thought they were VDR's. Or varistors to be more precise.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 20/05/2018 5:00 pm
Focus Diode
(@focus)
Posts: 729
Honorable Member Registered
Topic starter
 

I'm confident that Andrew was right. I've reassembled the set and the line spacing problem hasn't returned.

However, a new problem has occurred, with bent verticals now evident!

A high contrast setting makes it worse, so who knows what I've done to create this new problem.

A long soak has also shown the expected intermittent ragged verticals problem. Another that needs sorting out. 

At least it won't show up like the previous fault on watching a programme rather than test card.

Bits are accumulating between the CRT implosion sheet and face again too despite fitting draft excluder.Save that for another time.

My goal tonight

IMG 20180520 184249
IMG 20180520 184201

was to eliminate the frame creep problem once and for all.

This was achieved, thanks again Andrew!

Brian

 

 
Posted : 20/05/2018 5:35 pm
PYE625, PYE625 and PYE625 reacted
PYE625
(@pye625)
Posts: 5121
Famed Member Registered
 

The set is out to get you Brian !!

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 20/05/2018 5:36 pm
Focus Diode
(@focus)
Posts: 729
Honorable Member Registered
Topic starter
 
Posted by: PYE625

Well done Brian  ? 

Let's hope it solves the problem.

I thought they were VDR's. Or varistors to be more precise.

Yes, you're indeed right.

 

 
Posted : 20/05/2018 5:53 pm
Focus Diode
(@focus)
Posts: 729
Honorable Member Registered
Topic starter
 

Ah yes, the intermittent ragged verticals problem. Not the EHT tray, brightness control setting makes no difference either.

Through independent reasons the Lopt and EHT tray have been replaced without any effect on the problem.

New 30FL14, PFL200, EF80, PY801 and PL504 valves have been tried. The doubler also has new diodes fitted.

I don't recall seeing the fault on 625 lines. Must connect a source of signals to check this out.

 

 
Posted : 20/05/2018 6:21 pm
PYE625
(@pye625)
Posts: 5121
Famed Member Registered
 

Is it the same on 625 lines?

I could be completely wrong, but could the different VDR affect it somehow? Might be worth checking the boost voltage with the new VDR, and then with the old one as a comparison. 

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 20/05/2018 6:32 pm
Focus Diode
(@focus)
Posts: 729
Honorable Member Registered
Topic starter
 

Hi Andrew,

Yes, the creeping problem was just as bad on 625-lines.

The funny thing was the boost feed to the height control's voltage appeared stable hence why I didn't suspect the VDR. Replacing it seems to have finally cleared the fault at long last.

The shimmer is an entirely different intermittent problem which has always plagued the set. The line output stage has been ruled out.

That's one fault I don't recall seeing on 625 though. 

Cheers and thanks again

Brian

 
Posted : 20/05/2018 7:00 pm
PYE625
(@pye625)
Posts: 5121
Famed Member Registered
 
Posted by: Focus Diode

The funny thing was the boost feed to the height control's voltage appeared stable hence why I didn't suspect the VDR. 

 

Probably too rapid to see on a DVM, but a 'scope would likely show the fluctuations. ? 

Pleased that it's sorted now, nothing worse than a niggling fault.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 20/05/2018 7:24 pm
crustytv
(@crustytv)
Posts: 11869
Vrat Founder Admin
 

Latest video from Brian has been uploaded to the forum youtube channel

CrustyTV Television Shop: Take a virtual tour
Crusty's TV/VCR Collection: View my collection
Crustys Youtube Channel: My stuff
Crusty's 70s Lounge: Take a peek

 
Posted : 20/05/2018 11:23 pm
Focus Diode
(@focus)
Posts: 729
Honorable Member Registered
Topic starter
 

Thanks Chris.

I should point out the initial 40 seconds of the warm up sequence is omitted. The video starts as soon as the Raster first appears.

Cheers

Brian

 
Posted : 21/05/2018 9:56 am
Focus Diode
(@focus)
Posts: 729
Honorable Member Registered
Topic starter
 

Quick update: Beautifully clean raster developed after 50 seconds followed by an outstanding picture when fully warmed up!

Still kicking myself for not suspecting the VDR. It's the first time I've known one of these components to fail.

In conclusion to the thread I must thank everyone again, especially David Boynes for having a look, Chris for kindly supplying the frame transformer and of course to Andrew for pinpointing the cause of the problem.

Chris' You Tube page is an excellent idea, it's much easier to see a fault rather than describe one.

Cheers and my many thanks to you all again.

Brian

IMG 20180522 170924
IMG 20180522 170843
IMG 20180522 173032
 
Posted : 22/05/2018 4:32 pm
Nuvistor
(@nuvistor)
Posts: 4594
Famed Member Registered
 

You will not know what to do now it’s fixed.

You got there, that’s what matters, a few byways along the journey and guaranteed not to forget what the fault was.

Frank

 
Posted : 22/05/2018 5:01 pm
Focus Diode
(@focus)
Posts: 729
Honorable Member Registered
Topic starter
 

Thanks Frank. There's still the issue of the intermittent ragged verticals but otherwise the set is now working really well. 

Then, I've said that before. It hasn't been the most reliable of TV sets!

Cheers,

Brian

 
Posted : 22/05/2018 5:40 pm
Nuvistor
(@nuvistor)
Posts: 4594
Famed Member Registered
 

Lots of heat in a small space doesn’t make for reliability.

Frank

 
Posted : 22/05/2018 7:05 pm
TVJON74
(@tvjon74)
Posts: 680
Honorable Member Registered
 

Hi Brian,

Great job! Hope mine looks as good as that when it's working.

Is there something stuck to the lens of your camera or on the tube face? There seems to be a black dot on the top right corner of your pictures.

Jon
BVWS Member

 
Posted : 22/05/2018 9:09 pm
Page 5 / 6
Share: