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Frame transformer for BRC 960

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Focus Diode
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Here's the layout of the original 960 chassis shown with the line output stage screening cover removed.

It's utter madness really! The frame is top left, sound top right with the line output stage vertically on the right. The lower PCB is very much like the standard 950 with the above stages broken off.

With the confined space the PL504 anode lies very close to the pin cushion correction magnet. Wouldn't surprise me if it's tracking over.

The set was functioning perfectly when the photo was taken.

ch

Edited_ImageEasyImageEditor_20170728_434.jpgBrian

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Topic starter Posted : 28/07/2017 9:58 am
Focus Diode
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Yes, the earthing spring across the CRT has been checked.

As it is the set has become a bit of a hybrid between the different versions of the 950 chassis. The 20kV 950mkII used the same LOPT as the 1400 chassis. The original 950 and later 900s employed a different red encased jellypot LOPT with a half wave rectifier tray. The connections differ considerably.

This is probably a one off in the 950 series having a later MkII LOPT from a 1400 Fed to a 3-stick EHT doubler!

This has certainly improved the 405-line performance when the set's working correctly in addition to giving a much less intense line whistle compared to the original m

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Topic starter Posted : 28/07/2017 11:49 am
PYE625
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Focusdiode said
Here's the layout of the original 960 chassis shown with the line output stage screening cover removed.

It's utter madness really! 

Edited_ImageEasyImageEditor_20170728_434.jpgBrian  

It kind of looks to me as if it was almost a "stop-gap" between chassis design..... Lets have one of those, a little bit of that, oh and one of them.   grin_gif
 

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Posted : 28/07/2017 11:21 pm
Focus Diode
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An update for you!

Disconnecting the EHT doubler had no effect. I also replaced the 180pF disc capacitor on the LOPT tags I added on adapting the set to work with a 1400 LOPT

. I was never happy with that as it ran extremely hot. I found the correct 160pF on a spare 1500 LOPT I have.

Perhaps you're wondering why I didn't replace this earlier? Many years ago I ruined a perfectly good LOPT when replacing the capacitor. I guess I didn't have the confidence remembering that incident some 30 years ago.

I'm pleased to report the replacement capacitor runs quite cool in addition to not ruining the LOPT. Important seeing I no longer have a spare 1400 transformer!

When changing from 405 to 625 then back the system switch jammed requiring me to pull out the mains plug. Some lubrication restored reliable solenoid system switching and a perfectly stable frame!!!

Surely not, but not quite. When the frame was stable for the first time in ages I established the frame lin top and main lin controls were very touchy. They'll need replacing. Whether they're the cause of the fault I don't know.

 

Next switch on and the return of the earlier problem, but without the crackle or white spots. I must have done something right!

The set's been running for around an hour now with Test Card C via. the Aurora. The frame is occasionally juddery but not nearly as bad as before. It's actually quite watchable unlike before.

The fault is by no means cured completely but a great improvement nevertheless.

Next I'll obtain replacement linearity controls.

The occasional ragged vertices and slight occasional balloon ing persists too. Not particularly worried about that as it's usually soon after the signals appear. The manual does say additional time is needed to allow the circuits to settle down!

I must get some draught excluder too. The existing seal between the CRT and Feinbridge guard sheet is beyond useless. This involves CRT removal for cleaning.

Cheers and thanks for all your helpful input again.

Brian

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Topic starter Posted : 29/07/2017 9:54 pm
PYE625
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Hi Brian,

It's perhaps never a good sign that a capacitor runs hot, so I think you did the right thing there.

Have you cleaned the system switch?  Just wondering if this could be causing poor contacts in the LOPT department.

Preset controls certainly can be intermittent and MAY benefit from a squirt of servisol switch cleaner. Sometimes the carbon track can be worn away by frequent adjustment, so of course cleaning is then pointless.

Keep up the good work, you'll soon have it licked  grin_gif

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Posted : 29/07/2017 11:58 pm
Focus Diode
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Hi Andrew,

The actual fault persists, but in a far less extreme form. With the new tuner fault the image briefly balloons and become ragged as the picture reappears.

Think I need to completely dismantle the set and of course sort out the CRT's lack of dust seal. Dust etc. accumulates very quickly between the CRT face and Feinbridge guard sheet.

It's a very crude arrangement where the tube is secured by a plastic cradle and rests on the guard sheet. I wouldn't be surprised if static is building up between the two which resulted in the "interference".

Ideally the set could do with a reinforced CME1602 type in place of the original non banded CME1601 so the guard can be removed.

Little chance of getting one I'd imagine.

This early photo shows the CRT fixings.

Cheers

 

Edited_ImageEasyImageEditor_20170730_435.jpgBrian

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Topic starter Posted : 30/07/2017 9:56 am
Nuvistor
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Fenbridge guard plastic screens I always found a pain for CRT replacements, making sure there were no air bubble in between guard and CRT faceplate was never easy. Warm up the guard while stretching the guard over the faceplate by tightening a tourniquet. Tighten the clamp band and say ***** as you see a little air bubble.

The guards tend to yellow over time as well or was that due to staining by cigarette smoke?

Once sorted out at least dust was not a problem.

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Posted : 30/07/2017 11:15 am
Focus Diode
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Hi Frank,

This set differs in the CRT face actually resting on the straight sheet as it it was an afterthought. Totally unsatisfactory really as the CRT face is curved yet the implosion sheet is completely flat. Perfect in acting like a dust magnet but suppose it does the job of protection in the event of implosion.

Once I've removed the CRT for a thorough clean I might consider using a form of sealant, say the bathroom type to make it airtight.

What do others think?

cheers

 

Brian

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Topic starter Posted : 30/07/2017 11:45 am
crustytv
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Personally I think any form of sealant is a bad idea, messy and can react.

In the past I've always used with great success door foam draft excluder. Comes in a variety of shapes and colours and is perfect for the job, one side being contact stick. It forms a perfect seal.

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Posted : 30/07/2017 12:32 pm
PYE625
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Chris said
Personally I think any form of sealant is a bad idea, messy and can react.

In the past I've always used with great success door foam draft excluder. Comes in a variety of shapes and colours and is perfect for the job, onside being contact stick. It forms a perfect seal.  

Couldn't agree more.

Here is what I did with my Pye, and the stuff I used for a dust seal. Whether the same principal can be applied to your set Brian, I wonder?

http://www.forum.radios-tv.co.uk/viewtopic.php?f=5&t=5345&start=75

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Posted : 30/07/2017 12:44 pm
Focus Diode
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Having obtained some draft excluder I set to work yesterday evening. The photos show the work involved and the crude implosion sheet.

That was very difficult to clean on the inside due to the texture of the material, in other words rough on the inside, smooth on the out.

The only successful method of applying the draft excluder was to apply the adhesive side around the CRT as close to the implosion sheet as possible. Inevitably a couple of bits of dirt did find its way back on the CRT face when reassembled.

The CRT face just rests on this flat sheet held in place by the plastic cradle fixing. There's no evidence of any dust seal employed during manufacture.

They would be room for a reinforced CME1602 which is good to know and wonder if later sets were fitted with this CRT?

 

A word of warning I make no apologies to stress the importance of wearing eye protection when carrying out this exercise. Common knowledge for most of us but we do have newer members to consider.

 

The result? The top continues to break up as before on occasions but the ragged vertices and occasional ballooning seems to have been cured.

cheers

 

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Topic starter Posted : 04/08/2017 10:25 am
Cathovisor
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Chris said
Personally I think any form of sealant is a bad idea, messy and can react.

In the past I've always used with great success door foam draft excluder. Comes in a variety of shapes and colours and is perfect for the job, one side being contact stick. It forms a perfect seal.  

Or even draught... we're not in the Colonies, chaps! wink

Oddly enough, it was foam draught excluder used by Bush on the TV7x and 8x sets...

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Posted : 04/08/2017 11:34 am
Focus Diode
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Cathovisor said

Or even draught... we're not in the Colonies, chaps! wink

Oddly enough, it was foam draught excluder used by Bush on the TV7x and 8x sets...  

Absolutely right. I see I got the spelling correct when I did a post on the UKVRRR site!

Brian

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Topic starter Posted : 04/08/2017 11:58 am
Cathovisor
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Focusdiode said

Absolutely right. I see I got the spelling correct when I did a post on the UKVRRR site!

Brian  

It does seem to be a creeping import, that one...

Apropos of Fenbridge guards, if that's what we're dealing with here - I seem to recall there's a guide to fitting them in either Radio & Television Servicing or one of the Television Engineers Pocket Books.

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Posted : 04/08/2017 1:18 pm
PYE625
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Living in Chatteris, almost in the heart of the Fenland, I often admire the occasional Fenbridge that can be seen.

Here is a lovely example of the Fenbridge, it is at Turf Fen.  I'm not sure what happened to the Guard though.....

1271672_c21e233f.jpg

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Posted : 04/08/2017 2:24 pm
Focus Diode
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Photographic sequence of the two stage warm up.

Signals start to appear about 45 seconds after the appearance of the blank raster.

Sound on vision as the IFs come in to action, but no sound for another 20 seconds.

The PCL86 is the final valve in the second DC heater chain.

Very much the reverse of the usual valve equipment warm up, ie: Sound usually comes up first!

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Topic starter Posted : 06/08/2017 6:12 pm
PYE625
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Thats interesting to see Brian....must have had to explain it to a new owner for the first time.

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Posted : 06/08/2017 6:18 pm
Focus Diode
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Hi Andrew,

By great good fortune a good friend who is also a forum member sent me the original user instruction booklet for the Ferguson version. There is mention of the two stage warm up in it.

I've PDF'd it and will see if there's a way of uploading to the site. Perhaps Chris can advise?

Cheers

 

Brian

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Topic starter Posted : 06/08/2017 6:44 pm
crustytv
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Focusdiode said

[..] original user instruction booklet for the Ferguson version.I've PDF'd it and will see if there's a way of uploading to the site. Perhaps Chris can advise?

Cheers

Brian  

See here

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Posted : 06/08/2017 6:54 pm
Focus Diode
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Thanks Chris, but seems complicated using the mobile phone.

I've sent you the Ferguson 3638 instructions by Email. Hope that's ok.

I was wrong on mentioning the 2-stage warm up in the instruction booklet. This is in the Thorn 960 manual.

There is mention of allowing a few minutes for the set to warm up however!

Cheers

 

Brian

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Topic starter Posted : 06/08/2017 8:10 pm
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