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Old 9th Sep 2018, 3:23 pm   #21
Welsh Anorak
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Default Re: Stuck on a BRC 1400!

Are they the usual late 1400/1500 knobs? If so I'm sure I have some knocking about.
Hopefully the focus will sort itself out with time, or maybe a gentle bop!
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Old 9th Sep 2018, 4:39 pm   #22
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Default Re: Stuck on a BRC 1400!

Hi Glyn,

I don't think they're critical as long as they're matching. The existing knob and the one I found aren't robust enough to operate the on-off switch.

Another forum member owns this model with different style control knobs which appear to be the originals. The photo was taken before any restoration was attempted.

Cheers and many thanks,
Brian
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Old 10th Sep 2018, 10:56 am   #23
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Default Re: Stuck on a BRC 1400!

The problem with the later knobs is they tended to split meaning that they wouldn't operate the switch as you have found, though repair with a wire collar is possible. I'll have a rummage and see which knobs I have in the box.
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Old 11th Sep 2018, 8:32 am   #24
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Default Re: Stuck on a BRC 1400!

These are the correct knobs for a Ferguson 3645. I used to order Thorn knobs by the dozen back in the 70's! If all else fails I may have the correct ones.

The tube looks a little tired but check the focus supply from the boost rail including the pot. Lack of focus volts on an old tube makes it look a lot worse. John.
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Old 11th Sep 2018, 9:10 am   #25
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Default Re: Stuck on a BRC 1400!

Its looking very promising and perhaps with some running the CRT might clear it self.
Just a cautionary tale, I had a 1400 which went up in smoke resulting in the customer throwing the set out of a first floor window. The problem was down to the width resistor and width control burning and was quite a well known fault which led to Thorn bringing out a modification which reduced the current through both these components. I cant remember the values but it means changing both the width control and the resistor in series with the width control.
Looking at the picture it might be an idea to check the high value resistor that feeds the focus control as it might have gone high or open circuit.
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Old 11th Sep 2018, 10:31 am   #26
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Default Re: Stuck on a BRC 1400!

Quote:
Originally Posted by Hybrid tellies View Post
The problem was down to the width resistor and width control burning and was quite a well known fault which led to Thorn bringing out a modification which reduced the current through both these components. I cant remember the values but it means changing both the width control and the resistor in series with the width control.
The series resistor was changed from 330kOhm to 680kOhm and the preset pot from 1MOhm to 2.2MOhm.
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Old 11th Sep 2018, 8:45 pm   #27
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Default Re: Stuck on a BRC 1400!

Indeed Dazzlevision. This modification also applied to the 1500 chassis.

In my case I don't know if I have any suitable 2M/2M2 pre-sets but would imagine uprating the feed resistor to 680K would be better than nothing.

Unfortunately Simon the focus is good at lower brightness levels which suggests the CRT is at self the cause of defocusing at high levels. We've all seen this before. I'll be doing more work to the set tomorrow.

John - Thanks. Gary's set clearly has the right knobs then.

A lot more work to do on the set. I'll get back to it tomorrow.

Picture taken on 625 lines.
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Old 11th Sep 2018, 9:46 pm   #28
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Default Re: Stuck on a BRC 1400!

Quote:
Originally Posted by Focus Diode View Post
Indeed Dazzlevision. This modification also applied to the 1500 chassis.
In my case I don't know if I have any suitable 2M/2M2 pre-sets but would imagine uprating the feed resistor to 680K would be better than nothing.
That is probably true, but the range of adjustment of a 1MOhm pot may then be insufficient to set the width correctly.
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Old 12th Sep 2018, 8:05 am   #29
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Default Re: Stuck on a BRC 1400!

I have a set of three knobs removed from a 1400 (model unknown) about 40 years ago. Yours for the cost of postage or pick up at Golborne in November.

Keith
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Old 12th Sep 2018, 7:18 pm   #30
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Default Re: Stuck on a BRC 1400!

Thanks Keith. They would be great. I'll PM you with my address.

A little more work this evening while I await the arrival of the 10uf high voltage caps.

I was uncomfortable about the width control being set at maximum so the respective scan correction capacitors were replaced then the width was set to mid-way. I noticed the 600pF capacitor had already been replaced which turns out to be the only evidence of previous repair work done to the set apart from valve replacements.

I was gratified to note near full width with the 405-line boost voltage at 640v which is below that specified in the service notes (670V on 405, 730V on 625). The occasional ticking from the EHT tray rectifiers has also thankfully stopped.

Now I'll see if I can sort out the non vertical linearity.

Cheers
Brian
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Old 13th Sep 2018, 7:57 am   #31
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Default Re: Stuck on a BRC 1400!

Several components changed with no improvement despite removed resistors showing they've changed value.

Bottom cramping persists yet frame lock is rock solid. Not a fault I've had before on a 1400 that hasn't been the valve. Just to be sure another PCL805 was tried. No improvement.

Still a few components to change however.

It's occurred to me the valve heaters appear rather too bright for my liking. The voltage selector, (deleted on later 1400s), appears to be at the 240V position. I'm now wondering if the BY126 heater supply rectifier I fitted could be faulty? Later I'll check voltages.

So much for the easy fix!

Have found a used 2M pot so this will go in with a 680K feed resistor in the width position later too.
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Old 13th Sep 2018, 9:08 am   #32
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Default Re: Stuck on a BRC 1400!

For the frame lin problem you need to replace C93/C95/C96/C98. These very reliable capacitors are becoming leaky and also manage to double their capacity. [Odd one that!]

The heater rectifier must be OK. It will be either O/C or S/C. I've never encountered an O/C one but have changed a few S/C ones.

Bias for the frame output valve is derived from the heater line via R108/10 from the junction of V10 and V11.

A shorted heater rectifier will result in a folded up mess that is supposed to encourage the user to turn it off and summon the help of a service engineer. Unfortunately they usually left it on with the result that all the valves and CRT were over run and destroyed.... As a very rough guide you should see about 4.2V across the tube heater pins 1&8 on an AVO8.

The valves do look a bit bright in the 1400 series but the fact that the picture is locked and stable proves that everything should be OK in this area.

Regards, John.
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Old 13th Sep 2018, 9:12 am   #33
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Default Re: Stuck on a BRC 1400!

Good morning,
I am working on a 1400 at the moment. The 23”HMV version. Mine has bottom cramping as well a replacement valve made no difference. Looking to change the 1K pentode grid feed resistor to see if this helps as it has risen in value around 160 ohms.

The heater chain has a connection to the frame oscillator so that if the diode sent S/C the frame would not lock. Might be worth connecting an ammeter in the heater circuit best place would be on the tube base then at the top of the chain to see if any of the decoupling capacitors are leaking.

Christopher Capener
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Old 13th Sep 2018, 9:25 am   #34
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Default Re: Stuck on a BRC 1400!

Thanks John. I've yet to replace C96 or C98 so I'll do that later.

Christopher- would be nice to see a write up and images of your set. I used to have a 2640 23" HMV from 1967 that was in regular use until the CRT got so bad I had to retire it in 1993, still otherwise in excellent working order.

It benefitted from a better quality speaker than what would be found in a Ferguson for example.

Brian
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Old 13th Sep 2018, 1:30 pm   #35
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Default Re: Stuck on a BRC 1400!

Hi Brian,
Just to say I'm really enjoying this thread.
I like the BRC 1400, it's like a 1500 with more valves and capable of the right number of lines! I like its serviceability and the very well layed out PCB.

I've got the 17" Marconi version with a push button tuner and a very flimsy looking carrying handle.
Inter-carrier buzz on 625 was a reported problem with these sets, but mine seems ok for some reason. I've now got to sort out the usual sticking UHF tuner problem and have that job planned for Christmas.

Cheers
Andy
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Old 13th Sep 2018, 2:13 pm   #36
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Default Re: Stuck on a BRC 1400!

Pay particular attention to the coupling and linearity feedback components. The resistors are usually OK and within tolerance and if a little out, it makes no difference.

I have a Ferguson 3645 and could be persuaded to take it together with the GEC BT2147, ITT/KB VC200 [SV054]Ferguson 989T chassis and maybe a Ferguson 941T to the TV day on Saturday but I expect you are all bored with my rantings so maybe I will leave them at home. John.
PS we have a good representation of 60s and 70's TVs at the museum so don't just expect old crocks.
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Old 13th Sep 2018, 8:37 pm   #37
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Default Re: Stuck on a BRC 1400!

Always a pleasure to be in your company John. We can never become bored with your expertise. Sure I'm speaking for all of us here.

Unfortunately my order hasn't arrived yet so have postponed further work until next week as I'm working solidly this weekend. Bah!

You're right about the resistors John as I've replaced most of the higher rated ones that have changed value with no difference to the bottom cramping.

On the other extreme there was no vertical or horizontal sync due to C45 (47K). The original had reduced in value to 20K so was replaced with little optimism. It completely cured the problem!

Brian
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Old 13th Sep 2018, 10:46 pm   #38
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Default Re: Stuck on a BRC 1400!

Been playing around with the frame cramp this evening. Capacitors seem in perfect condition with the correct capacity and no leakage with the megger. Decided to adjust the two picture shuffle rings on the neck of the tube and this has helped a bit after then playing with the height and linearity controls. I have lowered the picture about half an inch and centred the horizontal scan and the picture looks better and the frame linearity has improved. There is now only a slight linearity issue but that is only the top pointing up arrow on test card C is longer than the bottom pointing down one. The rest of test card C is correct. I think I will leave it at that.

This set has a Cathodeon CRT fitted and looks good other than a few scratches on the tube faceplate. The aquadag coating has wrinkled on the lower side of the CRT bowl but hasn’t flaked off.

Christopher Capener
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Old 14th Sep 2018, 12:49 am   #39
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Default Re: Stuck on a BRC 1400!

I think the Cathodeon CRT's were Mullard ones.
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Old 14th Sep 2018, 9:00 am   #40
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Default Re: Stuck on a BRC 1400!

The capacitors should be replaced. The linearity presets should be set half way with plenty of adjustment either way.
You cannot test them accurately with any test gear.

I came across this just yesterday. I was working on a KB/ITT VC200 series for display at the TV day.

Fault was frame hold control on end but locking and overall linearity pot on end with slight bottom cramp. 'Passable' but far from 100% as these excellent chassis should be.

The components are all of excellent make and quality, the ones I had the mystery with were Plessey .022uf and .047uf 1000v DC plastic types that have a very good reputation.

I lifted one end of each cap, all in the coupling and feedback path and measured them on my reliable cap bridge. All four read exactly correct capacitance and a 750V leakage test proved them to be as near perfect capacitors as you will find.

I must admit I spent far too long messing about with new PCL805 valves and checking components that were obviously nothing to do with the fault.

I then had a cup of tea and returning to the workshop did what I should have done in the first place. I replaced all four caps with good quality replacements. Switching on produced a rolling picture and a massive increase in height.

Adjusting the presets produced a very linear picture with them set mid way and yes the hold control was now centered as it should be.

Testing the capacitors again showed them to be perfect! So be warned, it might save you a bit of head scratching.

The 1400 should give a 100% linear picture easily with plenty to spare. Hope to see you at the TV Day. Regards, John.
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