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Old 23rd Nov 2008, 9:45 pm   #1
Dr-Watts
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Smile Thorn 1400 Pt.2

Here's part two then,

After replacing
R92, R97, R94, R91, R98
C81, C83, C80, C115, C76, C100, C82, C101, C107 & C127 THE 1400 seemed to perform OK... until the frame started to slowly roll, then fastly roll.
This made me question the parentage of the little set, but after a nice cuppa some resistor checks showed that R101 was 350K instead of 220K, this replaced and the picture is now great - as you can see.
The frame does still roll a bit when first switched on, but I'm pointing the blame at V9. (I don't have one in stock)
Unfortunately V9's Valve base has seen better days so I'll need to source another one of those as well.

I suppose the reason it takes me so long to get things done is purely one of priority over the kitchen table, if it's not dinner time the kids are doing homework, I only wish I had somewhere to put a workshop !

Here's some more pics for you...

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These aren't all the changed components, I managed to 'bin' most of em by accident...

Faith has said that I can put the 1400 in the kitchen to ''Soak Test' it, I'll probably wait until I get another valve, and you know how long a 'propper' soak test can take

Thanks for your interest,

Dr. Dave
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Old 23rd Nov 2008, 9:48 pm   #2
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Default Re: Thorn 1400 Pt.2

That looks like a cracking set now Dave. Well done for sorting out all those faults.

Kind regards.

From Mike.
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Old 23rd Nov 2008, 11:32 pm   #3
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Default Re: Thorn 1400 Pt.2

Thanks Mike, I'm really pleased with it !
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Old 23rd Nov 2008, 11:40 pm   #4
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Default Re: Thorn 1400 Pt.2

It's looking good Dave and I look forward to seeing it in real life. I'll bring my Aurora so you can try it out on 405 lines too.

What is the model number?

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Old 23rd Nov 2008, 11:46 pm   #5
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Default Re: Thorn 1400 Pt.2

It's a Ferguson 3653.
405 ! There's no need for that Tas... I fear 405, I'll end up like the rest of the 405 nutters on here
You know the score mate, come over any time

Thanks

Dr. Dave
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Old 24th Nov 2008, 10:53 pm   #6
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Default Re: Thorn 1400 Pt.2

Faith's just gone out...
She'll be so pleased when she get's back
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Old 24th Nov 2008, 10:53 pm   #7
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Default Re: Thorn 1400 Pt.2

Excellent sets, well done on sorting out the faults.

Don't overlook the heater rectifier which could be the cause of frame roll if leaky. If it goes s/c it will be impossible to lock the frame and the valve heaters will be overrun. If it's a small diode it is suspect. A BY126 is a suitable replacement.

Although a "common" fault it's not one I encountered personally.


Brian
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Old 25th Nov 2008, 9:11 pm   #8
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Default Re: Thorn 1400 Frame Roll...

Well it's been on for hours and all seems good except for an almost constant need to adjust the Frame Hold...
From cold you set the Frame, it all seems nice, watch it for 10 - 15 mins and it will start to roll down the screen.
Give it a tweek and it'll probably be OK for an hour then it will need another tweek and so on.
Next time you switch it on the frame hold is miles out again and will need reseting to the 'cold' position.
I'm about to change the Heater Rectifier Diode because apparently this was a well known problem for these simptoms.
I replaced one of the Resistors on the frame hold pot because it was well out of spec, this was because the control was 'one ended'

On the good side, the more it get's used, the brighter the picture, it's super bright and super sharp.
I did have to make an attenuator for the antenna socket though, it didn't like a full strength signal, in fact it didn't like it at all

Anyone else have any suggestions ?

Thanks in advance

Dr. Dave
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Old 25th Nov 2008, 9:42 pm   #9
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Default Re: Thorn 1400 Pt.2

Hello again Dave,
The Thorn 1400 chassis did not like a strong UHF signal due to too much coupling between the video output valve and the sync seperator. This causes sync crushing and picture bounce at 'normal' settings of the contrast control. To overcome this remove R44 10k and C40 and replace with a single .003uf [approx] capacitor. This should calm things considerably. The frame roll is probably caused by a slow heating PCL85/805 [very common] Due to its age it may be a cap but they were reliable on this chassis as a whole. Regards, John.
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Old 25th Nov 2008, 9:43 pm   #10
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Default Re: Thorn 1400 Pt.2

Hello Dave.

Have you replaced the PCL85/805 yet? As for the overloading on high signals, have you tried adjusting the "local/distant" control, R11. It's tucked away at the bottom of the board near to the solenoid? It is accesible from the print side though, phew

Nice pics of it on your Facebook by the way



Sorry John, I was typing at the same time as you
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Old 25th Nov 2008, 10:00 pm   #11
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Default Re: Thorn 1400 Pt.2

Yes I've replaced the valve with a NOS one, but the fault is exactly the same.
As for the local/distance control - according to the manual it's for 405 only
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Old 25th Nov 2008, 10:18 pm   #12
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Default Re: Thorn 1400 Pt.2

Quote:
Originally Posted by Dr-Watts View Post
Yes I've replaced the valve with a NOS one, but the fault is exactly the same.
Try one more!
Quote:
Originally Posted by Dr-Watts View Post
As for the local/distance control - according to the manual it's for 405 only
Oh yeah, so it is
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