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Thorn 1400
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August 7, 2017
9:50 pm
mfd70
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Hi all, another retro-retrieval from the lockup, a HMV model with Thorn 1400 chassis. This set was given to me in the early eighties and to my surprise it worked first time. I used it to view the end of 405 line transmissions in ’84, and as a monitor for a spectrum computer but retired it soon after as the UHF gain was low off-air. 

Now almost thirty years on and two moves, I got it out of the lockup, applied power, stood back and it still works ! I guess this set has had an easy life for longevity.

One image is on 625 displaying bars.

The other on 405, I don’t have any signal source for this but suppose it would be OK.

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August 7, 2017
10:09 pm
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PYE625
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mfd70 said

Now almost thirty years on and two moves, I got it out of the lockup, applied power, stood back and it still works !   

It’s good to use a set every now and then   grin_gif

Andrew.                                                                                   

                         

August 8, 2017
9:28 am
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Focusdiode
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These sets certainly are tough as old boots. Performance might not be as good as other models from the era but reliability is second to none, not forgetting the brilliantly accessible swing out panel.

I was given a 23″ Ferguson 3655 in 1982 which was stored in a damp basement for several years. Wasn’t recommended but I plugged it in and switched on. It sort of worked with severe height variations and flashing. On investigation the top caps of the PL504 and PY801 had rusted to the point they broke off when attempting to remove them!

New valves were ordered while the set was allowed to dry out. This resulted in a good working set although the frame took a long time to open out with poor frame lock. Replacing the PCL805 cured that problem.

Our very own Till was asked to repair the bottom of this 16″ Ferguson version which was badly damaged by woodworm. None of the electrics had been touched and looked very original inside. We were surprised to find the set worked when plugged in although as expected attention is needed to sort out the lack of width and ragged vertices (probably the doubler).

Would be nice to get my hands on a 1400 again l. They’re an absolute joy to work on.

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Brian

August 8, 2017
12:25 pm
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malcscott
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Hi, i have never been a fan of the 1400 chassis. One of the worst sets when used on 625 UHF in my opinion. Never could eliminate the caption buzz, even with all of the Brc mods. The last ones, schedule E were not too bad, Malc.

August 8, 2017
1:58 pm
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acj1980
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 Hi mfd70.

What a nice little beautifull Television, its very amazing it still works after 30 years in lockup, we also have some brands from the past that never give up, for years ago i tested a Linnet&Lauritsen TV from 1960, it have been instock sincethe eighties and never being reparied, it still works, allmost every caps inside this TV is the yellow(somethimes they are dark green) philips.

YourThorn 1400 seems to bee near perfect, but i can se som deflection issues on the top, is the set 2-system, and finally, how do you make the 405 signal? 

Alex 😉

August 8, 2017
3:05 pm
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Focusdiode
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Hi Alex,

The set is indeed dual standard 405 VHF and 625 UHF. The basic design was retained for the single standard 625 UHF only 1500 hybrid series with the sensible move of moving the line output stage to the hinged end of the panel making it less hazardous for servicing.

As Malc says the UHF 625 sound buzzing is a problem. It isn’t always possible to eliminate the problem entirely. There’s also pulling on whites with modifications to help alleviate the problem.Certainly a disadvantage when compared to the earlier 900-950 chassis which give a superb 625 line performance.

As for pulling on whites I remember watching episodes of this onba 1400. The alternating black to white caused the picture to pull like mad.

On a 950 (picture shows a 950mkII) this is completely stable. A good test this title sequence!

To view 405 a standards converter such as the famed Aurora will be needed.

Cheers

 

Brian

August 8, 2017
3:39 pm
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Chris
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acj1980 said
how do you make the 405 signal? 

Hi Alex,

the whole area of standards conversion in the U.K. is a fascinating subject in its own right. A very brief history can be found here. From what once filled an entire room, can now be held in the palm of your hand with the Aurora standards converter.

One of our members Till Eulenspiegel (David Boynes), has the honour of being the very first amateur to build such a device, no mean feat back in the late 1980’s.

Another member Cathovisor, was part of the duo who brought us “The dinosaur” convertor

August 8, 2017
5:20 pm
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acj1980
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Thanks to booth of you guys for answering, it is indeed very interesting 🙂 

August 8, 2017
11:11 pm
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Jayceebee
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Pulling on whites on 625 was indeed a common issue on some 1400s, Thorn had a modification, the details of which I no longer remember involved changing a number of component values. An unofficial mod, but in my opinion just as effective involved changing just two. These were raising the value of R36 from 3K to 8.2k and C40 from 0.1 to 0.01uF.

August 9, 2017
11:08 pm
mfd70
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There is a bit of foldover at the top of frame, I think I replaced a PCF805 (?) for this fault at some time.

On the subject of 405, I can’t generate 405 at the moment, I think the simplest would be to try to generate baseband 405 and inject it direct.

I believe there was a “schools” version of the 1400 (there was certainly a 1500 schools) with video and audio inputs, i’d like to modify this set for baseband input (with PL259 video and PO balanced audio connectors), there’s room inside for an isolation transformer, does anyone have the circuit for the “schools” mod ?

August 10, 2017
7:07 am
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Focusdiode
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The Schools version was the 1415 chassis?

As for the top foldover this could simply be due to mis-adjustment of the Top Linearity control or change in value of a feed resistor to it.

If you can display a test card it’s a simple matter to adjust. I doubt very much a new PCL85/805 will cure the problem.

Cheers

 

Brian

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