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Old 28th Nov 2022, 7:41 am   #21
dazzlevision
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Default Re: Rather grim Thorn 1400 - Marconiphone 4649

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Originally Posted by Andy - G8MNM View Post
Having read this thread with interest , I dragged out my Ferguson 3645 14" transportable from its 7-8 year resting place, still wrapped up in bubble wrap from when we moved to France 7 years ago!
Andy
I have a Ferguson 3645 and it uses a 16" CRT (Mazda CME1602 - a Rimband type).
IIRC, as a consequence the LOP stage is different to the standard 1400 chassis version.
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Old 4th Dec 2022, 12:28 pm   #22
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Default Re: Rather grim Thorn 1400 - Marconiphone 4649

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So things are getting better but the picture is still very 'twitchy'. The frame scan keeps contracting in the middle and if you give the frame O/P transformer a whack, it either corrects it or the scan collapses to a line momentarily. There are no obvious dry joints on the transformer or anywhere else, but I resoldered it anyway without much hope of any improvement. Sure enough there wasn't any!

Nick
I have no idea why, but I resoldered three of the four connections on the frame output transformer - I completely missed the fourth one! Sure enough, when I examined it with a lens, there was a very fine crack around the pin and I could see it move when I flexed the transformer. Resoldering it has completely cured the twitchy frame scan.

I removed each valve in turn and gave the pins & the socket a light application of 'de-oxit' cleaner. The sockets are, or at least were, good quality ceramic ones, but were very dirty as were the valve pins. I worked each valve in and out of its socket half a dozen times to clean the pins.

The system switch runs horizontally across the board so is ideally placed to accumulate dirt. This also received the 'de-oxit' treatment as it was intermittent and absolutely filthy.

At some point in the past, the set has been 'de- 405'd'! The system switch has been de- activated and the 405 controls for line hold & contrast have been removed. Luckily, everything is still present, it's only the wire to the microswitch on the back of the 405 tuner that's been cut and the knobs for the controls removed, so easy to reinstate it all. I just need the knobs!

The end result of all this is that the picture has become much more stable - tapping the board with a screwdriver handle now does nothing more than cause horizontal lines, which is due to a microphonic 6F28 video output valve.

The other rather sad thing I've discovered is that I can no longer tell if the set is in 405 or 625 - audibly, that is. I could no longer hear 625 line whistle 15 years ago, but I can't hear 405 now! I guess age is taking its toll!

Cheers
Nick
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Old 24th Dec 2022, 11:53 am   #23
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Default Re: Rather grim Thorn 1400 - Marconiphone 4649

Nick,

I still have my Ferguson 3645 16" transportable on the bench.

I mistakenly referred to it as a 14".

I have now managed to find a replacement width control and fitted it along with the 680K resistor. The control had reduced quite a bit in resistance!

I also replaced the focus control as that was a bit dodgy too!

I decided to check more of the resistors located in various important positions - anode and cathode resistors in particular. Also the larger 1/2 watt feed HT feed resistors.

Quite a few out of spec. R38 (Video Amp), should be 39K - measured over 60K!

I found R74 to be O/C - it is only in use on 625 lines. It reduces the voltage on G2 of the sound IF amp and FM limiter V7.

I have to order some 2 watt resistors - I think they are two watt? For replacing some of the HT feed resistors and those around the Video Amp.

I suggest you do the same.

I do have the '1400 Series Dual Standard Chassis Manual Supplement', which lists all the required component changes required. Also includes two in the UHF tuner - to prevent squegging.

It also recommends changing the Line output valve to a PL504.

PM me and I will send you a copy. There are quite a few changes to be made.

The focus pot doesn't seem to do much, the boost HT voltage isn't shown on the circuit diagram. I have around 420V on the focus anode - measured with Fluke digital meter.

Anyone know what it should be?

Good luck with the restoration. I will post a pic of mine working once I have replaced all the duff resistors.

Andy
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Old 24th Dec 2022, 12:47 pm   #24
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Default Re: Rather grim Thorn 1400 - Marconiphone 4649

Hi Andy,

Good to hear you are making progress with your 1400! Hopefully, I can get some more done to mine over the Christmas period.

It's strange that the presets go low in value, often by a huge amount. I've found this to be the case in most sets I've worked on regardless of manufacture. I imagine that must have been the failure mode with the original 1 meg width pot - it went so low in value that it just incinerated!

I've never found that focus controls do very much on 'narrow neck' CRT's. Focus seems to be more a function of emission - a high emission tube will focus well across the whole screen regardless of the volts on the focus electrode, whereas a poorer tube will have poorer focus especially at the edges, even though it can produce a perfectly bright picture.

My resistors of choice are the RS 1W or 2W range. These are similar in style to the old Erie range found in almost all hand wired sets from the 50's & 60's. The 2W ones are the same physical size as the 1W. but unfortunately have a pink body! They are a little big to replace the Thorn 'PCB' style resistors in the 1400, but can be mounted vertically and look OK.

I guess the boost voltage will be a direct function of picture width, which is maybe why they don't specify a voltage for it. It is probably quite different for each screen size.

I would be very interested to see the 'modifications' supplement as it would be nice to know what values should be fitted. I'm sure it would be useful to other people as well. You can attach it to a post as a PDF but I'll send you a PM anyway. The other thing that would be really useful is the alignment instructions. Mine is way off and alignment is not my strong point so the more detailed instructions I've got the better!!

It will be interesting to see some pictures of your set.

All the best
Nick
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Old 24th Dec 2022, 1:30 pm   #25
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Default Re: Rather grim Thorn 1400 - Marconiphone 4649

Nick,

I have just noticed that R43 (which should be changed to 1M to improve AGC action) is just a link!

Perhaps you could check on yours and see what you have?

I will scan the supplement and post it here.

I do have the alignment instructions - just for 405 VHF though.

I couldn't find my Ferguson listed in the trader service sheets. Yours didn't appear either!

Andy
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Last edited by Andy - G8MNM; 24th Dec 2022 at 1:53 pm. Reason: update
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Old 24th Dec 2022, 2:24 pm   #26
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Default Re: Rather grim Thorn 1400 - Marconiphone 4649

Hi Nick,

Uploaded 1400 series data.

Regards

Andy
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Old 24th Dec 2022, 2:54 pm   #27
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Default Re: Rather grim Thorn 1400 - Marconiphone 4649

Hello.
You shouldn't need to do any alignment on that chassis as it remained very stable. Unless it has been twiddled with.
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Old 24th Dec 2022, 3:04 pm   #28
Andy - G8MNM
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Default Re: Rather grim Thorn 1400 - Marconiphone 4649

Hi Nick and others!

Here are two pics of the Ferguson.

Being a Mazda tube it is amazing that it it gets a picture at all!

The set has obviously had a fair bit of use in the past - the back cover over the dropper being burned and needing repair.

As you say the focus depends on the emission of the tube so the focus isn't great. Much better pic on my TV22 - really good focus and contrast.

Regards

Andy
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