Marconi 1400 birthday present
 

I know this is not normal but I’m lucky my partner likes old stuff so she bought me this tv a while back.
On first power up a few caps disided to try and explode . So they were the first to be changed.
First problem picture size only about 3/4 . I could pull it out so much with the hight and width but only so far. On tests H.T. 3 was down about 50 volts below what it should be.
It’s R135 on the main dropper where I tested and according to the diagram should be 1.5k. Yet mine is clearly marked 1.7 K and tests 1.7K
Also I have a new old stock dropper and that’s the same 1.7K
I checked on another old set I have and that’s 1.5K as it should be. So why is it different was their a modification on later sets. What’s going on here.
Also I got poor frame and line hold , poor contrast and focus and 625 dosnt work
Any help appreciate Andy

Re: Marconi 1400 birthday present
 

Please confirm that the chassis is a Thorn 1400.

If it is, I think the dropper value may have been changed during production.

Re: Marconi 1400 birthday present
 

Hi There was two types of dropper I am fairly sure the 1.7K was on the later dropper. I don't know why it was changed.
There was a modification on the frame stage supply I think a .1mfd was changed to a 10uf electrolytic this was to keep the frame going for a few seconds in the event of a line fault to stop a spot forming on the screen and burning the phosphor.
I have exactly the same set in my collection. I like the Marconi versions of Thorn sets they are usually nice looking .
The poor focus may be the Mazda tube it may improve with use. There is a resistor that goes high causing weak sync just like the 1500. 47 or 470 k I think... it is all a long time ago now... Check the system switch solenoid is moving the switch fully for the no 625 fault .
Nice set!
Rich

Re: Marconi 1400 birthday present
 

Certainly looks like a 1400, my regular set for years. Apart from intercarrier buzz on 625, excellent. They may have altered the mains dropper, I'll look at my notes.

Re: Marconi 1400 birthday present
 

Your set looks to be a model 4623.

Here is the final supplement to the 1400 service manual, listing modifications in production.

You will see that R135 was changed from 1.5kOhms to 1.7kOhms, to eliminate frame cramping.

There are several mods listed that are well worth carrying out.

You will almost certainly find that many of the paper capacitors (Hunts, Dubilier and TCC/Plessey-TCC) and those black cylindrical "Callins" (and any TCC in colourful plastic cases with radial leadouts) electrolytics are faulty, in addition to numerous printed circuit type carbon composition resistors.

I would certainly check the values of the high value resistors in the boost HT stabilisation circuit: R143 (fit a 680k), R142 (fit a 2,2Meg), R141 and R140.
I'd also replace R132 (3.9Meg) - the boost HT feed to the CRTs 1st anode and check the values of R130 and R131 (preset pot) in the focus circuit.
Check the values of R133 (220k) and R103 (330k) in the Boost HT feed to the frame timebase.

Sorting out these ought to allow a full sized picture/raster.

I'd get VHF/405 working first, before worrying about UHF/625.

Re: Marconi 1400 birthday present
 

Thank you all for the information. I will take that onboard.
Thanks as well dazzelvision for taking the time to send that information.
I have printed it our and also your items to check so that should keep me busy for now.
I have a similar set but the main difference is the speaker grill is black and the top bit is white I assumed this was the earliest version but it sounds like it’s the other way round. Andy

Re: Marconi 1400 birthday present
 

This style was the last Marconi model using the 1400 chassis, while this set is 19" the later sets were 20" but were the same design and were made concurrent with the 1500 for areas that hadn't yet got full UHF coverage. I have a Marconi sales Brochure which shows the 20" version of this set along with the 1500 and 8500 and 3500 colour sets.
Maybe your other set is a later model with the 20" screen?

Re: Marconi 1400 birthday present
 

I’d certainly replace the boost HT reservoir capacitor, C105 (0.22uF - use a metallised Polypropylene film type) and both of the S-correction capacitors C107 (0.1uF on 625) and C108 (0.3uF on 405).

By the way, the brand is Marconiphone, rather than Marconi.

Re: Marconi 1400 birthday present
 

Just a update
Going along with Mr Dazzlevisions recommendation so far I have done almost all the checks and replacement of parts. Some resistors on the check list were 50% higher.
So far I have normal hight now but the width has improved but not quite there.The focus is hardly any better.
The other thing I got to do is replace .R142 . Is this valve critical.I have about 5 new old stock 2.2M but on testing they come out at about 1.75 M ,they all read the same when they have 2.2M stamped into them.
Everyone’s help is very much appreciated.
That’s a good point and you are 100% correct it is a Marconiphone.
It’s interesting as in the 70s we had a couple Marconiphone TVs
At the time I can remember even the dealer and service guys always called them Marconi .
Andy

Re: Marconi 1400 birthday present
 

Just a update
Going along with Mr Dazzlevisions recommendation so far I have done almost all the checks and replacement of parts. Some resistors on the check list were 50% higher.
So far I have normal hight now but the width has improved but not quite there.The focus is hardly any better.
The other thing I got to do is replace .R142 . Is this valve critical.I have about 5 new old stock 2.2M but on testing they come out at about 1.75 M ,they all read the same when they have 2.2M stamped into them.
Everyone’s help is very much appreciated.
That’s a good point and you are 100% correct it is a Marconiphone.
It’s interesting as in the 70s we had a couple Marconiphone TVs
At the time I can remember even the dealer and service guys always called them Marconi .
Andy

Re: Marconi 1400 birthday present
 

Good to hear you are making progress. The mod to the width control (also referred to as the "set Boost HT" control) and the series resistor, is to prevent the original 1MOhm pot from failing. As you are nearly up to 2Meg with the replacement pots you have, that will be a considerable improvement to what is currently fitted (assuming it is a 1Meg pot).

If you still have reduced width and haven't yet replaced the Boost HT reservoir and 405 lines S-correction capacitors - which are almost certainly faulty - they could well be contributing to the insufficient width issue. Lack of width will also affect the Boost HT voltage and the frame output stage.

Another thing to check is whether the line linearity correction sleeve is pushed too far into the scan coils. If it is, this will reduce width and cause overheating in the line output stage.
If the original (red or black) plastic moulding is still attached to the paper sleeve and there is a gap between this and the scan coil's plastic moulding of around 5mm, then leave it alone. At this stage in its life, the line linearity sleeve usually parts company from the plastic part if an attempt to remove/adjust it is made and the sleeve may be stuck to the CRT's neck. You have to slacken the clamp securing the deflection coils before attempting to move the line linearity sleeve.

Re: Marconi 1400 birthday present
 

I think your set is a 19" model 4623, as the 20" successor model 4649 had a black loudspeaker grille and a black channel indicator ring on the VHF channel sector knob. In addition, the 19” CRT has “curvier” sides than its “supersquare” successor.

If you look at the copper side of the PCB, there should be either a white plastic (or paper in later years - cheaper!) label fixed to it, showing the model and serial numbers.

Re: Marconi 1400 birthday present
 

Brochure extract for model 4623.

Re: Marconi 1400 birthday present
 

It's amazing how the 19" looks far more dated (in a good way) when compared with the almost identical 20" version. Ditto sets made by Bush, ITT and Decca. Although launched in (I think) 1968, the square screen almost shouts 'Seventies'!

Re: Marconi 1400 birthday present
 

Here's the brochure page for the 20" successor model 4649. The difference between 19" and 20" is pretty clear when you compare the two photos. The 4649 brochure was date August 1969.

Re: Marconi 1400 birthday present
 

Bit of a late reply. The reason mostly is I don’t like just changing parts that you recommend without studying them on the diagram and try and work out what they do. Part of my hopefully learning strategy.
So far the width is almost correct. acceptable to me but another 1/2 inch would be better.
The clamp on the tube coils dosnt want to move I’m worried if I force it it will break being nylon.
I have been reading some articles by John Law from PT online . He said for poor contrast change valve PCF808 . That has worked wonders.
The focus has little affect as before but I think it’s got better.
I sorted the horizontal problem sorted it’s self out . For the vertical hold I changed a resistor again John Law . It helped but to sort it completely I changed PCL805 and 30FL1. It only sorted it changing both valves.

The tuner for 625 is at fault. I tried one from a scrap set . That sort of works but like the 1500 tuner the plastic bits to the tuner knobs go so it won’t hold in.
I will investigate the faulty tuner later.
Thanks for the pictures of the other sets .i do have that one as well . Although I might put that stand on it as shown in the picture as I have one .
There is no label on my circuit board as you said there might be.
Thanks as always Andy

Re: Marconi 1400 birthday present
 

If the label isn’t there, it’s probably came unstuck and was lost some time in the past (or might even be lurking at the bottom of the cabinet somewhere).

I have found that the contact studs of the UHF “biscuit” in the VHF tuner (the long one) sometimes don’t actually make contact with the springy fixed contacts or may just need cleaning and lubricating. This will cause no (or weak) UHF signals, even with a strong aerial signal.

Re: Marconi 1400 birthday present
 

The tuner rotor earth springs are a problem on the earlier tuner also [the one without the bar] as they are on the GEC models. probably worth investigating the grease problem before you start changing transistors. John.

Re: Marconi 1400 birthday present
 

Thanks john .
I havnt done much over the last couple days . With the tuner .what I did find so far is it does look like it’s been messed with . I will investigate further some of the tuning veins are touching and the whole lot seems lose. As soon as I took it out of the cabinet the fixing screws were lose and a buckle clip holding the cables was undone. So I thought this has been out before. Andy

Re: Marconi 1400 birthday present
 

Oh dear, this all sounds rather ominous!

There is an "play" adjustment at one end of the rotor shaft, to set the rotor vanes equidistant between the fixed vanes. That has probably been twiddled with.

I'd try to set that correctly first and then see whether the moving vanes are still touching the fixed vanes. If they no longer are, I would leave well alone.