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A Marconi 702 Mirror-lid TV restoration: Part 2
Topic Rating: +3 Topic Rating: +3 (3 votes) 
April 9, 2017
11:50 am
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Jac Janssen
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Those waveforms certainly look fine Brian!

Glad you sorted it out.
The heater current of the TRF unit is about 6.5 A and of the synch unit c. 8.5 A.
The sound unit takes c. 4.5A.

I'm still using an analog oscilloscope. Probably too old to change over to digital. I tried it once, but at the time it was not meant for me :=))
The more recent models might possibly come closer to my abilities...

Anyway, you're making very good progress!

Best wishes,
Jac

April 9, 2017
8:48 pm
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Brian Cuff
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6H07 appears on both the tie-on label and is printed (á la John Bull Printing Outfit). Actually - both on that label and the glued-on Emiscope label. Thinking "outside the box", the "H" in the number could refer to the same thing as the "H" in the EMI TV Set sequence of serial numbers, possibly meaning Hayes, the place where inspector No. 07 is based and who is inspector No. 7. This doesn't explain what the H/2 or Y/2 fractional numbers mean duno_gif.

No progress on the 702 today as we had visitors for lunch - Sarah did us proud with a Middle Eastern flavour of dishes including Iranian (my best mate is an Iranian) and Lebanese. Rhubarb and custard, fresh fruit salad and icecream for desert - lovely grub. Needless to say, I don't want any grub tonight.

The following users say thank you to Brian Cuff for this useful post:

peterscott

Cheers

Brian

April 9, 2017
8:53 pm
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PYE625
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Brian Cuff said

 Rhubarb and custard, fresh fruit salad and icecream for desert 

Yum yum....now you have my attention laugh

Andrew, a Fenland fanatic.                                                                                     

                         

April 10, 2017
8:14 am
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Brian Cuff
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Not to mention, Andrew, that there was lashings of root ginger sliced up in the Rhubarb - even better!

Cheers

Brian

April 11, 2017
7:31 am
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Brian Cuff
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Jac Janssen said  The heater current of the TRF unit is about 6.5 A and of the synch unit c. 8.5 A.
The sound unit takes c. 4.5A.

I've just checked on my order for the heater transformer, Jac, and am happy to say that I'm OK as far as ratings are concerned. The 4VAC winding is rated at 8A - it's the 6.3VAC which is rated at 6A. The unit won't be used for any length of time, only during testing, so 8A is fine - only one chassis at a time.

Cheers

Brian

April 12, 2017
7:38 pm
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Brian Cuff
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Well, I got some good sleep last night so got up feeling pretty good. - and it, for once, lasted a while so I was able to get on with the testing of the mostly completed 702.

Into the "Museum" with my trusty hammer tool kit ready to start the testing in earnest. All the chassis had been installed, just not connected, so I connected all the forked tags under their respective screws - I am going to replace all the screws because some of them are getting a bit tatty round the edges and new screws would certainly improve things a lot. After tightening all the tag screws, the system was connected up as discussed with the safety earth stopping at the isolation transformer and only L and N taken on to the Variac and hence to the 702. A DMM was connected again to the mains input tags and the Variac turned to half-way up. The meter read 122V so I left it there for about 2 minutes and then wound it up to 240V. Tone bust through extremely loudly but fortunately, the volume control was reachable and was very quickly turned down. The tuning trimmer, there to adjust out the inevitable tuning drift (1.3MHz IF so quite low) needed some adjustment but the proper position, after about 10 minutes, is well in range. So Sound we have.

I had taken the scan coils off the CRT to do some bench testing and they made, as described, a huge difference to the waveforms so I used an old rubber bungy hooky thing to suspend the coils, when connected to the sync chassis in mid air to take the strain from the tags.

Now to look at the vision: there is a reduced bandwidth video feed from the TRF for the two sync (filters as they are called) separators so I connected the other probe to this connection and was surprised to see a quite good video waveform. So Vision we have.

Now it was possible for me to put the line scan pulse and vision waveform on the same oscilloscope sweep. The first thing that I noticed was that the line pulses were at half-line frequency, something that I had missed during the bench testing. However, they were locked solidly to the video which said that the sync separator was working so I looked for the line hold control and tweaked it to increase the line scan frequency to the correct value but having done that, they would not lock so there is a fault in the sync chassis which I will chase tomorrow as will I chase the inevitable faults on the frame scan circuits tomorrow.

As to the CRT, it is still sitting upside down in its mask ready to be installed in the metal cage. The reason for leaving this till last, apart from minimising the danger of the EHT, is that the CRT housing makes it very difficult to get at things so it is far better left off until the last moment. The CRT mounting consists of a metal fram which bolts onto the cabinet with 4 bolts and a metal cage which almost totally surrounds the CRT, cradling it in foam rubber which I have now replaced.

So all in all, judging by the last few weeks, it has been a very successful day and I look forward to getting first light on the CRT screen tomorrow. Sarah say that I must have a knowledgeable friend with me tomorrow so my mate John Watkinson is going to join me and I suppose we will have to go to the pub for lunch - bubble and squeak perhaps!.

A few pictures:

702-Chassis-in-Place.JPGImage Enlarger

All the chassis in place ready for connecting up.

702-All-Tags-Connected-1.JPGImage Enlarger

All connected up - now for the real testing!

702-PSU-sShowing-TRF-Snd-and-Focus-Tags.JPGImage Enlarger

240V now applied via the Variac to the 702

702-First-Video-to-Sync-Chassis.JPGImage Enlarger

And Low and Behold, a video waveform!

702-Even-Wider-Angle-With-Coils.JPGImage Enlarger

The coils are slung mid-air here to keep the free of metal

702-Long-Shot-Showing-Work-Area.JPGImage Enlarger

This is the work area - plenty of room but I find it difficult to bend down all the time!

Tomorrow will be an interesting day so please call again tomorrow - just in case there's something interesting to see:                                                                   electro_gifelectro_gif

Cheers

Brian

April 12, 2017
9:19 pm
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peterscott
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Brian Cuff said 

 please call again tomorrow
 

Peter said

 You bet!

 Is that Test Card C on the scope? laugh

April 13, 2017
7:34 pm
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Brian Cuff
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 Well! - An eventful day today but not in the way I had hoped.

I installed the CRT support assembly with no problems. The pictures show the progress:

702-First-Part-of-CRT-Support-installed-1.jpgImage Enlarger

The first part in - access starting to get limited.

702-with-Second-Part-of-CRT-Support-Installed-1.jpgImage Enlarger

The second part is now in and covers even more stuff!

702-with-CRT-Installed-coils-upside-Down-and-Connectors-Reversed-2.jpgImage Enlarger

The 5/5 CRT has now been installed - The story continues:

With the installation of the CRT, I discovered a serious mistake in the restoration of the PSU. The Emiscope 6/6 CRT uses a special base with two separate free connectors mating with it, one with three sockets and one with four. Guess who got them the wrong way round bash_gif. This means that the PSU will have to come out and be rewired in that area, complete with the lacing of the cable forms. Not only did that show up but I also fitted the scan coils upside down but this is not so serious as I can easily change them over without recourse to a re-wire.

I can only assume that this all happened when I was not being careful enough with the original pictures. This is a picture which I took which clearly shows which connector is on which side and proves that I had the correct information but still got it wrong.

702-PSU-Top-Large.jpgImage Enlarger

In this picture, taken before restoration began, it is obvious which connector goes where doh_gif

702-Wrong-3-Pin-CRT-Connector-3.jpgImage Enlarger

Here is the  four pin Socket as installed on the wrong side of the CRT.

702-Wrong-4-Pin-CRT-Connector-2.jpgImage Enlarger

And similarly, the three pin socket in the wrong place.

All in all, a very disappointing afternoon. I have already called my son, James, to come and help me remove the PSU for the re-wire so no Spitzen und Sparken until that's done - I should finish the changes tomorrow and get ready for the final test procedures resulting in, I hope, first light!

Presently I am sitting in the dunces corner dunce_gifdunce_gif and feeling very sorry for myself, and for Peter, of course, who will have to wait a bit longer for electro_gif.  grin_gif

Cheers

Brian

April 13, 2017
9:09 pm
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PYE625
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Brian Cuff said
Presently I am sitting in the dunces corner dunce_gifdunce_gif and feeling very sorry for myself, and for Peter, of course, who will have to wait a bit longer for electro_gif.  grin_gif  

 Come out of that corner right now !!!  

A simple mistake ANYONE could make young man wink

Andrew, a Fenland fanatic.                                                                                     

                         

April 13, 2017
9:23 pm
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Cathovisor
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Oops.

Still, it's not like you've carefully wired and laced a JF2/15 only to discover the tielines read 24 -> 1, is it?!

All too easily done and let s/he who is without sin cast the first stone an' all that, but at least it can be rectified. You'll just remember not to do it the next time!

To know yet to think that one does not know is best; not to know yet to think that one knows will lead to difficulty. Lao Tzu
April 13, 2017
9:52 pm
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Hi Brian,

My dunces corner is well used so has an extra comfy chair in it .... I don't like having a numb derriere ! embarassed

As for you Brian, a wooden bench is all you need....after all you hardly ever get to use it ! wink

Marc.

PS. You have a PM.

April 13, 2017
11:11 pm
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No problem, I'll still be here. I've never seen one with the CRT cables laced.

Peterread04

April 13, 2017
11:59 pm
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Brian Cuff
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You're right Peter, nor have I. Probably, it's better not to lace them as it makes them stiffer and could put the CRT under more stress. I will give it a miss this time and see how much better it is. Nevertheless I will still re-build the PSU in the area of the CRT.

Cheers

Brian

April 14, 2017
8:19 pm
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Katie_Bush
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Oh dear, and what was I saying in that other thread? - "Wire Lace & Grommet". embarassed

I have a huge heap of stones, but I'm not casting a single one, and God knows how many foul ups I must have made over the years - and still do!

If at first you don't succeed, try a new fuse!

April 24, 2017
1:33 pm
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Brian Cuff
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Hi Guys

I’m sorry that this is taking so long but I do believe that I am nearly there!

All the chassis have been restored to the best condition that I can get them to and apart from learning to touch type to make these little breaks in the actual restoration shorter, I can’t get any better than that. The chassis, where possible, have been stripped of their components (the TRF vision receiver is the exception due to the RF wiring and layout involved) and cleaned and painted and re-assembled using new hardware where necessary – fortunately, BA screws etc. are still relatively easy to find on the ‘net, and strangely enough, silk or cotton covered interconnect wire is becoming more easy to find. I assume that this is as more and more people are getting fed up with PVC, they are harping back to the Art Deco era when things looked just that little bit “bothered about”.

I have had a series of bad times with my cancer during the last period and that hasn’t helped things too much but I seem, at the present, to be in a relatively quiet period, concentrating on the respite part of my caring rather than the more – “I can’t do anything because I feel so shitty” period and believe you me, that does happen!

So where does that get us?

Chassis-removed-for-CRT-extraction.jpgImage Enlarger

These are the chassis that have to be removed when extracting the CRT

The last post had the CRT back in the cabinet with pictures of the chassis all nice and clean and connected up.

Chassis removed for CRT Extraction – old 0003Chassis-removed-for-CRT-extraction-+JW.jpgImage Enlarger

I think that this is the place to pick up the story so are you sitting comfortably? Then I’ll begin. First of all, the drink in the mug on the table is coffee from an espresso machine and John’s drink is also coffee from the same machine but with foamed milk added (Wimp!).

First off, get the CRT in its place. As previously stated, the pile of bits on the table are those which need to be removed/replaced in order to do this – no 5 minute job here then. However, there is a 50,000ltr pond next to my “Museum” which gives us (and maybe the TVs) a lot of pleasure. For tenants, we have two extremely large ghost carp and lots of much smaller goldfish and the like. No Coi carp as they are much too expensive and it is really nice to relax having a cup of coffee/glass of beer and watching the fish just meandering around as if they have nothing to do – well, they don’t have, do they!

Fish-Large.jpgImage Enlarger

There is a large Prunus tree next to the pond - it was beautiful in its pink overcoat of blossom - look at the blossom now!!

After the chassis have been installed, the CRT mounting assembly needs to be fitted. This uses a cradle in which to mount a steel enclosure which houses the CRT and suspends it on two pivots. This allows it to swing backwards and forwards to mate properly with the rubber mask. This isn’t working quite as it should yet and will need later attention.

Ready-for-the-CRT-Housing.jpgImage Enlarger

 

That's enough for this post and I hope that I will have some really good news in the next one. I have now again set up the testing system with the Variac and Xfmr and a helper which Sarah insists on due to the very dangerous EHT of 6.75kV around. Seeing as this is backed up by 2 off 0.1mfd capacitors, it can pack quite a heavy punh - not for me! Another thing that had to be done was to modify the emergency interlock to remove the EHT when the rear cover is removed. This was the simple expedient of shorting out the supply and waiting for a heat-coil in the primary of the mains transformer to open circuit and switch off the supply - not a good system (which, I believe, has already damaged the transformer in my 703 Mastergram). More to follow (sorryinnocent)..................

Cheers

Brian

April 24, 2017
2:04 pm
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Hi Brian,

No apologies required, feet up and don't over do it, all in good time. 

Frank

Frank

April 24, 2017
2:09 pm
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So far the set looks to be coming along swimmingly....just like your fish !

Take things at your own pace Brian, no rush.

Marc.

April 24, 2017
2:58 pm
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Am sorry to hear about the health downs but great that you are getting a few up periods too.

+1 for the postings of Frank and Marc.

Peter

April 25, 2017
7:38 pm
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Here we are again.

As happy as can be.

All good friends and

Jolly good company.

The next stage of the test procedure is to make sure that the safety setup is correct and that there is no way that this can be bypassed – I know that I’m beginning to sound like the people whom I called “Wimps” but I now understand what is being talked about – LIFE and the meaning of life.

I am "dumping" the 3kW Isolation system (the red one which I can hardly lift) as I now have a 500W unit.  With this, together with a 2A isolation transformer which I bought years ago at the McMichael rally in Reading, I can now start looking for the Holy Grail :-   First Light!

500W-Iso-Xfmr-Custom.jpgImage Enlarger

500W-Variac-Large.jpgImage Enlarger

A little more compact than the 3kW components!

However, even after my lecture on safety, impatience is calling me and I will start the hunt with a temporary hook-up and do the more permanent hook-up, screwing the kit to a board later, so it's off to the Museum and on with the search (with John, of course).

After some fettling and general tidying up it was time to get the thing up and running, the 500W setup was employed to bring up the mains voltage until the HT rectifiers were both glowing a nice red and the 1000kHz sound woke up from the dead.

500W-Isolation-Setup.jpgImage Enlarger

At about 210V at the mains input, the first light appeared, a neat but very small raster followed by a larger and a little more unruly form took shape. With a little more tweaking, a test card C became very obvious, not as good as it could be, of course, but pretty good in the scheme of things. I will add the pictures to this post and close it as I would like to have some rest as I feel as though I am overdoing things somewhat. Whadyafink of me tele??

P4230040.JPGImage Enlarger

P4230042.JPGImage Enlarger
P4230043.JPGImage Enlarger
702-with-first-light-25-04-2017.jpgImage Enlarger

Cheers

Brian

April 25, 2017
8:02 pm
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I think you have achieved spectacular results and thats the first switch on.

Definitely feet up and a rest, not at lot more to say, absolutely fantastic results.

Frank

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