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A Marconi 702 Mirror-lid TV restoration: Part 2
Topic Rating: +1 Topic Rating: +1 (1 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                                                                                          

                         

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                                                                                          

                         

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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marc
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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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peterscott
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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!

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