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Old 29th Sep 2020, 12:07 pm   #41
Heatercathodeshort
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Default Re: My first foray into Old model TV repairs.

Pics of the ion trap magnet. Looking from the back the arrow should be on the left pointing towards the screen. Note it is a critical adjustment. Only a small twist will loose the raster.

If you put it on back to front it will work just as well but the magnet will be at the top.

I have also included a picture of the regular 1T9 ion trap with conventional securing strap. The original is completely over the top with a spring like a man trap, hence your scratched neck! I would suggest removing the spring and giving it a tug to relieve some of the tension. It should be just a snug fit.

The LOPTs on these are quite reliable but I would certainly suggest passing about 30m/a through the overwind EY51 anode to PL81 anode for a few days. Check that the overwind is just warm, if not increase the voltage. If your overwind is the high resistance spec you may need around 100-200v to create any warmth.

The MW36-24/44 is a good tube. It can suffer from internal shorts but this was not common.

Just for reference the CRT voltages measured with a DVM with a normal picture displayed are: Cathode- 148v Grid- 47v First anode- 534 and the EHT measured with an analogue meter- 16kv. The mains input here is high at- 245v.

Note when it comes time to adjust the Ion trap, it must be adjusted for MAXIMUM brightness. Corner cutting, picture position and focus are provided with their own adjustments.

Checking my Ferguson files I discovered that I have two copies of the advance service information for the 991T. You are welcome to it and together with your Trader sheets, may come in useful. John.
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Old 29th Sep 2020, 12:13 pm   #42
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Default Re: My first foray into Old model TV repairs.

Pictures of ion trap.J.
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Old 29th Sep 2020, 12:51 pm   #43
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Default Re: My first foray into Old model TV repairs.

OK thank you John

I must admit to be very surprised at what current you and others are saying to pass through the coil, I would have thought that amount of current would be a lot higher then normal operational limits and had a risk of burning out the wire,but I will do so. I can use the buck converter to give me the required voltages.


I have spent a bit of time getting the AVO 8 to work again and just measured the grid, pin 2 of the PL81 and had -34 Volts with the Avo and -37 Volts with the DVM. So I is that being driven enough or not enough?

I also measured the Line frequency again using pin2 of PL81 and got 6.5 KHz when warm, which I think could be a little to low, but will wait until I remove a smoking capacitor I have just seen before measuring again.

Thanks for the pics.

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Old 29th Sep 2020, 1:13 pm   #44
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The cap that is smoking is the three section one 8uF 32uF and 32uF, so that could well be responsible for the low HT, think it is starting to vent and give off smoke, That is nothing to do with me getting picture, that may be something to do with possibly the ion magnet moved or things drying out with use or??

Adrian
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Old 29th Sep 2020, 5:03 pm   #45
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Default Re: My first foray into Old model TV repairs.

First light Adrian, congratulations.

The best course of action with the main smoothing block is to restuff it with modern capacitors. You get peace of mind that it's electrically sound, and you get to keep the original can with its markings, which usually includes the month and year of manufacture.

I can show you the method I use to do this, just ask.
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Old 29th Sep 2020, 5:20 pm   #46
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Default Re: My first foray into Old model TV repairs.

WOW! Well done and a good tube into the bargain.
I too had the three section electrolytic cap u/s. It was open circuit giving an 'S' shaped picture. I used a double 50uf and added an 8uf after arranging a new securing clip for it.

Frame caps will need replacing of course, [remember the .05 linearity feedback on top of the FOPT..] but that raster is pretty good all things considered. I had a total collapse at first light. Great progress. John.
PS With regard to the current required. Start off low then check the overwind after 30 mins. If it feels warm that should be OK. It's trial and error. The idea is to drive out the damp from the inside of the winding. External heat will not do it. J.
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Old 29th Sep 2020, 6:15 pm   #47
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Hello Graham, I have re-stuffed the can two 47uF at 450 Volts and a 10uF at 400Volts have replaced the internals, I removed the tags and stuck the wires through the holes as there was no way I could solder to the aluminium wires. The date on the can was viewable after removal and showed November 1953. So points at a 1954 set which would be 5 years older than me.

John, I guess now is the time for me to look at the wax capacitors and start a replacement plan, there is also, I think four electrolitics underneath the chassis that I may as well replace, generally 25 and 50 volt.

I have left the set unpowered now for a few hours and will stick a crock clip onto the anode of the EY51 to the outer contact for the width control and use the buck converter, may as well use the Avo to monitor now I have it working again. Start at 20mA and work up checking at 30 minute intervals.

Then time to spend looking at cap values for replacements of the waxes. The larger smoothing cap is probably also going to get replaced as I am now seeing good signs, will have a look through CPC and Farnell etc for stock.

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Old 29th Sep 2020, 6:59 pm   #48
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Default Re: My first foray into Old model TV repairs.

Line frequency should measure 10,125Hz or 10.125Khz. You need a high impedance probe or you may be damping the drive.
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Old 29th Sep 2020, 8:47 pm   #49
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Hello Sideband;

Not sure if loading it or not, I think I will leave all adjustments until I replace a some waxed capacitors, the service manual talk of a method to adjust so will try that when things are looking better with it.

John.

I am running around 20mA through the coil at present and the temp 68 C at according to my IP thermometer. I will leave at that for a while.

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Last edited by AdrianH; 29th Sep 2020 at 9:06 pm. Reason: temp increased.
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Old 29th Sep 2020, 9:55 pm   #50
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This is a question I am sure has been asked many times before and will many times again.

I am looking at caps to use/or buy

I have a batch of 0.1uF and 0.01 all at 400 Volts rating DC. These are typical met film caps

I also have some at 630 Volts DC in 0.1 and 0.22uF although these have shorter leads, non of these are rated for AC, OK so it is on a rectified HT set, but what about the line and frame time bases where it is driving scan coils or the LOPT, I guess I am concerned over nothing really even the yellow LCR caps are DC rated?

I think they are the same construction! as the ones sold by the BVWS although not the same case style, i.e. in that they are metallized polyester film. So would just appreciate a comment especially on the scan coil use.

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Old 29th Sep 2020, 10:04 pm   #51
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Default Re: My first foray into Old model TV repairs.

I can't see a problem with any of those Adrian. The originals were just wax paper insulated. Any modern cap will be 500% better than the originals. I use mainly the BVWS types for everything with no problems. I also use any decent caps that have a suitable voltage rating. John.
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Old 29th Sep 2020, 10:48 pm   #52
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Default Re: My first foray into Old model TV repairs.

Thanks John, I guess the quality control and specs of these are much better with modern manufacturing.

So this little lot will start going into the TV from tomorrow.

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Old 29th Sep 2020, 10:57 pm   #53
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Default Re: My first foray into Old model TV repairs.

What I do when do when re-stuffing blocks, is to leave the tags in situ and drill a 1mm hole in the paxolin right next to the aluminium rivet and solder the component wires to the actual tag.
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Old 29th Sep 2020, 11:07 pm   #54
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Good idea Graham.

I think this TV will be function over form when it comes to the underside of the chassis, top side I can appreciate. At some point I will have to start looking to replace the plywood that is separating it's layers. I do not think there is a veneer on the outer faces, but could be wrong, It looks more like a sanded and varnished finish, well I hope so because that will be what it will be getting. I need to dampen down the back panel and then keep it flat whilst drying it out. I must make it presentable at the end of the day.

Still a way to go. Electronics first.

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Old 30th Sep 2020, 9:58 am   #55
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Default Re: My first foray into Old model TV repairs.

That’s excellent, it’s very satisfying when a set comes back to life. I went through my set a cap or two at a time, starting with the timebases (mine had total frame collapse when I first powered it up). That way you only change what needs to be changed, and if you go wrong anywhere it’s fairly straightforward to backtrack and identify where you went wrong. If you change ‘em all wholesale you might end up with the Devil’s own job of finding the fault..

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Old 30th Sep 2020, 2:26 pm   #56
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I need to get the HT up at the correct level. Testing the main cap the first section the 100uF is leaky, rather than a HT of 187 Volts or there about, the set HT is down to 155 Volts. So I am about to lash up using a couple of modern caps to see what the results are, then I will consider what to do next.

On the wax caps, I will replace batches of suspect caps at this stage while I have the soldering iron out.

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Old 30th Sep 2020, 5:49 pm   #57
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OK replaced the smoothing caps then wondere why the resistors off the PY82's were glowing red!

Switched off and for some who knows reason I have connected the 100uF cap the wrong way around so it quickly started to get warm.

OK take two with another bunch of caps and I get the 185 Volt HT on the Avo. Also got full raster.
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The HH2 arrived today so I had a think and stuck a piece of wire in the TV ant connector and one in the HH2 and set it to generate a test-card.

Flick the switch EGOR flick the switch! It lives it lives.
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OK a bit OTT

Tube seems a bit soft can not really tell wit a noisy signal so have to come up with something better. It tunes channels 1 to 5 OK I have the frame linearity to one end of it's travel at present, and if I turn the brightness up I can see fly-back lines, but as I said I really need to get a better signal in.

So what are the two pin plugs called for the aerial and where can I get some?

I also need to figure out a replacement 200uF/100uF can.

Cheers

Adrian
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Old 30th Sep 2020, 9:42 pm   #58
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Default Re: My first foray into Old model TV repairs.

Those caps will be fine, I generally fit 630v rated caps to be on the safe side.

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Old 30th Sep 2020, 11:38 pm   #59
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Bingo! That ain’t bad at all, doesn’t seem to have any serious distortion, it’s bright AND it fills the screen. You must be nearly there.

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Old 1st Oct 2020, 12:12 am   #60
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I have changed the wax's with to be honest little change that was noticeable. But they would have been changed at some point anyway, there was no way I was leaving them in.
There is still some frame linearity issues with expanded lines at the top of the screen and some hum bars on the picture, so the last 4 electrolitics will be changed, these being 3 x 50uF at 12 Volt and a 4 uF at 150 Volt. Two in the frame circuit, one in audio circuit, and one video interference limiter.

Once I have done these caps I will leave the chassis for a while, will need to order a 100 and 200uF HV caps in to re-stuff the main capacitor that has failed but considering it is 66 years old to be expected. Need to read up on the Band 1 tuner as it gets progressively deaf going from channel 1 to 5 and not sure if this is tracking or valves.

In a few days I will start on the cabinet and see what I can do with that.

Adrian

Last quick comment the camera is compensating the exposure, it is not as bright as in the pictures.
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