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Old 13th Sep 2011, 12:54 pm   #101
Heatercathodeshort
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Default Re: Restorers dream part 2 the chassis.

Hello Colin,
Please forgive me if I repeat here the good advice that other Forum members have posted. I have attached the timebase circuit of your Ekco with the relavent components marked in colours. The red ones are very much to do with the line timebase and obtaining 'first light'. You have snipped off the mains R.F. bypass cap and I think you have replaced three others, the boost cap, decoupling cap and line coupling cap. This should get the line timebase working fully producing enough EHT to give a glow of sorts on the screen. The valves,other than the U25 will probably be fault free and as you can hear the timebase whistle and draw a spark from the U25, it should work to some degree. You should be able to draw a spark from the single wire end of the U25 simply by holding a well insulated screwdriver tip close to the connection and drawing around a quarter inch of arc. Do not short the blade to chassis at this point. Moving to the twin wire end, heater and cathode, you will need to hold the blade to the chassis and advance the blade towards one of the twin end connections. It should produce a loud cracking spark [it may make you jump] quite harmless to both you and the receiver if you use a good quality screwdriver. The U25 should show a faint red glow from inside the bell looking from the twin wire end. If you can see the glow there will be usable EHT available. No glow will probably be down to a faulty valve if there is plenty of AC spark at the single wire end. The circuit does not use a CRT anode 1 decoupling capacitor so if all is working well around 300v should be available on the tube base. [Pin 10 counting clockwise] If the timebase is under strength it could be due to low H.T. that can be measured first on pin 8 of the PY32/33 and last on the 200uf section of the smoothing block. Expect around 200v plus for a working receiver. Once you have established that EHT is present, the receiver will give up it's secrets by way of tell tale displays on the picture tube itself. The green and yellow components will then have to be investigated. Keep cool! Regards, John.
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Old 13th Sep 2011, 1:19 pm   #102
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Default Re: Restorers dream part 2 the chassis.

The two pictures will give some idea of the degree of spark produced by a healthy EHT supply. This is taken from my Ekco T330. It uses the later type of plug in rectifier the U26 but other than that it is identical. Note the screwdriver is NOT shorted to chassis for the AC end, picture 1. [single wire] but is touched to the chassis [screening can] for the DC test, picture 2 [twin wire end] The DC side produces loud cracks! J.
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Old 13th Sep 2011, 4:14 pm   #103
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Default Re: Restorers dream part 2 the chassis.

Hi,

Today started early; I was wide awake in bed at 5.15 this morning fighting the urge to get into the workshop.

As caps play such an important role and this chassis was full of waxy caps I've spent the morning changing them rather than taking a lot of time trying to identify each one. Every cap I replaced was leaking badly on test. I used 630V units throughout with the exception of a Metalpack Visconol 0.02uF rated at 750V on a large transformer so I used a TCC Supermold 0.022 rated at 1500VDC.

All the caps removed were leaking badly on the 100/200V range of the Hunts component tester and their capacitance tests were a joke.

Most of the old caps were merely snipped out leaving 1/4" long tails to aid the fitting of the new caps and also this ensured I din't lose the location. The new caps had insulation and coils added using my miniature coil winder; it was very easy and saved a lot of frustration to solder these in place after scraping the tails with a craft knife.

I found I could vary the whistle a great deal by rotating the Horizontal hold control.

At last after spending yet more time I found the 500mA fuse and it was as Dom guessed being one of the 2A fuses on the rear panel; I was determined to find it and it was a struggle gaining sight of the rear panel but when I did I found both fuses marked on the panel; one at 1.5A the other the elusive fuse marked at 500mA. For the time being I've left the 2A in place.

I had to go out this afternoon and have just returned so many thanks John for all the additional information which I've just printed off. After tea I'll see if I can produce some illuminations at the LOPT following your instructions.

I took voltage readings at both 30P4 and U191 after the cap change but still no raster on the screen;

U191; Pin 1 84V; Pin4 83V; Pin5 168V; Pin6 295V Pins 7 & 8 0V.

30P4; Pin1 84V; Pin2 0V; Pin4 120V; Pin5 -23V; Pin6 282V; Pin7 0V; Pin8 4V.

I've built up a stack of paperwork already and whilst looking through it earlier noticed charts with valve pin outs and voltages; I need to slow down a bit as there is a great deal to absorb; why aren't days longer?

The channel position selector knob has been extremely loose all the while I've owned this set well today it isn't loose any more as it finally broke off giving me another problem to resolve later..

Kind regards, Col.
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Old 13th Sep 2011, 4:48 pm   #104
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Default Re: Restorers dream part 2 the chassis.

Hi,

I just had to try out John's instructions on how to obtain sparks and WOW; this is new to me; holding a well insulated screwdriver near the single wire of U25 I could draw a thin spark out at around 1/2" long but holding a thick plastic handled with an exposed blade and pressing the blade to the LOPT surround whilst advancing the tip towards the double wire end of U25 I could draw out a thin spark up to about 1" long from each wire; there certainly is some life on all three wires. Many thanks John I found it highly entertaining. I ensured I only held the screwdriver handle at the end with two fingers keeping my hands well away from the blade and any other metalwork.

Kind regards, Col.
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Old 13th Sep 2011, 4:55 pm   #105
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Default Re: Restorers dream part 2 the chassis.

Colin

The wound wire connections on the cap look very neat and saves the labour of desoldering the component ends from the tags (often not easy when the wires are wound round twice).

Good luck with the rest!

Regards

Ian
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Old 13th Sep 2011, 5:53 pm   #106
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Default Re: Restorers dream part 2 the chassis.

Assuming the EHT is getting to the CRT - check with a screwdriver - you should have first light. Wind up the brightness to full. Measure the CRT base voltages if necessary, consider shorting the cathode to g1 to force the CRT to conduct. Then it's fiddle with the ion trap until you see something.
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Old 13th Sep 2011, 6:04 pm   #107
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Default Re: Restorers dream part 2 the chassis.

Hi Col,

I'm enjoying reading part two of your TV restoration journey.
As you now have EHT and as yet no first light you could check the boost HT feed to the 1st Anode on the CRT base connector. I think you will find it quite a high value resistor which can go very high in value and result in no raster.
As I am not familiar with the set or the circuit I cannot be more specific than that. If you let me know what Tube you have in the set I could tell you the pin number to check on the tube.
I remember when I used to round the TV shops as a youngster asking for old TVs and was given one with a supposedly duff tube. It turned out the resistor feeding the 1st anode on the tube had gone sky high resulting in little or no voltage on the CRT resulting in no raster.
Good luck. You are doing great with your first TV!

Regards

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Old 13th Sep 2011, 6:28 pm   #108
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Default Re: Restorers dream part 2 the chassis.

Quote:
Originally Posted by Retired View Post
Hi,

As caps play such an important role and this chassis was full of waxy caps I've spent the morning changing them rather than taking a lot of time trying to identify each one. Every cap I replaced was leaking badly on test. I used 630V units throughout with the exception of a Metalpack Visconol 0.02uF rated at 750V on a large transformer so I used a TCC Supermold 0.022 rated at 1500VDC.
Hi Col.
Well done on the excellent progress you have made so far. One thing that I don't really agree with and something that I have given advice on before (Oldticktock, Chris comes to mind) is that blanket replacement of components is never a good idea. If you make a mistake its often much harder to trace a problem especially as you don't have much in the way of fault finding skills on TV sets. The other thing is if you change each cap in turn you will see the effect a faulty cap has on picture and sound, this is the way I recommend you do it, I am sure all the established repairers and restorers like my self will tackle the job.
Oldticktock is now one of the best restorers here and produces excellent and consistent work.
I am sure you will also have an excellent end result but you won't know what each component could cause if faulty
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Old 13th Sep 2011, 6:36 pm   #109
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Default Re: Restorers dream part 2 the chassis.

Only one i am not sure of that's EHT coming out, looks a bit like RF suggesting U25 duff?

David
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Old 13th Sep 2011, 6:37 pm   #110
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Default Re: Restorers dream part 2 the chassis.

Quote:
Originally Posted by HamishBoxer View Post
Only one i am not sure of thats EHT coming out,looks a bit like rf suggesting U25 duff?
If the spark on the DC side of the U25 is thin and (usually) yellow-ish then it's DC and the U25 is fine.
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Old 13th Sep 2011, 6:44 pm   #111
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Default Re: Restorers dream part 2 the chassis.

Hi.
If the U25 was shorted it would drag down the pulse on the anode severely and a shorted visconol would also drag down the anode's pulse and cause the U25 to glow blueish/purple. A quick check would be to remove the CRT EHT cap disconnect the EHT lead from the U25 and connect a jumper lead fron the U25 to CRT anode cap this would remove both metrosil and visconol cap.
Remember its possible the ion trap has been disturbed.

Shorting the CRT's G1 & Cathode together will up the beam current enough to give you a bright raster.
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Old 13th Sep 2011, 9:40 pm   #112
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Default Re: Restorers dream part 2 the chassis.

Hi,

Thanks for the good wishes Ian. Yes the little coils make a lot of difference. Here’s a link for you;

https://www.vintage-radio.net/forum/...ad.php?t=46540

Thank you Jeffrey; I'll measure the CRT base voltages in the morning and I'll need to establish the cathode and grid 1 to apply a short as I don't want to damage anything by making a silly mistake. I have however just popped into the workshop to check the DC end of U25 and the spark although long is very thin and also looks blue; there is no loud crack as I believe mentioned by John; the sound is very similar to testing the AC end; there is a strange smell when I am doing the spark tests.

Thanks also Andy; 1st anode is something else I need to work out and going through all the sheets I've so far collected is taking a fair bit of time every time I try to find something but I'll get there in the end; I've changed both resistors at the end of the CRT.

I'm very willing to learn from experienced people and many thanks for the warning about blanket changing components Trevor wise words indeed. I'm used to changing components on radio chassis and when I first started out I used to quickly get out of my depth after removing a resistor or cap as it is certainly very easy to lose the connections. At that time I also found out I needed three hands whilst changing components making the job most frustrating. It was this that got me into thinking about how to make life easier for myself and I came up with my miniature wire winder to add tiny coils onto the leads of the new components; all I have to do now is snip out the old component leaving a pair of 1/4" long tails and after these are scraped clean the new component simply slides onto the tails leaving both hands free to use the soldering iron and to hold the solder. Another bonus in using this method is that after snipping out the old component I can actually walk away to make a pot of tea knowing that the two tails are marking were the new component is to be installed. Designing and making the miniature winder was well worth the effort.

I did want to experiment by only changing one component at a time to see what difference each made but time is a factor and it won't be long before winter sets in again so although I'm not rushing this chassis restoration I have other jobs around home that require doing before the bad weather arrives.

Reinforcements are expected tomorrow; we are expecting two forum members to visit us and no doubt they will just twiddle a knob on the chassis to obtain first light to drive me mad.

I've put a lot of time in working on this chassis so far and tonight I have just watched a downloaded movie with Bron; I have a wonderful wife and we fully support each other in our hobbies; she never complains and it's a pleasure to spend some quality time with her; tomorrow is another day and I'll be fully charged up once again. It's been another long day today and I thought retirement would be easy.

Thanks everyone for your continued support and I'm at the head of the queue in wanting to see first light.

Kind regards, Col.
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Old 13th Sep 2011, 11:05 pm   #113
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Default Re: Restorers dream part 2 the chassis.

Fair play Col,

I have to admit first time I did a telly I did a blanket cap replace and I didn't get lost. However, I didn't really learn anything much. Last time I did it one by one and I learnt a huge amount about what all the bits and pieces do.

Having said that I think you were already close. If you can get big sparks like this you've got more than enough volts to light up a CRT. Either you have something that is making the CRT dim in the electronics - in which case shorting grid to cathode will light it up. Or the resistor chain is pulling the second grid low (I've no idea what this should measure in volts but I'm pretty sure you can prod all the pins of the CRT with your DMM on a high volts reading and report back here with findings to check)

Or. like I've had a couple of times now the ion trap magnet has got tired and so needs budging a bit closer to its sweet spot.

This is where the mirror will come in handy:

With the set on and looking at the mirror, cathode shorted to grid

1) note the position of the magnet (so you can get back to square one if needed - a felt tip and arrows on the tube neck will work)
2) slide ion trap back and forth
3) rotate by 10-15 degrees
4) repeat 2,3 until you get something lit up on the screen...

Good luck...I'm working away so might not be able to join in next week but will be following the fun on my mobile phone...

Dom
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Old 14th Sep 2011, 7:58 am   #114
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Default Re: Restorers dream part 2 the chassis.

The A1 supply [pin 10 of CRM172] is fed through a 680K resistor but strangely no decoupling capacitor. The DC side of the U25 should produce a 'crack'. It will make you jump the first time you do it so I think the U25 is duff. The strange smell is OZONE caused by chemical brakdown of air by electrical discharge[?] The ion trap is nothing like as critical with Mazda tubes but will cause screen black out if a long way off. Pictures here of a T330. Almost identical electrically. Shows ion trap position with yellow sleeve to bottom. The other is roughly what you are aiming for. Getting there Colin. Regards, John.
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Old 14th Sep 2011, 10:04 am   #115
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Default Re: Restorers dream part 2 the chassis.

Hi,

Thanks Dom & John. The ion trap was completely removed as were all the coils when I completely stripped the cabinet; I needed to carry both the chassis and CRT into the front bedroom for storage and couldn't handle both at once so separated them.

Many thanks for the pictures John and I notice the ion trap on your set is 180 degrees rotated to mine as I took plenty of pictures whilst stripping the set. Picture of mine below.

I'm a bit short of time today but I've just had an hour in the workshop and have a bit more information.

I dare not rush so have not tried shorting the cathode to g1 as I can't find my way around the pins which are baffling me;I notice if I pull the socket clear there are twelve connectors but only seven tags and the tag numbers don't make any sense to me so better safe than sorry and I can always spend more time on this later. I'm used to normal valve holders with all the pins numbered but this holder I notice a big gap between pins 5&6; these numbers are on the holder but it appears to me some of the connections have been skipped? Although I am racing forward at breakneck speed as a novice sometimes I get a feeling to hold back a bit rather than jump in and do something reckless.

I have however taken voltage readings on the tags that are connected and these read clockwise from pin5;Pin5 85V; the next pin I found varies with rotating the brightness control between 212V & 342V; 94v; 74V; 74V.

I notice a voltage drop between 94V & 85V these being capacitor resistor coupled (0.1 and 220K both new) but no voltage drop between 74V & 74V these being resistor coupled (100K also new) without all your expert help I would be curious at this and wonder if there is no voltage drop due to current not being drawn? Out of interest I snipped one end of each of these two resistors one read 111K the other 268K so whilst at it decided to change both with new items on spec.

Two pins read 0V on DC range but one read 13VAC so I assume these to be the heater connections? I'm slowly trying to find my way around and make sense of everything.

As I was wary about touching the ion trap with the set powered up I first checked to see if it had any voltage on it but as it hadn't I tried the ion trap in many positions and even rotated it 180 degrees wondering if this had anything to do with the LOPT phasing? Yes I get strange ideas but I'm not scared of looking silly as I'll never learn if I don't ask. I once rewound the primary of a LOPT and phasing was mentioned. I also had to phase balance my 3 phase machinery to the 10KVA transformer I wound so these are all snippets of information I have floating around in my head.

I'm now busy for most of the day as I need to catch up on mail and this afternoon we expect visitors but hopefully I'll be clear this evening.

Kind regards, Col.
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Old 14th Sep 2011, 10:26 am   #116
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Default Re: Restorers dream part 2 the chassis.

Col,

See attached, this will help clarify the CRT base pins in your mind, NP=no pin. Looking at the base end on there will be a key on the base count clockwise 1 & 12 (heater 12.6V) straddle either side of the key.

Another thing you may have already had first light albeit very dim. I'm working on an LV20 and my first light was just visible. If you darken the room its worth a check.

Chris
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Old 14th Sep 2011, 10:33 am   #117
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Default Re: Restorers dream part 2 the chassis.

Col
Ignore heater pins if it's glowing (which it is).

Pins 2 (grid), 10 (A1) and 11 (cathode) are the only ones of any significance to take DC readings from.

If the ion trap has voltage on it then that will be a first! EMail or phone if you want me to pop over tomorrow.
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Old 14th Sep 2011, 12:54 pm   #118
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Default Re: Restorers dream part 2 the chassis.

Hi,

Many thanks Chris for all the information it has helped me a lot. You actually raise a very good point about me already having seen first light without realizing it. The reason I say this is that I'm hopelessly colour blind so any slight changes in the screen would easily be missed by me and to compound the problem because of lack of space the screen is looking directly out of the workshop window with a mirror propped against the window. This morning I was looking at the mirror and could see reflections of wet laurel leaves glinting in the sun; I stand little chance of noticing anything in such conditions.

Thanks also Mike for your kind offer to visit; you are welcome any-time and I'm holding you as number one back up if this project looks like getting away from me.

Regarding voltage on the ion trap; being a novice I didn't know what to expect and certainly didn't want to be having a feel around the end of the tube having only just drawn 1" long "lightning" from the U25 last night; all this is new to me and I'm already told I look like the mad professor without making my hair stand on end; I didn't want an high voltage arc chasing me around my workshop.

We have visitors due shortly and these are both forum members so they can check the screen for first light and I'll report later today; I had better knock off for now.

Kind regards, Col.
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Old 14th Sep 2011, 4:12 pm   #119
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Default Re: Restorers dream part 2 the chassis.

Hi Col,

Sounds like those voltage should give something to me - but you will have to get a situation where you can see the screen (in subdued light) and adjust the ion trap. It really is no use trying to do that with the set off...beleive me been there done that. The main thing to get over with tellys is being overly ginger about them. They do bite but I've not had nearly so many nips off tellys than off radios where there is less room to get your hand in for adjustments and the ever present temptation to steady the chassis with one hand!

I'm sure between you and the visitors you'll get a picture up and be sat watching a film right now!

Dom
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Old 14th Sep 2011, 6:25 pm   #120
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Default Re: Restorers dream part 2 the chassis.

Colin, there is no voltage on the ion trap but a VERY slight static may be present on the picture shift and scan coil position lever. No more than a 'tick' that you might expect when stroking a pussy cat. Might be an idea to slip on a surgical rubber glove or similar to make your adjustment. That will reduce your stress, understandable if your not used to old tellies. I have over 100 in a box. I can send you a few if you cannot locate any. [Car spares factors, around £3.50 a box of 100] Regards, John.
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