Restorer's dream part 2 the chassis.

[ppppenguin]

It will have a finite resistance which is far from o/c. Provided that the leakage current of the electrolytics isn't enough to cause a significant drop across that resistance, which is unlikely unless the eelctrolyitcs are in serious trouble, the voltage will rise to peak mains.

[Amraduk]

Hello Col,

From your latest photos, the frame timebase is running at the wrong speed but not exactly half! It's difficult to tell from a still photo just what it is, there are, apparently, overlapping fields/frames, so could be almost anything! There is still the vertical non-linearity to fix but that can wait until other problems have been remedied.

Judging by your other two photos, the set was in a very sorry state when you got it but you have done an excellent job cleaning it up. Keep up the good work!

Regards,

Dave.

[PJL]

Linearity looks a lot better. Have you replaced all those green caps that John has marked up?

[Retired]

Hi,

Yes Dave (Amraduk) the whole set was in a terrible state when I obtained it; just perfect in fact as I love a challenge and they don't come much better than this.

Thanks PJL; I've changed all the wax caps so will already have changed many that John kindly highlighted but now the replacement PY33 is installed I can get down to checking both caps and resistors and the first to check will be every one that John highlighted; one thing I have not yet changed is the big D3 diode which I will do tomorrow.

I've been too busy today to do much work on the chassis but hopefully over the next few days I can settle down and start replacing components and I'll take the advice to only change one at a time then switch the set on to see if anything changes; I'm looking forward to this as I feel success is now well within my reach.

I intended to attempt restoration of the chassis during winter expecting it to take months given my inexperience but wow; with everyone's help the test card is showing after only a couple of weeks. I'll keep posting updates and won't give up until the set is fully working; once vision is sorted then I'll move on to audio.

The slow part now is to identify the components against the circuit diagram and replace as necessary; it will be interesting and a new experience for me to watch progress on the screen as work progresses and of course I'll be happy to post the details and can now look forward to the day I can post pictures of the completed set in working order.

Kind regards, Col.

[Sideband]

Looking at that last picture with the testcard (post 197), I can't help noticing that it looks somewhat negative. It may be just the way the set is adjusted at the moment but it might be worth checking the vision detector as shown by HCS. If this is at fault, it could also affect syncs. Don't want to bog you down with information but it's another thing to bear in mind. A few more cap changes in the frame stage should produce a better picture and it will be easier to see what's what.

Well done for getting this far!



SB

[Heatercathodeshort]

Hello Colin,
It is not necessary at this stage to replace the frame clipper diode. If faulty it will only cause poor frame sync and will not effect linearity in any way. You are very correct when you say you are going to study the components against the circuit, very important. It will be the capacitors causing your poor linearity. When correct the picture will be in correct shape with the preset controls around mid way. make sure the vision interfearance limiter is turned fully anti clockwise and the contrast around 3/4 clockwise.
The capacitors in the AGC circuit will upset smooth control of brightness/contrast but will not prevent a locked correctly proportioned picture even if a little pale. Sideband mentioned the vision detector diode and I would agree totally but the Ekco has an uncanny way of producing results under the most adverse conditions.
The important thing is to get the frame timebase working correctly. That must be the order of things. You are surprisingly close to completion of this overhaul but we must stick to a strict order otherwise new faults will be introduced. I know you are most careful in your approach but check that components are correctly connected during replacement. This is so easy to slip up on and as I've said before I still do it on a regular basis. Also check that you are fitting the correct value capacitors. Codes have changed slightly over the years and it's very easy to fit a .01uf in place of a 1000pf.
Identify the components and the rest will be just an Ekco in the breeze. Good luck! John.

[Mike Phelan]

Originally Posted by Sideband

Looking at that last picture with the testcard (post 197), I can't help noticing that it looks somewhat negative.

Could be that the white spot limiter is turned on fully (100k pot and V6B)or there's a fault there?

If this is at fault, it could also affect syncs.

Indeed true. Wonder if the 330 ohm cathode resistor in the frame output has gone high?
I'd be inclined to get the frame speed and linearity OK first, Col.

[Retired]

Hi,

Many thanks for the information SB; John and Mike.

I'm being extremely careful John whilst replacing components and appreciate your sound advice as it is so easy to make a silly mistake. All the non electrolytic caps are as supplied from the BVWS stand at the last Golborne meeting in small marked plastic bags and I've also double checked each value before fitting. I've only replaced one cap at a time and have left 1/4" tails where I've snipped them out to ensure I didn't lose their location; it was then easy to add coils onto the new cap leads using my miniature coil winder and solder them in. I too have been caught out many times previously and as it is even easier to make a silly mistake working on this my first TV chassis I'm taking my time.

In a previous post I mentioned I could not find a cap that is clearly shown on the circuit diagram and last night I was awake for hours with this running through my head as it was bugging me and I believe the cap in question was an important one.

I've been in the workshop since just after 8.30 and tried to locate this cap by tracing the circuit around V13A and the big fat diode D3. Not only is this cap missing but also a resistor is missing as well.

V13A Anode Pin1 is directly coupled to T1 which is correct; Pin1 is also directly coupled to D3 with a resistor reading 56K which is incorrect as according to the circuit diagram there should be a series coupling cap of 0.01uF which is missing on this chassis? The only other component coupled to this end of D3 is a 187K resistor directly to chassis.

The 150K resistor HT feed? is also missing? I've drawn a sketch and also taken a close up picture in the hope this will help.

Both terminal posts are chassis isolated and I can't see any evidence of previous repairs.

Having been caught out with the mains cap I'm on full alert now and working very slowly.

This has bugged me during the night and is still bugging me. I need to visit the post office before it closes and as it's only three miles return I'll have a walk but I'll be back in an hour or so and I wanted to post the update before leaving. This really is getting interesting.

Kind regards, Col.

[Retired]

Hi,
well that sidetracked me big style; I added the missing cap and resistor and the picture became worse as most of the test card was lost so I've just removed both items and returned the test card to as before. At least I tried and nothing other than time has been lost.

I'll now start the slow process of checking the remaining caps and start on the resistors. I have moved forward one step though because the new diode is in place replacing D3.

Kind regards, Col.

[Sideband]

It's possible that some modifications to the circuit have been made during manufacture. These can happen after the original circuit was drawn up so don't worry too much about any changes, especially if they appear to be original.

During the production of the set, manufacturers invariably made slight changes to circuits due perhaps to alternative parts being used or maybe a change of supplier or maybe they found that in some circumstances, some particular function of the set didn't operate as they would like. In these cases, minor changes (most times)! were made to improve performance. Sometimes the modifications were carried out some years after production had ceased. In all these cases, supplements to the original circuit would have been supplied to dealers or service agents as necessary. Sometimes if a part was ordered for a repair, a new modified part was supplied with a 'fitting instruction' along with perhaps a couple of other parts to make the modified component work properly.

As previously said, don't worry if you find some minor changes...it's not uncommon. Just concentrate on replacing the parts as fitted otherwise you'll get bogged down and waste time looking for faults that are not there.

SB

[Retired]

Hi,

Many thanks SB; as usual I always find out the hard way but its a learning curve. It was a bit disappointing as I thought perhaps after adding the two items I would see improvement; but just to make up for it I've had another good session and made slight progress; I changed two Hunts caps a 300p and a 0.001uF nearby and notice the test card is a little bit sharper which has cheered me up and confirmed that it is very interesting to change one item at a time then switch on as I agree with the advice given its fascinating to watch the slight changes in the picture.

I'm now going about this all wrong; I'm working under the chassis only knowing what certain valves are and with a chassis component layout from a very similar set but with parts in different places. I think in my case it would be beneficial to spend a bit of time and make a drawing of all the valve locations and adding the valve type then it will be much easier to follow the circuit diagram.

Just before knocking off I noticed another two Hunts caps this time they are wrapped with paper covers and I also noticed a couple of caps that look like resistors as warned about by John so I am making steady progress. The picture height remains about half what it should be but it is now looking much crisper; I bet I'll eventually change a component and the picture height will suddenly increase dramatically and I can't be far off now.

I've enjoyed myself today which is really what this is all about; its good fun.

Kind regards, Col.

[ppppenguin]

All the high value resistors in the set are suspect. Just the nature of old carbon resistors, they go high. There are a few in the field timebase, including a couple of 180K around the height control. If they are more than 10% out it may be worth changing them. If more than 20% out definitely change them. Check the resistances of the field timebase pots too, in case one has failed or a wrong replacement fitted in the past.

I assume you have changed all the nasty caps in the field timebase. Notably the 0.25uf from the oscillator trasnformer to the height control. 220n 400V will be fine here.

[PJL]

It might be worthwhile posting a picture of the chassis around V13. There are only a few components in the circuit that could cause the frame sync fault.

[ENGLISH VICTOR]

Collin it might be a good idea to check that the power supply feeding the Aurora is perfectly clean with no hum on it. I have no idea what kind of supply you are using but it might be a good idea to unplug the aerial lead and ensure that there is no horizontal shading on the screen i.e top of the screen bright and bottom of screen dark that alters position with vertical hold setting. If there is you have a hum problem in the set. Back to the aurora a poorly filtered supply can cause the problem with your picture, if it is the problem try using a known good battery just for a short time. AGC is another possibilty for trouble try partialy removing the aerial plug to simulate a weak signal or better use an attenuator say 18dB the Aurora produces a very large signal, at least mine does, 7 or 8mV on ch1 and can overload the set quite easily if the AGC is not operating correctly.You might be chasing a fault in the timebase that does not exist.
Victor.

[HamishBoxer]

A thermistor starts off high resistance and rapidly lowers as it heats up.

David

[Retired]

Hi,

I've already had a couple of hours on the chassis this morning and am making steady progress.

As this height problem appears to be associated with 30PL1 I took John's excellent detailed drawing into the workshop and started checking each pin against the drawing and then tracing the circuit diagram to see what was coupled to each pin.

The first to be changed was the Control grid1 10K resistor which was reading 12.32K but although it made no difference it is now on spec.

As I worked through I traced to the height pot and the two high value resistors kindly mentioned by Jeffrey; these read 218K and 226K so I replaced both with the correct 180K items checking the new resistors before installing them. The picture does look a little taller; Out of curiosity I un-soldered the single lead from one end of the height pot and found a reading of 1.27M? Now this looked interesting as this pot should read 1M.

I completely isolated the pot then took another reading and sure enough it read 1.263M. I don't have a duplicate pot but I'm sure I can find a 1M radio pot just to drop in to try. It is slow work but one by one I keep eliminating suspect components and thanks Jeffrey; yes I changed the .25uf cap and tested the replacement cap before installing it. Would this pot be LOG or LIN? Another thing to think about but hopefully the pot will be marked.

Thanks PJL; yes a picture might be useful so I'll post one then other novices can see where I'm working on the chassis.

Many thanks Victor for the information; I'm pretty sure the power supply I'm using is well smoothed but I can easily compare as I have another for comparison and as you say I could use a battery but the small 9V batteries drain remarkably quickly; connecting one to the Aurora is very nearly like adding a direct short as Mike and I found out. What am I thinking of; I can eliminate the Aurora completely as I didn't bother switching it on this morning for testing; I didn't need to because the picture is still very low in height with or without the Aurora; I appreciate your information though Victor as it won't be lost on me and something to think about each time I use the Aurora in a situation such as this; Mike actually very kindly gave me an aerial attenuator which simply connects in series and is adjustable.

As I'm gaining a bit of confidence I believe this problem is a simple height one and it is my lack of experience that is preventing me going directly to the component/s involved but eventually by elimination I will succeed.

I've just knocked off for a pot of tea and to add the update. I'm still working from all the information received and the bench is strewn with A4 pages. Is it normal to still hear line whistle after leaving the workshop? Thanks everyone.

Kind regards, Col.

[oldticktock]

Originally Posted by Retired

Is it normal to still hear line whistle after leaving the workshop? Thanks everyone.

Kind regards, Col.

Yes it happened to me when I first started on TV's see here https://www.vintage-radio.net/forum/...ad.php?t=52933

looks like it might just be me and thee as nobody else said yes I think it might have been something to do with putting in too many hours at the bench with the whistle ever present. Happy to say it does not happen now, but I've learned to take breaks more.

Chris

[Boom]

Originally Posted by HamishBoxer

A thermistor starts off high resistance and rapidly lowers as it heats up.

David

Some have negative temperature coefficient and some positive but yes that is what I would have thought. A thermistor with a cold resistance of say 10k in series with the diode and a bleed resistor across the smoother would stop the 1.4 surges. Once HT is being drawn then the thermistor would drop in value.

I'm pretty sure this used to be done with some tv sets.

[ppppenguin]

Don't worry about a 1M pot reading 1.3M. If it's over 1.5M I'd start to be concerned. The 180K resistors were not too wildly out - high value reistors can often increase by a factor of 5 or more.

[dominicbeesley]

Hi Col,

It's good to see you've made some progress while I've been away! I'd not get too anxious about the height and linearity until you get the frame speed right. It still looks to be running at about 1/2 speed to me and this will affect the rest of the circuit. You need to to try the frame hold at all extremes - it may seem like it is getting worse as you are turning it but it should then get better again....if you go the wrong way you may get three or four pictures above each other - that is the wrong way! Go the other way until you get one picture at a time.

If you can't then check the components around the frame hold control (resistors and caps) and the 100k resistor and 0.1uF decoupling cap that go to the top of the frame blocking transformer.

Dom