Novice's first TV restoration - Bush TV53 - 63

[ChristianFletcher]

I have restored many valve radios, but as of yet have not done any work with a television. I would like advice on how best to proceed with the restoration and how to identify any major failures that condemn the set to the skip before I spend to many ours on the job.

My first plan is just to get out the vacuum cleaner and remove all the dust and dirt, but then what next?

What is the best way to access the chassis? Should I remove everything from the cabinet?

What would be considered essential checks before powering up, should I treat it like a valve radio?

I am also a little worried about identifying the part that have EHT and how to discharge the tube safely. Should I disable the EHT for safety while I do basic checks?

I aslo intend to write up the resoration on my website so anyone can see my progress and make comment.

Where do I start?

[Steve_P]

If you've done radios, then TV sets are not that different. Apart from EHT, which you are aware of, and of course you've got the manual. Good.

First, read through this site: www.oldtellys.co.uk

Replace all capacitors and any suspect wiring. Check the mains supply, and things like smoothing blocks.

Then switch on and pray...

Cheers,

Steve P

[Sean Williams]

Aha, another willing victim!..oops, enthusiast........

Should be a doddle to get this going.......

Steve's site is as good a place as any to start - It taught me a lot.....

Cheers
Sean

[jim_beacon]

TV's are fairly straightforward, and suffer from exactly the same "old age" failures as radios - only there are more 'Moldseals' to change (especially in Murphy sets).

More likely to be a series heater chain, unless it's a very old set, and it pays to clean the EHT components really well (they do occasionally track).

Otherwise, it's two radios and a scope in one box

Jim.

[ChristianFletcher]

Update on progress.

I figured out that the best way to access everything was to remove the two chassis and I have reformed the electrolytic without any problems.

I was next going to proceed with changing all the coupling capacitors and what I think are the HF bypass capacitors on the series heaters chain.

I wanted to power up on the bench, where I can get at everything easily, but I see that the tube is part of the series heater chain. What's the best way to do any live testing?

Am I proceeding along the right lines?
I am a bit apprehensive of doing anything without discussion as I have not worked on a TV before.

Regards Chris

[Sideband]

Hi Chris.

I can understand you being wary of EHT...I am, after 35 or so years! As you have the two chassis out I would change as many waxies as possible especially if any of them will be in awkward positions/impossible to get at when the set is reassembled. In the line stage, make sure you change the boost capacitor. Clean all the muck and grime from around the line transformer and EHT rec.

Before you switch the set on for the first time, I would suggest you disconnect the screen feed to the line output valve. This will stop EHT generation without doing harm to anything. At least you can then run the set without worrying about possible EHT flashovers and it will allow you to check main HT and audio stages. If you have a standards converter, you may even be able to get some sort of sound. A scope should also tell if the field (sorry ...frame) stage is running. You will probably also be able to check the presence of line drive.

Once you are reasonably sure that nothing nasty is going to happen to the basic circuit, you can then be brave and connect the screen feed back to the line output valve. When you switch on again, arrange things so that you can disconnect the mains quickly should anything nasty be apparent when (if) the line stage starts to operate. Chances are nothing nasty will happen and it may even work!

Take things in stages. As you get more confident with TV you will decide for yourself, the best way of resurrecting them.



Good luck.


Rich.

[ChristianFletcher]

Thanks Richard

There really are quite a lot of capacitors to change compared with a valve radio. I was hoping to just change the coupling capacitors and anything that was looking stressed. I am sure that you are right, but I did not want to commit too much time and money unless the restoration is realistic.
I have already cleaned the tube and all around the LOPT with Servisol IPA.


Thanks Chris

[beery]

Hi Chris,
I have restored a couple of these sets now.
Generally in Bush sets the large canned smoothing caps will be fine.
I would replace all the round wax capacitors and all the small canned capacitors.

Don't power the set until you have at least replaced the mains supression cap 0.05uF, C98 on the trader sheet and C94, 0.5uF. As a temporary measure you can simply cut one lead of both these caps until you can get replacements. C98 needs to be an X2 mains suppression cap and for C94 use RS 348-7701 or RS 114-626 (this is cheaper but you have to buy 5).

Other than that the rubber wiring that runs along the top of the timebase chassis may need replacing.
The loptys in these sets are really reliable. You may find the HT rectifiers tired (replace as a pair) and the PL81 and PY81 may also be a bit worn out.

Oh yes, you may wish to keep all the wax caps you have removed in case you decide to re-build them one day and put them back. I wish I had saved the components from my earlier restorations.

Good Luck

Andy

[beery]

Hi Chris,
For nice looking axial caps I use 400V Vishay types.

For cheap caps I use X2 caps as they are generally good for 630V DC. RS 441-9616 for example, these have long leads.
If I need axial caps of 630V rating I buy them from a guy in Cananda at:-
http://www.justradios.com/capkits.html

Cheers
Andy

[ChristianFletcher]

Please could someone explain how the width control operates T2 of the LOPT?

Thanks in advance Christian.

[jim_beacon]

Hi Christian,

The width control will be a saturable inductor. You use the reluctance of the magnetic circuit to control the AC line ouput waveform amplitude (if it helps, think of it as a preset resistor which only effects the AC component of the signal through it). By altering the position of the core, you vary the magnetic reluctance, and hence control the AC current - when the core becomes saturated, the AC resistance of the coil increases.

Jim.

[ChristianFletcher]

Dear Friends

I now have the set powered up and can hear loud static coming through on the speaker and have a raster of sorts. The raster is very distorted and also very dim as it's only visible when the lights are off in the workshop. The brightness control works but does not bring up the brightness enough.

Is the next step to test the EHT? Some advice on the function of all the various tube adjustment controls at the back would be helpful.

I have twisted some of the adjustments and this has improved thing slightly but the raster is still skewed and twisted - reminds me of the astigmatism control on a scope.
How did anyone work on these? It's impossible to get at any test points with the chassis installed.

Christian

[Mike Phelan]

Chris
Try adjusting the ion trap magnet - fore-and-aft and rotation - for max brightness.
Twist the scan coils to straighten the raster.

[Sean Williams]

Hi Christian,

Ok, The Ion trap is adjusted by loosening the clamping screw (if it has one), then just slide and twist it slowly untill best brightness is found.

You have sound - that is good, as it proves that the front end and sound IF is working.

Yep, turn the set whatever way up suits you - so long as everything is bolted in it will not mind too much.

Logically I would get the raster as bright as possible with the ion trap before any further testing - then you may be suprised once you back the brightness off - a picture might appear - at present you have flooded the tube with a white signal, due to the tube having it's guts flogged to death - lets get the ion trap done first!

Just looked at the piccys - the ion trap looks too far back along the neck of the tube - loosen the screw at the bottom of the trap, power the set up, stick a mirror in fromt of it, and slide the whole ion trap assembly forward - if the picture dims then go backwards - a similar rule works for clockwise and counter clockwise.....

Cheers
Sean

[Heatercathodeshort]

Christian
It's time to get some sort of picture on the screen. The raster should be good enough to reproduce a picture of sorts. To start with turn the contrast on full and the 'limiter' [it's on the front under the flap I believe] fully anti clockwise.

Apply a video signal and see if you can see any trace of a scrambled picture. It was not uncommon to find owners watching very poor pictures with the room lights out when the tube was failing. The MW43-69 is an aluminised tube and gives a brilliant picture when in good health.
They did suffer from a partial heater short that can be repaired on a temporary basis by tilting the set backwards and GENTLY tapping the neck near the base while the set is on.

A trained eye may see some hot bits drop out of the heater assembly and the heater glow brighter. The screen brightness will increase as this happems. For the time being get some sort of picture on the screen.
The total lack of video may be down to something you have disturbed more than a component fault.

Pity you're so far away as I would love to have a go at it!

Regards John.

[ppppenguin]

If the sound is working then the Aurora is OK and you are on the correct channel. If you disconnect the video input to the Aurora then it will generate Test Card C (unless you have reprogrammed it). You can also look at the 405 video output with a 'scope and see that you have the video waveform present.

[Heatercathodeshort]

Hello again,
I think you have more than 3.5kv EHT as the raster is undersize.

Even at this low EHT a picture would be just about visible. It's very unusual on this model for the set to produce a 'no video' condition, but of course we have to remember the years that have passed since these were a regular feature of my workbench.

Christian, does the brightness control operate? I know it sounds daft but are all the valves in the right positions? I only say this because we have all made these mistakes and it can lead you a merry dance.
It will be the valves in the i.f. stages and video output that concern me most.

Regards
John.

[ChristianFletcher]

I wrote the valve number on the chassis and on the side of each valve as they were removed. I think they a probably in in right location but it wont hurt to doulble check.

Both the brightness control and width controls operate as this should but fail to give full adjustment. The brightness has to be turned full up to view the raster even in low light condition.

I think its time for me to stop poking around and start to test in more systematic manner with the valves.

I have already said I think this set is difficult to work on as its not easy to gain access to the valve bases with the chassis installed and connected to the picture tube.

What are my changes of finding another tube MW43-69?

Thanks Chris.

PS: Just found something - back shortly

[Heatercathodeshort]

Hello again Chris,
The fact that the brightness control works is a good starting point. You will have to obtain some sort of crude signal injector and work back from the tube cathode through the video output, detector and i.f. stages.

A simple 400c/s tone generator such as an old B.T. phone line tester is all that is required, the nastier the better. No need for involved test equipment with this one.
Remember to work backwards; you can waste hours and get nowhere starting at the tuner. You have sound so my guess is that the video output stage has a fault.

Don't worry about the tube at this point but the following tubes will work fine in your set together with a good many more from the lesser known makers of tubes such as Brimar and Cossor. CRM171, CRM172 [Mazda but probably low emission] Mullard MW43-64 the non aluminised version of the MW43-69 but gives a good picture.
These tubes are not difficult to locate and sets using them bring only a few pounds on Internet auction sites. The tube is 17" 70 degree with a .3amp heater.
Its the .3amp that matters not the voltage as the 50/60 series Bush sets use a series heater arrangement.
Anyway, let's see if we can get you a picture on the beast.

Regards John.

[ChristianFletcher]

Thanks for all the positive advice.

We have have a picture now but its very blurred and out of focus. I have tried adjusting the picture position lever and I think what is the focus magnet but this does not improve things. I have also adjusted ion trap magnet for maximum brightness.

The picture is also distorted and will not go full width even when the control is turned to maximum. Also noticed that turning the contrast control to high cause the frame hold to fail.

What is the procedure for setting up a new tube?

Thanks regards Chris..