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Old 8th May 2020, 11:45 am   #61
theredhouseinn
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Default Re: Fixing a GEC BT 330 Television

The dealer that I worked for in the 60's was a GEC agent and I repaired dozens of this model. There were 4 versions of this set, yours is the basic one, then there was the basic one with tamber doors, then the basic one with FM radio, and then this one with tamber doors was the 4th version.
Before you power this up, all the black hunts caps will need changing especially if they have a crack in the black coating. Change all electrolytics, especially the main power supply cap, that is the big ali cap, this is likely to explode when you apply voltage to it, it will shower you with hot wax and silver paper. Been there done it!! This was a common fault with 50's and 60's t.v.s.
All the valve bases will need cleaning with contact cleaner, as will the channel biscuit contacts in the turret tuner, be carefull here as the spring contacts are a bit fragile.
You have taken on a big job here, best of luck.
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Old 8th May 2020, 11:51 am   #62
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Default Re: Fixing a GEC BT 330 Television

I'll leave it to the experienced TV restorers to give advice on this one.

Good luck with the repair.
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Old 8th May 2020, 12:02 pm   #63
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Default Re: Fixing a GEC BT 330 Television

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Originally Posted by theredhouseinn View Post
Before you power this up, all the black hunts caps will need changing especially if they have a crack in the black coating. Change all electrolytics, especially the main power supply cap
I have to totally disagree with this!

This chap has absolutely no knowledge regarding repairing TVs and as has just been said in an above post, there may well be much more serious faults that he hasn't a hope on this earth of fixing, such as transformers, tube etc. He needs to get first light and then go fixing faults. All the black Hunts etc. capacitors will need changing eventually and possibly the electrolytic smoothers, he'll know if they're faulty as he can have it explained to him about how they soon start to feel warm to the touch if they're going to go bang and about monitoring HT voltage, but first things first - unless he want's to throw a whole lot of money, time and effort at it to probably end up getting absolutely nowhere.
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Old 8th May 2020, 12:10 pm   #64
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Default Re: Fixing a GEC BT 330 Television

I know its a large project but I am determined to learn a listen, I will try my utmost best to get it to work
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Old 8th May 2020, 12:39 pm   #65
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Default Re: Fixing a GEC BT 330 Television

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I know its a large project but I am determined to learn a listen, I will try my utmost best to get it to work
That's the attitude, remember to try and learn the basics, voltage, current, Ohms law etc 100% vital.

Ohms law never changes.

All circuits are composed of potential dividers (that's an easy one to remember)

Schematics (circuit diagrams) can appear intimidating.....don't be put off, they'll only appear intimidating if you let them.

A TV is just a radio with a picture, same basic circuit techniques...the only big leap (for monochrome TV) is the line output stage.

A good learning tool is the humble block diagram, learn what's supposed to go in to the block and why, learn what's supposed to come out and why.

Good luck with it.

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Old 8th May 2020, 12:43 pm   #66
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Default Re: Fixing a GEC BT 330 Television

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Originally Posted by deepspacedaz View Post
I know its a large project but I am determined to learn a listen, I will try my utmost best to get it to work
Well said and good to hear that!

I think that one of the problems that I've noticed, particularly on that record player thread, is that the reason that you don't answer all the questions and appear not to be listening is that you're not seeing all the posts that are coming back to you on whatever device you're using - probably a phone with a silly little screen, yes? An example was when you mentioned the black burn mark on the chassis, which I'd already brought up on a previous page and you obviously hadn't seen my post on it. I also think you're getting "information overload", and particularly as you've got more than one thread running at the same time, you're going to struggle.
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Old 8th May 2020, 1:02 pm   #67
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Default Re: Fixing a GEC BT 330 Television

Get the valve heaters going first. I agree about the Hunts caps but they can wait till later.
OK they leak but nothing like as bad as the waxies.
You should be able to get 'first light' without too much work. When you eventually make some progress, just check that the main electrolytic is staying cool. I have a couple of GEC BT302 series both with their main smoothing caps still in place and working well.
One step at a time unless you want a mixed up mess that will take 980 posts to clear up! Good luck with it. They are a simple receiver to service and give a good result. John.
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Old 8th May 2020, 1:12 pm   #68
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Default Re: Fixing a GEC BT 330 Television

Thanks for the info, yes I have been missing posts, I wasn't very good at finding my way around the forums
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Old 8th May 2020, 1:44 pm   #69
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Default Re: Fixing a GEC BT 330 Television

Can you give us a picture of your multimeter please. Sit down and read/learn about Volts, Amps and ohms so you understand what we are saying. Ohms law is the basis of all electronics and you need an understanding of it. If you have a Skype or messenger account I could explain what your meter is telling you. Be careful as you will get bitten, we all did when learning our trade. Don't start changing things willynilly, as has been said to get life into a set a bit by bit then you can make the call on spending money if it has a good line output transformer and tube!
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Old 8th May 2020, 2:12 pm   #70
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Default Re: Fixing a GEC BT 330 Television

Sure ill send one now

Yes I've been learning about ohms law I have a few books

My multimeter, its from B&Q. Is this OK ?
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Old 8th May 2020, 4:18 pm   #71
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Default Re: Fixing a GEC BT 330 Television

It will get you started
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Old 8th May 2020, 5:26 pm   #72
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Default Re: Fixing a GEC BT 330 Television

That's a good meter and perfectly fine for what you're using it for.

For working on valve radio and TV, it'll be the 600 volt DC range that you'll need to be using for most of the voltage tests.

Avoid using any of the current (mA) ranges until you know what you're doing. You can easily damage the circuit and blow up the meter using these ranges in the wrong way - remember, always double check what range your meter is set on BEFORE making a test when high voltages may be present.
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Old 8th May 2020, 5:50 pm   #73
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Default Re: Fixing a GEC BT 330 Television

Thanks for the advice ill keep that in mind.

Found a very good tv repair book from the 1950s
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Old 9th May 2020, 12:32 pm   #74
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Default Re: Fixing a GEC BT 330 Television

I forgot I have a record player from the late 60s do you think that may have parts I need ?
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Old 9th May 2020, 12:48 pm   #75
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Default Re: Fixing a GEC BT 330 Television

I hope that after all the help you've been given you're not planning to cannabilise your Westminster record player?

To repair this TV will probably require a lot of new components. The best thing you can do is to buy them. Despite the lock down most suppliers are still operating and eager to do business with you. The only slight snag is that deliveries are taking longer than usual.

You might do better selling off kit you don't need on eBay rather than stripping it for a few components which may well be faulty.
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Old 9th May 2020, 1:09 pm   #76
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Default Re: Fixing a GEC BT 330 Television

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Originally Posted by deepspacedaz View Post
I forgot I have a record player from the late 60s do you think that may have parts I need ?
There will be hardly any (or no) relevant TV parts in this record player and they may well be faulty.

You are either going to have to forget fixing this GEC BT302 TV or start to follow the initial checking and testing advice that you have been given.

Some of the most likely parts you will need to replace will not be available new:

The HT reservoir and smoothing "can" electrolytic (that large aluminium cylinder, with wires going to tags at the top of it, above the dirty wax capacitor you cut out)

The HT rectifier (if the original "metal rectifier" part, with its cooling fins, is still fitted).
This is probably only accessible after removing the complete chassis and picture tube assembly (unless there is a removable cover on the underneath of the TV).

As they are both long since obsolete parts, they will have to be replaced with equivalent modern parts.

The initial aim must be getting some sort of display onto the TV's screen, with the minimum of component part replacements.
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Old 9th May 2020, 2:12 pm   #77
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Default Re: Fixing a GEC BT 330 Television

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Originally Posted by deepspacedaz View Post
Found a very good tv repair book from the 1950s
What is the name of the book and author?
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Old 9th May 2020, 3:24 pm   #78
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Default Re: Fixing a GEC BT 330 Television

OK lets have a few thoughts on this saga. A lot of very good advice given here so I will add my fourpence worth.

Start by getting the valve heater chain to light up. This is basically simple and will probably be very rewarding.

Your meter is a good bit of kit and will do everything you need it to. [You must feel confident using it]
You can do the heater chain check cold i.e. with no mains applied.
First with your meter on the lower ohms range, place the black test prod on the end of the black mains lead wire. [This is where a few short leads with crocodile clips at each end comes in handy]
Put the other lead from your meter onto the metal chassis. Switch on and you should have continuity on your meter.
OK? Now transfer the meter test prod from the black to the red mains lead and check to see if you have continuity to both sides of the 1.5amp mains fuse.
Continuity?? Now leaving the switch on, check for continuity at the mains input terminal of the mains dropper. The terminal is coded D in RTS and I think it's the same in the GEC manual. It's the junction of R84 66 Ohms and R83 16 Ohms, the white mains adjustment wire.
Continuity?? Right, now check for continuity along the heater section of the mains dropper, R85 66 Ohms, R86 33 Ohms, R87 78 Ohms.
Continuity?? Next move on and check continuity of the heater surge limiter thermistor shown on the circuit as R88 with a dot in the middle of the symbol.It looks like a burnt out resistor but that is how it should look. If it is faulty it will have probably cracked or the connecting leads have deteriorated. A visual look should be all that is needed.
Continuity to the thermistor?? It is designed to have a higher resistance when cold to when it is hot, so take this into consideration when taking your meter readings.
Now you will have to check the heater chain. [Like old type Xmas lights, one off, all off]
The first valve in the chain is the line output valve N308/30P4 pins 2 & 7 OK? on to the boost diode U339 at pins 7& 8. B9A valves generally have their heaters pins at 4 & 5. B7G pins 3 & 4, and Octals 2 & 7 but take care because some like the U339 which is a Mazda U191 has it's heater pins on 7 & 8.
Continuity to both sides of the U339?? The quickest cheque now is to remove each B9A valve in turn and check for continuity between pins 4 & 5.
The D77/EB91 has what is known as a B7G base with it's heater pins 3 & 4.
By now you should have located the break in the circuit. Don't forget to check the B7G plug connecting the i.f. board to the main chassis.
Don't forget you may have a cracked circuit board [easily repairable] usually a careful visual inspection with verify this. The only thing left is the CRT..It's heater pins are 1 & 8.
This procedure should get the heaters going, then it will give up all it's faults, visually or audibly!
I spent my early years in the trade working on GEC receivers from the BT1093 to the last Coventry built chassis the BT337 which has similar circuits to your model.

I hope this helps. I'm sure you will get there but you must learn how to use and understand your meter. It is your best friend. Regards, John.
PS All tests with the mains disconnected! You must have a methodical approach. You don't pull the back axle out of a car if the owner brings it in to have the wiper blades replaced. it's the same with a television receiver.

Last edited by Heatercathodeshort; 9th May 2020 at 3:34 pm.
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Old 10th May 2020, 8:23 am   #79
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Default Re: Fixing a GEC BT 330 Television

Some sound advice on this thread. I definitely agree that you need to know the basics. It will take time but it'll be worth it in the end and the satisfaction that you get from actually understanding how and why something does what it does will be far better than that from changing components haphazardly.

Good luck!
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Old 10th May 2020, 10:24 am   #80
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Default Re: Fixing a GEC BT 330 Television

Good words from Tas there. There is no point in the random changing of components in the hope of success. It does not work and leads to frustration and loss of confidence.

Study the circuit and don't worry about the difficult to understand bits. Do the basics first then we can sort the other strange looking bits later.

Plan of attack!
1. HEATER CHAIN,
2. H.T,. supply including the mains dropper and observation of the main smoothing can under voltage, check that it remains cool.
3. Line output stage and EHT. You can't repair a television unless you can see what is happening. Get the LOP stage going first and establish that the EHT is present and you have around 400v or so on the first anode of the CRT. At this point you should be seeing something on the CRT. Usually the only component that completely stops the line output stage on this and other models is a complete short circuit of the boost capacitor C165 easily proved by running the chassis with the top cap of the boost diode U191/U339 removed. If the line output stage then perks up, replace the boost cap. This is all to come later. Get the basic faults that apply to any make and model of 405 vintage TV receivers sorted first.
4. Frame/field output osc/output stage to get a reasonably linear raster.
5. I.F. panel and tuner. These two items are very reliable on the BT302 series as they are on all GEC receivers.
Finally the sound. I usually pass this section on to my pet Orangutan, Interlace. It takes him ages to find that illusive high value resistor but he is learning the colour code.. He likes adjusting ion trap magnets but there isn't one one fitted on 110 degree tubes.
Basics first working in an orderly method of procedure. Don't commit the fatal mistake of wildly replacing components with no idea what they do in the circuit. The BT302 is very straightforward and hence reliable and a doddle to work on. Let us see how you get on. Learn to be familiar with that good meter and if you're not sure about anything, ASK! John.
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