My First Television Set Stella ST1017U

[1955APREN]

Cutting one leg of the Focus slider clear the height fault a quick bodge . If you have not got 2.2Meg slider preset connect two 1 meg resistors in series from the boost line to earth connect the centre to the lead from the centre of the
focus control. I would not worry about this , the set will work ok as it is. If the focus is poor then change the preset or adjust the value of the resistors
Regards
Derrick

[60 oldjohn]

Originally Posted by 1955APREN

Cutting one leg of the Focus slider clear the height fault a quick bodge .
Derrick

Would this have been obvious to a repair man back in the day? or was this recommended in some manufactures service information?
No point in me checking mine, I'm sure it's cut same as your set.

John.

[ChristianFletcher]

Interesting repair. These old service engineers had a lot of tricks.

Thanks for the information Derrick

Regards Chris

[Heatercathodeshort]

The AW43-88 tube has a pre focus gun assembly and requires little if any focus potential.
The 2.2m preset being connected across the boost rail rapidly dropped itself to around 500k reducing the decoupled supply to the frame oscillator and tube A1 supply.

This resulted is a lack of overall brightness that could be compensated by an increase of the brightness control. As the preset reduced the height control eventually ran out of adjustment resulting in a service call for lack of height.

Most guys simply cut the earth end of the control restoring brightness and height. There was no point in replacing the control as the fault would repeat itself after a few months.

As Derrick has suggested the correct procedure would have been the two 1m resistors but a busy field engineer would have simply cut the earth end of the slider.

Later receivers did away with the troublesome potential divider simply connecting the focus pin usually to earth on the tube base.

Just leave it cut for now. It will not effect the picture.

The LOPT was reliable in it's day and I can only remember changing one or two in service and the TG100 series were very popular receivers. Storage has not done them any good and it is usually the EHT overwind that fails due to damp. If I remember it has quite a complicated primary with taps for the width settings.

This is a picture from the pages of my old rewind notes that I made when I was 15! I used to rewind transformers for D&B TV with a couple of Douglas coil winders.

Happy Days! John

[Hybrid tellies]

This use to happen on the Decca 625 single standard black and white chassis including the MS1700, MS2001.
You would get lack of height with lack of brightness and sometimes found that the focus control had dropped down from 2 mega ohms down to as low as 150K!
As this fault started to show up when these sets were 7-10 years old we just replaced the slider control. We never just chopped the control out as the Focus and A1 voltage could rise up 700-800v, possibly higher but will need to check this up as its a few years back, which we considered to be to high for a black and white tube.
With a bit of a fiddle you could get a 2.2 Mega ohm slider control used in the Decca Bradford as a width control.
If its difficult to get a 2 megaohm slider control I would use two 1 megaohm resisters in series as a replacement and connect the focus anode to one of the three positions top, midway and earth whichever gives the best focus.

[Vintage Engr]

These are a great TV to start on, as they were mostly reliable, and easy to work on.
I can't believe that I used to work on them when they were nearly new! We rented them out & must have had hundreds of the variant model out in the field.

As others have stated, the LOPTs were never that reliable when new. There was also a problem with some of the early deflection coil units. They were resin encapsulated, and sometimes, due to contraction & expansion within the assembly, would go O/C.
I have two of the Stella models here & they are both giving excellent pictures.

Good Luck,

David.

[Niechcial,Steve]

In the innocence of my teenage years when I shouldn't have been let loose on anything I came across low height due to low boost due to a partial short in the tube. There was consequently a large drop across a high value resistor in the boost line. I didn't realise the fault was in the tube, and I didn't have a multimeter with a high enough range to check the resistor, so I just shorted it out to see if the boost line went up! There was a brief crack and flash from the tube neck. I felt sheer panic that I would have to account for wrecking the set but height had been permanently restored. Beginner's luck. The lady owner thought I was a magician!

[ChristianFletcher]

Thanks for the comments not had much time to look at the TV over the last two days as I’m busy at work. But I will provide some pictures and an update tomorrow. I’m always totally amazed at the depth of knowledge on this forum. I have a few TV books on the go at the moment and it feels like a bit of a slog and a lot of the terminology is quite new to me.

Thanks Regards Chris

[ChristianFletcher]

I was just looking for some more confirmation on warming the LOPT. I have measured the resistance of the winding installed between the top cap of the line output valve PL81 and the EHT rectifier EY86 and it measured just over 100 ohm. For some reason I was expecting a much higher Reading like the secondary of a car ignition coil.


I am running 15 volts through the winding which is around two watts and the right hand coil, see picture is just getting quite warm but not hot to the touch

Do I have this correct ?

Thanks regards Chris

[linescan87]

Sounds like it is drawing a little over a 100mA which is spot on. Leave it like that for a few days and you should be in business.

[ChristianFletcher]

Hello John

It’s drawing 125mA, probably a little volt drop in my wiring

Chris

[ChristianFletcher]

I have had the over wind drying out of the power supply for the last three days and I was thinking of connecting a separate HT power supply to trickle the main smoothing capacitor back into some kind of life. Now my thought turn to the first power up and I need some more advice. It will be run via an isolation transformer but do I run it up via a lamp limiter or variac. I was watching some shangoo videos where he says that it’s not a good idea to apply power slowly as the I think he was saying the oscillators won’t start up and this can damage the LOPT.

I’m still looking at changing the boost capacitor and some of the other components mentioned previous in the thread but did have some difficulty in locating the device’s on the schematic as again still coming to terms with some of the terminology and television circuits and operation etc. I’m at the steep bit of the learning curve

If you want to look at the actual TV I have posted a link below

https://www.youtube.com/watch?v=tJHhT_cjsG4

Thanks regards Chris

[McMurdo]

I would take shango066's videos with a pinch of salt. He's very experienced and knows where and when to take short cuts, and no doubt has an extensive inventory of spares should he damage a part by his 'shotgun' approach. Unless you've spent your life in the TV trade, such a repository of expendable spares in the UK seems pretty rare. I would continue cautiously as you are.

[ChristianFletcher]

I think I am being careful but it has to be powered up for the first time sometime. I’m thinking of a lamp limiter with a fair size lamp ? But want to check too low a voltage won’t cause other problems etc.

[mark pirate]

I think I am being careful but it has to be powered up for the first time sometime. I’m thinking of a lamp limiter with a fair size lamp ?

A 100w bulb & variac will be fine, just bring up the voltage slowly over quarter of an hour or so.

If all seems well, remove the bulb and bring up the volts on the variac while keeping an eye on things.

My advice is to change the boost cap first, this will be leaking badly, if my set was anything to go by!


Mark

[ChristianFletcher]

Thank mark

[ChristianFletcher]

Had the LOPT warming nicely for the last few days and getting ready to power up. Just wanted to check regards the boost capacitors can someone confirm that it is C608. I was going to change the across the mains capacitor 706.

Is there anything else I should change before applying power. The main smoothing electrolytics have been reformed and appear to test OK although a little high in capacitance as they often go.

Thanks Chris

[ChristianFletcher]

Just tried my first power up using both a 200watt lamp limiter and the variac. I get a very brightly glowing lamp and 200v AC and 170 volt of HT. All the valve filament are glowing gently and the CRT filament. I have static on the speaker and I can hear I very high pitch whistle which I think is coming from the LOPT so I’m guessing that’s the line oscillator. Looking at the power consumption for the set it’s being listed as 160watt so I guess I’m probably needing a bit more mains AC. Does this sound about right for a Television is my next step to remove the lamp limiter or is there anything I should stop and check now. I was hoping for signs of a raster but nothing yet.

Also I have changed the boost capacitor and had 200v HT on the set from a separate power supply to reform the capacitor. It was only drawing a few MA of current from the HT supply

Thanks Regards Chris

[ChristianFletcher]

I removed the lamp limiter and it’s drawing 144 watt. Plugged in a pattern generator and twiddled all the knobs to achieve a raster. I have two pattern generator both rebuilt by me so never plugged the in before and not sure how well they work but something is happening. I’m going to take this as a good sign

The picture is rolling with the checker board pattern. I can almost get it to hold but it starts drifting.

Chris

[ms660]

That pattern takes me back, nice Cossor.

Lawrence.