Alba T524FM my first restoration advice please

[FRANK.C]

Hi All
This is a follow-up to my previous thread https://www.vintage-radio.net/forum/showthread.php?t=18069]here[/url] I didn't get a chance to do much with the set until the weekend.

The Vintage TV Service Data CD arrived and after a bit of searching I was able to identify the model as T524FM.

The focus assembly was very seized. After a few days of soaking in WD40 and with the aid of a small vice grip I was able to free the threaded control shaft but the two bars each side that the assembly slides on remained seized.
After another few days of soaking and no sign of the bars to free I thought it time to adopt a different approach. I heated the assembly with a small pencil torch and when hot carefully punched the bars through. After the corrosion was cleaned from the bars and assembly everything ran freely.

I have replaced all the waxies and electrolytics.
I removed and dismantled the tuner unit and cleaned it was packed full of dust and sawdust.

Five of the six pots at the rear of the set were seized. I had to dismantled each one clean it and slightly enlarge the hole that the control knob protrudes through. The sixth one was a different type.

The rivets on the frame linearity slider had come loose. I bound the rivets with wire and soldered, but I found that then there was poor contact between the rivets and the track. So I painted the junction with silver conductive paint, it is making good contact now but whether or not it will hold out I don't know, if not I will have to replace it.

There was a crack on the overwind on the LOPT which I filled with wax.

After finding some used valves to replace the missing ones I decided to try powering it up with out the tube. I shorted out the heater pins on the tube socket (these are shorted out anyway when the set is in radio mode). I put the EHT connector in a clean jam jar to isolate it and wound the power up slowly on a variac. At about 180v the line sprang to life (the first time in nearly 30 years that I have heard the 10K whistle).

There is very little sound from the speaker even on radio but the output stage appears to work as what little sound there is responds to the volume control.

I refitted the tube and after adjusting the ion trap magnet and brightness control I was rewarded with a nice bright line across the screen. That's my progress to date.

I need to tackle this frame collapse fault. My question is what is the best way to place the chassis when working on the underside now that the tube is back in place? Is it OK to simply lay the chassis on one side that ways the side of the tube will be resting on the bench?

Regards
Frank

[Steve_P]

I tend to rest it where it wants to go, using some insulative material to prevent short circuits.

Anyway, the frame fault...

First, if you've got spare valves, plug them in. You never know. Otherwise, Check HT to the valves and also the Height Control, as these can go O/C, and also read the frame section of my site:

www.oldtellys.co.uk

Cheers,

Steve P

[FRANK.C]

Hi Steve
Thanks for the quick reply. There are 3 ECL80 in this set one the frame OP I have swapped all 3 around but it made no difference. I have noticed that the frame OP is the hottest of the 3.
Thanks for the link to your site; I will read it, do the checks and let you know how I get on.

Regards
Frank

[FRANK.C]

Unfortunately the news is not good. After testing the field OP coil (autotransformer) again it was found to be open circuit. I checked the cathode resistor and the new grid capacitor to make sure that any of them had caused the coil to go.

I removed the outer insulation from the coil hoping to find the break at the surface, but no luck. I don't think that there is much chance of me finding a replacement and it would be beyond me to rewind it. Is there a company that rewinds the likes of these?

Regards
Frank

[beery]

Hi Frank,
I have checked the specs on this transformer.
I think you will have to get it re-wound and it will need to be done on a machine with automatic feed.
Here is my reasoning...

Most manufacturers at this time had low impedance frame coils measuring around 10 ohms, the matching frame transformers were about 500ohm pri and 2 ohm sec.
Your set uses coils of 65 ohms total. The transformer is shown as an auto transformer, but will actually be wound with two different wire sizes. The primary and secondary are internally connected in series. The primary measures 1200 ohms and the secondary measures 20 ohms.
To get a 1200 ohm primary takes many turns of fine wire. My experience of trying to wind these with a manual wire feed has shown that if the wire crosses over itself a few times then the winding won't fit within the almination space, hence the need for auto feed.
Also although there are many spare frame transformers around, most of them are low impedance

Personally I would recommend Ed Dinning.

Cheers
Andy

[FRANK.C]

Hi All

Andy
You are right about the transformer: it has got two different sizes of wire. The larger one is next to the core and is plainly visible from the side of the windings. I will try and get it rewound.

In the meantime I had a go with bodging . I had mains 9V-0-9V transformers one a 500mA the other a 1A. I tried both and the two of the gave practically the same results. Hooking up the 0 and 9V gave me about a 50% filled raster and hooking up the 9V and 9V gave me about 80% filled raster at full height adjustment. It looks to have a lot of cramping/foldover, its hard to say exactly what, as I haven't got a suitable signal yet but there is an Aurora on the way.

I haven't tried a radio OP transformer as all I have found are considerably smaller than the frame OP one.

I have posted below a photo of the raster I got with the mains transformer. The HT is a little low at 175V; it should be 185V. I'll need to replace the PY82. The voltage across the cathode resistor of the frame OP valve was 8.8V with the mains transformer in place.

I will post again when I have any news.

Regards
Frank

[FRANK.C]

Hi All
This is my latest bodge attempt.

I found two 9V 2.3VA mains transformers.
By connecting the primary's in parallel and the secondarys is series I got DC resistance's of primary 1K and secondary 18R which is close to the original of 1K2 and 20R. I have posted a photo of the raster I got which is much improved over the other attempt but there is still some cramping.

There are some hum bars visible in the photo due to the camera.

Cathode resistor voltage is now 9.8 volts . I should have said in the previous post that it is normally 9.5V.

I have noticed that there is no snow as you would get in a modern TV is this normal or have I got a fault in the signal stages?

Regards
Frank

[Steve_P]

Looks to me like an IF Fault. Have you got a signal source you can put in to see what comes out?

Cheers,

Steve P

[beery]

Hi Frank,
it looks like you have hit the jackpot with the transformer.
You now really need a signal source.
If you still have cramping problems when there is a signal you may need to modify the transformer in the following way:-
Removing all the laminations
Put all the 'E' lams together
Put all the 'I' lams together
Put a piece of paper or thin tape along the face of the stack of 'I' lams where it will meet the 'E' lams to create a gap between the two stacks.
Put the lams back in the transformer (you may need to find a way of holding the lams in place)

As for snow, well I find that usually only a few 405 line sets produce visible snow. You will get more snow on Band 3 I think. Also because positive modulation is used on 405 the snow is less visible as it tends to produce de-focussed white splodges which merge.

Cheers
Andy

[FRANK.C]

Hi again

Aurora arrived today so I got it hooked up but no joy. I couldn't get any signs of a signal. I checked all the voltages around the IF valves but nothing amiss could be found. I was beginning to suspect a tuner fault. After a break it occurred to me to check the band sensitivity control, and sure enough they were both turned down to zero. After turning up the control there was signs of life. After adjusting the frame and line controls I got a stable picture.
I have posted a photo below. Height is not full and linearity is out but the tube seams to be quite good: a lot better than I had expected.

The contrast control would not work; it turned out to be the pot that was at fault. After dismantling the pot it was found that the carbon track at either end was not making contact with the end connections. A coat of conductive paint from the end of the tracks to the connections cured this problem.

After been reassembled the contrast control now works. I have noticed that turning up the contrast reduces the width and increases the height.

Sorry the photos are poor quality I will get some good ones taken later.


Frank

[Tazman1966]

Great news Frank and well done

That field lin is almost there. Is there no further adjustment on the control? Also I shouldn't worry too much about the reduction in width and increase in height when you advance the contrast/brightness. It's just slightly poor EHT regulation. The Pye 691/693/697 series of colour sets did exactly that many many years later. You could try another EHT rectifier.

All the best,

[FRANK.C]

Thanks tas for the info.
I will try a new EHT rectifier but the effect isn't too bad probably normal. The photo was with height, linearity and hold controls adjusted to optimum. I have now changed the wiring of the transformer. It was wired as a transformer but now I have wired it as a autotransformer which has given me extra height but still have the linearity problem.

I also have a sound problem. I can't get sound and vision, no matter what channel I have Aurora set to. The best I can get is with Aurora set to channel 5.
I then can get vision on the biscuits marked 11CF, the sound is two biscuits away on the ones marked 9CF. The 9CF biscuits can be tuned to make the sound interfere with the vision, giving black and white bars across the screen. I guess that it is probably the sound stages are misaligned, but I would like to get confirmation of this before I go changing them.

Regards
Frank

[FRANK.C]

Hi again
I knew I couldn't rewind the original transformer it and the wire it used was far too small.
Today I came across and old Maplin 50VA transformer kit with the windings gone and it got me thinking. So out with the drill and mounted the former on it. I got some 40SWG ECW (it was the smallest I had) and wound as much as would fit on one side. It ended up having a resistance of 1K4. On the other side I wound some 30SWG (at least I think it was the markings were gone from the bobbin) it gave me a resistance of 18R.
I measured the inductance of the secondary of the old transformer. I adjusted the number of laminations and the gap between the E and I sections to match the inductance of the new secondary to the old. The result is that I can get a full raster with good linearity. The biggest problem now is to find enough room to fit the much larger transformer.

I have a picture posted below. The raster is not full at the top this is because the set is on its side and I can't get at the shift control to centre it. But it will open out fully. I will have to mount the transformer before I will be able to put the set upright again.

I still have to tackle the sound problem.

Frank

[FRANK.C]

Hi All
The story so far.
I removed some of the turns from the primary of the frame OP to bring its resistance down to 1K2. This had the effect of giving me improved linearity control (the linearity slider is now in the centre of the track; before it was at one end); it has also improved the height control.

I bolted the transformer to its mountings and fitted under the chassis. The pictures below show the old and new transformers together and the new one mounted on the chassis.


I realigned the sound IF and now I have good sound.

I am having problems with flyback lines . They are in a sort of 'T' formation. I have got about three full ones at the very top. Then the rest of the way down the screen there are flyback lines about 2 inches long which are about one third the way in from the left hand side.
These flyback lines are not visible on test card C only when watching video from a DVD via Aurora.

I have checked the two 1 Meg resistors in the A1 supply; they are OK and the capacitor has been changed. The anode and grid resistors in the video amplifier was found to have gone high so I changed them. The resistor from the video amplifier feeding the tube was also high it was changed too. The .1 uF capacitor in parallel with this resistor was missing so I fitted a 1000V one in its place.

These replacements has improved the bandwidth as I can now see 4 of the gratings whereas before I could only see 3.
But the flyback lines are still there - any ideas?

There is also some pincushion distortion on the right hand side but its not too bad.

Frank

[FRANK.C]

Hi again
Still having problems with flyback lines. I was wrong in the last post when I said that they are not present when the test card is on. They are there but not as visible .

The A1 is a little low at 336V should be 360V. The cathode is also low at 154V should be 184V. The HT was at the correct 185V when these readings were taken.

I have checked all components around the video amplifier and A1 supply.

I have posted a photo of the flyback lines and of the test card. The test card is blurred and overbright - that's the camera or operator's fault, not the TV.

On the test card I can get what appears to be a good grey scale without the lines showing, but when playing back a video the picture needs more brightness and then the lines show.

Could this be a low emission tube?

Regards
Frank

[Steve_P]

Looks to me like the flyback line suppressor isn't suppressing the flyback lines. On the frame that is. The beam should be held off when 'flying back' to the beginning of the screen.

I haven't got the exact circuit to hand, but check what appears to be D1 and D2 on my diagram. If they are shorted, could you get this problem?

Cheers,

Steve P

[FRANK.C]

Hi Steve
Thanks for the reply. I assume that your looking at the diagram for T524 which is a bit different to mine. I have got no vision noise suppression circuit . D2 or an equivalent isn't present. The brilliance control consists of just a pot and resistor with no other connections to it.
There is however D1 in the same place and I have not checked it yet, but will do so tomorrow and report back.

Thanks again
frank

[FRANK.C]

Hi again

I checked D1 by substitution but no joy.
As the video amplifier shares its cathode resistor with the line OP valve cathode and the voltage here is a little low 2.5V should be 3V.

I decided to check out the line OP stage. I fitted a NOS PL81 and PY81.
I checked the cathode resistors. The two decoupling capacitors 400uF and .25uF were already changed.
A resistor in the grid circuit of the PL81 was high and was changed.
The resistor feeding the screen of the PL81 is in the diagram as 15K, there was a 8k2 fitted but it had risen in value to 14k (an early form of recycling?) I replaced it with a 15k.
After all that no improvement and the voltage at the video amplifiers cathode is still as 2.5V.
I have no idea what to try next.

Regards
Frank

[Ed_Dinning]

Hi Gents - back from hols today and on the case, thanks for the recommendations!
The trick with an old mains transformer is worth doing as it shows if the stage is working, sadly I've never seen it give anything like a linear picture, but still a useful test.

Ed

[FRANK.C]

Hi All
Just a update on how things are progressing.
I haven't spent as much time on it as I would have liked as I was ill for a while (chickenpox).

I am still having problems with the flyback lines. I have been through the circuit and can't find any form of flyback line suppression. If anyone knows that there is one on this set I would be grateful if it could be explained to me.

What I have done as a test is that I have copied one from another Alba set. I connected a .01uF cap and 100K resistor in series, connected one end to the grid resistor of the frame OP valve and the other to the slider of the brightness control. This has resulted in clearing about 80% of the flyback lines with only a few left at the top.

Ed has kindly agreed to rewind the transformer. I am hoping that when the rewound transformer is put back, it may help to clear the flyback lines.

The TV was left in a garage for years before I got it there was paint spilt and splashed on to it and the cabinet was badly scratched in places, so there was no choice but to strip it, which I have done. A lot bigger job than stripping a radio.

One of the bushings for the door hinge had totally rusted and disintegrated. I made a replacement from a brass nut of a 7.5V electric fence battery. I did this by enlarging the centre hole part of the way through and then jamming the drill bit in it. I held a file in the vice and by turning the nut in the drill filed it down to size.
Kind of poor man's lathe.
When I got the outside to the right size I drilled out the inside to the correct diameter. A picture is posted below of the type of nut I used the new bushing and a good original bushing. The new bushing is shorter but that won't make any difference to the working of the hinge.


Frank