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Old 19th Nov 2022, 10:46 am   #41
thermionic
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Default Re: Dynatron can you identify this set?

Somethings not right there.

Your meters on the power supply suggest that the resistance of the overwind is 55 Ohms, it should be much higher than that.

Can you confirm that you have connected the leads from your power supply between the top cap connector of the PL36 valve and the top connector of the EY86 valve?


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Old 19th Nov 2022, 11:14 am   #42
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Default Re: Dynatron can you identify this set?

Hi Simon, confirmed.
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Old 19th Nov 2022, 12:52 pm   #43
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Default Re: Dynatron can you identify this set?

Okay,


So a little update. I did a ring test on the scope and it shows that it’s shorted. It could be very damp.
I gently heated it up with a hairdryer and the voltage slowly creeped up.. but not much.

I’ll leave the psu on as suggested and check back later.

Correct me if Im doing it wrong…
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Old 20th Nov 2022, 1:34 pm   #44
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Default Re: Dynatron can you identify this set?

Hi.

I’ve just dug out the circuit for your set to check the resistance of the EHT overwind, and I’m surprised to see that they quote a DC resistance of 48 Ohms.

So, it seems that your readings are looking favourable. My apologies for jumping the gun and saying that it looked suspicious!

You may need to increase the current through the overwind so that it feels warm to the touch.

Good luck, and please keep us up to date.

Cheers.

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Old 20th Nov 2022, 3:39 pm   #45
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Default Re: Dynatron can you identify this set?

Oh ok..

Well its been on the psu all day yesterday anyway.

Ive decided to put it on the variac this afternoon.
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Old 20th Nov 2022, 7:19 pm   #46
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Default Re: Dynatron can you identify this set?

Okay,

So... the booster cap and broken pots have been replaced.
I've turned it on with the variac, after steady increase over time, line whistle can be heard and crackling from the speaker when volume is adjusted. But no light.

C91 started to complain (bubbling wax), so the tv was switched off and C91 was replaced.
Second attempt showed that, line whistle was heard again at a higher pitch, which then dropped when voltage was increased. Still no light on the screen, however I have noticed earlier that the new DY87 valve has been cracked in the base so it's likely it is broken.

I still have the old one which has a cap that is broken off. I will try varnish, to stick the cap back on after soldering the wire. (Any tips would be great for this!)

Then that old dy87 valve will be returned to the set.
I will continue next weekend, for now the set is safely stored in the dining room not the cold garage!
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Old 20th Nov 2022, 8:33 pm   #47
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Default Re: Dynatron can you identify this set?

Quote:
Originally Posted by Electricdreams View Post

I still have the old one which has a cap that is broken off. I will try varnish, to stick the cap back on after soldering the wire. (Any tips would be great for this!)
I find Gorilla (foaming) glue ideal for this. It's the one with a honey colour liquid in a smallish bottle (but last ages) and usually comes with a pair of gloves (don't wear any nice clothes while using this glue!)

Squirt it around on the glass where the cap will go, solder the cap and keep the valve upright for a few hours and it will be like new. The glue foams up inside the cap and spreads all around making a really good join.
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Old 21st Nov 2022, 9:00 am   #48
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Default Re: Dynatron can you identify this set?

Poundland sell a two tube card, resin and hardener of adhesive for £1. Also very effective. J.
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Old 21st Nov 2022, 11:13 pm   #49
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Default Re: Dynatron can you identify this set?

Quote:
Originally Posted by Heatercathodeshort View Post
Poundland sell a two tube card, resin and hardener of adhesive for £1. Also very effective. J.
Araldite?
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Old 22nd Nov 2022, 11:33 am   #50
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Default Re: Dynatron can you identify this set?

No not in name or price but makes a very good substitute. J.
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Old 24th Nov 2022, 8:18 pm   #51
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Default Re: Dynatron can you identify this set?

Would you say this has gone to air?

There’s white substance on the inside… DY86
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Old 24th Nov 2022, 8:25 pm   #52
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Default Re: Dynatron can you identify this set?

Yes.....definitely!
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Old 3rd Dec 2022, 1:45 pm   #53
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Default Re: Dynatron can you identify this set?

And we have life!
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Old 3rd Dec 2022, 2:38 pm   #54
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Default Re: Dynatron can you identify this set?

Well done - good progress.

Keep the brightness very low during this frame collapse fault, otherwise you could burn a trace into the phosphor.

Should be a straightforward fault - picture before the end of the weekend? 😮
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Old 3rd Dec 2022, 5:32 pm   #55
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Default Re: Dynatron can you identify this set?

Well unfortunately I ran out of capacitors, I do have sound however..
The brightness isn't working at the moment so I didn't keep the set on longer than half a minute.

At least I know the Tube and EHT is okay. Will keep you posted.
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Old 3rd Dec 2022, 6:04 pm   #56
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Exclamation Re: Dynatron can you identify this set?

When you do start to run the set for longer periods of time, I recommend that you monitor the Boost HT voltage (I find pin 3 of the CRT - first anode - is a convenient place to clip a meter test lead onto). It's usually between 500 to 650 V in a typical set of this era.

If the LOPT is in danger of failing through leakage between turns/windings, the Boost HT will steadily reduce over time - significantly. If you have a raster/picture, the width will gradually start to creep in from each side (or just one, if the picture entering is not adjusted correctly).

The black pitch coating on the LOPT will also become soft as it heats up - especially on the EHT overwind that feeds the top cap of the DY86/87 EHT rectifier valve.
Don't touch the LOPT to check this whilst the set is switched on!

I would certainly not run the set for long periods until all wax (or black Hunts Moldseal) capacitors in the line output stage have been replaced (on the sound output and line timebase/EHT printed circuit board):-

two on the system switch, one on the LOPT itself, and one at the bottom of the PCB (on some chassis, it might be mounted on a tag on the bottom horizontal chassis, by the the frame output transformer) and two above the system switch on the panel.
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Old 4th Dec 2022, 11:40 am   #57
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Default Re: Dynatron can you identify this set?

Hi,

For the lack of height, if you haven't already done so, it may be worth checking capacitor C84A, 0.1uF (Trader Sheet 1675/T269), which is located not on the PCB's but on a tag-strip below the CRT, close to the multi-electrolytic capacitor.

It is a wax capacitor, and in my set was extremely leaky, causing an identical symptom to yours.

Good progress so far - It's certainly nice to see some life on the screen!



Adrian.
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Old 4th Dec 2022, 3:35 pm   #58
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Default Re: Dynatron can you identify this set?

Thanks Dazzlevision for that tip, I will do just that.

I'm slowly just putting caps in and checking my progress.

Hi Adrian, I did replace C84 and 84A still getting a line. I have replaced so far
C91, C65,C66,c100,c101

Thats when I ran out.. I will continue next weekend when the extra caps comes in.
At least the brightness works now. I wasn't confident to leaving it on full brightness trying to change the controls on the back.
So far no effect on the adjustments but most of the pots were turned clockwise, one literally was forced to leave the track!
I think someone was trying to get it going one time.


It's a nice tube and loving the crt shutdown effect..

Cheers
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