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Mystery Ferranti Set

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Cathovisor
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Posted by: @sideband

Hmm....there might be some instability present or something may be arcing.

That looks like "brushing" to me. Listen out for a slight fizzing noise when the set's running.

 
Posted : 06/04/2020 3:26 pm
PYE625
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If there is local interference, the spots tend to be larger and much more spaced out. There probably should not be this kind of vision noise if the antenna socket has nothing plugged in, unless external interference is heavy. Does the picture noise clear when a blank channel is selected?

The concentration of spots at the left of the picture might suggest brushing in the line stage to me, but the line stage may be making hissy sounds with no signal to lock onto, so it could be hard to hear any slight fizzing EHT noise. It may be visible in complete darkness though.

I would probably suggest not to run the set for very long until you can obtain a proper 405 line signal with a stationary test card, then any other faults may be more easily identified. If indeed there are any, as it is by no means completely certain.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 06/04/2020 6:21 pm
lotsalines
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The noise is on 5 different channels.
The tuner has 9 columns populated, the dial has 4 channels but only about a third of the metal ring with them printed remains so it looks to have 9.
I only get the noise with a bit of wire connected to the socket.
Without the wire all channels are blank.
If I hold it up the amplitude of the noise goes up.
The EHT rectifier is not yet properly connected because the cap broke off when it arrived! for now the wire has been curled a bit to hold onto the EHT connection so the connection is not stable.
I never power the set on for long, only long enough for a raster to form so I can see what's going on.

 
Posted : 06/04/2020 6:48 pm
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PYE625
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Ah, well in that case, I would not be unduly concerned.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 06/04/2020 7:15 pm
Katie Bush
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I would also incline towards the diagnosis of brushing, as has been twice suggested above. Definitely time to get some sigs going into the ae socket.

 
Posted : 06/04/2020 7:23 pm
lotsalines
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Should be able to get a signal into it soon.
I'm still wondering what the wooden case is about though.
I've looked up the ferranti/ekco models using the chassis and I cannot find any reference of sets that aren't portables.

The construction does not look like anything that could not be achieved with some woodworking skills.
Do you reckon this could be a shop that's tried to do it up B&O style or could be a DIY job?

 
Posted : 20/04/2020 1:18 pm
lotsalines
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I have finally powered up the set with the modulator and after playing about with it for a while I was greeted with this lovely raster.

IMG 0263w

It's a 'little' unlinear and the corners are a bit soft but it is the first 405 line raster I have ever seen with my own eyes!

 
Posted : 27/04/2020 7:10 pm
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PYE625
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That is very good....well done sir !

The stretching at the top always adds a nice boost to peoples' hairdo's  ? 

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 27/04/2020 7:42 pm
lotsalines
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It's been a bit of while since I've given an update on the set but there isn't much to report I'm afraid.
I found a couple of old hunts capacitors that were giving me grief but they have now been replaced which has got rid of almost all the noise on the working channels.
The source of the egg shaped raster has still not been found.
It does not seem to be linked with the frame output linearity control or the HT voltage.
I did have a spare frame output valve so I decided to swap it in and see if it changed it in any way.
It made locking it in more touchy and amplified the distortion.
I will check any surrounding resistors to see if they have gone high.
I no longer seem to have the brushing issue.
There are still waxies in the set.
The tuner appears to have some which will need to be replaced and there is also C73 which access to is incredibly difficult.
Hopefully I should have an update soon but if I need to replace anything I don't have in it could take a while.

 
Posted : 19/05/2020 12:55 pm
crustytv
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Posted by: @lotsalines

The source of the egg shaped raster has still not been found.

As the B&W mob have not responded and without reading back through the whole thread, you seem to be doing and checking the right area and parts. Easy to miss things though, so double check your work thus far in frame timebase, re-test the linearity & height controls out of circuit, look for leaky caps or missed caps/ high value resistors gone higher, all frame timebase valves etc.

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Posted : 22/05/2020 7:21 pm
PYE625
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Posted by: @lotsalines

There are still waxies in the set.

Are there any in the frame stage?  (C75,78,80,84 and the cathode bypass electrolytic C77 would be of interest.)

Or indeed as Chris say's, worth checking the frame stage for any other faulty component, especially in the same circuit as the frame linearity control.

Does the frame linearity control have much effect when adjusted?

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 22/05/2020 7:51 pm
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Nuvistor
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C77 cathode bypass on the frame output valve was a common fault, its in a dual can with the sync separater screen grid decoupler. At the age of the set paper caps and high value resistors are just as likely.

 

 

 

Frank

 
Posted : 22/05/2020 8:10 pm
lotsalines
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All the relating waxies have been replaced so I'm moving on to the big can.
I have taken it off the board and I can already tell by all the crust underneath it that replacing it is necessary.
I'll get back to you all when the replacements arrive.

 
Posted : 29/05/2020 6:11 pm
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PYE625
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The can electrolytic, if faulty, may have it's guts pulled out and modern replacement capacitors discretely mounted inside the empty can (example technique here). It should then be possible to re-mount it to the PCB and nobody would know the difference. Except that the set would work properly, of course. ? 

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 30/05/2020 11:50 am
lotsalines
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This is more or less what I have done except I pulled off the base and removed the innards keeping the metal can in the same state.
I plan re-stuff the can with the new capacitor pair to keep the set as original as possible.
I have also kept all the old waxies so I can do the same to them.
The look of new components in vintage electronics doesn't normally bother me but the high-vis glare of the new capacitors along with chucking a decent metal can for no good reason is more than enough of a reason to give it a go.

 
Posted : 30/05/2020 9:44 pm
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lotsalines
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The can has now been replaced but sadly this has not fixed the issue.
This does now mean that the board is no longer being coated in electrolytic fluid/crust so it wasn't all for nothing.
Now I'm able to get to the back of the board I can go through the resistors and check if they're good or not and replace any that seem off.

 
Posted : 04/06/2020 5:01 pm
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