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Mystery Ferranti Set  

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crustytv
(@crustytv)
Vrat Founder Admin
Posted by: @lotsalines

I went to test the capacitor and it seemed OK

Without reading (yes I'm lazy 😉 ) through the entire thread, how are you testing capacitors? Some of my thoughts, I'm sure others will differ and have their own slant on this topic.

Unless your testing correctly in the right conditions, at rated or near, you're probably not really getting a true picture (excuse the pun) of a capacitors' health, as leakage current increases with voltage and temperature. The simple approach is if in doubt change it but if like many of us you prefer to be analytical and only replace when you have evidence of a faulty component, why not consider investing in a Megger. These devices can push 250V, 500V and 1000V across the cap. Using a normal multimeter (AVO etc) whilst OK for checking for shorts and getting a rough indication of its ohms reading, its more likely to give you false confidence with regard to leakage. Using a Megger will give you a clear indication if a cap is in trouble when it gets 500V+ shoved up it.

My Robin 3111

robin3111

Don't rely on a Megger for electrolytic capacitors, for these types you're far better considering either a bridge or reformer with a leakage indicator, as these can supply rated Voltage. Whilst the cap attempts to reform, you can monitor the sustained rated Voltage on the cap for leakage. In the absence of a bridge, you could build yourself a reformer, plenty of designs on the internet. Get a shaver transformer, caps resistors, diodes and a 1mA meter and you'll be away. Here's a good one was built a long while ago on Vrat, the link includes a circuit.

https://www.radios-tv.co.uk/community/general-discussion/electrolytic-capacitor-reformer/

Those little peak meters like the ESR70 are OK for giving the DUT capacitance and ESR and will show up low voltage caps being leaky. Not really much use for leakage on big power caps though. Same goes for the LCR40/45.

Below:
Photo 1:HUNTS CRB-3 can supply 600V+ into a cap in steps, Neon strikes to indicate leakage. Meter connected to monitor voltage attained during tests. Photo 2: Peak ESR70 showing same DUT, its capacitance and ESR.

capref3
capesr2

As I say, just some of my thoughts which are by no means definitive, I just felt you might or might not, find it useful.

 

Crusty's Collection: Read the repair blogs
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Posted : 03/04/2020 12:12 pm
lotsalines
(@lotsalines)
Busy V-Ratter Registered
IMG 0254

What about that then!

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Posted : 03/04/2020 1:29 pm
helloekco, freya, Cathovisor and 2 people liked
crustytv
(@crustytv)
Vrat Founder Admin

Well done, as some like to say, you have "First-Light". 

Now you have something on screen, things should be a lot easier and make sense. From here on out, the components in the various parts of the circuit will be telling you visually via the screen, what their state of play is.

Perseverance pays off. 👍 

Crusty's Collection: Read the repair blogs
Crustys Youtube Channel: If you want to follow me on Youtube, please consider subscribing

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Posted : 03/04/2020 1:36 pm
lotsalines
(@lotsalines)
Busy V-Ratter Registered

Thank you.

Well chuffed.
It was just starting to become not very fun. Still a long way to go but that is progress right there!

IMG 0255

Suppose i'd better figure out a way of generating a 405 line signal. I have a VGA port that'll go down to daft low frequencies, wonder if the VGA to composite resistor trick works on 405? Line hold also works as a bonus brightness control for now so that will need to be seen to.
Needless to say I would have not gotten very far without any of you so a massive thank you all round to the VRAT community!

 

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Posted : 03/04/2020 2:48 pm
PYE625 liked
Cathovisor
(@cathovisor)
Illustrious V-Ratter Registered

@lotsalines

@peterscott is your man for generating 405 from a PC.

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Posted : 03/04/2020 4:08 pm
peterscott
(@peterscott)
Prominent V-Ratter Registered
Posted by: @cathovisor

@lotsalines

@peterscott is your man for generating 405 from a PC.

Thanks for the recommendation Cath. 🙂 

Take a look here

Peter

www.nostalgiatech.co.uk

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Posted : 03/04/2020 4:13 pm
helloekco
(@helloekco)
Trusted V-Ratter Registered

For me, @peterscott's excellent page linked above was invaluable in getting a working 405 line source, as was this 405 line modulator kit, which was cheap and easy to build. If you build a modulator such as that one, first check what channel "biscuits" are fitted to your TV, because you will need to wind the coils accordingly (it's a fixed frequency modulator). I built mine for a very late 405 line set before I started working on my older Ekco set, and have since discovered that the Ekco doesn't have the channel for which I built the modulator...

If you plan on very regular use though, I recommend a Hedghog II converter. Since I bought one I haven't used my PC setup, because it's just so much more convenient combined with a cheap digibox. The direct 405 line video output is useful to help isolate problems, and the static test card is proving very useful.

@freya is selling Hedghog IIs ready-built (highly recommended).

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Posted : 05/04/2020 1:41 pm
sideband
(@sideband)
Famed V-Ratter Moderator
Posted by: @lotsalines
IMG 0254

What about that then!

What about that then!! Very well done...what wat the rogue component? Or was it some stupid something that had been left off?

 

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Posted : 05/04/2020 2:15 pm
freya
(@freya)
Noble V-Ratter Registered

@helloekco

@freya is selling Hedghog IIs ready-built

If its useful, i also have the pre-built 405 line VOL modulators available https://electronics.frankcuffe.ovh/vol

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Posted : 05/04/2020 2:44 pm
lotsalines
(@lotsalines)
Busy V-Ratter Registered

Can't say i'm too sure what it was. It may have been working for a while without me knowing.
Decided on a whim to set the width to max with the terminal connector on the line output board as well as turn the brightness/contrast all the way up just to see if I was getting anything at all.
To my suprise with the brightness all the way up it was drawing a raster.

Thank you for the information on 405 signal input on VGA as well as the modulators/converters on offer. I'll look into each one more shortly but before that I have to sort out a few more things on the set. I do not seem to have sound besides a bit of mains hum unless I can hold the volume dial in the right position and the contact cleaner has hardly helped so that will need to be replaced.

I do not seem to have any video signal going into the set as far as I can tell. The contrast does nothing. I get a bit of picture flicker when I change the channel but that's it. The raster is not that wide and I can see some mains ripple across it, so I think I'll need to look back at the supply again.

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Posted : 05/04/2020 5:59 pm
sideband
(@sideband)
Famed V-Ratter Moderator

As before.....golden rule....check supplies first. We know the timebases are working now so check the HT first. No point in adjusting width until HT and boost HT are confirmed to be OK.

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Posted : 05/04/2020 6:15 pm
lotsalines
(@lotsalines)
Busy V-Ratter Registered

HT is 197V with line hold at max frequency, 165V at lowest.
Will get back to you on boost.
I forgot to put the capacitor back in and it turned out it was fine.
Rasters looking quite good now.

IMG 0257
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Posted : 05/04/2020 8:03 pm
sideband
(@sideband)
Famed V-Ratter Moderator

HT probably isn't far out then and the boost is likely to be OK. I reckon if you can get a signal into the set, you might see something.

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Posted : 05/04/2020 8:17 pm
lotsalines
(@lotsalines)
Busy V-Ratter Registered

How would I go about that with a generated composite?

Do I just inject it into the control of the video amplifier through a capacitor?

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Posted : 05/04/2020 8:21 pm
Red_to_Black
(@red_to_black)
Noble V-Ratter Registered

Please don't even think about doing what you are contemplating doing, it will end in tears, other forum members I am sure will give you far better advice than I can.

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 05/04/2020 9:26 pm
lotsalines
(@lotsalines)
Busy V-Ratter Registered

Had a feeling it would end in tears.

Glad I got the warning before doing something stupid 😆 

Where would I inject the signal then?

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Posted : 06/04/2020 12:24 am
lotsalines
(@lotsalines)
Busy V-Ratter Registered

With power back to the tuner/if stages it seems to be working quite happily now (at least with stray signals).

Might ditch the video injection idea and make/get ahold of a modulator.

tellee

 

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Posted : 06/04/2020 1:21 pm
sideband
(@sideband)
Famed V-Ratter Moderator

Hmm....there might be some instability present or something may be arcing. 405 sets don't normally show noise on the screen with no signal....usually just a grey raster. It's a good sign that the RF/IF stages are working though....all you need now are some signals..... Do you have an RF signal generator? If so, does it cover 40 - 50 Mhz? You could use it as a means of getting something into the set by connecting it to the aerial socket and modulating it with 400Hz. Tune the generator until you see horizontal lines appear on the screen....probably somewhere around 45Mhz.....not very interesting but it will tell you that the tuner, IF and video stages are working.

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Posted : 06/04/2020 2:08 pm
lotsalines
(@lotsalines)
Busy V-Ratter Registered

Most the channels are blank. I was assuming it was picking up RF from some other radio devices in the area but it could be something else.
There are a few capacitors left in the IF stages and there is no shielding on the valves currently.

A signal generator was on my list of things to get that I never got round to but i'm sure I can pick one up easy enough.

I do have an oscilloscope though which is a bonus.

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Posted : 06/04/2020 2:23 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered

Does the tuner have a full set of channel coils (biscuits), most of this era only had the ones for the area it was sold to. Others could have been added later. It could be the cause of most channels being blank due to the absence of coils in every position.

 

Frank

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Posted : 06/04/2020 3:02 pm
helloekco liked
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