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Old 24th Sep 2014, 5:33 pm   #1
EF80TVVALVE
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Default 1970s Ferguson model 3738 TV

Hi, a few years ago I bought a ferguson colour tv from the 70s. I powered it up but the cap across the mains went up in smoke and it went in the shed until today. I tried powering it up today and cut the cap before powering it up... there is currently no life at all from the set, fuses however are intact so do I need to replace the mains capacitor in order for the set to work?
any advice will be greatly appreciated!
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Old 24th Sep 2014, 5:54 pm   #2
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Default Re: 1970s Ferguson TV

You can leave the capacitor across the mains disconnected, it will require replacement though when the tv is working.
Some Thorn TV's used a circuit breaker as well as fuses, this may need resetting. I would do some simple resistance checks across the mains supply and power supply before putting power back on again.
I never fixed many Thorn sets, just the occasional one so expect much more advice to follow from other forum members.
Frank
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Old 24th Sep 2014, 6:01 pm   #3
EF80TVVALVE
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Default Re: 1970s Ferguson TV

Hi, thanks for the help, I've noticed it was also connected with a few resistors and a wire that leads to another circuit board so I wonder whether it should be there in order for it to power up? I've checked everything else but I'm baffled!
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Old 24th Sep 2014, 6:22 pm   #4
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Default Re: 1970s Ferguson TV

The capacitor I thought you discussing is the one directly across the mains supply, if it is in the power supply then yes you may require it.
Have you got photos?
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Old 24th Sep 2014, 6:30 pm   #5
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Default Re: 1970s Ferguson TV

Hi, I haven't got any photos at the moment, it is the one that is across the mains supply, its on the on/off switch
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Old 24th Sep 2014, 6:43 pm   #6
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Default Re: 1970s Ferguson TV

You need to do some fault finding then unless Ferguson used that cap for something special, which I doubt. It is possible that the failure damaged items in the PSU, hence the suggestion of some simple meter tests.
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Old 24th Sep 2014, 7:07 pm   #7
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Default Re: 1970s Ferguson TV

You may find the cap blowing has taken out one of the poles of the on/off switch. The fuses in the set or the plug should have blown first of course.
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Old 25th Sep 2014, 9:32 pm   #8
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Default Re: 1970s Ferguson TV

After looking at the set more I have found that it is a thorn 8800 chassis. On the PSU there is a resistor that seems to be overheating and it has burned most of the board. Would this need replacing or would there be another cause as to why it is overheating. I have managed to get the CRT heater to glow but the rest of the set is dead.
Thanks!
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Old 26th Sep 2014, 12:33 pm   #9
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Default Re: 1970s Ferguson TV

Hi, if anyone has any circuit info regarding the 8800 chassis, could you possibly tell me what R704 is? It has no markings on it at all and I am unable to find any circuit information for it.
Thanks!
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Old 26th Sep 2014, 5:23 pm   #10
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Default Re: 1970s Ferguson TV

I only have the circuit shown on pages 242-243 of the 1975-76 Servicing book.
R704 is listed as 51 ohms. Its in the collector of VT702, MJE520. Collector voltage = 35.V
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Old 26th Sep 2014, 5:23 pm   #11
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Default Re: 1970s Ferguson TV

Is there a model number on the set anywhere
Likely to be 37??
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Old 27th Sep 2014, 10:44 am   #12
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Default Re: 1970s Ferguson TV

Hi, it is a model 3738.
Thanks for all the help!
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Old 1st Oct 2014, 11:59 am   #13
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Default Re: 1970s Ferguson TV

Hi, after looking more at the set today the symptoms are that it only powers the tube heaters, on the degauss board X801 (I believe is a PTC thermistor) is getting very hot as is R704 on the power board.
I have put in a request in the repairs wanted section as I'm not a fan of these tv's!
However, should it be something relatively simple I'm happy to do it myself!
Regards!

Forgot to add, is there any chance it could be one of the transistors on the power supply board?

Last edited by AC/HL; 1st Oct 2014 at 4:57 pm. Reason: PS merged
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Old 1st Oct 2014, 3:46 pm   #14
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Default Re: 1970s Ferguson TV

Your reference to the diode BZX61C220, which was been deleted on your last edit would appear to be a 220volt zener. There are many components that will shut down the power supply. Your approach for asking for help in your area is a wise move I feel.
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Old 17th Oct 2014, 1:23 pm   #15
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Default Re: 1970s Ferguson model 3738 TV

Hi everyone. Having replaced the power supply board I now have power to the rest of the set. There was still a fault with the resistor overheating but unplugging the Chroma, IF and video board (all one board) has stopped that from happening. Unplugging this has given me full EHT and the screen lighting up in a sort of purple colour. What should I now start checking on that board that could be causing the fault of the power resistor overheating?

Regards
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Old 17th Oct 2014, 1:44 pm   #16
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Default Re: 1970s Ferguson model 3738 TV

After doing a little more poking around, unplugging P.L.4 on that board will make the set work fine with the Chroma etc board all plugged in. As soon as it is plugged in, the set goes dead again.
Regards
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Old 17th Oct 2014, 10:18 pm   #17
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Default Re: 1970s Ferguson model 3738 TV

Sounds like one of the tantalum capacitors has gone s/c - one of the ones across the 25V line.
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