Ferguson 246T-sound ok but no picture - UK Vintage Radio Repair and Restoration Discussion Forum

SGT.Pepper · 30th Dec 2009, 11:21 pm

Please forgive me for my lack of knowledge on this subject-this is my first TV repair and I have previously only fixed much more basic stuff like Dansette record players!

Anyway, it's a big mid-1950s 17" console set with a light-up CRT mask. When connected to my Aurora the test tone can be heard from the speaker and can be made louder or quieter by operating the fine tuning control, but no life on screen. It's not lit up at all, just completely blank. Last week I could make interference appear briefly on screen by turning the channel change switch but it won't even do that now.

I can indeed hear a line whistle so I think the line output transformer is intact and the back of the CRT is glowing normally, and not some weird colour. I have tried replacing (according to the service manual) the frame charge capacitor and the part CRT coupling capacitor (both 0.1uf), admittedly only because these sounded important. The PY32 is above suspicion as this is brand new-the original had gone milky.

So my question is this: is it worth continuing? I don't really want to spend huge amounts of time and money on fitting all new capacitors only to find out that something irreplaceable like the CRT is broken! Any advice here would be appreciated!

Steve_P · 30th Dec 2009, 11:35 pm

No, it won't be the CRT. It's either the video stages or the Line Timebase/EHT section.

Run it for a few minutes and see if the EHT Rectifier is lit. If not, it's the line output/EHT section. If it is, then it's the Video/IF section that's playing about.

Check the Brightness and Contrast controls as well.

Cheers,

Steve P.

Peter.N. · 30th Dec 2009, 11:47 pm

A quick check for EHT function is to briefly short the grid and cathode of the CRT together, if you have eht the screen should light brightly, or according to the condition of the tube. Can't remember the pin numbers at the moment.

Peter

SGT.Pepper · 31st Dec 2009, 12:18 am

The EHT rectifier does not appear to be lit, if it is it's very dim but I think that's just the reflection in the glass off the valves that are next to it. There is a small blue glow from the plastic top cap thing when prodded with a knitting needle though but I'm not sure if this is good or bad. So I think we've narrowed it down to the line output stage, but that tends to mean certain doom, doesn't it?

PS. Peter N: I don't know the pin numbers either so I haven't tried your test yet.

Welsh Anorak · 31st Dec 2009, 3:56 pm

Hi
Doom? Not a word we know here....
That corona discharge sounds healthy, and I'd try and find out definitely whether the EHT recifier's heaters are lit - a dark room and some thin card to visually isolate the area are helpful here. This will save time looking in the wrong area later! While you're in the dark (literally and metaphorically) have a very close look at the screen while varying the brightness - you may see a small glow indicating low EHT - or possibly a full sized dim raster indicating a video fault.
If you've got low or no EHT the rectifier valve's the first port of call, followed by the continuity of the heater windings. I know LOPT is a bit of a worry, but you've plenty more to check first - and there are remedies to this so don't worry - yet!
Glyn

Boom · 31st Dec 2009, 4:37 pm

Quote:

Originally Posted by SGT.Pepper

There is a small blue glow from the plastic top cap thing when prodded with a knitting needle though but I'm not sure if this is good or bad.

Eh? You are touching the EHT with a knitting needle?

A much safer way to test if the the LOP stage is working is to wave a neon screwdriver near it. If the LOP is working the neon will light.

I'd have thought a set of that age would need a thorough recap before operating it or you will almost certainly cause damage.

Dave

Heatercathodeshort · 31st Dec 2009, 6:25 pm

This is a very reliable set. Our first television was a model 236T, it's the same but minus the doors. Its very difficult to see if the EY86 is lighting up due to its position on the Praying Mantis style of lopt. You will probably have to clean its glass and have a look at the bottom of the anode. If it is lit you will have EHT.The glow should be reflected in the ring at the base. Remember the ion trap magnet that is mounted on the tube neck just forward of the base. If you have moved this only a tiny amount after your original active screen you will find that readjustment will bring back the raster. There is a knack in adjusting them, ask for more info if you think you might have moved it. The fibre strap used to break on the early ones so you may have one with a rubber gasket. I reckon it will work especially as you had clicks etc when you changed the channels.As David suggests a recap will be required to bring it up to standard especially the frame timebase. Good luck with it! [I wish it was mine] Regards, John.

SGT.Pepper · 31st Dec 2009, 6:38 pm

I am now certain that the EHT rectifier is not lit. I have also noticed that a small part of the side of the PL81 next to it is glowing blue. And I've looked very closely at the screen whilst operating the brightness control and I cannot see any life whatsoever. Strangely enough I have faith in the LOPT though-it looks fairly ok, the black stuff it's covered in doesn't go all squishy and the line whistle seems to indicate that it's doing something useful. I'll try it with a new PL81 and EY86 the next chance I get, but brilliantly I've left all of my valves at my dad's house because I didn't think I'd need them! Silly me. Also, I've gone out of my way to make sure not to disturb the ion trap magnet so far, so I don't think that's the problem!

TV_Madness · 31st Dec 2009, 7:42 pm

I have only skimmed over the rest of this post, so forgive me if I'm covering old ground. Have you checked for presence of EHT at the AC side of the rectifier? You should be able to draw a spark with a screwdriver with a WELL insulated handle.

SGT.Pepper · 31st Dec 2009, 8:50 pm

I can draw a spark from the connections at the bottom of the valve, but they are somewhat pathetic looking sparks...

Laurdys · 31st Dec 2009, 9:06 pm

i think the pl81 will be ok if it has a small blue glow on the inside of the anode so long as its not glowing bright purpleish blue(make sure its not gassy). it will probarbly be the EHT Rectifier or its heater winding

Heatercathodeshort · 31st Dec 2009, 9:51 pm

This needs a recap. The .01uf [?] coupling capacitor to pin 2 of the PL81 is probably leaking for a start. J.

Danny · 31st Dec 2009, 10:23 pm

Hi you say you draw small sparks at the bottom of the valve which valve as if its the eht rec the sparks may seem small but dc doesnt jump as well as the ac unless you earth the screwdriver then it may get interesting. my guess is as already mentiond the ion trap magnet needs adjustment. use a darkend room with a mirror in front and with a torch carfully adjust the magnet you may be suprised. Oh and take care if you are not using an isolation tranceformer as the shassis is not isolated on these sets. Danny

Peter.N. · 1st Jan 2010, 11:11 am

I had forgotton all about ion trap magnets.

SGT.Pepper · 1st Jan 2010, 1:52 pm

The ion trap magnet's definitely ok-I've made sure not to disturb it. I'm certain it's the EHT-the rectifier's definitely not lit and I can only draw tiny little sparks from the connections under the valve, even the one that goes straight to the final anode of the CRT. And when I say the sparks are tiny I mean tiny, about the size of a pinhead. I think I'll try a new EY86 and PL81 (because it is indeed gassy) before doing anything else.

Heatercathodeshort · 1st Jan 2010, 10:54 pm

Hello again ?,
I doubt very much if the PL81 or EY86 valves are faulty. A more likely cause of your problems are the wax capacitors in the line timebase and frame [field] timebases. The coupling cap as mentioned and the boost capacitor will require replacement and it will probably brighten up. The picture when you get it will probably be very cramped at the bottom and again you will have to change some capacitors.
The coupling cap to pin 2 of the PL81 is C161, Its a .001uf but the recommended replacement was a .01uf. The boost capacitor C131 .25uf and the tube A1 decoupler C134 .01uf are screaming to be changed. You will need a circuit. Its extensively covered in the 1956/57 Newnes pages 351 to 368. I have scanned, marked and attached the components mentioned. If you are stuck for a circuit, please PM me and I will scan and forward. Hope this helps. Regards, John.

Danny · 1st Jan 2010, 10:57 pm

Yes you may be right but did you draw the sparks from free air Ie just hold a screw driver near the anode or did you connect the screwdriver to shassis ? . also the iom trap magnets do change in magnetizm and sometimes need reajusting or even replacing on some sets. good luck Danny

Heatercathodeshort · 1st Jan 2010, 11:15 pm

Just seen Danny's post. The spark test as he describes is correct and safe with flyback derived EHT as your Ferguson 246T employs. NEVER do it with a mains derived system but this is of no relevance to your receiver.
On the AC side of the rectifier i.e. the anode top cap connector you need to pull this off the valve and tilt it towards you. Switch the set on and with a well insulated screwdriver [such as a modern one with a plastic handle] switch the set on and allow the tip to touch the anode connection. A spark around a quarter inch should be able to be drawn from this. DO NOT CONNECT THE SCREWDRIVER TO CHASSIS. Just hold it and 'tickle' the clip inside the top cap shroud. If this is present you will need to test the DC end of the rectifier, [EY86] at the crt connector. Again using a well insulated screwdriver or probe but this time with the screwdriver connected to CHASSIS push the tip under the crt connector. A series of spark 'cracks' should be seen and heard. This is quite dramatic the first time you do it bit it's quite safe and was the standard practise before transistor circuitry became common place. Leave the ion trap magnet in place for the time being. You did say you had flashes on the screen so it should be ok.
I want to see this up to standard. I broke our 236T up around 1965 and have regretted it ever since...Take care and sensible precautions.
Regards, John.

SGT.Pepper · 2nd Jan 2010, 12:20 am

John-I've tried your method of touching the anode connections of the EHT rectifier and CRT, they both look and sound as though the EHT is there. Therefore I'm now convinced enough that the LOPT is working, and am now prepared to fork out some money for some new caps. Thanks everyone, I'll let you all know how it goes!

chipp1968 · 2nd Jan 2010, 2:15 pm

Im looking forward to seeing my old Ferg up running and preserved for posterity ! Its a very nice example and tidy cabinet . I was very reluctant to pass it on but as its huge I had no proper display area for it unfortunately as my pre war hmv and regentone tr20 take up that room.
Replacing caps is definitely the way to go first as even ones that are ok now will probably cause trouble later

30th Dec 2009, 11:21 pm	#1
SGT.Pepper Retired Dormant Member Join Date: May 2008 Location: Bath, Somerset, UK. Posts: 37	Ferguson 246T-sound ok but no picture Please forgive me for my lack of knowledge on this subject-this is my first TV repair and I have previously only fixed much more basic stuff like Dansette record players! Anyway, it's a big mid-1950s 17" console set with a light-up CRT mask. When connected to my Aurora the test tone can be heard from the speaker and can be made louder or quieter by operating the fine tuning control, but no life on screen. It's not lit up at all, just completely blank. Last week I could make interference appear briefly on screen by turning the channel change switch but it won't even do that now. I can indeed hear a line whistle so I think the line output transformer is intact and the back of the CRT is glowing normally, and not some weird colour. I have tried replacing (according to the service manual) the frame charge capacitor and the part CRT coupling capacitor (both 0.1uf), admittedly only because these sounded important. The PY32 is above suspicion as this is brand new-the original had gone milky. So my question is this: is it worth continuing? I don't really want to spend huge amounts of time and money on fitting all new capacitors only to find out that something irreplaceable like the CRT is broken! Any advice here would be appreciated!

30th Dec 2009, 11:35 pm	#2
Steve_P Dekatron Join Date: Sep 2003 Location: Bolton, Greater Manchester, UK. Posts: 6,644	Re: Ferguson 246T-sound ok but no picture No, it won't be the CRT. It's either the video stages or the Line Timebase/EHT section. Run it for a few minutes and see if the EHT Rectifier is lit. If not, it's the line output/EHT section. If it is, then it's the Video/IF section that's playing about. Check the Brightness and Contrast controls as well. Cheers, Steve P. __________________ If we've always had it, why is the Car Boot open? You're not sneaking another Old TV in are you...?

30th Dec 2009, 11:47 pm	#3
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	Re: Ferguson 246T-sound ok but no picture A quick check for EHT function is to briefly short the grid and cathode of the CRT together, if you have eht the screen should light brightly, or according to the condition of the tube. Can't remember the pin numbers at the moment. Peter

31st Dec 2009, 12:18 am	#4
SGT.Pepper Retired Dormant Member Join Date: May 2008 Location: Bath, Somerset, UK. Posts: 37	Re: Ferguson 246T-sound ok but no picture The EHT rectifier does not appear to be lit, if it is it's very dim but I think that's just the reflection in the glass off the valves that are next to it. There is a small blue glow from the plastic top cap thing when prodded with a knitting needle though but I'm not sure if this is good or bad. So I think we've narrowed it down to the line output stage, but that tends to mean certain doom, doesn't it? PS. Peter N: I don't know the pin numbers either so I haven't tried your test yet.

31st Dec 2009, 3:56 pm	#5
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,927	Re: Ferguson 246T-sound ok but no picture Hi Doom? Not a word we know here.... That corona discharge sounds healthy, and I'd try and find out definitely whether the EHT recifier's heaters are lit - a dark room and some thin card to visually isolate the area are helpful here. This will save time looking in the wrong area later! While you're in the dark (literally and metaphorically) have a very close look at the screen while varying the brightness - you may see a small glow indicating low EHT - or possibly a full sized dim raster indicating a video fault. If you've got low or no EHT the rectifier valve's the first port of call, followed by the continuity of the heater windings. I know LOPT is a bit of a worry, but you've plenty more to check first - and there are remedies to this so don't worry - yet! Glyn

31st Dec 2009, 6:25 pm	#7
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ferguson 246T-sound ok but no picture This is a very reliable set. Our first television was a model 236T, it's the same but minus the doors. Its very difficult to see if the EY86 is lighting up due to its position on the Praying Mantis style of lopt. You will probably have to clean its glass and have a look at the bottom of the anode. If it is lit you will have EHT.The glow should be reflected in the ring at the base. Remember the ion trap magnet that is mounted on the tube neck just forward of the base. If you have moved this only a tiny amount after your original active screen you will find that readjustment will bring back the raster. There is a knack in adjusting them, ask for more info if you think you might have moved it. The fibre strap used to break on the early ones so you may have one with a rubber gasket. I reckon it will work especially as you had clicks etc when you changed the channels.As David suggests a recap will be required to bring it up to standard especially the frame timebase. Good luck with it! [I wish it was mine] Regards, John.

31st Dec 2009, 6:38 pm	#8
SGT.Pepper Retired Dormant Member Join Date: May 2008 Location: Bath, Somerset, UK. Posts: 37	Re: Ferguson 246T-sound ok but no picture I am now certain that the EHT rectifier is not lit. I have also noticed that a small part of the side of the PL81 next to it is glowing blue. And I've looked very closely at the screen whilst operating the brightness control and I cannot see any life whatsoever. Strangely enough I have faith in the LOPT though-it looks fairly ok, the black stuff it's covered in doesn't go all squishy and the line whistle seems to indicate that it's doing something useful. I'll try it with a new PL81 and EY86 the next chance I get, but brilliantly I've left all of my valves at my dad's house because I didn't think I'd need them! Silly me. Also, I've gone out of my way to make sure not to disturb the ion trap magnet so far, so I don't think that's the problem!

31st Dec 2009, 7:42 pm	#9
TV_Madness Pentode Join Date: Jan 2008 Location: Titchfield Common, Hampshire, UK. Posts: 245	Re: Ferguson 246T-sound ok but no picture I have only skimmed over the rest of this post, so forgive me if I'm covering old ground. Have you checked for presence of EHT at the AC side of the rectifier? You should be able to draw a spark with a screwdriver with a WELL insulated handle. __________________ I don't want anymore junk in this house!

31st Dec 2009, 8:50 pm	#10
SGT.Pepper Retired Dormant Member Join Date: May 2008 Location: Bath, Somerset, UK. Posts: 37	Re: Ferguson 246T-sound ok but no picture I can draw a spark from the connections at the bottom of the valve, but they are somewhat pathetic looking sparks...

31st Dec 2009, 9:06 pm	#11
Laurdys Pentode Join Date: May 2009 Location: Stockton-on-Tees, County Durham, UK. Posts: 154	Re: Ferguson 246T-sound ok but no picture i think the pl81 will be ok if it has a small blue glow on the inside of the anode so long as its not glowing bright purpleish blue(make sure its not gassy). it will probarbly be the EHT Rectifier or its heater winding __________________ If it can be built, it can also be fixed.

31st Dec 2009, 9:51 pm	#12
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ferguson 246T-sound ok but no picture This needs a recap. The .01uf [?] coupling capacitor to pin 2 of the PL81 is probably leaking for a start. J.

31st Dec 2009, 10:23 pm	#13
Danny Heptode Join Date: Jul 2003 Location: North Walsham, Norfolk, UK. Posts: 516	Re: Ferguson 246T-sound ok but no picture Hi you say you draw small sparks at the bottom of the valve which valve as if its the eht rec the sparks may seem small but dc doesnt jump as well as the ac unless you earth the screwdriver then it may get interesting. my guess is as already mentiond the ion trap magnet needs adjustment. use a darkend room with a mirror in front and with a torch carfully adjust the magnet you may be suprised. Oh and take care if you are not using an isolation tranceformer as the shassis is not isolated on these sets. Danny

1st Jan 2010, 11:11 am	#14
Peter.N. Dekatron Join Date: Jul 2008 Location: Charmouth, Dorset, UK. Posts: 3,601	Re: Ferguson 246T-sound ok but no picture I had forgotton all about ion trap magnets.

1st Jan 2010, 1:52 pm	#15
SGT.Pepper Retired Dormant Member Join Date: May 2008 Location: Bath, Somerset, UK. Posts: 37	Re: Ferguson 246T-sound ok but no picture The ion trap magnet's definitely ok-I've made sure not to disturb it. I'm certain it's the EHT-the rectifier's definitely not lit and I can only draw tiny little sparks from the connections under the valve, even the one that goes straight to the final anode of the CRT. And when I say the sparks are tiny I mean tiny, about the size of a pinhead. I think I'll try a new EY86 and PL81 (because it is indeed gassy) before doing anything else.

1st Jan 2010, 10:54 pm	#16
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ferguson 246T-sound ok but no picture Hello again ?, I doubt very much if the PL81 or EY86 valves are faulty. A more likely cause of your problems are the wax capacitors in the line timebase and frame [field] timebases. The coupling cap as mentioned and the boost capacitor will require replacement and it will probably brighten up. The picture when you get it will probably be very cramped at the bottom and again you will have to change some capacitors. The coupling cap to pin 2 of the PL81 is C161, Its a .001uf but the recommended replacement was a .01uf. The boost capacitor C131 .25uf and the tube A1 decoupler C134 .01uf are screaming to be changed. You will need a circuit. Its extensively covered in the 1956/57 Newnes pages 351 to 368. I have scanned, marked and attached the components mentioned. If you are stuck for a circuit, please PM me and I will scan and forward. Hope this helps. Regards, John. Attached Thumbnails

1st Jan 2010, 10:57 pm	#17
Danny Heptode Join Date: Jul 2003 Location: North Walsham, Norfolk, UK. Posts: 516	Re: Ferguson 246T-sound ok but no picture Yes you may be right but did you draw the sparks from free air Ie just hold a screw driver near the anode or did you connect the screwdriver to shassis ? . also the iom trap magnets do change in magnetizm and sometimes need reajusting or even replacing on some sets. good luck Danny

1st Jan 2010, 11:15 pm	#18
Heatercathodeshort Dekatron Join Date: Jun 2005 Location: Warnham, West Sussex. 10 miles south of DORKING. Posts: 9,147	Re: Ferguson 246T-sound ok but no picture Just seen Danny's post. The spark test as he describes is correct and safe with flyback derived EHT as your Ferguson 246T employs. NEVER do it with a mains derived system but this is of no relevance to your receiver. On the AC side of the rectifier i.e. the anode top cap connector you need to pull this off the valve and tilt it towards you. Switch the set on and with a well insulated screwdriver [such as a modern one with a plastic handle] switch the set on and allow the tip to touch the anode connection. A spark around a quarter inch should be able to be drawn from this. DO NOT CONNECT THE SCREWDRIVER TO CHASSIS. Just hold it and 'tickle' the clip inside the top cap shroud. If this is present you will need to test the DC end of the rectifier, [EY86] at the crt connector. Again using a well insulated screwdriver or probe but this time with the screwdriver connected to CHASSIS push the tip under the crt connector. A series of spark 'cracks' should be seen and heard. This is quite dramatic the first time you do it bit it's quite safe and was the standard practise before transistor circuitry became common place. Leave the ion trap magnet in place for the time being. You did say you had flashes on the screen so it should be ok. I want to see this up to standard. I broke our 236T up around 1965 and have regretted it ever since...Take care and sensible precautions. Regards, John.

2nd Jan 2010, 12:20 am	#19
SGT.Pepper Retired Dormant Member Join Date: May 2008 Location: Bath, Somerset, UK. Posts: 37	Re: Ferguson 246T-sound ok but no picture John-I've tried your method of touching the anode connections of the EHT rectifier and CRT, they both look and sound as though the EHT is there. Therefore I'm now convinced enough that the LOPT is working, and am now prepared to fork out some money for some new caps. Thanks everyone, I'll let you all know how it goes!

2nd Jan 2010, 2:15 pm	#20
chipp1968 Rest in Peace Join Date: Jul 2006 Location: Somerset, UK. Posts: 2,356	Re: Ferguson 246T-sound ok but no picture Im looking forward to seeing my old Ferg up running and preserved for posterity ! Its a very nice example and tidy cabinet . I was very reluctant to pass it on but as its huge I had no proper display area for it unfortunately as my pre war hmv and regentone tr20 take up that room. Replacing caps is definitely the way to go first as even ones that are ok now will probably cause trouble later