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Old 12th Oct 2011, 5:22 pm   #361
HamishBoxer
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Default Re: Restorer's dream part 2 the chassis.

In a nutshell lack of line drive always caused PL to cook where as boost cap failure etc cooked the PY,back in the 60/70s when i was fixing them.

David

PS 45 years in the trade man and boy!
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Old 12th Oct 2011, 6:06 pm   #362
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Default Re: Restorer's dream part 2 the chassis.

Quote:
Originally Posted by Mike Phelan View Post
Not convinced on that one......
Neither was I even as I was writing it. Just trying to open a discussion. Assuming the fault appeared fixed after Col removed the chassis from the cabinet I wonder if it was simply a case of a disturbed wire becoming undisturbed.
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Old 12th Oct 2011, 7:29 pm   #363
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Default Re: Restorer's dream part 2 the chassis.

I once had a fault where there was an HT short on a TV that burned out the rectifier. It was a selenium type and the customer was not best pleased!! I replaced the reccy and before switching on, checked for shorts and found nothing wrong. The set worked and I returned it to the cabinet. When I tried the set again, there was an ominous crackling noise and an overpowering odour just before the HT fuse popped (accompanied by a cheer and mocking laughter from elswhere in the workshop)!

I took the bottom panel off and checked the HT for shorts again and found just a few ohms across the HT rail. Removing the chassis from the cabinet to get at the reccy again and the short had disappeared! It took me quite a while to work out what was wrong. Nothing to do with screws touching the HT when in the cabinet or anything like that.

Once the set was in the cabinet, the speaker had to be reconnected and there was one lead that connected the speaker frame to chassis. As soon as this lead was connected, the HT short came back. It turned out the output transformer was shorting primary to secondary so when the chassis lead was connected, the HT was shorted out via the secondary winding.

Lesson learned and I never forgot that again!



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Old 12th Oct 2011, 7:45 pm   #364
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Default Re: Restorer's dream part 2 the chassis.

Hi,

Thanks SB; at least I'm not the only one to be caught out. I think it just wanted to rain on my parade but it failed. It tested my patience though. I'll sleep tonight and it's a strange feeling to have finally brought this saga to a successful conclusion. Now what can I follow it with?

Kind regards, Col.
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Old 12th Oct 2011, 7:47 pm   #365
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Default Re: Restorer's dream part 2 the chassis.

Mind blowing but I can't see why the AURORA power supply has anything to do with an H.T. short. My guess is that something was shorting out on either the input to the PY33 or a direct H.T. short on the DC side. Incorrect even horrendously incorrect line speed will not cause the domino effect suggested with this Ekco receiver. The line linearity coil can slip down it's former and short to chassis causing the U191 to overheat but this will not cause such violent behaviour as to burn out the PY33 surge limiters. It would be interesting to note if the PY33 was heated before the resistors burned out. The fault may well reoccur but don't worry about it Colin as it will be an easy one to trace once we discover the exact symptoms as mentioned. My guess is that a wire is trapped or a blob of solder has lodged somewhere but it's only a guess. A 500m/a fuse inserted in series with the surge limiters will prevent further burn outs should the short return. It may never happen!
Regards, John.
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Old 12th Oct 2011, 7:58 pm   #366
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Default Re: Restorer's dream part 2 the chassis.

No,sorry a short on the input to the PY33 would burn up the dropper as there would be no feed to the PY.Or the feed reses to it but not overheat the PY.

David
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Old 12th Oct 2011, 8:11 pm   #367
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Default Re: Restorer's dream part 2 the chassis.

Completely agree David. I'm looking more of a spike of solder or a wire crossing the valve base making contact with the anode pin causing the short. The 10 ohm dropper sections feeding the PY33 are substantial high current windings and would take more abuse than the much smaller 35 ohm limiters. Just a thought. I still think it's mechanical rather than electrical as such. Cheers, John.
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Old 13th Oct 2011, 11:10 am   #368
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Default Re: Restorer's dream part 2 the chassis.

Hi
Just a thought, but it might be nice for those new to these threads to have a 'before' and 'after' set of pictures together, or maybe an edited version as a 'success story' (one to put us all to shame!)
Glyn
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Old 13th Oct 2011, 12:59 pm   #369
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Default Re: Restorer's dream part 2 the chassis.

Perhaps there were two problems:
1. The PSU for the Aurora and
2. A mechanical fault on the TV chassis causing the HT short.

Removing the set from the wonder-cabinet didn't cure the Aurora PSU problem but the mechanical fault was cleared.

If it had been the Aurora fault only, then the set would overheat when free-running and I bet it doesn't!

Sorry lads. I wrote this post after reading the posts on the penultimate page of the thread. I then found that there was another page. At least I came to the same conclusion!!

Last edited by brianc; 13th Oct 2011 at 1:03 pm. Reason: Blindness
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Old 13th Oct 2011, 1:48 pm   #370
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Question Re: Restorer's dream part 2 the chassis.

Hello All,

Just a thought here. Is the Aurora using a power supply with an earth attached? If so being connected to a live chassis tv could be causing all sorts of interesting/nasty problems !!
If so use an ordinary wall wart power supply and see if the problems dissapear.
Any thoughts?

Alan.
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Old 13th Oct 2011, 5:29 pm   #371
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Default Re: Restorer's dream part 2 the chassis.

Hi,

Many thanks everyone for your ideas but the plot deepens.

Yesterday the set was working perfectly when I switched it off after it had been running for a while. I've just invited our neighbour Terry to view it working as Terry saw it when I first obtained it.

The fault is intermittent. I did hear a "crack" and now the test card is "belly dancing". The top and bottom of the card move towards each other then away again with some side distortion and belly dancing is the best I can describe it.

I'm sure there is a short somewhere; the resistors are not overheating now.

My chum Mike Phelan is paying us a welcome visit tomorrow morning so I'll leave it alone to let Mike see what it is behaving like. I've got a feeling this will be a silly fault once found because when the set is stable it works fine.

I wish I had more space because it is very hard work carrying this set into the workshop each time I wish to work on it and it is heavy.

Good idea Alan about the PSU being earthed which it is so I removed the earth lead from the pin in the plug and the set still misbehaves so I've now re-connected the earth lead. I wish it was something as simple as that but to double check I've asked Mike if he has a spare PSU to bring along.

I hadn't thought about this being a success story Glyn but now you mention it the restoration has been a success apart from this silly fault and if other members would like to see a shortened version of the restoration I'm happy to add one under "Success stories" with links to parts one and two; thanks for suggesting it.

Kind regards, Col.
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Old 13th Oct 2011, 5:38 pm   #372
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Default Re: Restorer's dream part 2 the chassis.

Are switch-mode power supplies isolated? They are not things I know much about and there could be wider issues than this particular problem.

- Joe
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Old 13th Oct 2011, 6:00 pm   #373
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Default Re: Restorer's dream part 2 the chassis.

Quote:
Originally Posted by ThePillenwerfer View Post
Are switch-mode power supplies isolated?
Some are, some are not. Obviously any power supply providing safe low voltage from mains must be isolated. A simple switchmode regulator with a rough low voltage DC input and stable (say) 5V DC output would not normally be isolated.
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Old 13th Oct 2011, 8:03 pm   #374
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Default Re: Restorer's dream part 2 the chassis.

Hi
There is often a resistor and/or capacitor between hot and cold on a switchmmode device to stop the output wagging its tail, but I'd be very surprised if it managed to short out the HT on your set. A Megger might be useful here.
Glyn
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Old 13th Oct 2011, 9:09 pm   #375
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Default Re: Restorer's dream part 2 the chassis.

Hi Col
We really have had the cherry on the cake with this one, really wonderful.
In the unlikely event that your belly dancing is due to the main smoothing cap, I have a couple of new old stock that your more than welcome to.
Eddie
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Old 14th Oct 2011, 8:17 am   #376
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Default Re: Restorer's dream part 2 the chassis.

It would be interesting to know where the 'flash' came from. Belly dancing to that extent is usually due to O/C smoothing but a complete short of an old block is rare.
I know I go on about this [zzzzz] but ask Mike to check the TV/Radio change over switch when he calls at the weekend. I had a large number of these arc over and burn out a switch section causing destruction of the rectifier heater and fuses. They don't repair themselves and once broken down stay that way but you never know, it may be just about to fail. Worth a double check. It will be obvious if faulty.
Another possibility is that this fault did not appear untill you chopped the rear panel about fitting that mains connector. Have you trapped anything around the dropper? I'm sure Mike will sort it. Regards, John.
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Old 14th Oct 2011, 11:33 am   #377
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Default Re: Restorer's dream part 2 the chassis.

Hi Col,

Like everyone else, I've been following this restoration & have to say you've done a fantastic job.

There's only one thing that I probably wouldn't have done, & that is to modify the mains connection & fuse holders on the back. I agree 100% that what you have done is the correct & safe thing in bringing it up to modern standards & I can't argue with that, but I think that if it were me I would have fabricated some sort of plastic cover to just 'clamp' over the live parts on the back panel & left the mains cable semi-permanently connected somewhere behind or at the switch as you had previously done. Then, in the future, if an original mains lead & rear back cover for the set ever turn up, it can be immediately returned to original.

I'm wondering if it could well be, as said above, that in fitting this new mains socket that goes right back into the bit below the dropper, that this could have caused the issues you have at the moment - if it were me then this would be one of the first places I would be looking (although I haven't looked at the circuit to see just what is possibly happening).

That power supply shown in one of your pictures looks like one of the old Farnell ones - I've got one of those somewhere & I believe that they have a low & high range switch as well as a meter volts & amps switch. If I remember rightly, these power supplies can deliver up to 30 volts & I'm thinking that it wasn't just the meter switch that had been altered, but also the range switch. I think that you 'may' have knocked the range switch onto 'high' & you were very lucky that from what I've read, the Aurora has a good 'over voltage' protection circuit - hence the flashing & pulsing! When using one of these type of 'continually variable' power supplies (& I use one all the time), you MUST check the adjustment of the voltage output EVERY time that you use it & BEFORE connecting anything to the ouput sockets - it's SO easy to accidentally move the adjusting knob or any of the switches when the unit is not being used.

I would say that there is NO connection between the power supply to the Aurora issue & the HT short fault on this set & I would advise leaving the set in the workshop until you have tracked down what is causing the fault, which will more than likely be as has been said, a physical, rather than an electronic fault - but it could still be an 'internal' in the rectifier valve, but that's a long shot.

Anyway, a first class job & very well done. You're thread has given a lot of pleasure & interest to a lot of people. Remember, it's NORMAL to have these sort of problems after a job like this has been completed - it happens to us all, ALL the time!

PS, just as a 'foot note' - I'm also wondering about one of the sections in the main smoothing block...perhaps unlikely, but stranger things & all that.....

Last edited by Techman; 14th Oct 2011 at 11:55 am.
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Old 14th Oct 2011, 11:58 am   #378
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Default Re: Restorer's dream part 2 the chassis.

Col,

I'd get something like this: http://www.argos.co.uk/static/Produc...er/9829701.htm

There are even cheaper ones or go to a car-boot - there are millions of wall-wart adapters around and may of them will run the aurora and avoid the risk of blowing it up!

Good luck finding your fault. I know it may seem annoying but try and look at it as getting more restoration time for your money! If we all fixed tellys as quickly and effortlessly as the experts we'd soon run out of room to store them!

Dom
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Old 14th Oct 2011, 12:05 pm   #379
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Default Re: Restorer's dream part 2 the chassis.

Have you checked the rivets on the smoothing block Col? I have known them to come loose over time and they might well give a 'crack' if contact is intermittent. You can't solder them back but a bash with the sharp edge of a screwdrive might knock them back into place if that is what the trouble is. Wiggling the terminals might show something loose.

A 'scope on the rail might show if the 'belly dancing' is coming from the HT or maybe somewhere else such as a leaky h-k on a frame valve.
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Old 14th Oct 2011, 4:06 pm   #380
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Default Re: Restorer's dream part 2 the chassis.

Hi,

Thanks Joe; Jeffrey and Glyn; I'm now learning a lot about power supplies which I would have missed had the set behaved.

I have a hand cranked 1000v megger Glyn but would need to learn how to use it in this situation but I'm always willing to learn.

Thank you for the kind offer of electrolytics Eddie it is much appreciated; I'm pleased you are enjoying the story.

Thank you John for the information which is very helpful indeed.

Thank you Techman for your kind comments and normally I would totally agree about leaving the set as original as possible but this set is now so non original due to the extensive work carried out on the cabinet that I thought I might just as well convert to modern mains connector and fuse holders. Bron told me yesterday that she had just watched a very distressing story on the news were a small child had managed to open a washing machine door whilst the machine was on spin; the child's arm was ripped off at the shoulder. Like many I believe at times health and safety rules are just plainly ridiculous but I just wasn't happy looking at the two pins sticking out of the rear of the chassis.

I further agree with you Techman regarding the Farnell PSU (yes it goes up to 30V) and Aurora not being the cause of the fault and as always with hindsight I would have checked that the controls on the PSU had not been disturbed but as I said previously I was working in a black hole on my hands and knees coping with a soldering iron and a mains inspection lamp whilst the chassis was sitting on the bedroom carpet. Boy I love to do things the hard way but then if it was easy as Dom says I would have missed so much fun and had little to moan about. I'm delighted to receive all the replies though because they give me an insight as to how other members would think about and respond to this fault.

Thanks for the link Dom; I will indeed buy a dedicated PSU for the Aurora in fact I was thinking about making the Aurora and PSU as a single self contained unit.

No I haven't checked the rivets Boom but thanks for yet another excellent suggestion; the ideas are really flowing from everyone but please read today's update as follows.

I was awake in bed again last night thinking about this fault and reasoned that my new mains connector and fuse holders were installed correctly and that everything else I had worked on was also correct because the set did actually work very well indeed when it was on the bench so this ruled out a lot of errors that I could have possibly made.

At 7.45 this morning I was sitting in the car outside the supermarket reading the circuit diagram because to be honest this chassis restoration has been a ballistic learning curve so I was thinking about the advice Steve P gave years ago in this saga regarding only changing one item at a time and I was looking to see if I had possibly made a stupid mistake. One thing I realized by inspecting the circuit diagram was the function of the two 35R high power resistors; their function was to connect the mains supply to the anodes of the PY33; this is absolutely basic information for the more experienced but please be reminded this is my first TV restoration so I have a great deal yet to learn. On the vintage radios I restore the rectifier anodes are usually fed via tappings from the mains transformer and I thought these two resistors to be on DC whereas they are actually AC. A small point but worth mentioning as other novices are also interested in this story.

I just knew today was going to be special because my chum Mike was due to visit mid morning and we could then gang up and let this wayward chassis know who was boss because I was fully confident that Mike would make this fault disappear in no time at all.

Before Mike arrived I logged on and was reading John's excellent advice and although both Mike and I had checked the VHF switch arrangement declaring it to be in good working order I began to think about exactly what was happening each time I switched on. The resistors had stopped overheating but the test card was "belly dancing" but what had not occurred to me was that a buzz was now present once the HT came up?

The more I thought about this the more intrigued I became and eventually couldn't resist switching on once again; with the curtains closed it was quite dark so as I switched on I looked inside the cabinet and listened just in case there was a "crack" and flash but all appeared well and slowly the valves lit up and the test card appeared; the "belly dancing" was not so bad now but the buzz was pronounced; surely it couldn't be something so ridiculously simple could it? I turned the channel selector switch quite briskly a number of times and the set responded quite loudly but then when I let go of the switch the buzz totally disappeared and the test card remained rock solid. Just to be sure I left the set switched on for about twenty minutes until Mike arrived and gave him the good news as he walked in.

Mike kindly adjusted the contrast for me as he knew what the test card should look like then we stood staring at it for a while before it was switched off. Thank you T311 for winding me up!!

This will teach me not to work in a black hole because I think I've also now a good idea what the problem was to cause the overheating resistors. John and other members have mentioned solder bridges and wires touching and both these were highly possible but I did say previously that I had to renew the chassis terminal post connecting both ends of the resistors; well I had a good look at the pin which pulled out with the resistor and it's highly likely that whilst working in the gloom a solder bridge had formed connecting the resistors to chassis as the insulation of the post had become very charred and possibly split allowing the bridge to form out of sight. I've taken a picture of the pin and it can be clearly seen what state it is in and when I replaced the terminal post it would appear I cleared the overheating fault. As luck would have it the biscuit contacts decided to play games with me even though I took a lot of care in polishing them and the pick ups whilst the drum was out.

Thank you everyone for your replies as the fault could have been any one or a combination of them and I'm glad this extra information has been added.

I don't know where it came from but this morning I was suddenly full of confidence and having got the set working so well the fault would be something trivial but because of the fault I've now found my way around the power supply side of this set.

Just in case the set wanted to mess with me more because my back up in Mike having departed I've just switched on again and it is now behaving.

Kind regards, Col.
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