Thorn 1615B (3852) Continued

This is a set I have some experience of - my neighbours had one, and gave it to me when the picture vanished. I found that if you turned the luminance controls right down, the symptom indicated line collapse - I suspect it was the line drive transistor that was at fault, but the tube pins were damaged before I got a chance to sort it. Mine had the Polish (I think) tube, and did give a slightly blue picture when it worked.

Glad this one is working, with little to sort.

These sets have a bit of a reputation, if a Thorn rental field engineer came across one of these they were supposed to be withdrawn on sight. They were prone to arcing at the line linearity/width coil due to dry joints causing a burnup of the PCB, in the worst case resulting in a fire although I never ever heard of any although the were out in quite small numbers.

The lack of blanking could be due to a faulty blanking transistor VT6, BC147, flyback blanking was carried out at the emitter of the video o/p transistor VT5.

The withdrawn sets by the way were replaced with the older 1500 models or a CTV with the crystal shorted out. Some people say the picture wasn't as good as a 1500 but I thought they were ok.

Posted by: @jayceebee

They were prone to arcing at the line linearity/width coil due to dry joints causing a burnup of the PCB, in the worst case resulting in a fire

Tell me about it... a great-aunt of mine had one of these. I remember buying it for her - she was pretty tight-fisted and only had a colour telly for the last few years of her life because this thing was on its last legs.

But one day, on visiting my mother I was told "Aunt Rose wants to see you about her telly". So, I ate my lunch and walked down to her house. 

"It went off, Michael". I asked if there were any clues before it did. "Oh, there was a lot of smoke". 

So I took the back off and was greeted with a charred hole something like 3 x 1cm in the circuit board. I said that it was a write off, but much pleading later I took it home, much to the disgust of my wife who really didn't like her. Having donated a 15" portable, I set about removing components and cleaning the PCB, before patching the board with Araldite. Later, I drilled holes with a borrowed PCB drill and replaced the tracks with wire. To my surprise, it worked again, even allowing for the slightly flat tube.

It soldiered on for a few more years until the tube was so knackered it was barely visible in a darkened room and no, I couldn't get a tube for it! 

Thanks for the comments and advice, I'll take a look at the circuit around TR5/6 tonight after tea.

Well the fly back lines are now gone.

Cold checks on VT6, W18 & W13 suggested their innocence, so with the set powered up the voltage on the collector of VT6 was low at 200mV. Checked R76 (1k2) and it had risen in value to over 3 meg, Bingo!

Now does anyone fancy a Ferguson 1615 for their collection?

Nice one. Personally I would beef up the pcb tracks to said coils with wire to minimise the risks of dry joints.

It's great to see one of these being revived. Not many survive, since Radio Rentals recalled them after some of the aforementioned PCB burn-ups occured. Despite that, my grandfather had the 20 inch model Ferguson 3850 for many years. Nothing dramatic happened to it - no smoke or fire as far as I know - so I only have good memories of these sets.

Last year, I acquired a Ferguson 3850 from forum member Neil . The 420R section of the mains dropper was open circuit. Original spare parts for these sets are hard to find, so I ended up having to bodge it using part of another TV dropper plus some wirewound resistors to make up the value. This got it working but the brightness and contrast sliders were a bit flaky. The contrast slider was revived with Servisol switch cleaner. No such luck with the brightness control. I took it apart and found some green corrosion inside. After giving it a good clean and reassembling it, it worked a bit better but only on part of its range (it defaults to full brightness when not working).

After replacing the back cover, another fault appeared. The picture became a blank raster with flyback lines, then slowly faded away to nothing. Opened it up again, tapped the PCB with a screwdriver handle, the picture suddenly came back - Great! It must be a dry joint somewhere, but further tapping didn't cause the fault to return. I noticed the aforementioned line linearity coil PCB track had overheated, so I soldered a thick piece of mains cable across both ends of the track. I checked and luckily the original Rifa smoke-bomb mains filter capacitor had already been replaced. I had one go off in a Thorn Ultra music centre last year, producing a muffled pop and lots of evil-smelling smoke, so I was a bit wary. Anyway I put the TV back cover on again and the intermittent no-picture fault reappeared briefly, then cleared itself. That's as far as I've got.

The tube in my 3850 is a Mullard A50-120W/R made in Holland, although not the finest - it's slightly out of focus at the edges. The TV itself has a sticker on the back which says G9-50 - I think that means it was assembled in Gosport in the 50th week of the year 1979.

I must admit I'm tempted by Mike's offer to add a 24" 1615 to my collection of single-standard monochrome TVs. Only problem - Manchester is about 180 miles away which would mean a 360 mile round trip. Maybe if it could be moved further south...

Posted by: @hamid_1

I must admit I'm tempted by Mike's offer to add a 24" 1615 to my collection of single-standard monochrome TVs. Only problem - Manchester is about 180 miles away which would mean a 360 mile round trip. Maybe if it could be moved further south...

See your private messages - I may be able to help.

After returning from my holiday I took Johns advice & beefed up the tracks around the width coil.

This set is still available if any body wants it?

Mod Note: Set is now with Marion (Katie Bush) so no longer available.