Ryanbrownin Ferguson 3852 repair report

[1955APREN]

Hi every one
This thread was started on June the 17th and will all passed on very good advice to Ryan. He then asked for help in the repair section and the set ended up in my shack. I was pleased to see that Freya had very kindly posted the circuit diagram for this set.

First check was visual inspection for dry joints. The centre pin of the vertical hold control was broken from the print, but this was not the main problem. The voltages around the output transistors were high, but the 30 volt line was only slightly high. Time to switch the meter to diode test. A few seconds later and the fault was found, O/C base/emitter on the NPN transistor.

I replaced both output transistors with a TIP41C and TIP42C. This cleared the frame fault (Hamish You think like me). Now have another fault, the Horz Hold was out of frequency. This was due to the core in the line osc coil being broken and jammed in the former. I had to drill it out but the core was broken. The one in the width coil was the same type, but if I use this one I will have a width problem.

A request in the parts section, no one as replied as yet so I am bit stuck. The dust core is 25mm long and 5mm wide, this type was used a lot in TV about this age, some convergence coils and line osc coils (pye205) to name a few.
I would very much like to complete this repair, pleased to hear if any one can help.
Thanks Derrick

[AC/HL]

Three posts moved here: https://www.vintage-radio.net/forum/...d.php?t=118329

[1955APREN]

Further up date
I fitted cores to line osc coil and width coils, set up vert lin and height. Width was slightly over scanned, width control was very critical but width was just filling the screen.
Time to but back on and return to Ryan, but the next day disaster struck when set was switched on It worked ok for a little while then pic quickly lost height and width, then no pic no tube heaters and lopt stage taking a lot of current.
I inspected line output stage to find that line transistor (BU205) had been replaced with a R2482, but this proved to be ok. I did notice that R153 10 ohm across the emitter/base was missing. I suspect that the line transformer (flyback) is faulty. Can any one help either with a source or further technical advice.
Thanks derrick

[Heatercathodeshort]

Oh! What rotten luck after all your work! It might be very difficult to find a lopt for the 1615 chassis. I sold around 25 of the 20" version and never had a problem but of course they were new and used daily. Long term storage is a killer for lopts.
A jellypot conversion is not feasible due to matching and space limitations. Due to being a potted type it would be difficult if not impossible to rewind.
You never know! Put it aside and wait a while. It's amazing what turns up. Regards, John.

[Restoration73]

There's a 1600 LOPT bottom of page ;
http://markhindes.easywebstore.co.uk...T7.aspx?page=2

[1955APREN]

Thanks for that inf
does any one know if the 1600 loptx and the 1605 24 ins
are interchangeable

[neil29]

I've got a tatty 3852 here. and if you want to take a chance on the lopt being ok then you're welcome to it for spares.


Cheers
Neil.

[Heatercathodeshort]

Unfortunatly the 1600 transformer will not work in the 1615. The 1600 chassis was that nasty 16" portable with the arcing lopt and the diabolical frame chip! Horrible memories of these and the plastic back usually melted.. John.

[1955APREN]

HI John and Neil
John
Thanks for info regarding 1600/ 1605 loptx . As these set were the last of the large mtv Ferguson made I never got to grips as only saw a few , at this time most of time was spent on 3000 .
Neil
Thanks for offer regarding 3852
I will be sending you a PM in the near future
Kind regards
Derrick

[1955APREN]

hi neil 29
did you receive my pm regarding the above
please could you send me a pm
Regards Derrick

[neil29]

Hi Derrick, Could you send your details again as I've deleted my PM's and have lost the paper i wrote them on.

Thanks
Neil.

[ryanbrownin]

Hi,
Yesterday Derrick came over to take the LOPT out of Neil's 3852, that he kindly gave me, and put it in my set.
When Derrick had put the new LOPT in and turned on the set, the tube heaters came on and the screen began to light up! We then decided to plug the VCR into the TV to get a picture. As we were setting up the VCR, the picture disappeared and we were back to square one...

[Welsh Anorak]

Hi
The LOPTs on these are pretty reliable and generally let you know if there's a problem by spitting. So I'd think it's unlikely TWO fail in the same way. So what to do? The fact you got a picture makes me suspect that there's something breaking down under load. It could be the transformer, of course, but I'd start unloading it of the derived supply lines and seeing if the EHT and heaters come back. You mention the line stage is taking a lot of current. If so is the line transistor getting hot? If not I'd change it and check the insulating washer, also the tuning caps and any decouplers you don't like the look of.
Good luck!
Glyn

[1955APREN]

Hi Glyn
Thanks for your help with this set, back in the autumn, when the fist loptx went s/c, I checked C132/ C133 line output tuning, C136 S correction, all seemed to be OK. It was very strange, the loptx out of Neil's set failed after just a few mins. I Just had time to check that the shunt reg stage output voltage was 32 volts spot on, before the set went dead. The lop transistor was not getting hot, but the loptx was. The voltage on C105 had dropped to 102 from 180v, and R104 was getting hot. The line output transistor was an R2482, and had been replaced before. I hoped that is Eq. to BU205. Any further advice would be appreciated.
Regards Derrick

[Welsh Anorak]

Hi
I just think you've been very unlucky! I can't think of anything else that could cause this, especially as you briefly had a raster.
We didn't see too many of these sets as they were nowhere near as popular as the 1500s. Also Radio Rentals sent theirs to the crusher after a couple of house fires due to arcing around the scan coil socket and replaced them with 1500s for the lucky renter!
Finding one will be a challenge - fingers crossed!
Glyn

[FERNSEH]

I do remember having problems with the line output transformer in these sets.

DFWB.

[Heatercathodeshort]

The major problem with the 1615 transformer was arcing from the EHT stick. The overwind held up pretty well. That was the only stock fault I can remember with the 1615 series that performed very well. We are now 38 years on, 38 years damp air. Anything is possible.
The real nasty one was the 16" 1600. a lopt every six months! This was a real nasty chassis and did not match Thorn's usual high standard. J.

[Welsh Anorak]

The LOPTs did fail on these as they were more like the 1590 series transformers - i.e. not the good old jellypots.
I always liked the look of the 1600 series H/KS talks about. That was until I get one in for repair! That frame chip was almost welded to the board and as for the LOPT...
The 1615 was nice by comparison but suffered from the poor tubes available in the dying days of monochrome.
Glyn

[FERNSEH]

Many final production Thorn monochrome sets used CRTs bought from Eastern Bloc countries.
Philips/Mullard did make a quick heat monochrome CRT, the A61-520W. Not sure if this tube was used in 1615 sets.

DFWB.