Fault Of Horror! (BRC 950/960)

[Heatercathodeshort]

The long warm up can be very perplexing. Something must happen to the heater assembly in the valves that are fed through the H.T. line. They appear to go slightly low resistance but will work quite normally in a conventional chain. Replacing all four and you must change all four with NEW valves will reduce the warm up time from raster to around thirty seconds.
It really is most odd but I have discovered a number of CRT heaters fed from a winding on the LOPT display similar symptoms. Running them from a CRT transformer restores emission. Note I am not including heaters with partial shorts. These are CRT heaters that appear to have changed characteristics when run from unconventional supplies. John.

[FERNSEH]

It was the BRC/Thorn 980 series in which the bias for the 30PL14 frame output valve was derived from the heater supply. From page 504 of the 1967/68 R & T servicing book: "the frame output valve, V10B, is negatively biased from the DC heater line at the junction of V8 and V4 heaters".

DFWB.

[Focus Diode]

A big thank you to everyone again for your help. I have some components on order from CPC and will get back to the set in the latter half of next week.

Cheers,
Brian

[Focus Diode]

Got to re-install the dropper capacitor in the set this evening. Earlier in the week I found the original 4.33uF capacitor had bulged and had leaked oil though thankfully not to the extent of Dazzlevision's experience.

Utilising all due health and safety proceedures I set about removing the interior of the capacitor using a conventional high speed drill. The interior was removed and thoroughly washed out with meths.

Apoligies for the quality of some of the photos, not having the decent camera to hand at the time I resorted to the lower quality one and found the images out of focus on up-loading them.

The 4uF 425V AC replacement is nearly as long as the original though thinner in construction. This fitted inside the original can capacitor without problems though the additional X2 0.33uF 275V AC capacitor had to be soldered to it externally. The four tags of the new capacitor were certainly of help here. A new 470K 1W resistor was also wired across it as the original circuit. The new capacitor was secured inside the original can type with, ahem, Blue Tack then re-fitted to the set and soldered up.

Switch on, selected to UHF 625-lines with the multimeter set to the AC volts range. The volts gradually climbed from 40V, stabilising at 96-97V with a nice colour to the valve and CRT heaters visually. A narrow raster appeared which slowly opened out to full scan. Another 45 seconds later the signals slowly faded in followed by the sound, unlocked as expected though quickly adjusted with the user hold control. Thankfully the CRT and other valves appear to have survived the earlier overload. Performance on 405-lines showed all was well here too.

There's other issues with the set such as full setting up and re-spraying the silver screen CRT surround, having now found the ideal Satin Chrome colour which is closest to the original "HMV Silver" as I call it. This is beyond the scope of the current thread and will be attended to towards the latter half of next week.

I once again wish to express my gratitude and appreciation to those who've expressed and interest and for the helpful suggestions offered from members of this great forum.

Cheers,
Brian

[Focus Diode]

More photos to add.

[Focus Diode]

And more!

[Maarten]

It almost seems as if someone blanked out some text on the original capacitor. Any clue as to why that was done and when? It doesn't seem to have anything to do with date codes or warranty fraud.

[TrevorM6TSE]

Yes I was confused by that? It almost looks post photo?

[dazzlevision]

Hello,

I see from the first picture in post #25, that the tagstrips (with the wirewound resistors mounted on them) has been replaced (in part) at some time in the set's past. The upper sections are post-factory and are of a somewhat different type to the originals.

There was an official Thorn mod to re-arrange the wiring on these tagstrips in order to reduce the risk of overheating/tracking. It's in an old "BRC Bulletin" publication.

I'm glad you have restored the set to working order.

Missing from your set is an aluminium heat deflector that fits below the PCL86 sound output area, to keep most of the heat from the PL504/PY801 away.

Regards,

Dazzlevision

[Focus Diode]

Originally Posted by Maarten

It almost seems as if someone blanked out some text on the original capacitor. Any clue as to why that was done and when?

I blanked out the manufacturer's name as this is a public forum. Didn't want to risk causing any upset to them, (assuming they're still manufacturing capacitors), by giving the impression their components are troublesome.

I understand some 960 models were fitted with a 4.33uF capacitor from a different manufacturer which would be equally suspect.

Dazzlevision- I wasn't aware the set was missing an aluminium heat deflector. Many thanks for letting me know. Perhaps we can have a pic of your Ferguson model?

Cheers,
Brian

[FERNSEH]

Originally Posted by dazzlevision

Missing from your set is an aluminium heat deflector that fits below the PCL86 sound output area, to keep most of the heat from the PL504/PY801 away

Typical sloppy sixties style of TV servicing. Screening around the line output stage, tuner covers missing and the like was the norm in those times.
It's not if there was any real effort required replacing these parts.

DFWB.

[dazzlevision]

Originally Posted by Focus Diode

Dazzlevision- I wasn't aware the set was missing an aluminium heat deflector. Many thanks for letting me know. Perhaps we can have a pic of your Ferguson model?

Hello,

Certainly, although it is rather buried in my "museum", so will take a while to unearth!

Blu-tac should get a mention in this https://www.vintage-radio.net/forum/...d.php?t=102294 thread (improvising with houshold items).

[Hybrid tellies]

I am glad it's nearly all sorted and no damage was done. All in all a very interesting set.

[Tazman1966]

An interesting set indeed.

[Welsh Anorak]

Hi
Glad it's going again. I doubt any manufacturer would be too upset that a component of theirs failed after fifty years! Most modern capacitors struggle to reach five...
Glyn

[dazzlevision]

Hello,

Whilst getting one of my "museum" sets out of the store, I also opened up my Ferguson 3638 16" 960 chassis set, in order to take a few pictures of the chassis, which may be of interest:

Two showing the aluminium heat deflector fitted below the PCL86 audio sub chassis. It's made of two pieces rivetted together.

One showing the whole chassis.

One showing the card insulator that should be present at the very bottom of the chassis.

One showing the tag strip upon which several wirewound resistors are mounted, including the adjustanble one that sets the series heater current of the four valves in the negative HT line (early versions of the chassis only).

One shoping the paper information label stuck to tyhe LOP stage screen.

Regards,

dazzlevision

[dazzlevision]

Finally, a close up of the warning printed on the insulator fitted at the very bottom of the chassis.

Dazzlevision

[Focus Diode]

Many thanks for these interesting uploads Dazzlevision, always very interesting to see another example of these sets. Annoying to think on my example the audio stage screening cover was omitted during its history. I now see a protection card has also been omitted. I guess this must cover the PCB as the bottom ventilation slots are quite large.

Excellent uploads, many thanks again. Any chance of a view of the front of the set please?

Cheers,
Brian

[dazzlevision]

Originally Posted by Focus Diode

Any chance of a view of the front of the set please?

Hello,

I'm afraid the missing screen and insulator are typical of the lazy attitude to repairs by some "technicians". These often compromise safety or reliability. There are bodgers in most trades.

I've put my Ferguson 3638 back into storage again. I will take a front picture soon.

Dazzlevision