Stella dual standard (ST1099A)

[bionicmerlin]

Looking for a bit of advice again please.
I bought this tv for very little money about 3 months ago. looks reasonable apart from a couple knobs missing It has no model number that i can see. Anyway being a person of limited knowledge i have powered it up with a variac and the valves glow but thats about it.
i have so far found the top section of the right hand dropper (there is 3 in a row) is open circuit it gos on to feed the right hand circuit board through a 250ma fuse.located on the top of the board. just wondering if someone could tell me the value of the top section of the dropper so i can start here. I know a diagram would tell me but i dont have one.
Is there any more things i should be looking out for before powering up. All the capacitors are mustard colour so hopfully these will be ok. Hope these pictures help
Thanks Andy

[G8KBG Tony]

Looks like a ST1099A, the Stella equivalent of the Philips 19TG152A.

The faulty section of your dropper is 270 ohm and feeds the line output stage..

Cheers,

Tony

[bionicmerlin]

That was quick Thank you Tony

[Hunts smoothing bomb]

Hi Andy,

I had one of these years ago in a different cabinet, the Mullard mustards are not always what they seem, I had the set on the bench one day on test with the back off and all of a sudden the set appeared to die and the valve heaters went out, within seconds smoke was pouring from one of the droppers at the top of the chassis and it lit up like a light bulb!

The fault was traced to one of the mustards at the top by the droppers going short, it's position in the circuit meant that it effectively dumped full mains across the associated dropper!! Fortunately I switched off before it had chance to burn out.

Cheers

[FERNSEH]

I notice that the UHF tuner knob is missing. I've got one if you need one.
The Stella version of the Philips 19TG152 is truly rare. Nice to see one again, these were excellent receivers. A Cossor version was also available, not sure if a Peto-Scott was made though.

DFWB.

[bionicmerlin]

Thanks for the info guys.
Fernseh I will take you up on the kind offer . If I can get the set going thanks Andy

[Focus Diode]

I'm with Lee re his comments on the mustards. They rightfully have an excellent reputation for reliability but occasionally have been known to fail. There's often a hairline crack evident at one end towards the lead wire end for example.

As far as capacitors go they were the best ever produced in the '60s but that doesn't rule out the occasional failure.

Best of luck with the set. Looking forward to hearing more.

Cheers
Brian

[bionicmerlin]

Thanks I'm taking this all on board.
Update so far.
I put in a temporary make shift resistor for the time being .
Powered up and got a nice raster on both standards.
On applying a signal on 625 all I could get was very faint audio distorted and change of raster but no picture .
On 405 lines reasonable picture slightly distorted sound but maybe due to seized fine tuning slug . After about 10 mins picture failed with horrible smell. I think this is due to a faulty electrolytic capacitor as one was found to be very hot. On removing it it tests OK. Strange I thought. Will have to get a replacement and hope it's not taken anymore things with it. Andy.

[dazzlevision]

Hello,

If the original two boost HT reservoir capacitors are still present and from your photos, it looks like they are (Blue coloured plastic "Dubilier" 0.05uF 750Vdc, vertically mounted at bottom of the timebase panel - the left hand one, viewed from rear), I would replace them on sight, as they are probably leaky and are very likely to go short-circuit, disabling the line output stage.

Very weak UHF reception may just be due to worn out PC88 and/or PC86 valves in the (almost certainly) valve UHF tuner. You would need a very strong UHF tuner RF input in order to get a decently contrasted picture on UHF/625.

Regards,

Dazzlevision

[bionicmerlin]

i have got a bit stuck. I have replaced what i thought was the problem pointing to it it the picture with a pen as it was very hot. but maybe that was not the problem as its made no difference There is a couple resistors near by that test ok apart from one thats discoloured so i cant read it but it is not open circuit. i did test the capacitors as dazzle vision said may give trouble . they are not shorted but is it best to take then out to test or replace but i dont have high voltage ones handy.
there is a diagram on the back panel but its limited with no values shown.
anymore help would be appreciated Andy

[Focus Diode]

The modern day equivalent to 0.05uf is 0.047uf (47nf). High voltage ones can be obtained, this for example:

http://cpc.farnell.com/lcr-component...rfnonsku=false

If you have the service info you should be able to identify the burnt out resistor and identify suspect components.

Does the line output valve and /or boost overheat? Is line whistle audible?

Cheers
Brian

[Heatercathodeshort]

Just a few quick checks. The capacitor that was getting a bit warm [16uf] may now be OK. It has probably reformed itself. It smooths the HT supply to the line oscillator via R404 2.2K. This may well be O/C. If this is the case the PL36 anode will probably be glowing a dull red.

As Brian has mentioned, can you hear the line whistle on 405?
Remove the top cap to the boost diode PY800 and see if the line timebase livens up.
If it does the boost rail is shorted to the HT rail probably due to a shorted boost capacitor.
Remove the top cap to the EHT rectifier. It may have an internal short collapsing the EHT and putting a load on the line output stage.
The line output transformer is very reliable but could of course after 50 years develop a short. [I think unlikely] The next move is to check the voltages on the PL36 and the ECL80 line oscillator. The system switch could become intermittent but usually responded to a good clean. John.

[bionicmerlin]

Thanks Brian and John for your help
I did check resistor R404 it looks burnt but infact its spot on 2.2K.
I did or i think i have a very week line whistle on 405 lines.
After doing the tests that suggested it made no difference.After doing a bit of wire tracing i have found a wire wound resistor open circuit (orange) as in the picture.
My diagram in the back of the set says R458 (i think) but again the diagram shows no value and their is no value on the component.So hopefully you can help on that.Also what wattage should it be is it best to keep the wattage low so its more likely to fail than something else. Also has the part failed due to age or should i be looking for some other fault that made it go.
Thanks again Andy

[Restoration73]

R458 is also 2k2, a wire wound 4-7 watt type will be ok here. Note that on Philips sets
the resistors that were soldered to the flat tags were designed to drop off when the
solder melted under fault conditions (in theory)

[Heatercathodeshort]

The screen feed resistor to the line output valve. Probably failed when the line oscillator packed up due to the heating electrolytic. It will work when replaced. [It should do..] Circuit component values attached. I can send you a resistor if you need one. I have plenty. As a test you can use any wire wound 2k-6.8k. John.

[bionicmerlin]

Thanks guys for your help.im sure I got a resistors can find to test . If I don't I will get back to you John.

[bionicmerlin]

Update so far.
I have now got the set running on 405 lines . I replaced the open circuit resistor. The next thing I did was disassemble the 405 line tuner and free up the fine tuning slug. Been watching it for a good half hour. Not sure it might be just me but I think the sound should be a little clearer but picture is good.
Now the not so good news I can't get the 625 tuner to work.as before when I apply a good 625 signal all I get is very very minor sound and a change in raster but no picture when I try to tune. I did try 2 new valves in the tuner and looked inside and it looks very clean so nothing obvious wrong to the untrained eye. I also think the standard change over switch is working fine.
So any ideas please ? Andy

[Heatercathodeshort]

Mmmm. Could be a faulty UHF tuner but the Philips types are very reliable.It may be hardened grease on the tuning vanes earthing clips.
Check for HT on the input tag, if present scratch the IF output inner coax and see if you have any disturbance on the sound channel and screen.If absent trace back to supply point and the system switch. Make sure the IF lead from the UHF tuner is correctly fitted to the IF board. Recheck the PC86 and PC88. They were a bit temperamental. The PC88 is at the back nearest the aerial socket, the PC86 is nearest the tuning control. These receivers should give more than ample gain on UHF despite the valve tuner. John.

[bionicmerlin]

john
thanks i have checked all you said over and over. i dont know what i did but have made progress . i now have a picture and sound but i now have a multiple image distorted and larger scan lines . i hope it shows in the picture and hoping for more help. The 405 side still works fine.Thanks Andy

[Tazman1966]

The line frequency is way off on 625. Try adjusting the line hold from one end to the other for starters. Good progress though