Tv62

[Station X]

I've run out of knowledge here. One third of a milliamp through a 1M resistor will cause a volt drop of 300V, which is about what you're seeing, given that there were about 7.6 Volts on the anode of the PCL83.

7.6V sounds low for an anode voltage to me though. I'm sure one of the TV experts can advise what the reading should be, unless it's shown on the Trader sheet.

[Boom]

There's not a lot of components in the oscillator Chris, you can check R15-20
and also the vertical hold control.

Did you say you have changed all of the waxxies? There are only a few here, C12-16

If that doesn't help we'll have to wait until John resurfaces.

[PJL]

OK, we are in business. Don't use the AVO 7 as the impedances in this circuit are high and it will pull down anything you connect it to. At the moment we have to question the readings on your meter.

From above Pin 9 of the PCL83 is reading 108V! This is the grid of the pentode and that would be impossible. Can you check the measurement and make sure you are counting the pins the correct way. From underneath you count clockwise.

Also disconnect flyback suppression capacitor or whatever it's called, C30 820pF, just in case.

[oldticktock]

c14 now 310v
pin9 is 126v

oh and the frame collapse no longer fills right across the screen

[Boom]

Originally Posted by oldticktock

c14 now 310v
pin9 is 126v

As PJL says it can't be. Where are you connecting the meters negative lead?

[oldticktock]

chassis, fed up now been at this too long and no results and whats more tripped the house RCD and it's fried my main computer BSOD, Peeved off does not describe it. Now using my old cruddy pc

[oldticktock]

R36 must be running hot its the big wire wound at the end of the Tagboard, its paint is melting 94v one side 170v the other it should be 6.8k it's 8.2k it feeds into pin 8 of the PL81

[Heatercathodeshort]

If the output stage is still operating o.k. and I see no reason why it should not, the fault must be in the frame oscillator, one half of the ECC82 and the triode section of the PCL83. I suppose that both heaters are glowing in the ECC82? Silly but it can catch you out.
David's suggestion is agood one ref the capacitor to pin 2 V3a, pin 7 V2a. Check the continuity of the frame hold control and if your meter can manage it the height control as well. The height control is slightly strange as it works exactly like the volume control in the DAC90. [Thought I'd throw something in familiar] Check R20, its a 680k in series with the frame hold control and may be O/C. Check also R22 a 1.8m in series with the slider of the hieght control. I bet it reads well high. You will have to disconnect one end of these to get a reliable reading. There is very little to stop this oscillating now so take it easy and it will be interesting to see the results. I have loads of ECC82's if you need
one but I don't think it's the valve. Take it easy and it will be interesting to see the cause of this refusal to oscillate.
The resisitor is the screen feed to the PL81. Don't worry about that for the time being. No connection with the frame collapse. They run hot and always burn the paint. Replacing C23 .01uf should bring the line output stage to full width again. It's connected to pin 2 of the PL81. J.

[oldticktock]

Hi John changed R20 lastnight for a new one . I will check other as you say. I too have many ECC82's.

So want someting more than a white line after all this time

[oldticktock]

I have looked at R22 and its Green/Blue/Green 5.6M I have not snipped and measured with the meter yet but as you say schematic says 1.8M how is this so? It looks original too

[oldticktock]

Just a quick update in case your wondering what's going on.

Replaced R22 it was 6.6M replaced with what I had a 1/4W 1.8M
Replaced C23 line output stage restored to full width
Replaced ECC82 with new one

Still frame collapse



will check others now

[Station X]

Sorry to ask the obvious, but are you sure you've not mistaken R23 for R22? R23 is 5.6M.

[Heatercathodeshort]

That looks like R23 that you refer to. If you take the two triodes used to develop the frame oscillator you will see it is very similar to a two stage triode audio amplifier similar to the single stage UBC41 in the DAC90a. The trick is to introduce feedback at a rate that determines the frequency required. 50c/s for the frame, 10.125kc/s for the line.
That is carried out by varying the values of the coupling and feedback capacitors.
This is quite a simple circuit and we will get there but I suggest you put the set aside for the night and forget it before the men in white coats arrive to the sweet sound of test card music.. I have done this many times with a stinker after having spent a considerable time on a receiver. The mind plays tricks with you and in most cases the problem was solved within a very short time when a fresh mind was applied the following morning.
You can't expect instant results. This set has been asleep for 40 years and I find it incredible that you have got so far in just a matter of a few days. It takes years of mistakes, confusion, frustration, pain and suffering to learn how to repair television receivers to a reliable and satisfactory standard and quickly! I had customers waiting for their sets while I did a quick 'repair bar' service on a Saturday morning! People did not have second sets in those days and expected same day service or a loan set. It was the same with in house service and you certainly grew up quickly after doing that for 12 months. [If you only knew..] Don't get frustrated. It is supposed to be fun, a learning curve and you will be delighted when you get it working for the first time. All the guys on this Forum have been in your position without the help of others so you have a head start on them from the off. You need to unwind and check everything component by component in that frame section. You know the output stage is working so do as David has suggested with the cap from the heater rail to the control grids of V2b and V3a maybe a lower value say around 002uf. Close it up for the night or even for the weekend and start again with a clear uncluttered head. Regards, John.
PS Sorry Graham you beat me to it! J.

[oldticktock]

Kick a man while he's down

yup that's me being a twonk I counted from the old resistors forgetting the new one i had put in place that shunted me by one.


Ok I'm going to rectify my mistake and do one final switch on then take Johns advice, think I will go an play with my toddler he keeps popping his head round the door asking why the fat telly is not working

Cheers Graham & John.

Need to rebuild my Main pc which also happens to be the house media centre which pumps video to all rooms I was going to hook the TV62 up to it via the Aurora and watch vintage TV shows/films

Chris

[Sideband]

John's right about frustration. I've probably repaired more TV's than radio's since 1970 (when I entered the trade) although radio has always been my hobby. In the days of valves, we had to contend with intermittent valve holders (changing some of those on a wired chassis was fun)...in fact out in the field once and being nearly 6 o'clock on a Saturday, I found the only way to get a picture on the screen of one set was to push the video amp valve hard over in the socket....broken valve holder pin. A search in the tool box produced a strong elastic band which I doubled up, slipped it over the valve and hooked it to a convenient point on the chassis. The set worked like that for months until another failure and then it was fixed properly.

Don't give up yet! You are doing brilliantly . I've been reading the thread since it started and been facinated by your account. I keep thinking about that low anode voltage on the triode anode of the PCL83. The trader gives it as 40v. I reckon a careful check around there might be worthwhile.

I look forward to the next installment!


Rich.

[Heatercathodeshort]

just a final word. If the oscillator has stopped or stalled as suggested the anode voltage will be a lot lower than the manual suggests. It's from a high impedance source and the current dropped by a conducting valve will reflect this. Now I'm gonna go to bed and dream of TV62 field timebases....The Victorian Home for Faded television Engineers is just a call away..Good Night everybody, Good Night! Oh and don't forget to switch off your sets....[400c/s tone] Switch off spot...J.

[oldticktock]

Now it has 1.8M as R22 5.6M R23 and i've lost it now,no line whistle no line on screen.

[thermionic]

Chris,

definately time to put it to one side for the night, as John has suggested. You are now in danger of inflicting man made faults as your eyes water and your mind is on a roller coaster.

You have done well so far, and are so close now. Close the door on the workshop, sit in your comfortable chair with a beer or a single malt.

Tomorrow will bring rewards!


Enjoying this thread. Cheers. SimonT.

[oldticktock]

Ok line whistle is there but its seems higher in pitch almost to the point of not being able to hear but its there.

The weird thing was I was testing pins on ECC83 when I got to pin 7 it made a crackle in the speaker the screen flickered and the line was fatter. I adjusted the height and it got bigger and the fat band has interference going on.

It does not fill the full width or height but somethings going on.

See pic 1 before pic 2 after pin probed.

ECC82 readings

pin1 7v (anode) (V2A)
pin2 2.6v(grid)
pin3 2.6v(cathode)
pin4 4.6v(heater)
pin5 4.6v(heater)
pin6 177v(anode) (V2B)
pin7 13.1v(grid)
pin8 182v(cathode)
pin9 143v !!!!(heater centre tap)

When I rotate the turret the speaker crackles and the fat band shows little flashes of light

By the way still have the old C14 snipped out and croc clipped in a 2uf

Chris

[Station X]

The heaters of V2 are wired in parallel, so I would expect pins 4 and 5 to be wired together and show the same voltage.

The voltages are AC though, so you'll need your meter set to AC Volts to check the voltages. Expect to see about 6V AC between pin 4/5 and pin 9.

V2B seems to have more volts on its cathode than on its anode!