Ultra V1770 - my first telly and Im struggling

[Exiled Yorkshireman]

Hello all, and happy new year.

To take my mind off certain medical issues I've started to try to restore my first television, which is an Ultra V1770. I'm lacking experience and struggling somewhat. I appreciate that this set is not especially well thought of, but it's what I've got.

First step was to sort out the reservoir and smoothing caps, followed by waxies in the line and frame stages. I'm hoping to get a raster before moving on to the I/F and tuner.

The frame oscillator valve was missing and I've replaced it with a NOS one. The frame oscillator seems to be running OK albeit somewhat fast. 50Hz and below are only achievable by turning the frame hold control nearly to minimum.

The line oscillator runs, but a fair bit too fast. The line hold control operates, but the minimum stable frequency is about 6.7kHz. Any lower than this and it becomes unstable. I'm not currently (no pun intended) getting any EHT. I did for a couple of minutes, at which point even my hearing was able to detect a line whistle.  My homemade ring tester suggested that the LOPT is OK. The filament of the EHT rectifier is OK.

What should I check next?  Any help would be appreciated. I have a scope and diff probe which is good up to 750V, and all three service manuals (manufacturers, Trader and Radio Retailing)

[Mike Watterson]

Hunts etc (composite or card case) everywhere.
See what DC HT volts and heater chain volts there are.
The HV ceramics on LOPT stage can fail.

Though I last worked on these in 1970s!

I think 1959, so almost all caps of 1nF or more are suspect. Electrolytics of this era often reform if seal intact. No leakage current means it's dried out.

but the minimum stable frequency is about 6.7kHz.

Shouldn't it be 10.125 kHz? 405 lines x 25 fps, though 50 Hz and 202.5 lines interlace to get 405.

[Exiled Yorkshireman]

Hunts  etc (composite or card case) everywhere.
See what DC HT volts and  heater chain volts there are.
The HV ceramics on LOPT stage can fail.

Though I last worked on these in 1970s!

I think 1959, so almost all caps of 1nF or more are suspect. Electrolytics of this era often reform if seal intact. No leakage current means it's dried out.

but the minimum stable frequency is about 6.7kHz.

Shouldn't it be 10.125 kHz?  405 lines x 25 fps, though 50 Hz and 202.5 lines interlace to get 405.

Thanks very much for replying, Mike. I think I've got all the Hunts other than in the IF and tuner. Sadly the main (triple) cap was totally dead, Measures a few nF per section. restuffing beckons. I'll measure HT volts and heater chain and report back.

I'm confused  about the line and frame osc frequencies. The manufacturer's service sheets show waveforms and quote 25 Hz for frame and 5 kHz for line, but you're right, of course. It's 50 Hz for frame and 10 kHz for line, or a tad lower for each when free running surely?

[Mike Watterson]

Check you got any caps across cathode resistors! Open/dried out means low gain and short/high leakage means over current / poor bias.

[Mike Watterson]

It's in the R&TVS books

[Exiled Yorkshireman]

Check you got any caps across cathode resistors! Open/dried out means low gain and short/high leakage means over current / poor bias.

I noticed a collapsing letterbox of screen illumination on turning off the set. Then it suddenly occurred to me that I'd forgotten the cap that couples the video output to the CRT cathode. It lurks to the side of the contrast controll next to the IF board. All the leakage through that 0.25uF cap was biasing the CRT off. I snipped it out and now have a raster. It doesn't reach the bottom of the screen and the linearity is awful, but it's a start, at least it proves that it's worth continuing  and I'm sure there are plenty more newbie errors for me to make.

[Mike Watterson]

Indeed ensures a soft grey on full black scene transitions. I'd replace it with 400V metpoly with maybe 1 kV 1nF ceramic across it. Not too big or expensive.

[Exiled Yorkshireman]

Indeed ensures a soft grey on full black scene transitions.  I'd replace it with 400V metpoly with maybe 1 kV 1nF ceramic across it. Not  too big or expensive.

Yes, I'd read about the lack of black clamping because of the capacitive coupling. Was this normal for the time? My memories of our first telly, a KB 'New Queen' aren't clear enough to remember.

Thanks for the coupling cap advice. What's the reason for the ceramic in parallel?

[Mike Watterson]

Yes, very common. Even if DC CRT coupling, there would be no black level clamp and AC somewhere. I think also BLC is easier for 625 than 405 (Neg vs pos video modulation). Even some early 625 sets were poor.

The 0.25 uF cap may have too much inductance. A ceramic cap has very low inductance, no matter if single layer (normal for 1 kV) or multi-layer (miniature 0.1 uF). Some RF circuits might even have four different capacitors in parallel for decoupling to minimise inductance (1 GHz to 20 GHz systems).

However likely total bandwidth is less than 3 MHz, so might make little difference. Also depends on how the two metalised plastic foils for the capacitor are terminated to the wires.

[Mike Watterson]

I think EHT / Line drive is the hardest part of old TVs and once you have that with something filling screen width it's then the home straight and just like two radio sets sharing a tuner (video & audio).

Resist temptation to adjust any IF or tuner cores! But you probably know that!

So frame next.
Since it's 405 AM + AM, it's probably separate sound & vision IFs.

Do you have a 405 source or at least a signal generator that does to 45 MHz?