Hitachi CNP-192 Horizontal Centring of Picture

[chroma04]

Hi,

I am slowly working my way through a few issues with this television and am nearly there.

However, does anybody know how to centre the picture horizontally on this set? I've tried to show the issue in the photo's attached. The whole picture needs to be shifted about half an inch to the left. Is it performed electrically or mechanically?

As this is a delta-gun tube with many adjustments for static/dynamic convergence, I'm loathed to start adjusting anything!

I have the circuit diagrams, but unfortunately not the full manual.

For reference, the picture tube is an 490DKB22.

Many thanks in advance,

Best Regards,

Adrian.

[Mikey405]

Hi Adrian.

Those delta-gun convergence controls might look scary at first but they're not too bad when you get going and your Hitachi will be a lot more reliable and easy to converge than some of the British sets of that era (with their crusty overheated pots etc.) You can always try adjusting the control which corresponds to your convergence problem - and then if you don't like what it does, turn it back again.

The horizontal shift control in that set (if there is one) will be electrical. You may find the purity rings also move the picture slightly but you shouldn't use them for that.

I had it in my mind that there may not actually be any horizontal shift control in this set (although it does seem strange) but I'll check my service manual when I get home. I think this set uses the "PAL-2" chassis.

What engineers in 1970s may have done - although I'd never stoop to this - is to slightly adjust the line hold control. This will move the picture within the raster. Don't twiddle it too much though otherwise you'll get poor line lock. (Try disconnecting and reconnecting the aerial after each small twiddle to make sure you still get a well-synchronised picture.)

I'll check my manual and let you know.

Thanks Adrian.

Kind regards.

From Mike.

[Nuvistor]

I can’t find a horizontal shift but there are two parallel capacitors feeding the scan coils, S correction, these could be faulty, if one is leaky it will pass DC through the coils which could shift the picture.
There is R627 but I think this will affect pin cushion.

[Mikey405]

Hi Adrian again.

Looking in the manual I see no mention of a horizontal shift control (although there are three width tappings). The line hold control is set up as follows:

- Connect a 0.1uF capacitor between terminal B2 and earth.
- Turn on the set and tune to a test card pattern.
- Adjust coil T701 for a "floating" picture. (T701 is at the bottom-middle of the "power PCB" - the PCB with a vertical switch in the middle.)
- Remove the extra capacitor.

This should roughly centre the picture within the raster. Fine-centring of the actual raster appears not to be possible with this set (at least I couldn't find anything about it) but a slight tweak to T701 should shuffle the picture one way or the other at the expense of the correct line-hold setting.

Thanks Adrian.

Kind regards.

From Mike.

[chroma04]

Progress!

I've had a careful tweak of the convergence controls (after noting their original positions!) and have obtained quite an improvement in the overall registering of the three images across the area of the CRT. I'm now happy to leave these as they are.

I have also, as you suggested Mike, very carefully tweaked the line hold control a half-turn anti-clockwise, and this has centred the raster! This does not appear to have affected the line lock to any serious degree, so I will leave it as is.

Many thanks Nuvistor, for the head's-up on the capacitors for S-correction. A quick check doesn't appear to have highlighted any leakage, however, it's duly noted for future reference, should any issues arise in the future.

To be honest, I think I'm about ready for boxing the set up for the moment and giving it a few hours' usage to see whether any further issues arise.

Thanks for the help so far!

Best Regards,

Adrian.

[chroma04]

Hi Mike,

I've just spotted your last post!

Many thanks for taking the time to look at your manual on my behalf! Most helpful!

Best Regards,

Adrian.

[Welsh Anorak]

I think there was an electrolytic, possibly non-polarised, on the convergence board that could make it hard to set the convergence when it went faulty.

[chroma04]

I have spent a little more time carefully setting up the convergence and have obtained quite a big overall improvement.

I think it's time to call this finished for the moment and give it a few hours' usage.

For a 45 year old set, I think it gives a reasonable account of itself, and required only a few replacement components.

Thanks to everybody for their help!

Adrian.