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Old 16th Mar 2007, 9:01 pm   #1
Colourstar
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Default Hitachi CPT2226 - shading and greyscale

This 23 year old Hitachi CPT2226 has a strange picture fault. The left hand side of the screen is at peak white all the time, whilst the greyscale on the remainder is all over the shop. Turning the brightness up or down only affects the right hand part of the picture. Occasionally the whole screen flickers white for a moment. Presumably I'm looking at a duff tube, but wouldn't a grid/cathode short in one of the guns affect the whole picture?

If it is the tube, I suppose it will have to join all those other unloved woodies at the tip this weekend. A shame as it's a quality set and I guess we really should be saving decent 1980s sets now in the same way that we rescued all those 60s tellies back in the 80s!


Steve J
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Old 16th Mar 2007, 9:13 pm   #2
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Default Re: An Unhappy Hitachi

Don't tip it!

I'd start with an emissions test and a clear short circuits session while the tube tester's out. See what that does. Then a trip round the luminance/video stages and the flyback circuits.

Come back with what you find.

Tip it?... I thought you knew better LOL!

Cheers,

Steve P
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Old 16th Mar 2007, 9:19 pm   #3
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Default Re: An Unhappy Hitachi

I think the most likely cause of this fault is a faulty electrolytic smoothing the HT to the video output stage(s).

An HT of 200 volts or so is usually derived from the LOPTx for the video output. If the electrolytic in this supply (typical value 10uF) goes o/c the picture gets shaded at line rate.
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Old 16th Mar 2007, 9:36 pm   #4
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Default Re: An Unhappy Hitachi

Is that so? I haven't got much post-1980, maybe it's time I should. Colourstar, find this cap and change it before you do anything else.

Cheers,

Steve P
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Old 16th Mar 2007, 9:39 pm   #5
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Default Re: An Unhappy Hitachi

Hi Steve,

Try C715 (4.7uF/250V)

Regards
Stu
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Old 16th Mar 2007, 10:50 pm   #6
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Default Re: An Unhappy Hitachi

My Gran has one of these sets; I got it for her about 4 years ago from 'Cash Generator' in Hyde for the princely sum of £2.

Most of the controls were intermittent, but with a dust-out and a shot of contact cleaner, all was well, and the picture on the set is truly exceptional.

I have a Hitachi portable CAP 162 with the same problem as the set above, albeit not quite as bad.
Although I have not had time to look into this fault yet, I did look at some fault reports which suggested a leaky 4.7uF electrolytic, smoothing the HT to the video output stage.

I know it's not the same set but a similar fault maybe.

Jay
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Last edited by Mike Phelan; 27th Dec 2007 at 3:03 pm. Reason: Edited for readability
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Old 16th Mar 2007, 11:18 pm   #7
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Default Re: An Unhappy Hitachi

I would agree with what col, stu and jay say here, look for a faulty electrolytic that smooths the HT to the video output stage.

From memory I think that the offending item may be situated on the tube base PCB.

Regards
Andrew
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Old 17th Mar 2007, 12:23 am   #8
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Default Re: An Unhappy Hitachi

Thanks everyone, your suggestions and help are really appreciated.

Steve P- The tip was an idle threat! I got the set from a charity shop across the road from work, where it was stood on the pavement looking a bit vulnerable. It was only a fiver so there was nothing much to lose. Luckily I have several friends who want 'retro' style TVs and also older relatives who want something simple to use, so these 80s models generally fit the bill very well and I'm glad to find them good homes. Nearly all of them still give excellent results.

I'd much rather take a set from the tip rather than to it and I'm sure many other members feel the same.

Time to hit the Ovaltine now, but hopefully I'll be able to look more closely at the Hitachi over the weekend.

'Night all.
Steve
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Old 17th Mar 2007, 2:00 am   #9
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Default Re: An Unhappy Hitachi

Steve

If the whole pic flickers white intermittently, resolder the field chip as well as changing the cap

Stu

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Old 17th Mar 2007, 6:36 pm   #10
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Default Re: An Unhappy Hitachi

I seem to remember a cap being responsible for this ?

Anyway, BLIMEY !

You must have the only living example with a good LOPT !
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Old 17th Mar 2007, 6:49 pm   #11
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Default Re: An Unhappy Hitachi

Glad to report another success thanks to the mighty forum! Stu- you were bang on the money. C715 was whipped out and changed and now all is well. In fact the picture on what appears to be the original tube is excellent as you'll hopefully see. I'll also follow your tip regarding that chip.

Just hope the LOPT holds out after Dr Watts comments!

Thanks again to all who have helped me. That's another set saved.

Steve
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Old 17th Mar 2007, 8:19 pm   #12
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Default Re: An Unhappy Hitachi

Well saved Steve

Picture looks great!

As regards the LOPT, in the event you were unfortunate with yours, I wouldn't be at all surprised if there wasn't still a Konig equivalent available.
It might be questionable economically, but I guess it depends how much you like the set!

Well mended once again

Regards
Stu
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Old 18th Mar 2007, 7:28 pm   #13
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Default Re: An Unhappy Hitachi

Well done - I remember having this fault on a brand new set (such a long time ago)!

It took me all one afternoon to find it, after having phoned Hitachi tech. services to be met by their standard reply

- "Dunno mate, never seen one of these, if you find out let us know."

It has to be said that Hitachi were no worse than anybody else in this respect.

These sets outperformed most of the opposition though - with the exception of Sony!

(Ducks behind the parapet to aviod the inevitable brickbats )

Regards,
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