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Philips 1756U

 
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

Thread originally started over on the original VRAT here.

It's some time since I collected this set from Exeter, actually over 2 1/2 years ago, how time flies. I did fire it up again a couple of weeks ago and with the inclement weather we're having at the moment and unable to get outside there was no excuse but to make a start to try to get some useful pictures on it. Having no dedicated workbench makes life rather difficult, it's currently sat on top of a filing cabinet but here we go.

Sadly it's long slumber seems to have had a detrimental effect on the CRT, the last time it was powered the frame frequency was around 100Hz but even though the CRT had the dreaded partial short on the heater the emission looked as good as new. When fired up the frequency was still fast but the CRT looked very sick although it did improve somewhat after around 30 mins running but nowhere near as good as during the initial tests.

Obviously there are likely to be severel of the notorious black tar "Goudron" capacitors to be in need of replacement, checks in circiut of resistors showed they were all near enough in tolerance apart from R105 which was replaced. The extra components which had been added for whatever reason were removed, rather than just block change I decided to tackle the frequency problem. First, most likely culprits would probably be in the multivibrator section so it seemed logical to try C90 0.033uF. Bingo, this had the desired effect and gave a locked but non linear testcard lacking in height but with the frame hold almost at mid point.

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1756U Field

On replacing C99 I expected to improve the linearty somewhat but didn't, what it did do was now give me bags of amplitude but still with the top foldover and bottom compression, bridging C89 for the bottom compression made no difference at all. Replacing C98 though produced the desired effect and after a little adjustment of the focus/centering magnets we have what you see below.

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Still a tiny bit of top and bottom compression to sort out, the audio suffers from hum with the volume at mid point and below, also the contrast conrol has no effect but the set is coming along.

John.

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Topic starter Posted : 04/03/2018 10:36 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

Whoops, don't know why I can't edit it only a couple of minutes after posting as the pics went a bit awry. Below is how it looks now.

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Topic starter Posted : 04/03/2018 10:42 pm
PYE625 liked
crustytv
(@crustytv)
Vrat Founder Admin

Hi John,

I also can't believe 2½ years have gone by!! The Philips is certainly coming along quite nicely, that's a very good test card C.  ?

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Posted : 04/03/2018 11:01 pm
Katie Bush
(@katie-bush)
Illustrious V-Ratter Moderator

Hi John,

That looks pretty good in those pictures, and remember, it's a Philips, weren't they always weird anyway?

I wish I could find a way to get round this back issue, and get something on "the bench" - the metaphorical bench that is! I have bench that I was given, but it's in the garage, and as such, I don't really have anywhere to call a workshop right now - not a proper one anyway.

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Posted : 04/03/2018 11:05 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

Hi Chris, I don't know where the time has gone either, it just seems to have flown by. One of the factors is that I do so much overtime (mostly willingly) but that may change as several of our  customers are upgrading their kit so I may have more spare time.

Hi Marion, this particular Philips although probably very advanced for it's time seems pretty straight forward now although the AGC operation is a bit strange to me.

As for as somewhere to work I do have a garden shed which was filled bulging with all sorts of gardening equipment but this has been transferred to one of those large plastic storage boxes. The shed though leaks very badly and will need some major work to make it usable, that will have to wait until better weather. At the moment it has a the old rubber liner from our decommissioned garden pond over the roof protecting it.

John.

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Topic starter Posted : 04/03/2018 11:37 pm
ntscuser
(@ntscuser)
Prominent V-Ratter Registered
Posted by: Katie Bush

Hi John,

That looks pretty good in those pictures, and remember, it's a Philips, weren't they always weird anyway?

There are three ways to build a set: a right way, a wrong way and a Philips way!  ?

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Posted : 05/03/2018 12:48 am