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Philips 1756U, my first restoration

 
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

The Philips 1756U was my families first TV set, bought around 1957 when I was two years old and I have been looking to obtain one for many years. Thanks to Chris “The Teleman” who alerted me to this one, I am now it’s proud owner. This is my first restoration project and may take a considerable amount of time to progress due to work commitments, days off are few and far between and I am often away from home for a week or more at a time. I have little in the way of spares having been binned or given away long ago along with my once huge collection of manuals, also I have no standards converter as yet.

The set was collected from Exeter a few of weeks ago, today I have managed to give it a bit of a clean and some inspection. A few cold checks which have shown up a couple of problems.

The photos show its condition and it appears pretty fair with just a light covering of dust, some rust which is a bit of a concern, but no smoke/soot from coal fires and no nicotine stains or smell which being a non smoker I am really pleased about.
All the valves other than the PL81 and PY81 appear to be original but the two replacements used were of Mazda manufacture, they will be changed to Mullard asap :qq1 . There are a few problems, both mains fuses were found to be o/c but don’t have the appearance of having blown by a short, the live pole of the mains switch is also o/c.

The only work that appears to have been done on the underside is in the frame stage, a tar cap with one end snipped and a 1000pF mustard cap being fitted. A couple of extra resistors have been connected across originals and a 1 Meg also being in parallel with one of the added resistors, the large electrolytic on the signals chassis looks to have been oozing and probably will need to be replaced.

The CRT appears to be the original MW43-64, I hope it doesn’t have the dreaded partial heater short.

Watch this space but don’t expect rapid progress.

John.

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Topic starter Posted : 04/08/2015 12:17 am
Marc
 Marc
(@marc)
Famed V-Ratter Registered

Hi John,

Ah ha, now we get to see the beasty properly and I have to say it doesn't look half bad at all, I reckon you've dropped on a decent set.
I shall look forward to further instalments of it's restoration as and when they appear. :)

Cheers
Marc.

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Posted : 04/08/2015 12:59 am
sideband
(@sideband)
Famed V-Ratter Moderator

Yes agreed, that looks in pretty fair condition. I would only changed the Mazda valves for Mullards if necessary....no point in being too critical on things like that. Personally I don't care what make valve I fit...and neither would an engineer of the 50's or 60's as long as it got the set working again. Perhaps a rare set or a special may warrant a particular brand valve if perfection is sought.

Anyway I look forward to reading your progress.

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Posted : 04/08/2015 1:21 am
crustytv
(@crustytv)
Vrat Founder Admin

Hi John,

Very happy for you managing to find a long sought after set, It never ceases to amaze me what turns up if we just wait long enough.

I know you're extremely busy and hope you manage to find some bench time. Like everyone else I'm looking forward to following your repair, I'm sure it will be a fascinating project to follow.

As I mentioned before I have the original manufacturers service manual, packed with superb information, circuit description, Chassis plan views ( top and underneath), component lists, wave-forms, circuit diagrams, installation and alignment data. You are welcome to have it to keep with your set, I'll never use it and its fitting it resides with an actual set for completeness. I will scan it for the library beforehand though. No doubt you will find it extremely useful when you come to work on it, much better than a Trader sheet.

If you want any of your Valves or CRT testing for peace of mind, you know where to come. Also I have two new Mullards ( PL81, PY81) waiting for you when you're ready. Anything else I can help with, you know where I am.

Chris

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Posted : 04/08/2015 2:07 am
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

These were superb sets and there was still quite a few of them still around when I came into the trade in 1960
Unfortunately, I think you will find those tar "goudron" capacitors will need replacing. Last year I serviced an earlier two unit Philips TV set and almost all of those capacitors needed replacing. Good job if you can find the Philips polyester capacitors.

Till Eulenspiegel.

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Posted : 04/08/2015 6:34 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

Hi Marc,

I'm really over the moon with the condition of the chassis, I really didn't expect it to look as good as that. Unfortunately the cabinet has some quite bad gouges and the gold line around the screen is partly missing, it appears before I won the set on ebay it had made the rounds of a few car boot sales and picking up said damage, but at least there is no woodworm and definitely no deceased mice inside :ccf .

Hi also Sideband, the comments about the Mazda valves were very much tongue in cheek but I would like to fit a NOS PY81 instead of the PY81/800 fitted so as to recreate the lengthy warmup period of the original boost diode, as an impatient child it seemed to take forever for the picture appear after the audio.

Thanks very much for the offers Chris, certainly the trader sheet is useful but limited. I would be extremely grateful for a copy of the original manual. Christmas seems to have come early for the two of us, lets hope "first light" is not far off for us both also.

After the OP on Monday evening I decided to remove the LOPT and give it a ring test, the results below look reasonable but I had hoped for better. Due to the slight rusting of some parts the set has obviously not been stored in ideal conditions, I'm just a little concerned but that is the first ring test I've done with that scope so have no comparison.

John.

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Topic starter Posted : 06/08/2015 1:14 am
EDDINNING
(@eddinning)
Member Deactivated Account

Hi John, the ring test looks Ok but put the lopt in an airing cupboard for a couple of weeks to be on the safeside and dry out any moisture that might cause problems when it has the full voltage on it.

Feel free to give me a call if you need any of the valves, I'm pretty certain to have most of them here, as well as high wattage resistors ertc

Ed

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Posted : 06/08/2015 10:36 pm
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

If you have a bench power supply then the best method to warm up the line output transformer is connect the overwind and anode connection of the PL81 to say 20 volts, this action will bleed a current of 15 to 20mA though the windings. The transformer will be warmed up but not too much that the pitch melts.

See my topic about the restoration of a rusty ViewMaster home build TV: viewtopic.php?f=5&t=11603

Till Eulenspiegel.

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Posted : 06/08/2015 11:01 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

I have managed to restore the off/on switch live pole continuity by soaking it in WD40 and heating the solder terminals, whether this will be a lasting repair remains to be seen. I was a bit suspicious of gunge found around the main smoothing cans on the signals chassis. A further inspection of the two cans show them to be in good physical condition, no bulging and whatever the gunge was it doesn't seem to be from the capacitor even though its original and almost 60 years old. In fact the whole chassis looks in remarkably good condition so I thought, lets give it some juice.

Call me stupid but this is what I did, with the LOPT removed I also disconnected the screen grid of the PL81. The mains filter tar cap was replaced, two new fuses fitted and with a meter attached to the HT rail I powered the set. No flash, no bang and the heaters began to glow, as the set uses two PY82's for HT rectifiers I waited, watched the meter slowly begin to rise to 50v then switched off. Let the rectifiers cool and repeated this a number of times eventually allowing the HT to rise to 100v then 150v at which point I heard some audio from the loudspeaker, pickup from my mobile phone!!! the annoying "Brattt de de tatt de de tatt" of the phone signaling back to the network. All seemed ok, nothing looking distressed so I let it go all the way to 200v for 20 mins listening to white noise from the speaker. The tuner and IF's are certainly doing something :bba

As suggested by Till, during the last few days the LOPT has had a few sessions on a PSU to gently warm and hopefully dry any moisture out of the EHT overwind. Further ring tests failed to produce any significant improvement over the original picture posted but I will refit it see and if we can get get first light.

John.

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Topic starter Posted : 12/08/2015 12:47 am
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

Following on from the last post the LOPT was refitted late last night, PL81 screen grid reconnected and the set powered. Line whistle was heard but no sign of a raster, removed the LOPT screening can saw that the EY51 heater was lit and an earthed screwdriver moved toward the final anode connector produced very healthy sparks. So why no raster? A1 volts were checked and found to be around 350v, I next shorted the grid and cathode together which produced a very very weak and off centre frame collapse. A liitle tweak of the ion trap magnet produce a very bright horizontal line :bba

Switching off the set at that point immediately produced a frame scan as the HT began to decay, Very odd!!!! My attention was immediately directed to the work carried out previously by Barney Bodger, removing the extra components that had been fitted in parallel with R109 and R111 now produced a non linear frame scan running at about 100Hz. The original 820k resistors were found to within tolerance also so why the extra ones were added are a mystery. :aab Probably a misguided attempt to correct the frequency, I suspect one or more leaky tar caps.

This afternoon I was given a service call about 15mins away from Chris CrustyTv so on the way home I called to collect the manuals he offered, he has also kindly loaned me his Aurora and this evening I gave it a try. Not withstanding the frame fault the results nearly blew me away!!! Both pictures and sound, the CRT emission is incredible though it does have the dreaded partial heater short so it may be short lived. Remember the only components changed so far by me in this 60 year old set are the mains filter cap and mains fuses.

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Topic starter Posted : 13/08/2015 12:44 am
crustytv
(@crustytv)
Vrat Founder Admin

Hi John,

That's a great start, it makes all the difference having a signal source and the CRT visually telling you about the circuits faults, via the test card. I'm sure I read that one solution to the HKS short problem was to turn the CRT upside down, this would stop the sag, might be worth a try.

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Posted : 13/08/2015 1:55 am
mark pirate
(@mark-pirate)
Member Deactivated Account

The results look very promising, I would go through the set and replace all those nasty tar capacitors one by one, starting with the boost cap. Powering up after each change to note the improvements.

I agree with Chris, it is certainly worth flipping the tube to ease the heater sag.
Check the value of the resistors, no doubt quite a few will have almost doubled in value.

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Posted : 13/08/2015 10:52 am
sideband
(@sideband)
Famed V-Ratter Moderator

An excellent result so far! It never ceases to amaze me how some of these old 405 sets are coaxed back to life with minimal effort after being dormant for 30 odd years.....

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Posted : 13/08/2015 10:58 am
Terry
(@terrykc)
Famed V-Ratter Rest in Peace

If, when you've sorted out all the components in the field timebase and rectified any more of the bodger's handiwork, you find the timebase still runs fast, check the field integrator capacitor in the sync feed.

This gave me real headache on a GEC once - if I'd had a scope handy, I would have spotted it right away!

The fault is that the field oscillator gets bombarded with line sync pulses which initiate the flyback very early in the cycle ...

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Posted : 15/08/2015 9:00 pm