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Old 7th Nov 2015, 12:21 am   #1
Electricdreams
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Default Philips 1200U First Light.. ish

Just a couple of things about the Philips MW31-16 and the Philips 1200uf chassis.
I found some interesting changes to the set.

Firstly the ion trap was in reverse (arrow pointing toward the base) the Philips Mw31-16 service manual states that the arrow on the ion trap should be facing towards the screen.

If you look at 1043 (Philips 1100U Trader Service Sheet) there is C40 (just above the CRT and R64) this C40 has been snipped.

It seems someone is determined not to have the TV working at all.

Am I right?

P.S. This is an ex-rediffusion set.
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Old 7th Nov 2015, 2:41 am   #2
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Default Re: Philips 1200U First Light.. ish

The ion trap magnet will be effective when the arrow points away from the screen. The approved position however is with the arrow pointing towards the screen and the magnet near pin three. Some MW31-16 tubes have a line on the neck to show where the ion trap magnet should be positioned, When the magnet is positioned the other way at 180 degrees to pin 3 it will be closer to pin 8.
At the time writing this I have no information to hand for the 1200U.

DFWB.

Last edited by FERNSEH; 7th Nov 2015 at 2:48 am.
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Old 7th Nov 2015, 1:19 pm   #3
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Default Re: Philips 1200U First Light.. ish

Service information for the Philips 1200U can be found in volume III of the Malloy and Poole television servicing book. Pages 78 thru to 87. The component references differ from the Trader service sheet.

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Old 14th Dec 2015, 2:33 am   #4
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Default Philips 1200U First Light.. ish

Right,

I've powered it up slowly on a variac at first. Loud crackling and buzzing from speaker, but no light.
Attempted to discharge CRT, no spark.

So I've done a cap change, I also discovered the resistor before anode of CRT connection has gone O/C. Also as this was a ex-Rediffusion set, I returned the circuit original schematics (Traders Sheet and Electrical and Radio Trading Sheet)
Cathode and Contrast was D/C so returned that to circuit with a new pot as the other was of different rating.

Powered up carefully again. Faint Whistle, but no light. Healthy buzz from speaker. Plugged in Aurora, no testcard tone on any channel. Possibly needs tuning. Turned off all lights in room and could see a very weak halo spot in middle of CRT.
No change when adjusting brightness and contrast.
Can smell ozone and focus control produces a very bright spark when adjusted.

LOPT is not warm and there is a small spark when discharging CRT
Should I check resistors on HT?

Any Suggestions?
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Old 14th Dec 2015, 7:13 am   #5
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Default Re: Philips 1200U First Light.. ish

I don't know this TV chassis. Valve or transistor?
It sounds like a 'no HT' fault in the power supply, but you say that the line osc is running & there is some EHT?
The 'halo' on the screen is the stationary electron-beam. Under full HT you'd have a spot burn by now.
It may sound daft..... Are the scan coils plugged in & making good contact?
Do they show continuity if the resistance across the plugs is measured?

If this is a valve TV all the heaters will be showing a glow, as a o/c heater anywhere will mean the set is totally dead. Is HT rectification from a solid-state diode or a valve rectifier off the mains? If you can unplug the different stages from the PSU you should do so. If you have HT under no-load conditions there's something on one of the other stages dragging it down.
If not....... I would suspect the rectifier and the big reservoir & smoothing capacitor. It may be leaky, in which case it will be getting warm.
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Old 14th Dec 2015, 10:07 am   #6
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Default Re: Philips 1200U First Light.. ish

Its valve Neil, trader 1043/T25
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Old 14th Dec 2015, 10:45 am   #7
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Default Re: Philips 1200U First Light.. ish

The Philips 1100/1200 series should be a straightforward overhaul. The twin linked chassis is thoroughly reliable and will present few problems.
I would suggest you start at the power supply, work forward to the line output stage and get this working fully first. The rest will be obvious from the screen indications.
There is a EHT smoothing capacitor mounted on the LOPT. Make sure this is not leaky. Disconnect it, the chassis will work just as well as the CRT is coated. [MW31-16/74]
Can you measure the EHT? What is the voltage on pin 10 of the CRT? [first anode]
All the black tar covered capacitors will require replacement but all in good time. Many have odd Philips values that need to be maintained to avoid man made faults.
Get a good raster first before attempting the application of the AURORA. The receiver unit is a superhet that will tune to any of the five BBC channels by way of plug in coils for aerial, bandpass and oscillator. They are similar to B9A valve bases and lack of signals is often due to dirty pins on the coils. They are colour coded for each channel.
The 1200 will give a very bright crisp picture when operating correctly and still give years of trouble free viewing 60 years on.
I would suggest this sequence.
Power supply
Line timebase.
Frame timebase.
Front end/IF
Video
Sound.
Blanket replacement of capacitors especially in this chassis is not to be recommended due to the odd values and connecting tags. It needs to be carried out in a strict methodical manner. This chassis was the launch of extreme reliability from Philips from 1951 to the 300 series in 1970. Many similarities can be seen on the chassis. Good luck with it. Regards, John.
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Old 14th Dec 2015, 10:49 am   #8
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Default Re: Philips 1200U First Light.. ish

Were the C73 and C74 re-formed with separate source of DC. They may be leaky now, which could be dragging down the HT.
There's a winding around the tube neck, L19 that is linked to the HT via connector D and supplies the audio stage pin 9 & 10 of connector 'C'. Is there voltage on pins C9 & C10?
If not look at the state of Connector D. Is it clean & making good contact on all pins?
If that is dirty it may stop HT getting aroud the set and also be why there is no visible raster.
You said there was line whistle, which suggests some level of HT, so why is the rest of the set apparently not working. There should be audio 'hiss' from the speaker with no signal input. Is there HT on the primary of the o/p transformer, T3?
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Old 15th Dec 2015, 10:01 am   #9
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Default Re: Philips 1200U First Light.. ish

The coil around the tube is the focus coil. This is connected in series with the HT supply to the class A audio output valve to maintain the correct focus as the winding warms up. [decreasing its resistance]
A hiss as such that is so familiar with some fringe models such as the PYE CTL58F and later transistor tuners and IF strips will not be apparent on the receivers from the pre 1960 era. The AVO 8 with the aid of the manual should sort the HT as the circuit is quite conventional.
Just a thought, the tube employs an ion trap. Do not move it as you said you had a dim blob on the screen. As soon as you have enough EHT [EY51 heater glowing a cherry red] and around 300V on pin 10, switch the lights out and adjust it for maximum brightness ignoring focus, picture positioning or corner cut off. Maximum brightness is the correct setting. Adjust it a very small amount around the neck and backward and forwards, note a very small amount or you will lose the setting and with the chassis operating below efficiency, you will probably find it difficult to locate the original position that gave the 'blob'. Tipex may help. Regards, John.
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Old 18th Dec 2015, 9:57 pm   #10
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Default Re: Philips 1200U First Light.. ish

Forgive me, I am not ignoring your posts, just my room is full of xmas presents at the moment. Once they are budged I can get back to the set!
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Old 2nd Oct 2017, 1:58 pm   #11
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Default Philips 1200u

Well due to issues at home, family and work I had a major clear out purely for my mental health. Well that aside, Mikey405 picked up the Philips set and I was grateful that it went to a good home. He just reported to me that all he did was change the CRT and it works! (see photos)

He has complimented my work and I am quite overjoyed by this...

Oh I did replace the resistor on the LOPT just by melting the wax (and I did replace the wax!)

I also replaced the focus pot and rewired the brightness (or was it contrast?)

Thanks Mikey405 for these photos!
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Old 2nd Oct 2017, 8:40 pm   #12
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Default Re: Philips 1200u

Probably the most reliable television of the 1950's. Many of these excellent and good looking receivers worked for well over ten years without a service call.

Brilliant picture, absolutely stable, cool running, Fault free LOPT, Mullard MW31-74 tube and fantastic build quality. The valves seemed to go on for ever! [Mitcham Works RIP] John.
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Old 2nd Oct 2017, 11:28 pm   #13
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Default Re: Philips 1200u

Chassis look very similar to my (parents) rather less reliable 1400A.

Peter
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Old 3rd Oct 2017, 7:05 am   #14
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Default Re: Philips 1200u

Hi Paul.

Other than the tube, all that really needed sorting was an arcing EHT smoothing cap (filling the air with ozone) and a couple of low emission EF80s in the IF.

The tube had absolutely no emission whatsoever. The meter didn't move a single mm on my tester and there was nothing with which to start a reactivation.

I think it was quite brilliant that you got such a good picture without actually ever seeing a picture.

As John says, these are amazingly reliable sets and always manage to produce a tip top picture. Even the cheaper less-complicated 1100U / 1238U produced an excellent picture although that nasty mechanical focus arrangement with a Bowden cable wasn't perhaps all it could be.

Anyway, the set has your name on it when the time comes to part with it.

Thanks Paul.

Kind regards.

From Mike.
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Old 4th Oct 2017, 5:22 pm   #15
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Default Re: Philips 1200U First Light.. ish

Mike,

I can't wait to see it and should you part with it, I will welcome it back with open arms!
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Old 5th Oct 2017, 4:46 pm   #16
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Default Re: Philips 1200u

Quote:
Originally Posted by peter_scott View Post
Chassis look very similar to my (parents) rather less reliable 1400A.
Yes Peter, This basic design was employed in many Philips receivers dating from 1951- 1955. The 1400A tended to suffer faults that were exclusive to projection receivers [EHT ringing choke etc, screen burns and all the other odd balls associated with projection circuits. Nasty things....but fun! John.
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Old 5th Oct 2017, 5:31 pm   #17
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Default Re: Philips 1200U First Light.. ish

Speaking of projection sets, I have one that looks almost identical to that.
Did they do projection and direct view versions?
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Old 6th Oct 2017, 8:38 am   #18
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Default Re: Philips 1200U First Light.. ish

Not exactly but the general Philips 'theme' continued through this period. J.
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Old 6th Oct 2017, 9:09 am   #19
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Default Re: Philips 1200U First Light.. ish

what a nice set, makes a change from the drab walnut consoles of the era. It almost has a tinge of american about its looks.
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