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Old 12th Oct 2019, 8:19 pm   #21
FERNSEH
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Default Re: Pageant P50


"The picture below doesn't look good to me. If I turn up the brightness I get bright edges."


Check the CRT first anode voltage. It should be at least 150 volts above the cathode so you should be looking at >300volts.
The first anode is supplied from the boost HT via a resistor R72 (1Mohm) and decoupled by C67 (0.1mfd). Frame flyback blanking is applied to the first anode via C35 (250pF). There is a stand-off resistor R74 (68Kohms) between C67 and C35.
So if the A1 voltage is near HT volts it can be assumed C67 is s/c or short circuit.

DFWB.
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Old 12th Oct 2019, 9:06 pm   #22
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Default Re: Pageant P50

Oh dear, it's not good.

H.T. is just about spot on at 194V.
CRT first anode (pin 10) 250V, should be 342V
Cathode (pin 11) 78V should be 153V
Grid (pin 2) 56V should be 112V

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David
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Old 12th Oct 2019, 9:22 pm   #23
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Default Re: Pageant P50

Low CRT cathode volts might the anode load resistor of the video amplifier valve has gone high value, it should be 6.8Kohms. Tube cathode is connected to the video amplifier via parallel C70 and R78 and series corrector choke L37.
CRT grid is decoupled by C69 (0-1mfd). That capacitor is likely to be leaky.
The first anode volts are too low.

DFWB.
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Old 13th Oct 2019, 5:53 pm   #24
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Default Re: Pageant P50

Is the AGC line voltage varying when you adjust the contrast? J.
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Old 19th Oct 2019, 2:07 pm   #25
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Default Re: Pageant P50

I've spent a fair amount of time changing many components that were out of spec. V7, 30FL1 has also been changed as has V10, PCL82 as they had very little emission.

Unfortunately the test card is now a funny shape. The height control is at minimum and I can't find a width control. I'm not sure how I deal with the egg shape (if there's a technical name please tell me). On the plus side it looks like the contrast control is now doing something.

The Grid volts (pin 2) is now nearly spot on at 110V (should be 112V).

Cathode (pin 11) measures 150V (should be 153V) with no signal or 80V with one (I'm not sure under what condition I'm supposed to measure it?).

A1 voltage (pin 12) is still the same at 250V (should be 342V) but I notice my chassis has an 2.2M resistor, in addition to C74 680K, which isn't shown on the circuit diagram. If I measure before this 2.2M I get 304V.

Thanks
David
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Old 19th Oct 2019, 5:10 pm   #26
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Default Re: Pageant P50

Hi Dave, frame timebase linearity controls, or leaky caps/ high value resistors gone higher, or frame TB valves low emission.

Your are nearly there, these were common faults 60 years ago

Ed
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Old 19th Oct 2019, 6:03 pm   #27
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Default Re: Pageant P50

Looks like you have an incorrect value capacitor in the frame linearity feedback. The shape was good before you changed capacitors. Worth a double check. J.
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Old 24th Oct 2019, 5:29 pm   #28
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Default Re: Pageant P50

It looks like I haven't got a Pageant P50 after all! My telly has HOME, THIRD and LIGHT radio stations and a PCL82 output valve instead of a 30PL1. Although I can't identify the exact model a better circuit diagram is for a Defiant 7109FM and 7609 FM, page 310 year 1959-60 R&TVS books.

C40, 2uf electrolytic, is original but fitted in the opposite direction to what is shown on the circuit diagram. I'm not sure what direction it should be?

Thanks
David
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Old 24th Oct 2019, 5:57 pm   #29
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Default Re: Pageant P50

"C40, 2uf electrolytic, is original but fitted in the opposite direction to what is shown on the circuit diagram. I'm not sure what direction it should be?"

Hi David,
I'm sure not if the circuit diagram is correct or not or that the capacitor in your set has been fitted wrongly fitted during assembly. C40 is in the FM ratio detector so nothing will go bang even it is connected the wrong way round. I'll check the circuits in other Plessey chassis TVs with FM and report back later.
The 7109FM was fitted with a 90 degree CRT, either CRM173 or CME1702. Your set has a 70* CRT type CRM172, is that right?
However, the FM radio circuits will be much the same in your set. For some reason certain sets were supplied with two PY82 HT rectifier valves instead of the PY32. Certainly it was like that in 21" models which all used a 90* CRT.

DFWB.
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Old 24th Oct 2019, 6:12 pm   #30
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Default Re: Pageant P50

Follow up to my last post. Checked out the circuit of the Regentone T21FM and the 2uF capacitor in the FM detector is connected with the positive tag to chassis.
So C40 in your set is correctly wired.
Information for the Regentone T21FM is in the 1958/59 R & T servicing book.

DFWB.
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Old 25th Oct 2019, 12:45 am   #31
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Default Re: Pageant P50

Hi David, thanks for your help. I'll leave it with the positive connected to the chassis.

All these Plessey chassis circuits seem more or less the same so it isn't causing me too much trouble at the moment. Just in case anybody can identify my telly it's a Pageant with a CRM172 tube and a 2 x 6D2, 2 x 30F5, EF85, 30L1, 30C1, 30F5, 30PL1, 30FL1, PCL82, 30P4, U191, U25 & PY32 valve line up. One of the capacitors is dated October 1957.

To update progress I'm still carefully checking over the whole circuit to make sure nothing's out of place, or the wrong value. I've found that at best the wipers on the potentiometers are intermittent and at worst making no contact at all! Where a carbon contact sits in brass carrier there's corrosion. Hopefully once I've disassembled and cleaned them all I'll have a better test card to show!

Regards
David
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Old 11th Nov 2019, 11:24 am   #32
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Default Re: Pageant P50

I was making progress until I rotated the tuner from a TV station to a radio one. As soon as I did there was lots of loud, white, sparks from the EHT area of the chassis. I turned off quickly and removed the EHT transformer. I was expecting to see evidence of burn marks and tracking but I couldn't see anything! I put it back, set the tuner back to BBC but as soon as the EHT rose there was the same sparking again and nothing on the screen.

Considering switching to a radio station should have turned off the EHT what on earth could have happened? For reference I'm now using the Defiant 7109FM and 7609 FM circuit on page 310 year 1959-60 R&TVS book.

Regards
David
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Old 11th Nov 2019, 11:37 am   #33
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Default Re: Pageant P50

Changing from radio to television will not burn out the line output transformer. At a calculated guess I am going to suggest that the radio/tv change over switch has broken down. It is probably of Paxolin construction and breaks down between the HT switching sections, very common with the Ekco series. Check it visually very carefully and if a section had broken down, wire it permanently for 'TV'. Just a guess. John.
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Old 18th Nov 2019, 2:35 pm   #34
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Default Re: Pageant P50

Oh dear I'm not sure if I'm fixing faults or just finding new ones! The diode connected between the AGC to the chassis was a Brimar M1 selenium diode and as discussed earlier it was open circuit, so I replaced it with a 1N4148.

I've now found out that it's gone short circuit and I'm hoping it's the reason for the TV/FM changeover switches arching (or is it the arching switches destroying the diode?).

I know it sounds simple and I should just swap it out but I've checked photos I took of the chassis and the Brimar M1 was connected to the chassis with the red end (described as +ve in the data) to the chassis but the circuit shows the -ve (cathode) connected! The diode I connected was as shown on the circuit diagram with the cathode to chassis but was this right?

Regards
David
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Old 18th Nov 2019, 3:59 pm   #35
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Default Re: Pageant P50

Be very careful using the terms "positive terminal" and "negative terminal" when talking about diodes! The cathode of a diode can be thought of either as the positive terminal (because current flows out of it) if you are thinking in terms of series connections, or the negative terminal (because it is at a lower potential) if you are thinking in terms of parallel connections.

All Selenium rectifiers I have ever seen with + and - markings had the cathode marked as + (which is quite reasonable, since the output of a bridge rectifier also has the positive terminal labelled +), and the convention if only one pin of a diode is marked is always for that to be the cathode.

1N4148s, marked with the yellow-brown-yellow-grey bands, I test every time because I can never remember which way they are ordered .....

When I was in the industry, we never referred to the terminals of a diode as anything other than "the business end" and "the blunt end" !
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Old 18th Nov 2019, 4:22 pm   #36
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Default Re: Pageant P50

So far as I remember from my TV days with those selenium diodes:

-ve (metal case) = Anode

+ve (red disc) = Cathode.

Lawrence.
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Old 18th Nov 2019, 4:32 pm   #37
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Agree! Can be mind blowing.. Reversing the diode is not going to damage it as the AGC potential is very high impedance and of low voltage. It is more likely that a flash over had occurred around the FM/TV switch especially as I think you said there was some smoke and a pop after you switched it to FM.
Look for brown burn marks on the switch first then plug it in again whilst observing the general area. You may be able to see some tracking taking place. J.
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Old 18th Nov 2019, 5:18 pm   #38
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Default Re: Pageant P50

Thanks for all the replies. I don't think I'm ever going to be a television repair man but I am learning a few things along the way.

Regards
David
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Old 19th Nov 2019, 12:06 am   #39
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Default Re: Pageant P50

One thing you should be aware of with selenium diodes (and I'm not referring to the vile stench they make when they fail....at least the big ones anyway). They have a high forward resistance and can't be checked properly on a normal ohm meter....a multimeter just can't put enough voltage across it to forward bias it. I got caught out by this back in my early learning days when building a mains radio. I used a specified contact cooled rectifier and measured its forward and reverse resistance....and it showed O/C both ways. I ordered another and it measured the same.....I was advised by the supplier to try it anyway....'You might have a surprise' he said but gave no further advice. I decided to take his advice and to my surprise, the rectifier was perfect and gave normal HT....but it still measured O/C both ways...at least on my modest multimeter which I think was 10,000 ohms per volt.

Basically you need to test the rectifier at somewhere near its rated voltage so with a mains selenium you should check its voltage output when connected to the mains. With smaller diodes like your AGC diode you would need to find its voltage rating and feed it from a similar source.

Mind you with the reputation that seleniums have I'd stick with the 1N4148!
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Old 23rd Nov 2019, 2:52 pm   #40
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Default Re: Pageant P50

As shown in the picture below it's obvious where the switch was flashing over and blowing the diode on the AGC line. Even though I'm fairly confident I can remove the switches and hard wire it to TV use only I'm really struggling to find the motivation to do it.

Prior to the switch and diode problem I was failing to find the reason for virtually no contrast control and and then a cramped testcard arrived. Will I still have to resolve these problems or could they be related to the failing switch insulation?

Regards
David
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