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Old 13th Jan 2018, 7:55 pm   #1
Tazman1966
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Default Philips 570, a cheapo Pye in disguise!

Good afternoon and Happy New Year!

It's been ages since I posted on here and it nearly was going to be again as this is the second time of writing this lengthy post I had finished writing it and uploaded the attachments and was checking that the circuit diagram was readable and instead of opening the attachment on a new window, it opened it in the existing one and when I went back in my browser, all the test had disappeared Anyway, I'll try to remember what I said.

My sister picked the set up for me from Newport (not too far from her house) and delivered it to me on my birthday It had certainly been bashed around a bit but was complete!

It had its first look at up at Mike Bennett's house when a couple of us visited for logistical reasons, in other words to exchange junk!

To cut a long story short an open circuit surge limiter and a blown HT fuse were eventually traced to being nothing more sinister than the HT being on the high side and triggering the high tech glow switch which places a short circuit across the HT line in the even of an over volts fault. A twiddle with some of the controls produced a half decent result but time beat us again - time always seems to gallop at Mike's house - so on with the back cover and into the car with it.

Fast forward to today. After lacerating my fingertips repairing my mate's car key fob connections, this set was staring at me begging attention!

There was one niggling fault and that was that there was a fault with the line phase. The picture was shifted by a large amount to the right. It was easy to see with the HT reduced such that the edges of the raster were visible. The Line Shift was fine as the raster was absolutely central.

I changed some suspect electrolytics around the TBA920 line oscillator chip[ and a couple of them had completely dried out. The only improvement was that the verticals were not wrinkled anymore. Adjustment of the Line Phase pot only made the fault worse. I checked the resistors around the chip but all were within spec.

My question is, is it likely to be a faulty TBA920?

Here are the pictures.
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Old 13th Jan 2018, 8:09 pm   #2
neil29
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Default Re: Philips 570, a cheapo Pye in disguise!

Hi Tas, Despite the shifting of the picture it looks really good from here on my recently fixed laptop which still doesn't work properly... and the set certainly had been in the wars where it had been sat in the pub with the muddy sewage water running around it.
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Old 13th Jan 2018, 8:17 pm   #3
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Default Re: Philips 570, a cheapo Pye in disguise!

Are the voltages correct, if they are very often the ic will be ok, I seem to remember that there were a couple of different versions of that IC, just something to be aware of.

We ordered a dozen of these sets when new, sent them all back as not good enough. Did not try to sell them, they were Pye not Philips, don’t think the rep was very happy.
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Old 13th Jan 2018, 8:37 pm   #4
flyingtech55
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Default Re: Philips 570, a cheapo Pye in disguise!

Is that not a CT200? ISTR that fault was caused by a resistor going high...I just can't remember which one.

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Old 13th Jan 2018, 9:54 pm   #5
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Default Re: Philips 570, a cheapo Pye in disguise!

Check R512 (100K) which supplies the line flyback pulse to pin 5 of the TDA920. Also the phasing pot R513. Adjusts the mark-space ratio of the line drive waveform.

DFWB.

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Old 13th Jan 2018, 10:47 pm   #6
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Default Re: Philips 570, a cheapo Pye in disguise!

Hi

That's quite a decent picture displayed on that set.

I think it was only the Pye CT200 (713 Chassis) that had the horrible low focus CRT. The later 715, 717 and Philips 570 had the normal high voltage focus CRTs so weren't as bad sets as the CT200.

Reading through Mike Phelan's servicing articles in Television Sep to Nov 1979, the timing capacitors around the oscillator section of the TBA920 are known to cause problems. Might be worth referring to the servicing article which includes the circuit diagrams.

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Old 14th Jan 2018, 1:01 pm   #7
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Default Re: Philips 570, a cheapo Pye in disguise!

I'd have to agree that this chassis was not one of Pye/Philips' finest. However, given that it was designed down to a low selling price, its shortcomings are understandable. I think that, given the choice, I'd prefer this to Thorn's 8000 chassis! The sets with the high voltage focus CRTs gave a better picture, but those Japanese made 18" tubes were not long lived in service.

The chassis is in fact a joint effort between Pye at Lowestoft and Philips in Croydon, as the various panels are clearly made in different factories (as are the complete sets). The Pye made boards being the tuner/IF and decoder; all the others are Philips made. Look at the silk screen printing and compare this to the Pye 697 and Philips G8 PCBs. The cabinet backs and associated type number labels are also different.

Pye Lowestoft did produce an export version, with UHF and VHF tuners and proper pincushion distortion correction.

The Pye panels suffered from the dry joints on the small ceramic capacitors in the IF module and the unreliable thick film RGB unit.


If you haven't already checked, I'd replace on sight the flyback tuning capacitor (which if original, will be a darker green cylindrical axial type of Philips manufacture). These go leaky and slowly "cook" internally and will cause the EHT to rise, blowing the LOP transistor and sometimes the LOP transformer/EHT multiplier.
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Old 14th Jan 2018, 3:52 pm   #8
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Default Re: Philips 570, a cheapo Pye in disguise!

Hello there!

Thanks for the replies and interest in this old bit of tat!

The flyback tuning capacitor is still the original and will be replaced as will the mains filter capacitor which is the same type

I have had the opportunity to spend some more time on it today and have checked out the suggestions. R612 at 100k was almost spot on but I replaced it anyway just in case it was going high under load. No change.

Time to do some voltage checks. In spite of the 155V HT line being spot on from where the supplies to this section are obtained, some of the voltages were a little high including the 11V input which was sitting at 12.5V. I checked out R617 which was spot on. I also checked R614 which was also okay. Just as an experiment, I altered the value of R614 from 3.3k to 3.9k and this brought the phase adjustment well within the range of the control R613. Now will my conscience allow this minor bodge or should I investigate further? Be blunt friends!

Here's the little Philips as it stands so far. The CRT is warming up very nicely thank you! Incidentally, there was another fault in that the colour faded out after about 20 minutes or so. I went through the "Callins" electrolytics on the decoder panel and every one was dried up. The colour is now stable and very pleasant indeed.
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Old 14th Jan 2018, 4:09 pm   #9
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Default Re: Philips 570, a cheapo Pye in disguise!

Only ever saw the CT200, didn’t look at the later versions. That set is coming along fine, what is it 45 years old or thereabouts?
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Old 14th Jan 2018, 4:16 pm   #10
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Default Re: Philips 570, a cheapo Pye in disguise!

What's the zener voltage?

Lawrence.
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Old 16th Jan 2018, 3:03 pm   #11
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Default Re: Philips 570, a cheapo Pye in disguise!

Look at that picture. Now come on - that can't possibly be a 570!
Either you've got the one good one they made or else you've been at the Photoshop!
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Old 16th Jan 2018, 9:11 pm   #12
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Default Re: Philips 570, a cheapo Pye in disguise!

Hi Lawrence.

The zener voltage is 12V - possibly the zener isn't zenering!

Glyn! Wash your mouth out! It is as it is! The damaged cabinet makes up for the nice picture!

I think it's getting on for 45 years old or so Frank. I also have the Pye version although that disgraced itself just before Christmas by going pop and is not dead - at the moment.
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Old 15th Aug 2019, 7:29 pm   #13
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Default Re: Philips 570, a cheapo Pye in disguise!

Thread reopened at OP's request.
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Old 16th Aug 2019, 12:10 am   #14
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Default Re: Philips 570, a cheapo Pye in disguise!

The picture on yours certainly looks great, but they all seemed to suffer from an unstable ballooning picture when the brightness and contrast were advanced.

Are there any modifications for this symptom?

Thanks, Mark.
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Old 16th Aug 2019, 9:02 am   #15
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Default Re: Philips 570, a cheapo Pye in disguise!

Picture blooming, crowbar firing, dry joints in the IF. S\C bridges. Numerous faults. We used to cringe when one of these came in. We binned them even when they were working. The low focus version was terrible, I prefered g6's. People were scared of these but I liked them. Even some of the rare continental sets (Autovox, Emo and Finlux Peacocks) were more welcome in the workshop. Re the blooming I seem to remember the HT would go up and down in sympathy, there may have been a mod, these were so bad even scene changes would send the picture wild. Just reduce the brightness and contrast. Things are no better today. Lower your backlights or kill the screen. Leds ( we were told last a long time) WRONG!!!
Not when used as backlights.
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Old 16th Aug 2019, 11:47 am   #16
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Default Re: Philips 570, a cheapo Pye in disguise!

Taken from Len Briggs' know how No 8 Nov 1972 (Pye inhouse CT200 guide to diagnosing
faults))

"If diode 618 (OA47) becomes o/c it has no effect on line speed,only line phasing is affected. The values of condenser 628 and resistor 629 have the most effect on line speed
and only close tolerance components should be used"
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Old 16th Aug 2019, 8:01 pm   #17
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Default Re: Philips 570, a cheapo Pye in disguise!

Quote:
Originally Posted by gec2110 View Post
...they all seemed to suffer from an unstable ballooning picture when the brightness and contrast were advanced.

Are there any modifications for this symptom?...
Thanks Mark. The picture is, in fact very pleasant indeed but yes does suffer from ballooning on contrasty scene changes somewhat akin to the corners of the raster being suspended by elastic band! No modifications that I have ever read about!

Quote:
Originally Posted by toshiba tony View Post
...Picture blooming, crowbar firing, dry joints in the IF. S\C bridges. Numerous faults. We used to cringe when one of these came in...The low focus version was terrible...
This is one of the later ones - Philips designated it the A4 chassis which was, of course a Pye 715 which used the standard "high" focus voltage derived from the EHT doubler.

Quote:
Originally Posted by Restoration73 View Post
...If diode 618 (OA47) becomes o/c it has no effect on line speed,only line phasing is affected. The values of condenser 628 and resistor 629 have the most effect on line speed
and only close tolerance components should be used...
I'll dive into the set again in the next few days and check it out although I did effect a "fix" with a slight bodge by changing the value of R614 from 3.3k to 3.9k as noted above which brought the line phase to the middle of the line phase control.
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Old 16th Aug 2019, 8:32 pm   #18
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Default Re: Philips 570, a cheapo Pye in disguise!

Unfortunately the set had been languishing in the workshop for months and months now waiting for me to get cracking with the cabinet too but I did power it up from time to time.

Each time though, I did notice that the picture was bigger than the last switch on. I checked the HT and it had risen to 162V. I backed off the control to minimum and got it back to the correct 155V but only just. Clearly something was amiss. That was as far as I had got for another extended period! I'm so slow these days

Bringing things bang (bad choice of words!) up to date and Whilst mucking about with a Bluetooth module (not in this thread ) I powered the Philips up again to have some test card and music playing in the background. Once again the picture was much bigger and a quick check on the HT indicated 163V. Much too high and with the Set HT control on minimum.

I suspected the thyristor of being leaky as they used to from time to time so with a quiet confidence, I replaced it with a new one. On switching on, I now had 165V getting close to the crowbar trip (glow switch) firing point. So it wasn't the thyristor. Looking into the control circuitry and measuring the voltages on VT516, a BC147 showed incorrect voltages there - not that it was easy to measure with the set on its side, main chassis board hanging precariously, and me needing a new prescription of reading glasses!

A cold check on the high value resistors in the base of the transistor showed that R531 had risen to almost 800k instead of 470k! With this changed, the HT was back to normal with the Set HT pot in the middle. In fact, I set it to 150V instead of 155V and the picture was still big enough.

Here's some pics and an extract of the circuit.
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Old 18th Aug 2019, 1:05 pm   #19
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Default Re: Philips 570, a cheapo Pye in disguise!

I only ever sold one Philips 570 and frankly, it was an embarassment. Within a month of selling it to the customer in 1976, the tube developed a fault and had to be replaced. It presented numerous other faults within the warranty period.

The only thing that can be said in favour of the Philips 570 is that the cabinet and channel selector were of superior quality to the Pye CT218 equivalent.
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Old 18th Aug 2019, 5:53 pm   #20
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Default Re: Philips 570, a cheapo Pye in disguise!

That picture looks a belter, in focus, bloom free, linear, up on IF gain, converged. Not the CT200's I remember.
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