Philips G17T320-02 B&W TV schematic/help please.

[zens.tv]

Hi all.

iI have just joined the forum. Have been in the electronics repair trade since iI left school (about 25 years) mostly I repair modern flat screen TV's, but recently I have been asked to repair some vintage equipment, hence why iI joined the forum.

This set came in with 2 issues:-

Firstly, power up was intermittent.

Secondly the picture was very dark.

Discovered the voltage on the large smoothing capacitor strapped to the chassis (2 X 400uF) was way too high at both of its positive terminals. Roughly 280V. It had been obviously overheating and became damaged due to the excess voltage.

On the upright PSU module iI discovered the following:-

R633 (220k) measured high at 611k.

R632 (56k) measured high at 66k.

R640 (180k) measured high at 685k.

Voltage on cap now down to 178V.

I also replaced the cap. Now set powers on every time, but due to the previous excess voltages have other issues.

Set then had frame collapse. Discovered R561 was o/c. Suspecting it's a low value, tried a few in there but no go. Just get a blank partially illuminated display.

The BD type frame o/p devices measure OK.

Also replaced the line tuning cap C461 (2n2,1500V), as it had a small bulge.

Now iI'm stuck

[chompy1]

Hi,
welcome to the forums! I think this set was manufactured in the early 1970's, but unfortunately I am not familiar with this chassis as I have never worked on any of the models that employ this chassis.

I'm sure the guys who are familiar with this chassis will be happy to help.

Is this set a hybrid? (a mixture of transistors and valves?)

Paul

[Mike Fulton]

Hi!
I have a circuit for this model. I'll also have most, if not all, of the semiconductors used.
The resistor R561 is 15 ohms and it feeds the frame output stage, obviously you've sussed that. HT on the 400Mfd should be 163v so 178v with no picture sounds good to me.
I really think you need to peruse the Cct and set to with a scope to find what's where pulse wise, and what's happened to your drive to the tube. If you're working on flat screen TV I'm sure your 250Mhz scope will be able to handle the mind boggling standards employed on this chassis
It may be that the CRT is so flat that it's incapable of a display - they were absolutely terrible in these sets.
PM me with your address and I'll post a photocopy of the circuit to you - unfortunately I don't have a scanner although I can photograph it and try to PDF it if you send you email address,
Kind regards,
Mike

[Restoration73]

You may be familiar with the annual "Radio & TV Servicing" series of books
The circuit and other info appears in the 1973-74 Volume page 457

[Heatercathodeshort]

The Philips 320 series was their first large screen all transistor monochrome chassis. It was very reliable other than the power supply mainly suffering from short circuit bridge rectifier diodes or in the early production models the BY164 bridge pack.
The high value resistors you have replaced in the power supply were a common fault giving no/slow start up and excessive H.T.
The 17" tube employed in your model is very reliable giving brillaint pictures as can be seen by the picture. The UK produced 20" & 24" tubes were as Mike has suggested, rather short lived giving poor focus due to impaired vacuum. The 17" tube was sourced from abroad and like the much earlier AW43-88, never fails.
You may discover that the increase in EHT under the fault condition has caused flash over damaging some silicon in the signal stages. Another cause of violent flash over is the third harmonic line output tuning capacitor, usually green in colour from the collector of the BU105 to chassis. Failure here will increase the EHT to around 75kv for a fraction of a second usually damaging the BU105 and the line oscillator section of the TBA720Q chip. If this capacitor is green in colour it MUST be replaced as failure will write the receiver off! I think it has a value of around .002uf at 2kv, only a guess as the Philips service manuals are stored in a file cabinet that is out of reach at this present moment!
As suggested you will require a scope check around the signal stages to locate where the fault lies.
I sold many of these receivers and generally got on with them very well.
The picture is outstanding! Just a thought. The power supply will run under fault conditions at around 90V shutting down the line oscillator. It can be confusing if you don't know what is happening.Regards, John.
PS I have added a picture of the offending green capacitors often found in third harmonic tuning circuits such as the G8 G320 and other makes such as the GEC and Thorn. Replace on sight.

[Sideband]

Originally Posted by Heatercathodeshort

The picture is outstanding!

agreed...due in part to the fact that it has basically a G8 colour TV front-end using exactly the same modules if memory serves.....

[Heatercathodeshort]

It was easier than I thought! Hope you can read this. The nasty cap is 2461 a .0022uf special quality 16kc/s at 2kv. happy days! J.

[Nicklyons2]

Just to 'third' the remarks of above re the picture quality of these sets. The early ones seemed to suffer from PSU main thyristor problems. (The Thyristor) Sometimes occasionally breaking down and intermittently pulsing the HT rail. If the pulses were short and infrequent the neon glowswitch crowbar would 'miss' them and eventually the set would suffer damage from this intermittent high HT.

Also. to those not familiar with this set - the mains input is via a bridge rectifier and therefore the chassis is 'half live' regardless of the mains wiring. - just a cautionary note.

[zens.tv]

Thanks very much guys

Thanks for the offer of schematic Mike. I have sent you a pm

Thanks also for the info John. I have already replaced the line tuning cap ( 2n2,1500v ), as it had a small bump and yes it was the dark green type.

Cannot make out the schematic though John, will try to save and expand it.

This set is giving more hassle that the flat sets I'm used to working on

Wasn't far off with the value of the frame supply/safety resistor. I used a 10R, not bad for a guess.

[AC/HL]

Originally Posted by xenis stylianou

This set is giving more hassle that the flat sets I'm used to working on

That's familiarity, it's the opposite for many of us!

[zens.tv]

Hi Bill.

Yes, it all comes down to experience no matter how good,or bad in my case, the electronics theory is

[zens.tv]

Hi all, hope you don't mind but iI have posted a YouTube link updating the issue on the set. iI find it much easier, have been using this method for some time now on the other forums iI belong to and it seems to work OK.

Video clip is locked out from the public domain and only viewable where iI a post link, eg here.

Here's the link:-

https://www.youtube.com/watch?v=YnpX...ature=youtu.be

[Nuvistor]

Did you check the video drive levels with the scope and the voltages on the tube?

[zens.tv]

Not yet, but will do. Cheers

Did discover the following:-
https://www.youtube.com/watch?v=1BG0...ut2lTQlvnMHCfg

Also found a BF196 in the other can reading one way, collector/emitter junction.

[Tazman1966]

Hi Zen!

Depending on how well or not the set has been stored, these "Lokfit" style of transistors don't seem to be holding up too well these days. The encapsulation seems to have a problem with moisture ingress causing all sorts of problems from gain issues to open circuit junctions.

Good luck and welcome to the forum by the way

[toshiba tony]

It's OK Zen, I'm not stalking you, its PCL82 here, (tony) from the other forum, good luck with it.

[zens.tv]

thanks Tas,i'm going to need all the luck i can get with this one

hey Tony,stalking again i see

[zens.tv]

anyone know of equivalents i can use for BF196 & BF197

ones i received from a colleague also reading one way collector emitter junction.

as Tas mentioned,storage issues poss

[KeithsTV]

These transistors do not have the normal E B C pin out where the Base is the centre pin. The pin out on these and similar RF types is B E C where the centre pin is the Emitter.

If they are faulty the BF496 and BF497 are exact equivalents but in a TO92 package.

Keith

[jay_oldstuff]

From a quick search on the web try NTE107 as a sub for both. i have a vast quantity of 1970's semiconductors when next at the stores ill see if i have any BF196/197's would be interesting if i do to see if they are suffering the same symptoms.

Jay