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Philips G17T320

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6.3volts
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I originally bought this set for its looks and recently have been working on it having left it in store for several years.

It came with a fault. It didn't work and smoke was coming from a small component next to a replacement capacitor.

Having sorted the basic power supply section I moved on to the smoker which was a high voltage diode producing boosted ht(tp20) from a winding on the LOPT. The cap had presumably failed and taken the diode with it. Having replaced the diode (2469) I was rewarded with a picture with reduced width. I checked the boost voltage to find it was 1050volts on a 1kv cap (2468) and the voltage on the focus anode was very high. (no wonder the original cap failed). I had already replaced the tuning cap across the line o/p transistor,(2461) as the original had lost most of its capacity. Now I assumed this would have caused the over-voltage in the set's previous life but it still had the same problem. I've checked all components in this area including the drive from the line oscillator i/c (point 30) and can find nothing out of spec. The line signal @point 30 is 9.5 volts and is correct. The signal @ point 31 should be 180 volts but is way over 200. I cannot fault any components and the DC conditions are right. I assume this is why the boost voltage is way too high. The line drive transistor (2404, BF337) checks out but is showing a gain of 80 when all the listings I can find are talking about a minimum of 20 with no upper limit listed. In the meantime I have added 500pF across the tuning cap to bring the boost ht down to a safer level and have increased the value of R2414 to 2.2k which has lowered the ht even more.

Can anyone advise me about TWO things.

Is this high ht a symptom of too much gain in the BF337 line drive transistor and given this work so far there has been absolutly no change in the width problem. I have ring-tested the LOPT and I believe it to be fine. The LOP transistor (4460 BU105) checks out with two diode drops and a gain of 4. The only clue might be that the raster is very cramped on the left edge (possibly with a fold)

IMG 1121 (Large)
IMG 1119 (Large)
IMG 1120 (Large)

with little or no actual linearity problems over the rest of the scan. Nothing seems to affect this so far. I'm hoping this problem is recognised and I'm hoping for a bit of help as I've run out of ideas atm.

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Topic starter Posted : 05/12/2017 4:53 pm
crustytv
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Hi Jonathan,

Lovely sets these, I've often been tempted to get one, they look especially nice on their chrome pedestal stand.

Have a look in the data library, you find an excellent article by LLJ covering this chassis. Its also recommended you change the BU105 for a BU205.

Anyway have a look in the data library under "Service Dept"| " Service Data Library", then.

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Posted : 05/12/2017 5:26 pm
sideband
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Check to see if any work has been carried out around the line driver chip (I think it's a TBA720 A or AQ). It's years since I saw one of these and when I was at Philips I know some changes were made in this area. From memory (which is not what it was) the chip was changed from a TBA720A to an AQ (possibly BQ) type. They are not directly interchangeable and some changes were made to accommodate the new chip. The data library may cover this with the article mentioned above. I mention this because if the mods weren't done, there may well be a drive problem. I can't remember now what happened if the chip was changed without the mods being done.

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Posted : 05/12/2017 6:36 pm
Nuvistor
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With the HT being high does that point to a fault in the PSU, or is the HT tied in with the line stage in some way?

I don’t have a circuit at the moment, I will try and look at the articles posted by Chris later.

Frank

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Posted : 05/12/2017 6:39 pm
PYE625
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I can remember seeing one or two of these set's whilst at the co-op in the late 80's. They were normally a nicotine yellow ! This one is nice and white and looks a corker. Very stylish 🙂

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Posted : 05/12/2017 8:29 pm
crustytv
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Brochure page

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Posted : 05/12/2017 8:31 pm
Nuvistor
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The LLJ article does document the TBA720 IC, worth a read, the conduction of the driver transistor is quite critical and is adjusted by “select on test” of R2409 with one of the versions of the IC.

Frank

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Posted : 05/12/2017 10:52 pm
Till Eulenspiegel
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There's upstairs above the shop.  Given time to recover and then I'll have  go at it.

The wood cabinet models 322 and 324 must be quite rare.   Didn't have many out on rental, customers liked the super slim teak cabinet.  But by 1973 demand for black and  white TVs was in decline.

Till Eulenspiegel.

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Posted : 05/12/2017 10:59 pm
Nuvistor
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Isn’t it past your bed time in the ward, be getting to trouble with the nurses. 🙂

Frank

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Posted : 05/12/2017 11:02 pm
Marc
 Marc
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Posted by: Nuvistor

Isn’t it past your bed time in the ward, be getting to trouble with the nurses. 🙂

Or is that the plan David 😉

Marc
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Posted : 05/12/2017 11:22 pm
PYE625
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Let's hope it's not the other way around ....... erm, ahem.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Posted : 05/12/2017 11:22 pm
Marc
 Marc
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Hi Jonathan,

I'm stunned just how 'white' the cabinet appears to be, all the ones I've seen have all gone cream. Nice set.

Marc
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RSGB call sign 2E0VTN

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Posted : 05/12/2017 11:25 pm
ntscuser
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Posted by: Marc

Hi Jonathan,

I'm stunned just how 'white' the cabinet appears to be, all the ones I've seen have all gone cream. Nice set.

Perhaps it was kept out of direct sunlight, or has had the peroxide treatment?

Then again some plastics were more resistant to fading than other. I own a 1983 Teleton which is still pristine white and also a Braun hairdryer where parts of the case have yellowed whereas other parts have remained white.

Classic TV Theme Tunes

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Posted : 06/12/2017 6:27 am
6.3volts
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Thank you all for your replies. The cabinet has been 't-cut' and looks well if still a little yellow. If or when I have it working properly I'll strip and spray the pedestal which has oxide breaking through the paint. I wonder if anyone has advice on the scan problem. I think I have forgotten what causes left cramping and folding. Can anyone remind me please.

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Topic starter Posted : 06/12/2017 7:00 am
6.3volts
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Posted by: Chris

Hi Jonathan,

Lovely sets these, I've often been tempted to get one, they look especially nice on their chrome pedestal stand.

Have a look in the data library, you find an excellent article by LLJ covering this chassis. Its also recommended you change the BU105 for a BU205.

Anyway have a look in the data library under "Service Dept"| " Service Data Library", then.

Thank you Chris. I believe I have not yet qualified for access to the libary.

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Topic starter Posted : 06/12/2017 7:04 am
crustytv
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Hi Jonathan,

if you had tried you would have found you had an early Christmas prezzy and do have access. 🙂

If did try but found you were blocked, try logging in and out and if that still fails clear cache and cookies

Chris

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Posted : 06/12/2017 7:53 am
Nuvistor
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Have a look at the on time of the driver transistor, as per the LLJ article. I am not sure from your first post if it is HT that is high or just the Boost volts.

I have not worked on these sets, so advice from me is going to be sparse.

Frank

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Posted : 06/12/2017 9:15 am
sideband
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I think the main HT on these is 160V, the boost I can't remember but probably around 600-700V

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Posted : 06/12/2017 10:20 am
6.3volts
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Posted by: Chris

Hi Jonathan,

if you had tried you would have found you had an early Christmas prezzy and do have access. 🙂

If did try but found you were blocked, try logging in and out and if that still fails clear cache and cookies

Chris

Wow Chris thank you very much.

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Topic starter Posted : 06/12/2017 10:58 am
6.3volts
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Posted by: sideband

Check to see if any work has been carried out around the line driver chip (I think it's a TBA720 A or AQ). It's years since I saw one of these and when I was at Philips I know some changes were made in this area. From memory (which is not what it was) the chip was changed from a TBA720A to an AQ (possibly BQ) type. They are not directly interchangeable and some changes were made to accommodate the new chip. The data library may cover this with the article mentioned above. I mention this because if the mods weren't done, there may well be a drive problem. I can't remember now what happened if the chip was changed without the mods being done.

Thanks for the suggestion but it's the original 720 Not the 720AQ.

I've done some work to correct the dc conditions but this had no effect on my two problems and the signal voltage and duty cycle are correct at the output.

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Topic starter Posted : 06/12/2017 3:53 pm
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