Thursday, 29 March 2012

Philips 23TZ323A 23" TV

This Philips S8 is another recent addition to the collection and since I already have three of these I decided to get this going to use in the workshop.
I found some interesting stuff on how the S8 was created, it was copied from a European design and here are a couple links to a website which shows the direct derivatives that the NZ version was based on. It seems to be a mix of two sets shown in Link 1 & 2.
Thanks to Marcels TV Museum for such a great website covering vintage Philips TV's and more.

Marcels TV Museum

Link 1

Link 2

Unlike all the other S8's I've seen or worked on this one still has its original line output transformer and virtually no dry joints on any of the valve sockets and hardly any damaged or lifted print on the boards which leads me to think this hasn't not had much use but it did take some work to get it working properly.

After replacing a busted EF183 and boost cap that had split open I applied power via the variac and raised it to 200 volts and waited....nothing much was happening so increased the mains some more...got humming from the speaker and that was it, did a quick measure of the B+ rails, which were all present but it no other real signs of life...hmm a bit odd as these usually were a bit more lively than this!

Started with the horizontal drive and found not much happening there so replaced the PCF80 and things started happening we now had EHT and a line across the screen! Done some more poking only find the vertical oscillator wasn't working either, another PCF80 later and now had a full raster.

But it was rather dead in the tuner/if stages with a signal fed in just a blank raster...Found the 2nd IF EF184 had no emission and a short, so replaced it, still nothing....I then checked the PCF86 mixer and PCC198 RF amp in the tuner and found the PCF86 to be gassy, it lit up pretty colours on the the AVO and got pulled out pretty quick.

So in went another PCF86, now we had something but still no picture just flashes of snow/lines and I just happened to knock the board around the 1st IF valve and that made the picture go nuts, so some prodding indicated something was loose here. A look at the board revealed broken tracks around the IF can and a shoddy past repair to the print.

I fixed all that up and tried again, there now was steady snow, so I rotated the tuner to the desired channel for the RF modulator output...still nothing... then the picture started flashing/pulsating every few seconds...What the hell was going on! I could now smell something getting hot and happened to glance down to tag strip on the tuner where the B+ supply resistors are and saw one of them glowing red so lunged at the kill switch on the variac!

Ok so buy this time I was starting to think nasty thoughts about this set (Mental images of pulling it off the bench by the power cord and laughing madly as it hit the floor!)... This was mean't to be a quick fix and now turning into a rather drawn out affair.

I checked for shorts to that stressed 560 ohm resistor to ground and found nothing so removed the tuner and pulled the covers off to investigate inside and a rather burn't looking resistor to one of the valve pins was staring me right in the face, ah-ha! The circuit called for 3.3k and this little charcoaled delight was reading 220 ohms. I wasted no time in replacing it, reconnected everything and applied mains while monitoring that supply resistor and to my disgust the 3.3k started belching smoke and the poor 560 ohm lighting up again like a tiny bar heater.
This thing was really starting to test my patience so I walked away and left the thing alone and just as well as that evening my wife went in labour with our second child so that put a stop to TV tinkering for the time being.

Once back on the job I went over my work done on the tuner and could not see or find any shorts within the tuner. I did have some spare tuners but my gut told me not to replacing the tuner only as a last resort. Then I had a thought about the tuner valves again wondering if the replaced PCF86 or the original PCC189 was faulty? So for a laugh I put in another PCC189 and tried it to no avail so I put in another PCF86 and tried it again...This time the voltage wasn't dropping and it was stable...so I waited expecting smoke, then sound burst forth from the speaker and then my test pattern DVD appeared on the screen! HORRAY!

So what the hell was up with that so called 'good' PCF86? A quick test of it again revealed several shorts, so why did it decide to die? Probably to irritate me which it did but then maybe that 3.3K resistor was already faulty and maybe have damaged the valve? Who knows? Talk about a double edged sword with the tuner fault!

The set was now giving a pretty good picture apart from flashing white lines intermittently and varying brightness accompanied with a slight hum bar going through the picture. A check of the filter capacitors indicated they were all low so I replaced them along with some other electros around the vertical and audio output stage. With all that done, the hum bar was gone and so was the excessive hum in the audio too, but the flashing was still there, which turned out to be one of the PCL85's in which the triode section does the clamping for G1 of the CRT which was faulty. The pentode section does one half of the push-pull for the audio.

Since this thing seemed to be suffering from 'dud valve disease' I went through and checked them all and found the PCL85 vertical and the other PCL86 audio both to be very weak and a couple of other PCF80's that were a low but the rest checked out ok.

All that was left now was to clean all the controls and check and adjust the boost voltage and picture geometry/horizontal/vertical oscillator presets in which both were pretty close and replace the mains filter cap.

So now after the so called 'quick fix' the final result is a very nice working Philips S8 and it does have a stunning picture. Lets hope it keeps behaving itself from now on.




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