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Philips TVette (11TG190AT)

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sideband
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sideband said

Actually you've just given me an idea....I noticed the possible distortion after removing the PCB's for the first time....a bit like a rubbing speaker but not quite. It might be worth checking the bias pot....the bottom PCB is a bit of a job to remove and it's possible it got moved while fighting to get the PCB out. When I replaced the AF117 AF amp/AGC transistor I was going to check the bias afterwards and never did......  

I decided to have a quick look at the audio output stage. I simply unsoldered the collectors of both output transistors and then ran the set without sound, monitoring the total current from the 11v supply. It stayed at around 780mA and the set was on for well over an hour. I made the decision to replace the output pair and checked a couple of new transistors (AC127/128) against the originals. The old AC128 measured the same as the new but the old AC127 had a very noticeable leak between collector and emitter compared to the new. Having fitted the new transistors I was just ready to check it when a white lead broke off from somewhere near the edge of the main PCBenraged_gif I've decided to find out where it comes from next session.....read04 

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Topic starter Posted : 26/07/2017 11:37 pm
sideband
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....Sorted!

 

It was in fact the output transistors. I found out where the white lead had come from, switched on and the improvement in sound quality was immediate. I continued to monitor the current on the 11V rail and even after two hours, it didn't rise above 800mA. I've actually reassembled the set and had it running for another hour so I think we can say that it's well and truly fixed.

 

To be honest, the sound quality last week wasn't too bad and of course I didn't have another set to compare it with. That's why I didn't think audio stage when the fault showed up. Anyway it was fun to fix and I've learnt more about these early transistor TV's which I didn't see too many of as they were at the end of their service life when I started in the Trade.

Thanks Jayceebee for the nudge in the right directionthumb_gif

I'll post some pictures later.

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Topic starter Posted : 27/07/2017 11:58 pm
sideband
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...and here are the final pictures. The set has been running for about four hours with no problems. Very pleased with the way it turned out. I decided to watch a 'period' DVD film. By period I mean one that would have been shown around the time the set was made so mid-sixties. Out of interest, can anyone guess what the film is? 

Among the cast are a very young Dennis Waterman and an even younger Suzy Kendall. It was shot in and around Battersea in London.

js640_SAM_1360.jpg

js640_SAM_1363.jpg

js640_SAM_1364.jpg

js640_SAM_1358.jpg

Bit of a giveaway.....

js640_SAM_1366.jpg

Testcard. The brightness is a bit low to

reduce artefacts produced by the camera.

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Topic starter Posted : 28/07/2017 11:32 pm
PYE625
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Up The Junction 

"Oo oo oo...Bloody Hell"   Guess what part of the film that is from?    grin_gif

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Posted : 28/07/2017 11:35 pm
sideband
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PYE625 said
Up The Junction 
   grin_gif  

Too easy!! I always liked the film...hard, gritty and probably quite an accurate portrayal of working-class life at the time. It's nothing like that now...Battersea and Clapham are very sought-after areas.

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Topic starter Posted : 28/07/2017 11:43 pm
PYE625
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I first saw the film when it was shown on TV in the 80's and I had it on VHS tape for years.  After getting it on DVD, it became clear that some slight editing out of a certain scene took place for television  wink

Manfred Mann was involved with the music and I even have the LP  doh_gif

Was the film preceded by a series on television?

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Posted : 28/07/2017 11:49 pm
sideband
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I first saw it when it came out in the 60's! I do remember it being repeated much later so that was probably the 80's. 

 

I don't think there was ever a series. It might have been a TV film....I can't imagine it being released for the big screen.

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Topic starter Posted : 29/07/2017 12:15 am
PYE625
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Well, here it is..... The Wednesday Play..... (not a series as such, but the individual plays probably were).

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Posted : 29/07/2017 12:18 am
sideband
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...except that is not the original.

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Topic starter Posted : 29/07/2017 12:22 am
PYE625
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sideband said
...except that is not the original.  

Not the original play?

(Happy if you want to split this off from the TVette thread).

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Posted : 29/07/2017 7:52 am
Marc
 Marc
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Hi Rich,

The little TVette looks great now, one of these days I might have to treat myself to one.

As for 'Up the Junction' it was a play by Neil Dunn and directed by Ken Loach which was screened on TV in 1965 and became a feature film in 1968. Loach directed a few hard hitting films for the Beeb, I think 'Cathy comes home' was another Wednesday play he did. 'Junction' is a great film in fact I might even dig it out later for viewing....but which version ? I'll flip a coin.wink

Marc. 

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Posted : 29/07/2017 12:43 pm
Cathovisor
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marc said

The little TVette looks great now, one of these days I might have to treat myself to one.

This is where I get into trouble for pointing out there were two (as one lot) on eBay recently... in Wakefield <DARFC>

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Posted : 29/07/2017 1:58 pm
Marc
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Cathovisor said

marc said
The little TVette looks great now, one of these days I might have to treat myself to one.

This is where I get into trouble for pointing out there were two (as one lot) on eBay recently... in Wakefield   

I saw them on bay but the sheckles weren't available duno_gif

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Posted : 29/07/2017 2:40 pm
sideband
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Well back to the set after a break of a few months, all was well when I last used it back in September. Firing it up over the holiday produced a weak picture with a hum bar on the screen. When I checked the supply rail, I was horrified to see it at over 14 volts....I switched off PDQ! Knowing how delicate the CRT heater is I unplugged the tube base and checked the supply again...15.4 volts, it should be 11V and it wasn't controllable by the set 11V pot.  I spent time going around the regulator circuit and deduced that there was something wrong around the AD149. I removed the transistor and checked it....O/C collector! I fitted a replacement and the supply dropped to a more respectable 11.1 volts. I carefully adjusted it to 10.8 (I prefer it to be a few hundred millivolts lower) and then refitted the CRT base. A slight readjustment of the supply to bring it up to 10.8V and everything was back to normal. The CRT had survived and picture was good. 

Clearly there is a need for some sort of protection. I suppose a simple 1 or 2 watt zener diode across the output would work and hopefully blow the supply fuse if the supply  rose above say 11.5V. Alternatively maybe a 'crowbar' type circuit using a thyristor that fires when the supply rises above 11.5V....something to think about.

Anyway at the moment, all is well and the set is giving superb pictures.

 

js1024 SAM 1517

 

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Topic starter Posted : 31/12/2017 3:15 pm
TVJON74
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Hi Rich,

I have a recollection that such a crowbar circuit was discussed on VRAT1 and a zener/resistor combo was used. Can't remember if it was added across the 11v rail at the PSU or on the tube base, but IIRC blown fuse was result if the 11v rail went too high.

 

Jon

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Posted : 31/12/2017 3:31 pm
sideband
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I've just had a search through the old VRAT Archive and there are a couple of posts that mention a zener diode across the supply resulting in a blown fuse if the supply rises too high. That seems the simplest solution. Another mentions a fuse in series with the CRT heater and a zener diode after the fuse (effectively across the CRT heater) so if the voltage starts to rise above the zener voltage, the fuse blows. 

Something to think about.

Two 5.6V zeners in series would give 11.2V...maybe that's a bit close taking into account the usual tolerances....5.6 plus 6.2 will give 11.8V.....hmm I'll see what's in the spares box.

 

 

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Topic starter Posted : 31/12/2017 4:13 pm
PYE625
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An appropriate caption on the screen photo above... "Essex Police, Whats your emergency? "

                   "Me heater's too high....can you help? "

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Posted : 31/12/2017 4:34 pm
TVJON74
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Hi,

Using the BZX85 series diodes, a 3V3 and an 8V2 will give 10.8V minimum and 12.2V maximum if the tolerances of each diode is stacked to the min/max limits. Nominal would be 11.5V. So in reality you should be safe if you set the HT1 to 10.8V. Using 2 x 5V6's you could end up with the minimum being 10.4V.

I was thinking along the lines of a small value fuse fitted in series with the heater wire to the tube base PCB (heater current is 68mA@11V, so I guess something around 80mA would be OK) and then fit the diodes and a low value resistor in series across the heater pins of the tube base. If the HT1 rail then went too high the fuse would blow and the fault condition would then be no picture.

Jon

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Posted : 02/01/2018 11:27 pm
6.3volts
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Posted by: sideband

I've been plagued with intermittent problems on this set due mainly to dry joints but I'm getting there and I've just replaced the AF117 audio amp/AGC transistor with an AF127. That has cured the annoying intermittent crackle on sound. I'm left with an intermittent power supply problem which only shows up when the PCB's are fitted back in the frame.....

It's too late now as you have replaced the Af117, but I 'repaired several of the af11's by connecting the EBC wires together and applying a few volts between them and the case. It zapped the tin whiskers and hopefully they will take a long time to grow back.

Have any members used this method?

Mod Note: Fixed the quote, your response should be outside the quote box, not within.  Hitting return twice, drops the cursor out of the box. Hope that helps  ? 

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Posted : 02/04/2018 7:53 pm
sideband
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Time to revive this thread. When I got the set there was a corner missing from the rear PCB where the contrast control had been. I bodged in a 1K pre-set so that at least I had some sort of contrast control.

A recent request for a rear PCB was answered by forum member JayCeeBee (thanks John) and the replacement board arrived yesterday. It is in excellent condition and, most importantly, is in one piece with the contrast control. A few minor repairs are required, notably replacement of a 10K pre-set which has lost it's slider and the set 11V pre-set which is a little corroded. Both of these can be removed from the broken PCB which will now be used as a parts donor.

It's pushed the Philips TV to the top of the 'to be finished' pile and is now on the bench ready for the transplant!

 

First thing I did was to remove the wire stumps from the replacement PCB and clean up the solder tags. I'll replace the two pre-sets next and then donor PCB and patient are ready for the transplant operation.

 

js1024 100 0161
js1024 100 0162

First shows the original PCB with the corner missing and the bodged pre-set. Second shows the replacement PCB before I removed the wire stumps.

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Topic starter Posted : 08/11/2020 11:48 am
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