CTV 1978 Pye CT450 - Philips G11 Chassis

@wayned 

Ah now is the buzz mechanical or is it intercarrier? I've never known intercarrier buzz with these but a mechanical buzz....well that was caused by the choke/s in the power supply. The only answer was replacement which isn't possible now except from a scrapper and they will probably buzz anyway. I have heard that dipping them in varnish makes a big difference but I've never been in a position to try it. 

@sideband definitely mechanical! It's clearly coming from the power supply. Like I say, I'm pretty sure the one my parents had did the same. The audio is so good that you don't really notice it unless the volume is all the way down.

A little bit more work on this tonight, I've been replacing the original electrolytic capacitors with Japanese ones:

Getting quite a collection of old bits from it:

 The HT smoothing capacitor is ok but the one @CrustyTV gave me tested way better. In fact most of these capacitors have tested ok, but I'd rather replace them whilst they're still working rather than after a catastrophic failure.

Most of those blue electrolytics will probably be OK (with the exception of the 470uF smoother). This is where an ESR meter comes in handy. You could whizz over them quickly while in circuit and any duff or mediocre ones would be immediately obvious. 

Here's the video on this whole thing from start to finish:

A quick video, this was just replacing the old mains switch that had been bypassed and giving the tuner board and pots a good clean with contact cleaner.

Brilliant vid's.... I like 'em 👍 

"That guy's crap!"   hahahaha 😆 

@pye625 for some reason my Pye CT450/G11 videos are performing way better than all my other videos according to YouTube (that's not saying much tbh). I'm considering doing a documentary-style retrospective on the G11 project. As long as @crustytv doesn't mind me using a few images from the G11 project page on here.

Posted by: @wayned

As long as @crustytv doesn't mind me using a few images from the G11 project page on here.

Hi Wayne, feel free to use whatever you like. 👍 Perhaps give the website a plug in the credits, it could do with any and all publicity it can get.

Posted by: @wayned

for some reason my Pye CT450/G11 videos are performing way better than all my other videos according to YouTube

I've given up trying to fathom YouTube. Three of my videos went nuts recently, over 8,000 views on one, 3,500 on another and 2,000 on the last. These were 3-year-old videos on Philips N1500 VCR repairs. I never found out why.

@crustytv I always quote my sources, VRAT particularly in my first Pye CT450 video! 

No doubt I'll put the effort into this video and it'll just bomb....🙄

Not much to report but I've been replacing the electrolytic capacitors gradually and one thing I've noticed is the G11 chassis seems to be very good at masking underlying issues with faulty components until a problem occurs. This may explain why issues weren't addressed prior to production? 

Philips certainly tried very hard to prove the design before production. I worked for a Pye dealer when the set was launched and went on the Len Briggs lecture on the chassis. Philips had pre production sets running in all sorts of environments to provoke faults. We were given one of these sets as a panel repair jig it was a Pye like yours but not fitted with any cosmetic parts. the whole set was black and 'sooty' so I guess it had been run for long periods in a hot environment. We could see from the repairs that had been carried out where the lightly weak spots were going to be, I remember the area around the frame chip had seen some work!

To be fair I think few common faults were down to poor design most were component failures. Weak design points were mains filter on first models which was quickly solved by removing the fuse in the neutral line and replacing it with a resistor this solved bridge rectifier failure caused by poor mains connections and slot meter contacts arcing. we were advised on installation to always fit a new mains plug not to use the one from the "old set" and not to use two way adapters if possible.

The sets did suffer from poor soldered joints, two on the convergence panel where the line output transistor collector feed looped through were common and caused failure of the BU208.   It seemed that the sound output transistors were soldered before the heatsink was fitted which put the joints under strain it was common to find broken joints where the joint had been pushed through the panel, again quickly solved later models not affected.

Considering how hard they had tried early models must have been a disappointment for the design team. But they cannot be blamed for poor capacitors, noisy chokes and the like.

To be fair later models were much better and the early ones chugged on for years once they had been modified and reworked. I have a Philips version as a bedroom set and so far (since I have owned it) it has only needed a new frame chip and holder.  I had some out as slot meter rentals at well over 10 years old, only replaced when the tube got past it's best. 

The K30 was much more reliable from new and again went for years often without a single call, the main problem with early models being the 30AX tube getting weak but there was plenty of Amstrad "superwide" sets on the scrap pile as donors for that! 

Viva G11 !  

@slidertogrid yeah, I've mentioned this before but I can certainly sense a bit of pride in the design. Brilliant picture and a joy to work on.

Oh, the video I did earlier regarding replacing the mains switch - it's failed again! It seems to have welded the contacts together which seems consistent with what had happened to the old switch. I think relay time and I've managed to find an NOS replacement. 

Posted by: @wayned

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I think relay time and I've managed to find an NOS replacement. 

Hi Wayne, I have one NOS, in stock your FOC.

Regards

Chris

@crustytv apparently there's an NOS one on it's way to me but that would be fab if anything goes wrong with this one (after this year I'm not ruling anything out!) Cheers!

Is there a resistor and capacitor wired across the switch? I can't remember if that was the G11 or another set, probably an attempt to 'quieten things down'. 

From memory, there were a couple of 470K resistors wired across the switch contacts. This was to help suppress contact sparking when the switch was operated. The resistors were shorted out when the switch was 'on' so they need to be wired across the closed contacts

@slidertogrid nothing at all across the switch although that's not to say there wasn't originally as someone had unsoldered the mains lead coming in and soldered it directly to the wires coming out the switch.

What is interesting is the neutral fuse is still intact, it hasn't been bypassed with a resistor like I'd expect. Looking at the circuit I have reason to believe it did experience flashover and that's what took out the red channel of the decoder along with the diodes. The HT smoothing capacitor that was in there had a manufacturing date of 1986 but wouldn't have solved the blown diode problem and the set was 8 years old by this point so was junked. Luckily the CRT didn't take the brunt of the flashover.

I replaced the switch with the NOS one and this time I've added a relay. The neutral is now connected permanently so only the live is interrupted. The switch is installed between terminals 2 and 3 so it activates the main live feed to terminal 1.

Now here's something I wasn't expecting, the typical G11 buzz from the power supply has got quieter! I honestly don't know why though, was the resistance that bad with the old switch? 🤔

Solid State Relays. These can cause a major problem. They can fail in a way that produces the positive or negative half cycles of mains, in other words raw rectified mains. I'm sure a G11 will not like this as it conducts on both the positive and negative cycles of the mains. I first became aware of this problem when an audio unit was brought to me for repair and the toroidal mains transformer primary was open circuit. This was replaced and put back into place. Three weeks later same thing again, so out with a scope across the mains input lead to find in this case only positive half cycles of the mains! We had many of these mains distribution units which after two failures like this all had to be replaced with proper relay switched units. Be warned.