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Old 11th Feb 2017, 6:19 pm   #1
TV_Madness
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Default A VERY lucky find indeed (Philips G8 (G22K530).

Afternoon all

This is a set that I have been itching to get into, however with work and home commitments in the way, getting anywhere close to an old TV at the moment has been proving very difficult! With that said, this is a set that I have pulled to the front of the queue as it’s a bit of a cracker. The queue gets longer but the output of actual working sets gets smaller and smaller!

This virtually immaculate example of a Philips G8 (G22K530) was thrown my way in VERY lucky circumstances by an informant about a month or so ago (basically, a very understanding friend!). It was found plonked alongside a skip (on its stand!), sat in the driveway of a house which was being renovated in New Milton, Hampshire. Luckily for the Philips, whoever had put it there either didn’t have the energy or the inclination to heave the thing into the skip which would have surely caused major cabinet damage or worse, necked the tube. When my other half drew a bead on it, she immediately said “you don’t need another TV! Haven’t you already got one of those? (Points finger at the forlorn looking G22K550 that is still sat gathering dust, awaiting the next instalment)”. Anyway, here it is. This is also the slightly later version of the 520 series G8 (with the RGBY Matrix sub panel substituted for a TBA530).

Initial inspection had revealed that the mains fuse on the power supply panel was blown, and R1381 (the big 68R dropper) had gone OC at some stage in its life. This had been bridged with a very dodgy looking setup consisting of two large 100R power resistors wired in parallel for 50R. All of this was held together with twisted / wrapped bare wire, hanging about in the breeze. The main 600uF smoothing filter on the power panel had also spewed its guts out of the end of the can, and the BT106 SCR was SC in all directions. Clearly the entire board was essentially knackered and had seen better days. Just to prove a point, I pulled the working power panel from the (still dormant) G22K550 and set it up for 205V. After powering the thing up on my Philips PM5509 pattern generator, the set immediately rewarded me with a set of bright, sharp colour bars. One thing I had noticed during its VERY brief run was that the brightness control seems to be completely inoperative. I kept the power on for a limited time only, as I am fully aware of the dangers of leaving those nasty green line stage tuning caps in place (much to Taz’s detriment! ). The tube is very bright, so risking this would be a catastrophe.

So the set itself works for the main part at least (aside from the brightness issue). Without scavenging the K550 for parts, I have set forth on repairing the original power supply panel. I have replaced the main smoothing filter with a NOS can (which has been reformed and tests out fine) and I have also replaced the SCR and the dropper with NOS parts. Now aside from these components, is there anything else I should be aware of before testing the PSU? There are a lot of other semiconductors on this board and given the state things were in originally, I cannot be 100% sure that these will be ok (short of removing them all from circuit and testing everything individually).

What are people’s thoughts on this?

Cheers

Matt
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Old 11th Feb 2017, 6:39 pm   #2
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Default Re: A VERY lucky find indeed

Congratulations matt on saving the G8.
I cannot offer help with the power supply board but I remember there was a good write up In Television magazine about restoring these sets .
I think it was 1979.

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Old 12th Feb 2017, 12:48 am   #3
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Default Re: A VERY lucky find indeed

When I was working at Philips, the recommendation was to replace the thyristor and diac together...in fact I think they came as a pair in the early days. It's worth checking the other diodes and transistors with a meter before apply power.

Ages since I worked on one of these.....at least 30 years.....!
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Old 12th Feb 2017, 1:20 am   #4
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Default Re: A VERY lucky find indeed

Does it have the pair of BU205's.. or the single BU208 line output transistor.

Sometimes a single BU205 will die ..but the set can still work and the picture will have less oomph and look more like a Decca Bradford (ducks behind grassy knoll )
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Old 12th Feb 2017, 2:04 am   #5
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Default Re: A VERY lucky find indeed

Lucky ...!! That's the G8 I've been after forever!
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Old 12th Feb 2017, 4:46 pm   #6
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Default Re: A VERY lucky find indeed

Quote:
Originally Posted by Sideband View Post
When I was working at Philips, the recommendation was to replace the thyristor and diac together...in fact I think they came as a pair in the early days. It's worth checking the other diodes and transistors with a meter before apply power.
Sound advice. I'll go ahead and order a handful of BR100s (These appear to be readily available). I'll test the two transistors and the remaining Zeners out of circuit.

Yes this set does indeed have two BU205s in the line output stage.

Thanks

Matt
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Old 12th Feb 2017, 5:20 pm   #7
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Default Re: A VERY lucky find indeed

Happy days! I have the 20" version and a rather nice Roberts Video 22" RCT221 with folding doors.
A great design. I was chatting with the guy that designed a couple of the panels only Friday last. John.
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Old 14th Feb 2017, 1:48 pm   #8
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Default Re: A VERY lucky find indeed

Hi
There was a useful article in Television magazine circa 1983 about the G8 and how to check and balance the line output transistors. Not sure about the brightness control fault - should be fairly easy to sort out, bearing in mind they didn't always black the screen out.
The matrix panel you mention was hastily made as the TBA530 was late going into production - Philips had always intended using this IC and the boards were ready for them. They were something of a disaster as the greyscale would vary randomly. It's rare to see one nowadays as these decoder boards were usually replaced early in the set's life.
That looks a nice example. I always felt they had the edge over the 550 both on design and performance.
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Old 14th Feb 2017, 1:58 pm   #9
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Default Re: A VERY lucky find indeed

Would greatly appreciate some pix with the back off!
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Old 16th Feb 2017, 3:02 pm   #10
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Default Re: A VERY lucky find indeed

Quick update on the 520

I have acquired all of the replacement semiconductors for the PSU panel now and will set forth on replacing these later this evening.

Glyn - Yes I thought that may well have been the case with the earlier versions of the decoder panel. You can clearly see in the service manual diagrams where the TBA530 would otherwise go, just that it is all hardwired off to the little stand-off RGBY Matrix panel. I had heard about supply chain issues with the TBA530 before.

Threeseven - I will gladly pop up a picture or two with the back off later on when I'm home. The chassis was covered in an quarter inch layer of dust when I got it, so I removed each panel in turn and dusted them off with a small, soft brush. It looks a lot better than it did!

John - That is very interesting! I bet he's got a few stories to tell?

All the best

Matt
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Old 16th Feb 2017, 11:26 pm   #11
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Default Re: A VERY lucky find indeed

Couple of pics with the back off as promised.
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Old 21st Feb 2017, 12:29 am   #12
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Default Re: A VERY lucky find indeed

Very quick update here.

The power panel is now done. The BC147 in the trigger section of the panel tested a little odd, so this was duly replaced. It would measure with a forward voltage of 0.7V Emitter - Base but only 0.2V Collector - Base. Whilst I was there, I also replaced the second BC147 in the over voltage protection circuit for a brand new device (even though it really didn't need doing). The Diac has also been swapped out for good measure. I have tested all of the diodes on the panel and they all test out 100%.

So that's new transistors, new dropper, new Diac, new smoothing filter and a new SCR! If this thing doesn't work, I'll eat my hat!!

I have an order of 3.15A fuses turning up tomorrow, so will set forth on actually running the supply up on test (unloaded for the moment).

The eagle eyed may well spot that the previous pictures were taken prior to me fitting the new smoothing filter. I'll dig out a picture of the sorry state the panel was in when I got it. You can see the scorch marks in the top right hand corner where the string of polo mint power resistors were located.

Cheers

Matt
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Old 21st Feb 2017, 10:40 am   #13
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Default Re: A VERY lucky find indeed

Looking great so far, such a clean rare set

I can't wait for the next instalment.

Cheers
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Old 21st Feb 2017, 3:15 pm   #14
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Default Re: A VERY lucky find indeed

Hi
A SOLUS regunned tube appears to be in there - one of the better rebuilds.
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Old 21st Feb 2017, 3:48 pm   #15
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Default Re: A VERY lucky find indeed

A G8 was my first ever television repair. It was the first television I owned (didn't have a TV at all until I was 18 and left home) and it wasn't new, so became a television engineers training course for me.
Good to see pictures of the insides. Who'd have thought I could get nostalgic about a transistor TV?
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Old 22nd Feb 2017, 10:16 pm   #16
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Default Re: A VERY lucky find indeed

Hat duly eaten

I have got around to testing the power panel out this evening and it isn't having any of it.

Measuring the output at TP67, I get a whopping great 1.2VDC. Measuring the Anode side of the SCR, I can see only 133 VAC whilst at the Cathode, there is 25 VDC present. This is with the panel unloaded and disconnected from the rest of the set.

What am I seeing here? The rest is being dropped somewhere but where? I was assured that the new smoothing can had reformed fine (it certainly tests OK). I have run the set for about 3 minutes and nothing is getting warm / hot and I cannot see any obvious signs of distress.

To be honest, this power supply scares the life out of me a bit!

Thanks

Matt
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Old 22nd Feb 2017, 10:36 pm   #17
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Default Re: A VERY lucky find indeed

Scrap that.

I had the ground lead clipped to the chassis, not the ground plane on the PCB!!

So... Doing this properly now, I get a perfectly clean 207VDC at TP67.

I'm going to leave this on soak for a while then carry on with the rest of the set when I'm satisfied that all is fine.

Silly s*d!
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Old 23rd Feb 2017, 10:25 pm   #18
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Default Re: A VERY lucky find indeed

Evening all

Ok so I have made some good progress with 520 and at last, I have the set running on its original power supply. This wasn't without the thing having one last laugh!!

After satisfying myself that everything was ok with the supply after its heavy overhaul, I connected everything back up again and ran the set with the tripler disconnected for the time being. After double checking absolutely everything, I gingerly turned the power on... Nothing... Not a sausage. No line whistle (yes I can still hear it!), absolutely nothing at all.

Clipping the ground lead of my meter to chassis and prodding around revealed a very similar picture to what I was seeing before. At the main 800mA fuse on the line panel, I could not get anywhere close to the 205 Volts that should be present here. What on earth was going on? Hooking the meter back up to the ground plane on the power panel revealed the full 207V that I was seeing before. At this stage, I was satisfied that there had to be a grounding issue somewhere.

A few quick continuity tests revealed that if I connected one lead of the meter to the ground plane on the PSU board and then started prodding about on the chassis, there was a clean open circuit present. Working back to the panel itself then... BINGO! The track that comes back from the ground pin of Plug "L" on the power panel was blown about halfway along its length (see attached picture). The quality of the print here looks to be a bit dubious, so I'm wondering it this was a bit of a weak spot in general. I put together a bit of a quick and dirty repair, however it is effective and does the job.

Running the set back up again, I was greeted with that healthy hum that these SCR based PSUs make, a line whistle and a nice arc could be drawn from the EHT Overwind cap (not to chassis and with a well insulated screwdriver!! )

After setting the supply line back up for 205V, I decided to have a look at what the picture was doing with the tripler reconnected. Once again, a bright, crisp set of colour bars were immediately on display with the pattern generator rigged. Even the convergence was pretty much spot on when looking at a crosshatch! Oddly, the brightness issue seems to have self resolved itself, so I will do a bit more digging about here to find out what had happened to this. There really isn't much to go wrong so I'm not really sure.

That's about it for the moment. I don't want to risk anything by running it for longer than absolutely necessary with those tuning caps still present in the line stage. Once these are swapped out, I can't really think of anything else that needs doing to it.

I'll get these replaced and will hopefully post up a picture of thing displaying a proper picture, then it's case closed I should imagine.

Thanks

Matt

P.S - Initially I said that the set was a G22K530. It isn't. It is in actual fact a G22K523. I'll put this down to a typo (possibly something else!).
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Old 25th Feb 2017, 8:38 pm   #19
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Default Re: A VERY lucky find indeed

Quick test via a cheapo DVD player.

Not bad really considering this set very nearly ended up as landfill!

Matt
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Old 25th Feb 2017, 9:22 pm   #20
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Default Re: A VERY lucky find indeed

Hi Matt
Congralulations what a great job you have made of this set, love these set when I was work. the first all transistor set Phillips made. I attened a phillips lecture at stoke on trent tech collage in 1972 just after the set had been released .The first part of the lecture was taken by the head of design for the g8, all in the room lost , but after tea break all in the room enjoyed the help given by a member of the service dept.As regards the brightness i think there is a preset brightness control on the line time panel aslo there is 12v zener that seem to drift, replace with a higher wattage type.
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