7th Feb 2021, 10:00 pm | #181 |
Octode
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Re: Philips G8 G22K522
Evening all,
I've replaced C170 and it's made little difference. I also resoldered the edge connectors and L4501, which also made little difference. I've noticed although it speeds up when out of sync, then slows down, locks for a fraction of a second, speeds up, slows down, locks for a tiny bit longer, speeds up, slows down, and so on. Each time the lock gets a little bit longer, but it's never permanent. I played around with the set a little more and found that all the controls do in fact work, it's just they're broken in the sense that you have to pull the controls slightly, and twist for them to take effect. Oh I haven't got a blue screen since, so I'm hoping thats been cleared up! Thanks '77 Last edited by 19Seventy7; 7th Feb 2021 at 10:07 pm. |
7th Feb 2021, 10:42 pm | #182 |
Octode
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Re: Philips G8 G22K522
I've just discovered that the set is fussy with colour images. Displaying a B/W image and it's overall a stable picture for the majority of the video, one or two small scrolls and a couple shakes here and there, but over all it's stable.
If displaying a picture with weaker colour or a small amount of colour if it's not too vivid, it'll hold for a little while, lose sync for a while and return again. If displaying a lot of colour will completely throw it off with very short stable picture. If it'll help I can upload a video to YouTube to show what's going on and how it reacts with different sources and colour levels. The first picture is stable, the second will scroll a bit and the third is continuous scrolling Thanks '77 |
7th Feb 2021, 11:40 pm | #183 |
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Re: Philips G8 G22K522
I'm not sure what sources you are using, but at this stage I suggest you use a Freeview box to make your assessments rather than VHS recordings. The latter opens a whole other can of worms on a set like this.
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7th Feb 2021, 11:48 pm | #184 |
Octode
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Re: Philips G8 G22K522
I'm actually using my Xbox 360 with YouTube for a video source. I don't think this set has been converted for VCR use, so I've never bothered with VHS.
The colour picture especially looks like a VHS picture, but it's not, i think that was just me hastily getting a photo before the sync was lost Thanks '77 |
8th Feb 2021, 12:02 am | #185 |
Heptode
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Re: Philips G8 G22K522
You're using a xbox as a source, so how are you converting to RF in order to feed the tuner input? It could be signal overload, which will cause high contrast and often rolling vertical images. Scenes at low video level (contrast) will sometimes be OK, but a fully contrasted picture may be unstable.
There was a old saying 'get it right in black and white' you did all this before worrying about colour! SJM.
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8th Feb 2021, 12:34 am | #186 |
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Re: Philips G8 G22K522
I'm using my Technomate RF modulator, which converts the composite signal from the xbox to RF. It works fine on all of my other sets. I've got an attenuator which didn't seem to do a great deal. I think you might be right about the contrasting scenes, it can hold on some music video scenes, such as on the audience, then an up close shot can lose sync.
I'm wondering if the issue could now be stemming from the tuning sections? I'm not too worried about colour, but I just noticed that when the xbox went onto a 60s music video, in black and white, it locked much better than colour does '77 |
8th Feb 2021, 10:58 am | #187 |
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Re: Philips G8 G22K522
I'm beginning to wonder if the fault is a bit earlier on as signal level and content seems to affect the sync and the chroma. Most of the processing is done in those two cans, called vision gain and vision selectivity. That's U300 and U800 respectively. Luckily we do have diagrams for those. They don't appear to have any troublesome electrolytics in them, and I can't say I recall any problems with them in the past.
There are some more capacitors it won't do any harm to look at. There's C4191 (80uf, use 100uF) that decouples the IF AGC line which could upset things, also C4160 (125uF, use 120 or 150 uF)) which decouples the supply line to the IC. It would be very handy to borrow an IF panel to be absolutely certain this is where the faults lie. Another thing - if you hang a meter on the 12v line does it remain absolutely stable with picture content? And the same with its 25v feed on the edge connector? |
8th Feb 2021, 9:02 pm | #188 |
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Re: Philips G8 G22K522
I've just checked C4191 which to me seems faulty. I removed it from circuit, discharged it and couldn't get a normal reading, mainly 0, discharging it and retrying, flick of a number and 0, then third time of discharging and testing I got ~1.330. I've replaced it for now to do the checks.
Testing the 25V line from the edge connector is all over the place, it can go down to 17V and up to around 30V. I'm not sure where to test the 12V line Edit: Oh, forgot to check C4160. I'll test that now Edit 2: I got 1.26 for C1460, which I'm guessing is well within tolerance? (I'm not too sharp on reading capacitors on a DMM) Thanks '77 Last edited by 19Seventy7; 8th Feb 2021 at 9:09 pm. |
8th Feb 2021, 9:39 pm | #189 |
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Re: Philips G8 G22K522
It's not easy or accurate to read capacitance on a DMM. Far better is an ESR meter which can go on your Christmas list!
Now this 25v line is interesting. It should be stable - well, within a couple of volts. It arrives at edge connector pin 4.This originates from the line scan panel, plug J pin 2. It's fed from the LOPT pin 2 via D539 and D 564 (paralleled) and is decoupled by C538 (180uF). The LOPT pin also feeds the negative line pulse to the oscillator and decoder. Might we be getting warm? I'd change that capacitor with a 220uF, min 35v and go from there. |
9th Feb 2021, 12:44 am | #190 |
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Re: Philips G8 G22K522
I took the reading from Pin 4 if that should make any difference? I've only just noticed TP11 is on the 25V rail too. I got a stable 39V on that, though the .XX numbers varied.
I'll keep an eye out for an ESR meter, I've been planning on getting some much better test equipment now I'm actually getting a little bit more in depth and starting to understand them a bit better. I'll order a 220uF capacitor and fit that. I don't really mind changing caps, even if they're okay, just for reliability. Just to clarify, where should I connect my meter to the 12V line to measure? Thanks for your help '77 |
9th Feb 2021, 12:35 pm | #191 |
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Re: Philips G8 G22K522
Pin 5 of the TAA should not dip below 12v as it's zener stabilised. However if the 25v rail is varying then it might and would upset the IC's operating conditions.
G8s rarely suffered from capacitor problems, but that was forty years ago! Many forum members, myself included, are happy with the cheap Chinese ESR meters availble ready cased or as a module. They aren't up to the standard of, say, a Peak but do the job (and more) pretty well for under £20. |
9th Feb 2021, 4:12 pm | #192 |
Octode
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Re: Philips G8 G22K522
I took far too many years to buy an ESR meter. Finally bought the automatic unit from Peak Electronics. Hardly a day now goes by without using it, well worth having!
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9th Feb 2021, 4:44 pm | #193 |
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Re: Philips G8 G22K522
Is it okay for pin 5 to go over 12V though? It's at 13V, if I remember rightly it was stable. I can recheck if need be. Where are all the testing points of the 25V rail? I'll go back and check each TP but I don't have a manual so I've no idea where 25V comes from and goes to and what's on it to upset it.
I'll definitely grab an ESR meter soon, if not later on today Thanks '77 |
9th Feb 2021, 9:56 pm | #194 |
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Re: Philips G8 G22K522
Years ago when I was given the job of looking after G8 pcb's, I do recall getting quite a few come in with bad IF response, crushed rolling pictures etc. Admittedly this was with the later combined pcb. You could rock the cans from side to side, and the response would vary. The usual fix was to remove the can and then twist the pcb to see what changed. It was said in Television Magazine that the filter and gain units suffered with tiny dry-joints and a mass re-solder would often put this right. I had about a 50% success rate with this, but it still might be worth a try.
When you're doing this type of fault finding, you really do need a 'scope to be able to look at quality of the video signal coming out of the IF detector. I'm not sure what test gear you have at this stage. Just remember that this is a 'live-chassis' and the neutral of the mains is wired directly to the metalwork of the chassis. Therefore you also need an isolating transformer to be able to connect the scope to the TV safely. I know, yet more expense! As Glyn has pointed out, ensure the supplies are both stable, you should be able to do this with a meter alone. There is a manual for this Tv on this site as far as I can see. (1.99) SJM.
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9th Feb 2021, 10:03 pm | #195 |
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Re: Philips G8 G22K522
Whilst I would always agree that an isolation transformer is a sensible item to have and use when working on any TV sets, I use a Velleman scope for most of my work. Being a battery powered device, it avoids the pitfuls of connecting to live chassis. And its a pretty decent scope for a small budget, so if you don't already own a scope I can recommend it.
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9th Feb 2021, 11:06 pm | #196 |
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Re: Philips G8 G22K522
I'll have a go tomorrow of wiggling the cans round and seeing if that makes any difference. It's funny you should say that as I did actually look in one of the cans out of curiosity of what was inside the day I got sync for the first time. I wonder if it's just coincidental or it did actually play a part in getting me sync.
I don't have a scope so I'll look into the velleman scope, I've been planning on getting one anyway. The only equipment I have is a soldering iron and DMM. No transformer and no scope. Thanks for pointing out the manual. I never thought of looking on this site. I'll buy a copy now! Thanks! '77 |
10th Feb 2021, 10:37 am | #197 |
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Re: Philips G8 G22K522
Don't worry too much about an isolation transformer at the moment. You'd need quite a big one for a G8, and as long as you're very careful with the chassis then it shouldn't pose a problem. It's only when using earthed test equipment or you're dealing with so-called 'half-live' chassis that you need to worry.
I've never actually resoldered the cans as back in the day they were very plentiful on the surplus market so they could be changed with 100% confidence in the repair. Not now though! |
11th Feb 2021, 9:42 pm | #198 |
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Re: Philips G8 G22K522
Evening all thought I'd just give a bit of an update
I was kindly given a tripler to take a rubber cap from for mine (Mine's just got several layers of electrical tape insulating it ) So I've waited until I got this tripler before powering it up again, as I'm not too keen on letting it run too long without proper insulation. However, what was left of my rubber cap has stuck to the metal stud and it managed to snap the board in it's reluctance to come off. Luckily the wire is still intact so I've decided to leave it for a while, and I'll apply some adhesive every once in a while to bring strength back, and maybe give it a splint somehow. I've got the 120uF caps to fit too. Once I've managed to change the rubber cap I'll try the cans as I'd like to be able to do them one by one and test after each one, to find out what one (if any) was at fault Thanks '77 |
12th Feb 2021, 3:25 am | #199 |
Octode
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Re: Philips G8 G22K522
I've been up all night trying to get this G8's tripler cap back on to no avail, then it turns out the cable has worn away with all the soldering and wont reach the LOPT. It was always a tight fit anyway. I've had a look on Donberg to see if they've any triplers, which they do. I think I'll have to grab one which'll put any more repair on hold
Not having a good time with this set today. |
12th Feb 2021, 8:02 pm | #200 |
Heptode
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Re: Philips G8 G22K522
Burning the midnight oil with this one!
If you get a so called universal tripler, be careful that the diode and capacitor leads are connected correctly. If not you can get all sorts of odd picture effects. I'm sorry but I cannot ever remember fitting a universal into a G8, but maybe someone on the forum may be able to to advise. Whatever you do don't crop any of the leads until you're quite sure everything is OK.. From what I recall you could use a universal for any TV, but the diode and cap lead connection varied model to model. SJM
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