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Old 25th Jan 2021, 4:33 pm   #161
19Seventy7
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Default Re: Philips G8 G22K522

Afternoon all

I'll make sure to set up the HT and overvoltage protection when I've got the sync sorted. I've got some caps on their way.

I'll order some grease and get the coil sorted out too when it's ready. Thanks for linking page, I'd have just sprayed some contact cleaner in it and given it a twiddle

Thanks all for the help
'77
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Old 25th Jan 2021, 10:00 pm   #162
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Default Re: Philips G8 G22K522

It has been a joy reading all the posts here. Takes me right back to my early repair days.

Well done 19Seventy7 - look forward to seeing the completed results photo. Looks like you have a decent CRT anyway!
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Old 27th Jan 2021, 6:10 pm   #163
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Default Re: Philips G8 G22K522

Quote:
Originally Posted by agardiner View Post
It has been a joy reading all the posts here. Takes me right back to my early repair days.

Well done 19Seventy7 - look forward to seeing the completed results photo. Looks like you have a decent CRT anyway!
Glad you're enjoying it, I am too! I'll make sure to get lots of snaps when it's completed. The CRT isn't even at its best there! There's a dry joint somewhere that makes the screen go dimmer, it can go a lot brighter than that!

Quote:
I've got some caps on their way.
Replaced C4520 (With a 33uF as thats what was fitted and what was written on the diagram) with little to no improvement, so I put two 33uFs in series (Not parallel - I've learnt ) but this had no effect on it either.

I'll start tracing back and hopefully find a component at fault

Thanks
'77
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Old 27th Jan 2021, 6:40 pm   #164
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Default Re: Philips G8 G22K522

Do you have the full manual? If not I can scan the relevant circuit description and the voltages you can expect on the TAA.
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Old 27th Jan 2021, 6:47 pm   #165
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Default Re: Philips G8 G22K522

I'm not sure to be honest. I'm using the one in Television from June 1978. It looks to me to be all there, but I'm not 100% sure.

The description might be helpful though, if it's different to what's in the Television article. If you wouldn't mind scanning it I'd appreciate it.

Thanks
'77
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Old 28th Jan 2021, 5:03 pm   #166
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Default Re: Philips G8 G22K522

TAA700 description here including the line phase detector at mag. page 542 if that's any help:

https://worldradiohistory.com/UK/Pra...on-1971-10.pdf

Lawrence.
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Old 28th Jan 2021, 6:26 pm   #167
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Default Re: Philips G8 G22K522

Hi
Here are the sheets I mentioned.
Attached Files
File Type: pdf G8 description.pdf (81.4 KB, 74 views)
File Type: pdf G8 TAA diagram.pdf (52.8 KB, 78 views)
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Old 28th Jan 2021, 11:22 pm   #168
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Default Re: Philips G8 G22K522

Thank you for scanning those for me, and for linking that too, ms660. I'm sure they'll definitely help.

I'm going to be a nuisance here and ask how do I tell on the diagram what number is the voltage? I've not much idea on diagrams so I'd just like to make sure.

Thanks
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Old 29th Jan 2021, 12:53 am   #169
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Default Re: Philips G8 G22K522

Quote:
Originally Posted by 19Seventy7 View Post
Thank you for scanning those for me, and for linking that too, ms660. I'm sure they'll definitely help.

I'm going to be a nuisance here and ask how do I tell on the diagram what number is the voltage? I've not much idea on diagrams so I'd just like to make sure.

Thanks
'77
On that circuit, voltages are indicated by the numbers inside a rectangle with an arrow pointing to the testing point
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Old 29th Jan 2021, 1:37 am   #170
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Default Re: Philips G8 G22K522

Thank you, I thought that was the case. TP9 threw me off a bit as I thought it said 0.45 somehow, I see it as 6.45 now.

I'll test the set tomorrow and report back

Thanks for clarifying
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Old 2nd Feb 2021, 2:28 am   #171
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Default Re: Philips G8 G22K522

Sorry for the late reply, haven't had much chance to get the back off the set.

Went and prodded round the IC, testing straight off the legs and this is what I got.

The first numbers are mine, the second is what's written on the diagram

1: 6.7 - 6.45
2: 6.8 - 7.35
3: -0.8 - -0.8
4: 6.4 - 2.2
5: 13.5 - 12.6
6: 1.8 - 1.65
7: 7.7 - 6.1
8: 13.6 - 12.3
9: 705.5 - 0.7
10: -1.9 - -0.2
11: 2.4 - empty
12: 4.4 - 9.8
13: 4.1 - 2.2
14: 13.4 - 12.1
15: 205.9 - 11.8
16: 2.6 - empty

Pin 9 and 15 are a bit concerning as to why they're reading so high. Somehow I'm doubtful that it really is 700 volts on pin 9 (I'd not expect the IC to physically survive that - could be wrong of course) but I don't know any better so that's stumped me a bit, especially as pin 8 and 9 are connected and 8 is reading near-ish it's expected value. I've got the full readings noted down if that'll be of any help

Oh, and I've raised the HT to 195V

Thanks for the help
'77
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Old 2nd Feb 2021, 3:53 am   #172
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Default Re: Philips G8 G22K522

are you sure its not 705.5 millivolts?

pin 15 would be more worrying if it was 205.9 millivolts.
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Old 2nd Feb 2021, 12:38 pm   #173
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Default Re: Philips G8 G22K522

Yes - you're readfing millivolts (mV) as volts! Have a closer look at your meter and you'll see what we mean.
The ones that are way out are pins 4 and 15. Pin 4 is not a worry as it varies with signal and will have no bearing on the fault. Pin 15 is frame sync, and as you've got good sync it could be a misprint on the manual.
Pins 1,2 and 5 are concerning us here. I'd say your readings are pretty close to the specified values, so there's nothing wildly out electrically.
Two things. Have you replaced C4170 (decoupling pin 1)? Also does varying the preset balance control have any effect?
Failing that I'll have a look for a TAA in the box.
We'll get there!
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Old 3rd Feb 2021, 5:24 pm   #174
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Default Re: Philips G8 G22K522

I did wonder if I had misread it somehow, even to me 700V didn't seem right. I never thought to look at the other indications on screen - something else I've learnt!

I've not replaced C170 but I've ordered a replacement, Its been replaced before and all the caps I have had to replace have been of the same type. I should probably replace the remaining ones as there's only a couple - but one thing at a time.

Which balance control? Sorry if it's daft but just wanna make sure - don't want to twiddle things that are best left alone

Thanks
'77
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Old 4th Feb 2021, 10:54 am   #175
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Default Re: Philips G8 G22K522

The preset R4177 is mounted vertically by the chip.
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Old 4th Feb 2021, 10:09 pm   #176
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Default Re: Philips G8 G22K522

Just checked, Pin 5 is now reading 5.3 for whatever reason and it varies with the sync, but if I adjust R47177 the voltage reading on it changes (Should it?) I'm not sure why it's gone so low as nothing has changed from last night. Out of curiosity too, I tuned away from the signal and the voltage went up to around 10V which I guess is right.

I suppose just wait for the replacement cap to get here and take it from there?

Thanks
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Old 5th Feb 2021, 12:04 am   #177
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Default Re: Philips G8 G22K522

Update: I had left the TV on longer than I usually do as I was doing the tests. I then went to adjust L4501 to see if that altered the voltage on pin 5.

I got a locked picture, and it stayed locked. I let it run for a bit longer and some colour appeared. I didn't get a very good picture as where it is, the screen is about 2" away from the wall, but here's an idea. You can see some weak colour on Kiki Dees face.

I also think there's a dry joint contributing to the sync fault, as I can lose sync, give the set a tap and it returns - after 10 or so minutes of the set being on.

When I get the capacitor, ill fit it and then go over and try cure any dry joints I come across - they're really not helping matters here.

Edit: The blue monochrome picture is also caused by a dry joint - game of luck to get a locked colour picture with each smack of the set

Thanks
'77
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Old 5th Feb 2021, 9:29 am   #178
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Default Re: Philips G8 G22K522

Progress! You'll need a good strong light and possibly a magnifier to look for the dry joints and pay particular attention to the edge connectors, also the connections to the oscillator coil. The blue picture is probably due to dry joints on the the RGB output transistors - they run quite hot.
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Old 6th Feb 2021, 1:00 am   #179
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Default Re: Philips G8 G22K522

Great to read you're making progress on this. The G8 seemed to suffer with DC drift in the RGB output stages. This led to poor grey scale and many engineers thought that the CRT was duff when it was OK. A careful set-up of the RGB amps to give a cut-off at 150v and then a grey scale adjust too, will make a big difference to the picture quality. This isn't complicated if you've got the manual, one of the test points is on the pcb edge connector.

I'm not sure what you know about this chassis in general, but Philips issued a later signal pcb that integrated the IF tuner and decoder onto one large pcb. This could be retrofitted into earlier models. The so called 'combined pcb gave a cleaner picture than the early separate pcb's in my opinion.

Keep up the good work, you're doing well.

SJM
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Old 7th Feb 2021, 2:39 am   #180
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Default Re: Philips G8 G22K522

Sorry all for the late reply. I had replied yesterday using my phone, but for some reason it never submitted, and i've been fairly busy today so haven't been able to come back and check for replies until now.

Quote:
Progress! You'll need a good strong light and possibly a magnifier to look for the dry joints and pay particular attention to the edge connectors, also the connections to the oscillator coil. The blue picture is probably due to dry joints on the the RGB output transistors - they run quite hot.
We're getting somewhere! The caps have turned up and so tomorrow I'll replace it and search out those dry joints. Thanks for giving me a heads up on where to look, I'd have no idea other wise. I think so far there's 3 (or 3 groups) that I've got to search out - sync, blue screen and HT. HT one isn't too bad but it shows up occasionally. I did actually get a gut feeling about the coil being dry jointed, we'll see if it was true or not.

Quote:
Great to read you're making progress on this. The G8 seemed to suffer with DC drift in the RGB output stages. This led to poor grey scale and many engineers thought that the CRT was duff when it was OK. A careful set-up of the RGB amps to give a cut-off at 150v and then a grey scale adjust too, will make a big difference to the picture quality. This isn't complicated if you've got the manual, one of the test points is on the pcb edge connector.

I'm not sure what you know about this chassis in general, but Philips issued a later signal pcb that integrated the IF tuner and decoder onto one large pcb. This could be retrofitted into earlier models. The so called 'combined pcb gave a cleaner picture than the early separate pcb's in my opinion.

Keep up the good work, you're doing well.
It's great to be making progress on it too! I didn't know that about the DC drift, that's pretty interesting. Wonder how many tubes were replaced due to it... I don't have a manual to use myself, only an article in Television and the excerpts Welsh Anorak has kindly given to me.

I know a bit about this chassis, probably more so than any other, but that doesn't say much haha. I know some basic, surface level stuff, but the more in depth things, not really, or at all. I'm actually glad to have the original separate PCBs as opposed to the combined, not that I'd mind either, I just like having early examples of technology too. It'd be interesting to get a combined panel set and compare them side by side, or even temporarily fitting one into my set. I find the G8s oddly interesting for some reason, more so than other chassis.

Thanks
'77
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