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Old 11th Jan 2021, 1:53 pm   #141
ms660
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Default Re: Philips G8 G22K522

Might also be worth checking the line discriminator balance control if not already done so as that will affect the voltage at the reactance transistor.

Lawrence.
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Old 11th Jan 2021, 9:25 pm   #142
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Default Re: Philips G8 G22K522

Quote:
Originally Posted by 1100 man View Post
As everything changed when you changed C498 (4mfd), I still think this is the cause of the oscillator running way too fast. After all, it was running at the correct frequency before C498 was changed, but there was a sync fault.

Look very carefully at the value on the new capacitor- is it really 4.7mfd? Not 0.47 or 47mfd? Is it actually connected? Check for lifted print or hairline cracks around its legs. Do you still have the original capacitor you could try?
Sorry all for the late reply, It's definitely 4.7uF but I do still have the original and have replaced it, which seemed to have made no difference. (Picture one is my replacement, Picture 2 is the original)

Quote:
The voltage on T4500's collector should be 17.8v, base 7.35v and emitter 6.9v
Testing this the collector was 17.83, the base was 7.190 and the emitter dropped from around 6.660 to around 6.450 (Written as seen on DMM)

Quote:
T4511 C 13.0, B -2.45 and E .014v
C is around 17.15V, B is 026V (not 2.6) and E is 027V (Again as seen on DMM)

Quote:
An important voltage is at TP47 - 7.35v - this is the control voltage to T500's base.
Tested this and it read around from anywhere between 7.000 to 7.060. It started off around the 7.060 mark and dropped down to 7.000 (Same as what was displayed on the DMM)

I'd do checks tracing backwards from the fault but I'd not be sure at which components to be looking at.

Quote:
Might also be worth checking the line discriminator balance control if not already done so as that will affect the voltage at the reactance transistor.
Where would this be or what would it look like? There's a few controls that I can see but they're for height, linearity and the likes.

Thanks
'77
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Old 11th Jan 2021, 10:07 pm   #143
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Default Re: Philips G8 G22K522

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Originally Posted by 19Seventy7 View Post
Where would this be or what would it look like? There's a few controls that I can see but they're for height, linearity and the likes.
I don't have a layout but it should be near to IC2001, the circuit ref. I'm looking at for the preset pot is 2177 (220 ohms) The preset pot sets the emitter voltage on the phase detector transistor inside IC2001 which is pin 1 the collector is pin 2 which is the output to the reactance stage.

There should be a procedure in the manual for setting the line frequency, if you follow that it should give an idea as to whether it's the oscillator or the voltage that controls the reactance stage.

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Old 12th Jan 2021, 1:12 pm   #144
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Default Re: Philips G8 G22K522

Those voltages look almost exactly right - you only need to go to one decimal place at most. Just check the adjustment slug hasn't fallen out of the coil - that frequency is so far out it has to be either that or a tuning component. There was no need for these oscillators to be crystal controlled, just to free run at approximately line frequency. Yours is galloping!
I'll get the manual out tonight and copy you the setting up procedure.
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Old 12th Jan 2021, 8:14 pm   #145
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Default Re: Philips G8 G22K522

Quote:
I don't have a layout but it should be near to IC2001, the circuit ref. I'm looking at for the preset pot is 2177 (220 ohms) The preset pot sets the emitter voltage on the phase detector transistor inside IC2001 which is pin 1 the collector is pin 2 which is the output to the reactance stage..
I think I might know the one actually, I noticed a control last night near the start of the yellow flylead from the central bottom PCB which would be board 2. I'll wait until I've got the setting up procedure from Welsh Anorak and take it from there.

Quote:
Those voltages look almost exactly right - you only need to go to one decimal place at most. Just check the adjustment slug hasn't fallen out of the coil - that frequency is so far out it has to be either that or a tuning component. There was no need for these oscillators to be crystal controlled, just to free run at approximately line frequency. Yours is galloping!
I'll get the manual out tonight and copy you the setting up procedure.
That's definitely a relief. I wasn't too sure about them. I'll check the coil and let you know. If it has fallen out, and I'd made adjustments would it still affect whats on screen? It does still adjust.

Thanks for help, much appreciated
'77
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Old 13th Jan 2021, 11:11 am   #146
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Default Re: Philips G8 G22K522

Here's what the manual says:-

Tune the receiver to a transmission and adjust the controls for a normal picture. Connect a voltmeter between TP9 and chassis and adjust R2177 for a reading of 6.4 volts. Reconnect the meter to TP8 and adjust L4501 for a reading of 6.9 volts.

The two test points and R2177 are at the rear of the IF panel by the audio output transistor T225. You'll notice a 10uF capacitor C2170 nearby. Although it's a good quality component, it's possible this is faulty.
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Old 21st Jan 2021, 3:50 pm   #147
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Default Re: Philips G8 G22K522

Sorry for the late reply, just haven't had to chance really to do the set.

I've just done the adjustments, TP9 and R2177 was reading around 7.2 volts at first and is now at 6.4.

TP8 and L4501 were at something stupid like 2 volts, and the coil was almost hard over to the anticlockwise. It's now almost hard over clockwise at 6.6V but we've a MUCH better picture, and the line-whistle isn't making my ears bleed anymore.

The picture isn't stable with this, as it still scrolls left to right, but it's not slanted like it used to be. As you can see in the photo too, there's also a greeny-yellow/purpley-blue variation that overlays the main image and flies from right to left, and of course, no colour, but one step at a time.

I'm starting to think this set's been the victim of a twiddler.

Thanks all for the help, I really appreciate it
'77
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Old 21st Jan 2021, 7:17 pm   #148
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Default Re: Philips G8 G22K522

Weird discovery, I turned the set on again to see how it'd perform from cold, and there was loss of sync again, adjusting L4501 sort of brought it back to how it was before, with the scrolling, but I noticed if I take my coil adjusting tool out, it loses sync again, but there's not the 4 pictures this time so it's still somewhat of an improvement

Edit: My fault, I realised it's a metal tool, using a plastic one sorted this out. It still scrolls side to side but much slower.

'77

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Old 22nd Jan 2021, 12:01 pm   #149
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Default Re: Philips G8 G22K522

You're losing sync, which does point to the Taa IC or an associated component.
I'm a bit concerned about excessive width and height - cleck the +205v rail. If that's OK you'll need to balance the BU205s.
The lack of colour is possibly just the reference oscillator off lock as I think you can see unlocked colour in the display.
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Old 23rd Jan 2021, 3:41 pm   #150
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Default Re: Philips G8 G22K522

I’m hoping it’s not the IC... I’ll check the other components later on when I’m home, along with the 205V rail. I think it’s running at around 200V, but I’ll check again. If that’s okay, how do I balance the BU205s? Is that the coil next to the green tuning caps which I think was mentioned earlier on in this thread?

I’m not entirely sure if it’d be the cause, or part of it, the colour control seems to just spin, so I’m not sure what condition the pot itself is in, there’s no difference if the control is at the maximum or minimum.

Thanks
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Old 23rd Jan 2021, 6:58 pm   #151
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Default Re: Philips G8 G22K522

Been working on a G8 this afternoon with no line sync. It turned out to be c4520 on the timebase panel. It decouples the emitter of T500. It is 16mfd.

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Old 23rd Jan 2021, 9:25 pm   #152
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Default Re: Philips G8 G22K522

Thanks for the heads up, I’ll give it a check in a bit and let you know.

Thanks
‘77
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Old 24th Jan 2021, 1:47 am   #153
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Default Re: Philips G8 G22K522

Had a check, C4520 in mine was a 33uF cap, I checked the capacitor and it seemed way out of value, so I've ordered some. Hopefully this cures the sync fault, we'll soon find out.

Quote:
It is 16mfd.
As I say, mine was 33uF, so I checked my circuit diagram I have which also said 33uF. Just wondering why they'd be different in our sets? Could it be the VCR modification?

Quote:
cleck the +205v rail.
checked the 205V rail, it's at 191V on the dot. This isn't too low is it? I know some people run them at 195V but it seems to be working just fine at 191V. Not an issue to raise it to 195V if need be.

Thanks for the help
'77
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Old 24th Jan 2021, 6:03 pm   #154
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Default Re: Philips G8 G22K522

When I was at Philips, we used to set the HT to 200V....not official but we got fed up with changing line output transistors and transformers.
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Old 24th Jan 2021, 6:31 pm   #155
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Default Re: Philips G8 G22K522

I've set several of my A823's to around 190-195v whether it makes a difference or not because on occasion the pot has become intermittent and it has shot up to 220-ish volts.

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Old 24th Jan 2021, 10:46 pm   #156
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Default Re: Philips G8 G22K522

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Originally Posted by Sideband View Post
When I was at Philips, we used to set the HT to 200V....not official but we got fed up with changing line output transistors and transformers.
I’ve seen people say 200V too and, as i say, I’ve seen some say 195V too. It’s working fine (well...) at 190V and I’d have thought it’d be even easier for the set at 190V. Should I raise it or leave be? I’m surprised that even a 5V difference improves reliability so much.

Quote:
I've set several of my A823's to around 190-195v whether it makes a difference or not because on occasion the pot has become intermittent and it has shot up to 220-ish volts
Whats the likelihood of that happening with a G8 pot? I’ve cleaned the track so hopefully there shouldn’t be a fault there, but the actual pot itself? In the threads I’ve read I’ve not seen that mentioned on the G8, but as I’ve no prior experience on G8s (or any other set really) I don’t know what does and doesn’t go wrong.

Thanks
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Old 24th Jan 2021, 10:55 pm   #157
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Default Re: Philips G8 G22K522

If the HT goes too high, the power supply tends to 'hunt' giving you a pulsing picture. If you check the setup details there is a 'course' and 'fine' adjustment. I really don't remember the sequence now but I seem to recall that you set the HT pot to 210V then adjust the other so that the picture hunts and then back off the HT pot to 205V....something like that anyway.
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Old 25th Jan 2021, 12:27 am   #158
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Default Re: Philips G8 G22K522

I don't recall a fine adjustment, just a set HT and an overvoltage protection pot.

The pulsating was the overvoltage protection kicking in.

To set the latter empirically, we would set the HT correctly on a meter, then set the overvoltage pot until the picture pulsated, then back it off a bit.
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Old 25th Jan 2021, 11:20 am   #159
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Default Re: Philips G8 G22K522

To answer your question, the balance coil is indeed on the small sub-panel. However the core will be stuck, so it needs to be soaked to free it off. Once you get the sync sorted out then you can adjust this - it's fine for the moment.
As said, around 200v is fine. It's quite well stabilised, but not up to later standards so as long as it hovers around 200v then it's OK. Graham's method of setting up the overrvolts is the one we all used.
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Old 25th Jan 2021, 12:34 pm   #160
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Default Re: Philips G8 G22K522

There is a page on sorting out the stuck core, the information was originally in Television magazine from 1985.
https://www.radios-tv.co.uk/vintage-...tor-balancing/
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