Philips G8 G22K522

[Welsh Anorak]

No - the lack of sync may well affect the colour lock because of the distorted line pulse, but not the other way round. So forget the colour and concentrate on the sync separator and line oscillator part of the TV. I know it doesn't help that it's spread over two boards, but you can't be too far off.

[19Seventy7]

Ohh, never knew that, I thought maybe the colour intensity of the signal could through something in the IF out, throwing out the line hold, though it was only really a thought I had more than anything.

I've possibly got some spare boards being sent to me for me to test with, see which board the fault lies in in my set, so fingers crossed that helps a lot, though don't think I'll be getting them until the week after next.

I did notice that in 'Television' they mentioned the VCR modification could affect line sync, and I noticed one of the caps mentioned was lower in value that what should've been fitted, so I'm going to order the right value and try that

Thanks
'77

[19Seventy7]

Sorry all for a late update

I tried replacing that cap to no improvement. In the end I recapped the entire board excluding two original caps, 400uF and 10uF. I replaced the more modern replacements as my fault finding skills aren't the greatest as you all probably noticed I didn't think it'd do any harm for reliability either.

I do have a question though, off topic, there's a grey lead that either feeds the LOPT, or is fed from the LOPT which can go to one of two connections "Min" or "Max" This is on the line scan panel of course

When I got the set it had been removed so I put it on min. I have no idea what it does but was wondering if anyone has an idea? If I had to guess it could be for width?

Thanks
'77

[Welsh Anorak]

Spot on! Yes, it includes L548 in series with the LOPT winding for minimum and links it out for maximum width.
You know, I don't think I've ever adjusted that.

[19Seventy7]

Oh I'm learning! I actually got the idea from a BT318 I've got, I noticed that has different 'tappings' for width so I thought it could be the same.

That's interesting really, I wonder if they ever did at all, it seems a bit odd to me to not have a mid range too? I suppose if they didnt really need adjusting there's no point.

Thanks
'77

[Welsh Anorak]

It would have given inexperienced repairers something else to twiddle! If the PSU is supplying a good 205v then the width should be correct. If not there's a balance problem in the LOP stage. The tap was just for fine adjustment for the fussier customer.
Of course there were the "engineers" who assumed the set HT presetl was a width control...

[19Seventy7]

That's always fun, I think my PSU is delivering 195v and the width seems okay, though that might change when I have to balance the OP transistors. I'd imagine there were plenty of fussier customers out there too. Two in one control, extra brightness and width! (and x-rays if you're lucky )

No improvement on the sync as of yet. Could it be that the IC is faulty? I'm hoping not as I hate changing IC's but you never know?

Thanks
'77

[Welsh Anorak]

Unusual, but possible. Why not get one of those heated desoldering pumps? You can get one for around a tenner.

[19Seventy7]

I just can't think what else it might be, other than a resistor (or more) though for those I still really wouldn't know which to look at.

How would I know where to look in the circuit diagram? I know the bit we've been referring to, but how would I figure out where abouts to look for a particular fault? - I really don't have a clue yet when it comes to circuit diagrams

Oh thats a better option, I'd been looking at soldering guns, the cheapest I saw was £25 I think? probably do a better job with a pump like that instead. I'll put one of those in the trolley...

Thanks for that recommendation

'77

[Welsh Anorak]

Just keep the nozzle clear and it's an invaluable tool for small jobs.
The G8 isn't an easy one to start on as the circuit is spread over two boards and goes in and out of the chip. Did you mention you might have the loan of one or both boards? That way you'd have a definite answer as to where the fault lies.
It's a steep learning curve but you'll get there!

[19Seventy7]

Will do for sure.

I’d agree with you there. Though I think I’ve started on so many, I have several different project sets on the go, which probably doesn’t help matters.

I thought I did but unfortunately nothing came of it. I don’t suppose too many people are happy lending out their boards which is understandable really. I wonder though... I know of a store with a G8 in the window, wonder if they’d let me borrow the boards from theirs? I’ll have to ask.

It definitely has been a learning curve but I think I’ve learned a fair bit from it. It’s been fun (and frustrating at times) as you say, we’ll get there - after all most of it’s been done with help from you and others. I’d still be at square one if I were alone in it!

Thanks for the help
‘77

[davyrocket2]

Hello you have got my contact details so send me pictures of what panels you want to borrow and perhaps I can come to yours at a mutual time as, I would rather not post them.

Regards, David.

[19Seventy7]

Hi all

I replaced the TBA550Q with a TAA700 to see if that was indeed the fault, after installing it I now get no raster, but the CRT heaters are lit and there is EHT, as I can hear it and the screen flashes when turned off. There's no raster with either no signal or a signal.

Does the TAA700 deal with rasters or do I have a new fault on my hands?

Thanks
'77

[19Seventy7]

I read on a list of stock faults that it could be part of the beam current limiter, I thought with a replacement IC it may now be out alignment, i made a note of where it was and adjusted it both ways with no results so have reset it to where it was

Thanks
'77

[Chris55000]

Hi!

Have you checked all the small fusible resistors (4.7 Ω mostly!) on the line scan panel?

It's very easy to accidentally pop one off whilst fault–finding in this chassis, there's one feeding the 25V line rectifier, and the raster will blank off if that goes o/c, and there's another one (R5539 if I remember correctly!) in the line–pulse feed from the auxiliary winding taps on the line o/p transformer, and again (it depends on the design of the signal panel) you can get either a very dim blank raster or the CRT is blanked beyond cutoff if these pulses go missing from the I.F. and decoder panels!

(If I remember correctly, I think Uncle Les said it was TP39 where these pulses should be!)

I bought all the DVDs advertised up top but I don't know if the full G8 manual was on my set or not!

Chris Williams

[19Seventy7]

I don't think I have knocked any, although possible. I removed the panel not too long ago to redo some possible dry joints, replaced it and tested, and it was still working then, then today all I've removed is the central (I have the 3 boards) tuner/IF panel to refit the IC so haven't touched/knocked the line scan as I push the boards up and out from the bottom.

Though I have had another inspection just to make sure and nothing looks out of place to me. The only 539 I can find is a diode so not too sure, and I unfortunately don't have a scope to look at the pulses :\

Thanks
'77

[Chris55000]

PS!

I strongly recommend you check the 390 k Ω resistor (R1372) between the top of the set H.T. preset and the HT+ 205V line, this has a nasty tendency to wander up in value, causing sporadic increases of h.t. line voltages, and R1386 (100 k Ω) between the a.c. mains and the ramp charging capacitor/diac junction, this can also be responsible for erratic firing of the thyristor – I advise you to bin these two resistors and fit new ones!

Very occasionally the diac can also be responsible for intermittent picture jumping – you can still get these online eBay or elsewhere – it's a four–layer "pnpn" two lead device like a thyristor without a gate connection, and "breaks over" to become a low resistance at about 33–35V, and a replacement can be fitted either way round!

Chris Williams

[Chris55000]

Hi!

You can look at the pulses with a simple diode probe, a 1K 1W resistor in series with a UF4004 or UF4006 diode (positive band end to your meter + terminal), with a polyester cap about 0.01μ @ 400V across the meter terminals will do!

[Sideband]

Originally Posted by 19Seventy7

Hi all

I replaced the TBA550Q with a TAA700 to see if that was indeed the fault,

Are you sure that the TAA700 is a direct swap for a TBA550Q? I've never tried it but then when I last fixed a G8, spares were still available. BE CAREFUL with so-called substitutes. I'll dig around in my bits and pieces to see if I can find a 550Q. Very dodgy trying subs when you don't have the means (a scope) to see what is going on.

Sometimes a sub will work in some sets and not others. You could be chasing your tail and getting nowhere.

[Chris55000]

Hi!

I'm totally in agreement with Member Sideband's note – I think the '550 will replace the TAA700 but NOT the other way round – there have been innumerable small and major design changes during the six–seven year production run of this chassis, many of them concerning these ICs!

I would get the "G8/G9 Mods" file from up top as well as the basic circuit diagrams for one of these, and if you can find a G8 Book in the blue binder on eBay etc., you'll save yourself much heartache by investing in it!

Alas to say mine went decades ago!

Chris Williams