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Old 24th Sep 2021, 12:02 am   #241
19Seventy7
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Default Re: Philips G8 G22K522

Quote:
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!
Thanks for that info, i didn't actually know that, ill test them tomorrow, it's a little late now haha.

I'll keep the picture jumping in mind too, should that come up.

Quote:
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!
If i don't sort this fault too soon, I'll try that, just as I don't have any of those components in stock so would have to buy them all!

Quote:
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.
I went with the TAA700 as thats the one that was mentioned the most, so I thought that possibly the IC had been swapped over at some point and the TBA550Q wasn't a suitable replacement, hence the fault. I'll order a TBA550Q now to try. Shame the TAA700 didn't work.

HOWEVER - The pitch of the line whistle didn't change like it did when the picture had no hold, so it's looking sort of promising!

Quote:
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!
Well that would make sense! Didn't realise there was a modifications file, I'll download that now. I have a circuit diagram but it's pretty much useless to me as I haven't much clue how to read them! I use it to try and follow what others have said, and find components easier.

I've been looking for one of those blue books for a while now, I've only seen one on ebay. One day!

Thanks
'77
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Old 24th Sep 2021, 8:00 am   #242
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Default Re: Philips G8 G22K522

You must look at what is on the circuit. I am quite sure that Philips have clearly marked the chip as a TBA550Q so that would give no doubt whatsoever as to the correct chip to fit. As to your other comment about the circuit not meaning much as you haven't much clue how to read it....I suggest you get some practice in! Hoping and poking at a complex circuit is not going to get you far, you won't learn much and it could be expensive in just changing parts for the sake of it.

Anyway you need to replace like-for-like and another word of warning...if you come across a chip with an A or B suffix (example TBA550AQ) and you have a TBA550BQ don't assume it will work! Very often there are subtle differences within the chip and possibly some component changes on the PCB so using the wrong suffix can be the difference between the set working or not working. Been there done that and got several T-shirts!
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Old 24th Sep 2021, 10:51 am   #243
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Default Re: Philips G8 G22K522

Seconded. Thiis is particularly the case with Philips TVs. For example the line oscillator IC in the 320 mono had to be exactly correct or else it wouldn't work. Find the correct IC then let's see where we are.
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Old 24th Sep 2021, 4:21 pm   #244
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Default Re: Philips G8 G22K522

https://worldradiohistory.com/hd2/ID...50%20taa700%22

Lawrence.
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Old 24th Sep 2021, 8:44 pm   #245
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Default Re: Philips G8 G22K522

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Originally Posted by Sideband View Post
You must look at what is on the circuit. I am quite sure that Philips have clearly marked the chip as a TBA550Q so that would give no doubt whatsoever as to the correct chip to fit. As to your other comment about the circuit not meaning much as you haven't much clue how to read it....I suggest you get some practice in! Hoping and poking at a complex circuit is not going to get you far, you won't learn much and it could be expensive in just changing parts for the sake of it.

Anyway you need to replace like-for-like and another word of warning...if you come across a chip with an A or B suffix (example TBA550AQ) and you have a TBA550BQ don't assume it will work! Very often there are subtle differences within the chip and possibly some component changes on the PCB so using the wrong suffix can be the difference between the set working or not working. Been there done that and got several T-shirts!
The circuit diagram also lists it as a TAA700, so I’m a little unsure, I’ll try the 550Q and see where that takes us. I googled the difference and they were said to be almost identical electronically - I guess just not enough!

I’m getting better with circuit diagram reading, I know the basics but thats about it, though I am very slowly learning. There’s not many places online (That I’ve found) which teaches you how to read more complex ones. Though I have to say as much of a hassle this set has been, it has taught me a lot

I’ve got an IC in the post so shouldn’t take too long to get here. I’ll fit it and post results ASAP

So i take it they’re somewhat interchangeable in some circuits, and not in others

Thanks
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Old 25th Sep 2021, 9:11 am   #246
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Default Re: Philips G8 G22K522

I think you need to know which BA version you have. Curiously, my book has most of the versions of the twin panel signals unit to BA06 which all appear to use a 700. However the spares list also has a 550 under a different part number! The combined panel used a 550 exclusively and there are some differences between this circuit and that using the 700.
Short answer - wait for the 550 then worry
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Old 25th Sep 2021, 5:53 pm   #247
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Default Re: Philips G8 G22K522

Sods law…

I have detailed photos of all boards except the one we need! Just out of curiosity I’ll take a look later. Shouldn’t take too long for the 550 to get here and get fitted and then I’ll report back

Thanks
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Old 25th Sep 2021, 6:37 pm   #248
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Default Re: Philips G8 G22K522

Hi.

In part 2 of Mike Phelan's servicing article on the Philips G8, TELEVISION magazine, July 1978, he quotes:

"Video IC Faults

The two types of video i.c. TAA700 and TBA550Q
differ only in the way the pins are bent - also the
TAA700 has wider pins. So it's possible to interchange
them. A faulty TAA700 can give no video at all, no sync,
or what appears to be a black hum bar, with a buzz on
sound, variable by the a.g.c. crossover control. The TBA
550Q can give any of these faults plus no field sync and a
noisy picture due to faulty a.g.c. action."

Regards,
Symon
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Old 25th Sep 2021, 8:24 pm   #249
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Default Re: Philips G8 G22K522

Hi!

Still on the subject of G8 books, I believe the Original G8 Loose–Leaf Blue Binder didn't go up to the combined signals panel, that was covered by a thin floppy paper covered "550" manual in the dark blue cover with silver lettering!

Oh yes, if you do get a Combined Signal Panel to try in your set, please don't forget to look at resistor R3212 (750 kΩ) connected from the brightness clamp pin of the '560CQ to the +205 V h.t. line, if this goes high in value or o/c., you get a raster that's black on the left and gradually shaded to white on the right, sometimes with hazy monochrome picture content on it, sometimes not, depending on how the '560CQ likes not having the d.c. clamp bleed current that should come down from the h.t. supply line!

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Last edited by Chris55000; 25th Sep 2021 at 8:34 pm.
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Old 25th Sep 2021, 10:44 pm   #250
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Default Re: Philips G8 G22K522

Quote:
"Video IC Faults

The two types of video i.c. TAA700 and TBA550Q
differ only in the way the pins are bent - also the
TAA700 has wider pins. So it's possible to interchange
them. A faulty TAA700 can give no video at all, no sync,
or what appears to be a black hum bar, with a buzz on
sound, variable by the a.g.c. crossover control. The TBA
550Q can give any of these faults plus no field sync and a
noisy picture due to faulty a.g.c. action."
Funny it mentions the wider legs, as i had to spend some time carefully trimming the width down so they'd fit, and trying to get the pins bent to fit. It may be entirely possible that i've damaged a connection inside. I doubt it as I was very careful but not impossible. I'd also imagine there's just as good a chance it was already faulty.

I'll keep in mind R3212 if i do get a combined panel to try. That'll 100% be my next step after trying this 550Q. I think I actually saw a post on VRAT about R3212 failing.

Thanks all
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Old 29th Sep 2021, 9:06 pm   #251
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Default Re: Philips G8 G22K522

Hi all

Just an update, i've fitted a 550Q and have got an unlocked raster (Which will of course need adjustment) But thats only when I've got EHT, which is never very long. There's obviously a dry joint somewhere but I just cannot find it, I've reflowed the PSU and the Linescan panel both, and have gone over the other panels and any joints that looked questionable. I've always had this issue of a dry joint preventing the EHT from kicking up but never this bad and has always been solved with a quick smack - Not even a beating is working now.

I just wanted to give an update to say that the 700 was at fault, but unsure yet as to whether the original 550Q was faulty too.

Now on to reflow even more joints - again

Thanks
'77
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Old 29th Sep 2021, 9:24 pm   #252
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Default Re: Philips G8 G22K522

This is where you need a scope. You'd probably locate the area of the fault in a few minutes. We only had an hour and a half to find faults on these when in the Philips workshop. It rarely took that long except perhaps with a tube change. If it looked like being a nasty intermittent, we could fall back on the replacement panel solution. We didn't do that often as they were basically reserved for the field engineers who were always on a tight schedule.
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Old 29th Sep 2021, 10:04 pm   #253
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Default Re: Philips G8 G22K522

I'd like to get a scope but i really don't have the money to get one and an isolation transformer, unfortunately. I'm going to go over any that still look poor and remove the solder completely, and give it fresh solder, hoping that works.

Thanks
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Old 30th Sep 2021, 11:13 am   #254
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Default Re: Philips G8 G22K522

Might be worth having a look at the small sub-panel beside the LOPT - the one with the balancing coil on it. Also have a look at the plugs and sockets between the line driver and output panels - pull each wire gently in case there's a bad connection there. Also check the screws on the output transistors for tightness.
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Old 30th Sep 2021, 12:12 pm   #255
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Default Re: Philips G8 G22K522

Hi!

Another tip I've just remembered in relation to the line output transistor balancing coil – if the core has a hex hole, you can use one of the plastic knob adjusters from the timebase or convergence panel (some of the very early line scan units came with a knob adjuster already clipped to the balance coil) to assist in adjusting this!

(Don't forget to give the core of the balance coil a squirt of WD40 before attempting to move it!)

I recommend you also remove the line driver transformer from the line scan PCB, clean up it's pins with a fibre–pen, thoroughly tin the pins with fresh solder then refit to the panel – a lot of cases of jumping width and intermittent line transistor failure can be attributed to invisible dry joints on this transformer!

If the wirewound line shift potentiometer R5555 in the middle of the panel is scratchy or burnt, turf out the BA148 line shift rectifier and the electrolytic across the control and replace with new ones before you fit a new line shift pot!

Chris Williams
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Old 14th Nov 2021, 10:42 pm   #256
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Default Re: Philips G8 G22K522

Hi all, I come bearing news!

I hadn't worked on the G8 for a while as I like to swap sets around when working and make progress slowly on each one. I felt like coming back round to work on the G8 and searching for the dry joint. I believe it was on the balancing coil, but I'm not 100% sure.

(Chris, I apologise, I somehow never saw your post until now, but I will certainly look into all of them before I next switch on. I hadn't heard of fibre pens until now but looking into them they sound very helpful, I'll have to get one! I've not yet had to work with R5555 so we'll see)

On switch on the EHT rustled up, sounding slightly off, but I expected that, I got a raster which was unlocked, so I tried adjusting L501 which didn't do anything. I switched off to go get a mirror from another room and switched the set on and was met with a horizontally locked test card! The picture rolls vertically very slowly but I'm chuffed to have got a lock on the horizontal. 3 days short of having had and worked on the set for 2 years!

There's still faults to be cleared, such as the lines on photo 3( I'm not sure if they're flyback lines, but I don't think they are) But we're finally getting somewhere now we can actually see something on screen!

Thanks
'77
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Old 15th Nov 2021, 9:28 pm   #257
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Default Re: Philips G8 G22K522

I have further news!

I realised I had accidentally left the yellow fly lead from the signals board unconnected. I reconnected thinking maybe that could help with the vertical hold, turned the set on and the line frequency was way out, so I disconnected it again to make sure and I had line hold again, but still no vertical lock.

I thought to re-read the voltages on TP8 and 9 as I'd changed the IC and wondered what difference it would make. Turned the set off, connected up, and turned on to a fully locked test card, both vertically and horizontally. I was getting a reading 6.2 volts on TP9, but with a locked raster I didn't check TP8.

Still some niggling faults but at least we've a picture we can work with!

'77
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Old 21st Nov 2021, 11:38 pm   #258
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Default Re: Philips G8 G22K522

I've worked on the set some more and managed to get the height and linearity better, the circle is now closer to a circle, not fully yet.

The lines I mentioned are gone, and were in fact fly back lines, but i think I'll need to redo them as it's pretty dark, even with brightness near full.

I have a massive purity splodge which needs curing, too big for internal degauss to deal with, so need to find a way to manually degauss.

The faults left are red striations on the left of the screen, as seen in the picture. (Manual says to change R5554 but I can't see a 554 on that board) One of the blue convergence pots has broken and so I can't converge properly, but it's not too bad on actual video so not to worried about that at the moment, a broken, but functional volume control and some lines at the top of the screen, also seen in the first picture.

Does anyone have any idea what the striations could be, the stock faults list I have says

Quote:
R5554 (1.5Kohm replace with wire wound).
but like I say, I can't find R5554 at all, anywhere.

Slowly getting there though!

Thanks
'77
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Old 22nd Nov 2021, 10:11 am   #259
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Default Re: Philips G8 G22K522

Check lead dressing first. Striations like that can be caused simply by video leads draping over or too close to the timebase or line scan boards. Perhaps try moving any long leads with an insulated rod (knitting needle) and see if you can improve it.

I was caught out once and had really severe cogging and striations when I was just starting out repairing these at Philips over 40 years ago. The 'old lag' engineer next to me didn't even turn round to look at the fault. He just said 'Is the RGB lead to the CRT base trapped around the signal board'? (it was). I untangled the lead and clipped it up....instant cure! So be aware of silly things like this.
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Old 22nd Nov 2021, 7:11 pm   #260
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Default Re: Philips G8 G22K522

Thank you, I think there are a couple leads draping over the timebase panel so will have a look into that. Would never think something like that, overlook the simple and assume the worst!

If that doesn't work I also found this

Quote:
The trouble with this set is a narrow vertical orange strip on
the left-hand side of the screen. There seems to be some
ghosting associated with this.
This symptom usually arises when there is a fault in the
application of flyback blanking to the decoder board. Check
the connection from F5 on the timebase panel to D9 on the
decoder panel for continuity. Then if necessary check the
flyback blanking transistors T4488 and T4524 on the
timebase board, and for breaks in the print, including the
edge plugs, on both boards. On the earlier separate decoder
board there could be a faulty component in the blanking circuit, for example C7213 (1µF). If the combined signals
board is used, check C3216 (1µF), D3218 and the
TBA560C chrominance/luminance processing i.c.
So hopefully will get a cure soon from one of these.

Thanks
'77
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