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Old 27th Aug 2020, 11:42 am   #1
cmjones01
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Default Philips 14CF1114 (CF1 chassis) - no colour

I've had this Philips 14CF1114 since it was new in 1986 and it's been in use most of that time. It's an unusual variant of the CF1 chassis with audio, video and RGB inputs. It spent its youth connected to our family BBC Micro, and I still find it handy around the workshop. The separate connectors for audio, video and RGB are much more convenient than a SCART socket for experimenting and testing things with.

It's been unused for a few months (I had to shift it out of the way to set up my Covid-19 lockdown home office) but I went to use it yesterday and found that the PAL decoder no longer works. It produces a perfect black and white picture. I tried more than one video source with the same results.

I tried twiddling the tuning capacitor on the 4.43MHz crystal. Over most of its rotation, the picture was resolutely monochrome, but sometimes I'd get a "coloured" picture, with all the colours wrong and very strong Hanover bars.

The decoder is a TDA3561A. I tried cleaning the pins and socket and reseating it in its socket (it's given trouble before) but with no effect.

Before I dig in further and start measuring things, does anyone have experience of this chassis and could point to a likely cause?

Thank you
Chris
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Old 27th Aug 2020, 12:17 pm   #2
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

Hi,

I recall many years ago, a fault report in 'Television' magazine, in which a set (I can't remember the make or model number) containing a TDA3562A displayed a similar issue to yours. It turned out to be hash on the supply rail to the I.C. due to poor regulation of the supply.

The implications were that it can be a fussy device if the operating conditions aren't correct. I believe it was one of their 'Test Case' puzzles, which they used to run.

Regarding your fault, I wonder if it would be worthwhile scoping the supply rail of the TDA3561, to ensure it's within specification, with no hash or ripple?

Adrian.
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Old 27th Aug 2020, 6:39 pm   #3
John123
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

Indeed, it might be one of those caps surrounding the chip. Perhaps give old hairdryer and freezer spray trick a go. It'll either be a rogue cap, the crystal, trimmer, or (worst-case scenario) the chip itself.
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Old 27th Aug 2020, 8:31 pm   #4
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

I'd suspect the trimmer first. No need to blow greenhouse gases into the air just yet.

Maybe note it's position and give it a good tweak.
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Old 27th Aug 2020, 9:06 pm   #5
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

I agree go for that green trimmer , these gave trouble in Sony & Matsui .
Sony had a mod replace trimmer with a 13pf Cap

Derrick
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Old 27th Aug 2020, 10:41 pm   #6
cmjones01
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

Thank you for the thoughts about the trimmer. If it was open circuit, I guess there's a chance the oscillator might stop altogether or be way off frequency. I'll investigate that when I get a chance. Need to clear space on the workbench for the set!

Chris
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Old 28th Aug 2020, 7:51 pm   #7
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

another thing we had with them was the i/c socket used to remove it and solder the i/c direct to the board .it was usually that or the crystal
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Old 28th Aug 2020, 11:18 pm   #8
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

Hi.

I never came across any faulty TDA3560 and TDA3561 single chip decoders so these ICs seem to be quite reliable. It may be worthwhile overriding the colour killer by connecting pin 6 to the 12V rail (see attached Mullard data). Pin 6 is for saturation control and is normally in the range of about 2 to 4V. This will vary according to the setting of the customer colour control. The interesting point is this voltage will appear to be low and uncontrollable when the colour killer is in operation which may be due to the reference oscillator being off frequency.
As has been suggested, the 22pF trimmer cap is worth a check as is the 4.43MHz crystal.

Regards,
Symon

EDIT: As is always the case, certainly worth checking the 12V supply rail and for ripple as has been suggested.
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Old 2nd Sep 2020, 5:25 pm   #9
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

I'd also be tempted to remove the socket and solder direct to the PCB, especially if you have a known good IC to replace it with. Socketed decoder ICs weren't a good idea IMHO.
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Old 30th Nov 2020, 11:20 am   #10
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

A quick update on this. I've just done some more investigation but with no luck so far. Chroma is definitely getting to the TDA3651A chip, and the reference oscillator is running but I can't check the frequency accurately because I don't have a frequency counter at home. According to the scope, it's running at "a bit less than 10MHz" which is probably about right but I'd like to check properly.

I tried substituting the trimmer - no change. I couldn't find an 8.86MHz crystal in my spares box so will have to order one.

The colour killer is definitely operating, but twiddling the crystal's trimmer seems to override it and give incorrect colours.

There are a couple of low-value electrolytics in the reference oscillator loop filter. I tried substituting those - no joy.

In the process of dismantling, I've discovered a green wire hanging off the CRT's dag with a blade connector on the end and can't figure out where it goes. There's another, black, one which is correctly connected to the CRT base PCB but this other one remains a mystery! It's unlikely to be connected with the fault, though.

Chris
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Old 30th Nov 2020, 11:45 am   #11
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

Just in case, have you checked the colour control is supplying a varying voltage?
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Old 30th Nov 2020, 11:45 am   #12
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

...unless the missing 'dag connections caused electrostatic damage to the TDA3651A??
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Old 30th Nov 2020, 2:32 pm   #13
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

The colour control is definitely working, and the voltage from it is present and correct when the colour killer is not operating. When the colour killer is on, the control voltage drops to nearly zero as expected.

Chris
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Old 30th Nov 2020, 7:02 pm   #14
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

I also got rid of endless I/C holders in the Philips range. It is a simple matter of unsoldering the holder with a pump or wick, quilling the chip and soldering directly to the board. It was a very common no colour fault. I never had a faulty chip. J.
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Old 2nd Feb 2021, 1:36 pm   #15
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

I hadn't had time to look at this for ages, but needed to use the set for something else today. I had to take the back off to adjust the vertical hold to suit a 60Hz source, and while the screws were out curiousity got the better of me again and I had another look at the PAL decoder (from an actual 50Hz PAL source, of course). I had bought some replacement crystals so tried fitting one. That changed the behaviour. Now, when I connect a colour signal to the set, it appears at first in black and white but twiddling the trimmer next to the crystal will lock up the decoder and produce correct colour. There's then an optimum position of the trimmer where the hanover bars are minimised. Either side of this, obvious horizontal stripes are visible on a picture showing colour bars. Once it's locked, it stays locked, and isn't intermittent, and no amount of twiddling the trimmer will break it. Disconnect and reconnect the signal, though, and it's back to black and white.

So it's got better, but still isn't right. I haven't checked the supply rails for ripple yet. No time for that today.

Chris
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Old 30th May 2023, 12:29 pm   #16
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

Thread reopened at OP's request.
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Old 30th May 2023, 2:16 pm   #17
cmjones01
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

Thank you for reopening the thread. I've recently had time to take another look at this monitor because I'm determined to get the PAL decoder working properly. I've now got a colour picture out of it, but it's definitely not quite right. The attached picture shows as good as it gets. Note the distinctly pinkish tinge to the red bar, and very strong Hanover bars (I hope they're visible in the picture).

The symptoms are that it will show a colour picture reliably now, but the colours are just a bit wrong, especially red, and there are these very visible Hanover bars. Twiddling the 8.86MHz crystal trimmer C2223 makes the colour come and go and can dramatically change the hue of the picture. I'm sure that's not supposed to be possible in a PAL decoder!

Adjusting the delay line balance control R3216 changes the picture from monochrome at one end to oversaturated with rather dimmed luminance at the other end. That doesn't feel quite right either, though I don't have another set to compare it with.

The colour killer is definitely working, as extreme adjustments of the crystal trimmer drop the colour out leaving a monochrome picture.

I've tried:
- replacing the TDA3561A's IC socket
- replacing the IC itself (with two different ones)
- replacing the crystal (with three different ones)
Replacing these parts just changes the place on the crystal trimmer's rotation where the "best" picture occurs, which is pretty much what I'd expect.
- I've added decoupling to the TDA3561A's supply. No change.
- I've replaced the loop filter components between pins 23 and 24. No change.

The luminance and chrominance inputs look fine on a scope, and the sandcastle pulse is present and correct, though it extends a couple of microseconds longer than the actual colour burst. I don't know if this matters or not.

Help! Nothing seems to make any sense...

Chris
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Old 30th May 2023, 9:18 pm   #18
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

Hi,
i'm not very good for TV troubleshoot, but i'm pretty sure of this :
philips aluminium capacitors can really go bad, and i see 3 of them in the TDA area.
if you can check them, do it. otherwise, replace them.
on the schematic sample you put here, check the 2,2µF, 1µF, 4,7µF (specially this one, as it seems in coupling)
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Old 30th May 2023, 9:36 pm   #19
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

Have a go at replacing C2218 (2.2uF) connected to pin 5 of the IC, and also check R3600 (18k) if brightness/ contrast seems low.

*EDIT* Post crossed with above.
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Old 31st May 2023, 11:52 am   #20
cmjones01
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Default Re: Philips 14CF1114 (CF1 chassis) - no colour

Thank you for the suggestions. I subsitituted those small electrolytics and found that C2228 (4.7uf) was leaky, probably because it's spent its whole life running with no bias voltage. I fitted a replacement and the decoder was much better-behaved about locking to signals, but the weird hue errors remained. I found that, with the saturation turned up, reducing the contrast would leave only the blue component the picture visible! It was possible to vary the colour balance of the picture using the brightness, contrast and saturation controls. I checked all sorts of things, the components round the delay line, the clamping capacitors round the RGB output stages of the chip, nothing seemed to help.

Eventually I decided that the only things that could cause hue errors would either be the matrices in the chip itself, which I'd eliminated by substitution, or the one component whose job is to eliminate PAL hue errors: the delay line.

I popped the top off it and found that the crystal inside had shifted a bit, leaving two of the connections just barely shorting. I pushed it back to the correct location, refitted it and...we have correct colours!

So there were two faults: leaky C2228 causing reluctant lock, and an actual mechanical problem which resulted in odd hues. I won't forget this one for a while!

Chris
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