Odd fault with GEC 2028

[Hunts smoothing bomb]

Hi all,

I was giving this set a bit of attention today and a strange fault has come about, I'm wondering if it is where I have moved the chassis about from the service position and back again.

It was fine and now all of a sudden the picture cannot be resolved unless the aerial is pulled half out attenuating the signal. If it is pushed fully home there is no vertical lock, if you adjust the vertical hold as best as you can then you see that the picture is very patterned like it is not properly tuned, no amount of tuning corrects this. Pull the aerial half out so it is attenuated again and you get a good colour picture albeit with weak vertical lock.

Any ideas as this is puzzling me no end.

Another question, what does ACC stand for? it is an adjustable POT in the decoder that appears to depict how much saturation the front panel colour control has.

Cheers
Lee

[Red to black]

ACC = Automatic Colour Control

A sort of "Automatic Gain Control" for the Chroma level, independent of the signal level/strength.

[FERNSEH]

Seems you have an AGC fault. Might be something simple as a lead come away from the tuner.
I've got the service manual here so I can do some swotting up on the 2028.

DFWB.

[Hunts smoothing bomb]

Hello David,

Thanks, it's appreciated, I'll see if I can get some time today/this evening but probably won't be able to have a look at it until tomorrow night, I also have the manual so will have a look at the area controlling the agc.

Cheers

[dazzlevision]

Originally Posted by FERNSEH

Seems you have an AGC fault. Might be something simple as a lead come away from the tuner.

Hello,

Several individual wires from the two tuners push onto the "pins" visible on top of the IF panel's 405-625 system switch. Maybe one has come adrift or is in the wrong place?

Regards,

Dazzlevision

[FERNSEH]

Two types of UHF tuner have been fitted in the 2028. Early sets employ a Philips sourced tuner employing two AF186 germanium transistors. Later sets designated 2028A use a UHF tuner equipped with silicon transistors, two BF180s.
The AGC connection in both early and late models is PC8 on the IF board. PC1 supplies the switched 20 volts to the UHF tuner.
Transistor TR12 (BC107) is the AGC inverter, not used in 2028A sets.
I believe PC8 is a push-on connection on the system switch SW103.

DFWB.

[FERNSEH]

From the 2028 service manual. Information and modifications for sets that use the later tuner with silicon transistors. Models 2028A and 2028B.

DFWB

[Hunts smoothing bomb]

I have now found the issue and resolved it, it turns out that when I made adjustments to the set at the weekend I over tweaked the preset contrast!
Had me on a bit of a goose chase for a while but it's working well again now.

Cheers

[mark pirate]

Nice to see you got it sorted, Picture looks great
I really regret selling my 2028 on, it really did have an excellent picture.

Mark

[Peter.N.]

Excellent picture. Very nostalgic that, I had quite a few of those out on rent in the '70s, later replaced by the single standard one, forgotten the model number now but they were Granada sets with a different power supply to the GEC version.

Peter

[ukcol]

Originally Posted by Peter.N.

Very nostalgic that...

Same here, my first CTV repair was a GEC 2028 (short circuit HT rectifier).

[bc312]

My first colour TV repair too. At the time - around 1983, I was working in a Post Office Telephone Repeater Station, and used to do the odd radio and TV repairs when the station was quiet. Chap brought in this 2028 with poor colour purity at the edges of the CRT. No amount of external deguassing would clear the problem, so the chap decided to buy a new set and sold the 2028 to me for £10. I eventually resolved the purity problem by placing some small permanent magnets in strategic positions around the tube - not perfect but ok from a viewing distance. It became the station set - a very nice design and from which I learned a great deal about how colour TV's work, together with books written by the late Gordon King. Finally gave the set to my parents who had it running for another two/three years before moving house. Happy memories.

[FERNSEH]

The GEC 2028 was my first colour TV repair, and that was in 1968. The fault condition was "no colour". Fault finding was considerably simplified because the 2028 has that "colour beacon" lamp. The lamp was not lit up so we know that the fault must be in the early stages of the colour decoder.
Disabling the colour killer showed unsynchronised colours. The sub-carrier generator had gone off frequency.

DFWB.

[Peter.N.]

The 2028 was my first ever colour TV and it terrified me. I used to buy ex Granada TVs from John Carter in Nottingham, later in Ilkeston, I had bought many mono TVs which didn't pose much of a risk but I was very fearful of getting a colour set with a duff tube as the sets were very expensive in the early days, about £60 in the '70s. Ther were only a few available initially and you had to arrive early before the lorry came in and then there was a scramble for maybe half a dozen colour sets.

I never did get one with a u/s CRT though but colour was a whole new ball game and I was on a very steep learning curve for the first six months or so, I even had to buy myself a scope!. I got there in the end though and then the 2040 single standard set and I eventually had about 150 out on rent, I could live off that, how things have changed.

Peter

[Hunts smoothing bomb]

The colour beacon on mine is very finicky to light, at best it glows very dimly, that's if it comes on at all!
All the same it is a lovely set.

Cheers

[Focus Diode]

R51 which feeds the colour beacon should be 390 ohms. Seems common for the wrong value resistor to be fitted from new, suggesting the beacon must never have worked properly.
It's easily found, close to the bridge rectifier on the right underside of the chassis.
The beacon is beneficial in detecting no colour faults. If the fault is in the CDA stage the beacon will still light but not if there's a fault in the decoder.
Brian

[Hybrid tellies]

That looks nice, glad you sorted it.

[gec2110]

The picture is really brilliant, did not realise that these sets showed such a nice warm picture. The ones we used to have at British Relay were unreliable and showed awful colour pictures
Any chance of a photo of the chassis ?

[Hunts smoothing bomb]

Hi gec2110,

I'll take some pictures tonight and post them if I get chance.

Cheers

[Nuvistor]

Surprising how good the colour pictures were on some early CTV's, I think the CDA drive as opposed to RGB drive helped. Thats just an opinion though, perhaps the sets I saw with RGB drive were not quite not the best although new and set up correctly.

Frank