GEC 2121 colour tv from 1974

[marcus 3500]

Hi all

Just started to look at this set i got a spare psu unit off my old mate Tom last year. The picture shows the set connected up to a variac it's running at a current of 680MA and at 220Volts ive ran set at 240V but the picture was still small, any clues anyone to the cause.

Sadly i dont have the service manual all offers of help most apppricated im going to call it a day at 8.30 so sorry if i dont reply untill Tomorrow.

Regards

Marcus..........

[Steve_P]

Are you sure the new unit works!! With equipment this old, a new panel is just as suspect as an old one....

Look in the 1973/4 book for details of the PSU. On the PSU, there should be a pot (R701) for setting the HT. Adjust for 186v at R58/59. (The dropper.) It's worth checking/changing C701, TR701, D701, SCR701, D702.

Check all voltages leaving the PSU.

What are the voltages on the Frame Stages, PC467. The Collector of TR454 should be at 40v. If not, trace it back.

Cheers,

Steve P.

[marcus 3500]

Hi Steve

Just managed to sneak back into the workshop Carol my better half is playing a new game on her phone and little Marcus is a sleep.

The original fault on the PSU Steve was a O/C BT106 making the set dead, i've nicked the BT106 off the PSU Tom gave me because Toms one had a crack straight across it i'll take some voltage readings on Sunday and if i can't find my 1973/4 book i think a copy of tv mag from 1976 deals with this chassis. Thanks for the quick advice mate

By the way if this jogs members memories of GEC first all transistor set do they know why channel neon number 3 and number 6 are flickering and why the neon on the IF board is also flickering.

Regards

Marcus.........

[Steve_P]

The neon on the IF board you can leave for now. As for the tuning neons, the first thing you do is clean the panel where the channels are selected. Thouroughly.

Then, if there is no improvement, change all 6 neons.

Cheers,

Steve P.

[marcus 3500]

Hi all

Today i had a good visual check of all the boards no damage until i looked at the convergence board and blue tilt control P501 is burnt up do any members know the value of this please.

Hi Steve the voltages are spot on 40V line correct and HT checked at R60 is 195V, in tv mag September 1976 it says ( Adjust P701 for 190V plus 5V at point R60)

Think i might swap all the caps on Board PC467 some of them look unhappy, any more ideas anyone to the fault.

Regards

Marcus...........

[Steve_P]

Check the transistors on this panel too. That O/P stage is push pull. If one has gone, change them both.

Also check caps around the Line Output and Oscillator Stages too.

Take that Green Tilt control off and clean the area. It's 500 Ohms by the way.

Cheers,

Steve P.

[mickash]

Hi Marcus, I'd agree with Steve on the cleaning of the touch buttons. A build up of dirt and grease can cause flickering of the neons or annoying random self channel changing. I have in the past had to dismantle the unit to clean all traces of dirt. Faulty neons also do cause these problems. A look at the state of the neons is usually a good indication of the customers favourite channel - the corresponding neon will be more blackened than the rest!

Also be cautious if any of the customer control sliders need cleaning. Certain aerosol sprays will rot the plastic of the escutceon, sometimes almost instantly. The next time you press the on/off button the switch will push through into the cabinet. Avoid Sl in the white cans with red lettering. We learned the hard way after wrecking a few chargeable customers escutcheons!

Sorry, can't help with your pic. fault my memory's not that good but have a look at the elec. caps. on the frame board including the little blue tantalums.

Michael.

[marcus 3500]

Hi all

Hi Michael

Thanks for the advice regarding my GEC cheers mate

Hi Steve

Your spot on with the output transistors TR455 dead short Base Emitter, ill see if i have any.

Regards

Marcus...........

[Mikey405]

Originally Posted by marcus 3500

Your spot on with the output transistors TR455 dead short Base Emitter, ill see if i have any.

Steve is seldom wrong.

I'm looking forward to seeing your set working Marcus - I do like these sets, even though they seem to get through tubes quicker than most TVs.

[Focus Diode]

Interesting comments about CRT life Mikey. I got a 20" model branded "British Relay TV" which had a Hitachi CRT in the mid '90s, untested for a fiver. Turned out to have a superb tube in it. I later put the tube into my CVC5 and is as crisp as ever!

Brian

[marcus 3500]

Hi all

Cheers Mikey i too will be glad when this ones done i feel like pulling my hair out

My problem is my set is fitted with type RCA16334 in position TR455 and RCA16335 in position TR454, the R&T 73/74 servicing book says type ON447 and ON448. Can a kind member please tell me a modern equivalent

Regards

Marcus.........

[FERNSEH]

Very early versions of the first GEC solid state CTV chassis employed BD131 transistors in the circuit positions TR454 and TR455.
The RCA transistors were introduced to address reliabilty problems.

I'm sure that the BD131 is still in current production. Perhaps Maplins still stock it.

DFWB.

[Steve_P]

Charles Hyde do them.

http://www.chsinteractive.co.uk/search.html?query=bd131

So do Grandata : http://www.grandata.co.uk/

Cheers,

Steve P

[Mike Phelan]

As a slight aside, this sort of frame output stage was used in most CTVs of this era, and if you have to diagnose a problem, it is worth remembering how it works, as this is not quite what it seems.
It is indeed a push-pull stage, but avoided needing a PNP + NPN pair.

The 'lower' transistor is a Class A amplifier, and the 'upper' one is a current source acting as a load. Look at where its base goes to and the fact that there is an emitter resistor.

[Studio263]

We handled quite a few of these, my abiding memory of them (aside from the holed punched in the top of the plastic cabinet version (C2111) by owners bashing the set due to the inevitable bad joints on those wretched double-sided PCB's) was that a few of the lower voltage supplies came from an odd arrangement in the emitter circuit of the line output transistor. There were a few spring resistors, a couple of big zener diodes (bolted to the cage around the transformer I think, they look like two-legged BUT11AF-type transistors), a small zener diode on the back of the line output transistor and an electrolytic capacitor, all of which were quite troublesome.
Anyone with an ounce of sense could see that the circuit was all wrong, any overload in the line stage or failure of the line output transistor would cause the disipation in this area to soar, ruining some (or all) of the components. I'd check the voltages around here, leaky zener diodes and open circuit capacitors could cause symptoms like those in your first picture.
I though the Hitachi tubes were quite good, funny colours but they seemed to have a good life.

[Hunts smoothing bomb]

Hmm..

How much current is the set supposed to draw?
680mA @ 220v sounds on the low side to me.

Cheers
Lee

[Dr-Watts]

I had one of these in my shop.
I tell you what Marcus, when I got it running the picture was brilliant !

Dr. Dave

[Welsh Anorak]

Hi
I agree with Mr Studio - that line output stage seemed to be a recipe for disaster which often happened. Those huge zeners - even bigger than a BUT11 - just dissipated watts and the heat dried up the capacitors. Wasn't the little 'I fail all the time' zener 47v? Luckily yours is a wooden cabinet - I'm sure many engineers tilted the plastic version forward only to be rewarded by a crash and a jagged piece of wood-effect plastic in their hand! Add to that the 'where's the on/off switch gone?' problem mentioned earlier and the power supply that would happily deliver anything up to 260v, you would be right to think the old hybrid was regarded with some affection, even when the solid states were quite new.
Good luck with it anyway - any set from the seventies is a rarity now!
Glyn

[Studio263]

47V does seem to be a very familiar value, I think this one was deliberately undersized to protect the others, just like the "fuse diode" in the later ITT models ("80" chassis and derivatives) and the R2M in those late '80's Saisho/Matsui 14" sets (like a poor man's TX90, if you can imagine such a thing!) that Orion made.

The GEC arrangement seems a lot of faff compared to just adding a couple of extra windings on the LOPT. I think the G9 uses a similar idea (though far better executed) in which the key troublemaker is a 2200 uF capacitor that leaks everywhere and causes baffling symptoms.

Ah yes, the mains switch falling inside, hold on, where's the epoxy and the matchsticks...

[mickash]

We used to refer to TVs with this chassis as "Kingsleys" The lettering above the customer controls on some models (can't remember which) was "GEC Kingsley Colour" I never knew what Kingsley referred to but everyone at our firm used that name for similar sets.

Michael.