This "desirable" TV belongs to a collector friend Pete in Albury (about 6 hours on the freeway south of where I live. on the interstate border)
It has a date stamp of January 1967, which makes it one of the last T21 chassis Pedigrees.
The serial number is in the 280 thousands, which gives you some idea of how popular this model was.
Anyway, this one has had a fault in it for many years which has defied the efforts of several techs to track down.
The fault initially was that, over half an hour's running, the picture would gradually shift to the left on the raster by about 20%, leaving a black bar on the RHS and a folded edge on the left.
By last weekend, the fault had become permanent.
Since this circuit is probably familiar to UK techs, I'd be interested to know where you would check first and how you'd track it down.
Some clues - H and V lock is solid, the usual suspects (the selenium double diode and related parts) had already been replaced.
This is the same TV that had the leaky styro cap in the sound.
V6T is the triode of an ECL84, V5 and V11 are ECF80s and V12 is an EL36.
@irob2345 As a quick quess and your mention of polystyrene caps, perhaps one of the two 220pf caps from the phase splitter to the ref diodes. After that the reference pulse from the line stage could be corrupted.
Plenty other options though.
Yes that's what I thought too. Nope!
Let's not draw this out as long as it took me to find it, and I kicked myself when I did.
BOTH 56k resistors on the anode of the sync separator were O/C! Despite this, both V and H lock was strong and the anode measured 12 volts.
What gave it to me was, with the scope on the anode, putting the meter probe there halved the sync amplitude.
But how did it manage to work at all?
My guess is the resistors had gone up in value beyond the 20 megohms I could measure. Or maybe breaking down with applied voltage.
But BOTH resistors? There is nothing there that would make this happen!
Yes I know IRH carbon comp resistors never enjoyed the best of reputations, but an identical failure of two of them in the same circuit?
Anyway, the resultant sync pulses were ramps instead of narrow pulses. I should have picked up on this straight away, but I went down the same rabbit hole you did!
One of the things I did discover is that resistors in the AFC and Line Osc could be as much as 40% high without affecting the performance of the circuit. I replaced them and it made not a scrap of difference!
I used to find that carbon comp resistors in pulse circuits was not a good combination. However given the components of the time there was little we could do to improve the situation. We found that doubling the wattage helped so half watts replaced by 1 watts etc. seemed to give a more reliable repair as long as it could be done neatly.
@irob2345 They were probably too high to read but let enough voltage through to work until one perhaps went O/C completely or many 100 Meg ohms.
Its a decent picture on the set.
Thinking about it since, both resistors were hard up against the 6DX8 (ECL84) video OP socket. A bit of extra heat probably had something to do with it.
Some setmakers used 1W in place of 1/2W fairly extensively in the 50s and 60s. Kriesler comes to mind. In the late 50s they also used Styro caps wherever they could, as soon as they became available, in place of paper.
Of the 3 local brands of carbon comp resistors around at the time, IRC / IRH seemed to be the least reliable, but that might have been because they were the most numerous.
Those resistors would be amongst the last carbon comps made by IRH at Kingsgrove, before they changed over to metal glaze. Just as well, colour happened a few years later. The metal glaze resistors were a huge improvement (they needed to be!), I never saw a bad one. The other resistor makers (apart from Philips) gave up after that.
On the subject of changeovers, the picture geometry on that set is pretty good, n'est pas?
Early in the T21 chassis run, Pye at Marrickville bought a new NC turret winder and started making their own yokes instead of importing them. Guess what CRT was used when the pincushion magnets were tweaked? Yes, a 23HP4, same as in that TV. No wonder it's good!
