Despite roadworks and a plane crash I eventually got to NVCF on Sunday afternoon, where I met Steve (colourstar) who had two Rediffusion TVs for me (Thanks Steve !)
I got the MK13 on the bench first as it is a worker, now I've not seen the insides of one of these before, quite a departure from the MK10,11 aerial and cable sets. Odd looking LOPT, but neat construction with servicing in mind. The set is fitted with a Unitra CRT from Poland, it seems to have an defect in the glass under the face-plate, I'm surprised that passed Rediffusion QC even if Unitra let it go ! Maybe large screen CRTs were in limited supply by the mid-late seventies.
The set works with a nice picture but seems to have an intermittent fault with line drive, sometimes the line output stage will just sit there valves lit but no oscillation, there is no overheating or distress from the PL504 then eventually it will just start.
I've not got a circuit for the MK13, just the field service technicians handbook, layout and fault finding only. This is a nice set, which I think will be worth a cabinet clean up.
I've not got a circuit for the MK13, just the field service technicians handbook, layout and fault finding only.
Have a word with David Till Eulenspigel @till I believe he has the full service manual for the MK13 chassis as he used to rent a fair few of the sets out to his customers.
Here is the brochure picture of your set
The last production run used these type Polish CRT. They often gave a green cast to the picture. The line stage pcb should be checked for dry joints, the single plug socket often gave int line probs. The 47k resistor at the top of the pcb was a common fault for low line drive/small pics. The t/b board has a large w/w resistor which gave int no line probs when dry jointed. Dark pics are due to the focus slider u/s. All in all a very reliable, well made set, wish i had one, Malc.
Did those Polish CRT's also not have a very course phosphor?
Hi Mark, it was really good to meet you at the NVCF Mark and hand over the sets.
I think this Mk13 is a late example with date codes on the components and inside the back cover suggesting 1978 if memory serves. The 'lazy' line oscillator is an odd one. The set will sit there quite happily with the valves glowing, then without any poking or prodding will suddenly start up after a few minutes when it's good and ready.
Despite having a transistor audio stage, the sound arrives at the same time as the picture comes through. Presumably it derives it's power from the valved line stage.
A very nicely made set. Hope it revives some good memories for you!
Hi Malc, yes the phosphor is noticeably coarse on close inspection. Even the flat sides of the crt where it pushes through the cabinet have a strange textured feel to them!
Top quality large screen monochrome CRT’s were difficult to source in the late 70’s, all the manufacturers had to source from wherever the could.
Extracts from the Mark 13 service manual.
Thanks for circuits, I've got the line/frame drive board out of the set in about 30 seconds, then whipped the line output board out for good measure. A 1/4" nut spinner is all you need (50p at local car boot sale), these TVs must have been a dream to service in the field if you had a kit of working boards. So much easier to inspect for dry joints and cold check components with the board on the bench, Rediffusion must have spent a lot of time thinking about serviceability of their products, it lasted through to the MK4 colour sets.
In the 1970s a few manufacturers designed their sets on a modular basis so that the boards could easily removed & replaced by another, with the faulty board being taken back to the workshop for fixing.
I've taken another look at this TV and it turns out the intermittent no line oscillation was due to a dodgy PL504, I had a boxed NOS and with that in it starts every time.
But there is now another intermittent problem, after about 10 minutes of operation, the picture shrinks to nothing over about a minute then sound drops out too, the line output is still oscillating and the drive to the PL504 is OK but the boost volts drop down to nothing, Ive tried a different PY88 but it was not new, there does not seem to be any distress or overheating and the set works normally if switched off for about 30 seconds ? Its very intermittent though, sometimes it will work for hours.
I think I may have mentioned that the set performed a similar trick just before I passed it to you. I had it running then looked up a few minutes later to see the picture had vanished. I noticed that a large metallic blue cap on the line timebase board was hot to the touch. This was the day before the NVCF so I didn't have time to look into it further. I assumed it was the boost cap in distress, although I admit that's a guess as I had no service info.
Very smart looking set and servicing this looks great with the boards being easy to remove like that. It sounds like that boost cap is causing the issues going by Steves post. Hopefully changing that will cure the fault..Nice looking picture it has too, a healthy tube no doubt. Cheers Glen
My money would be on the boost cap too! Really nice looking set very much of its era and in a similar vein to the Rediffusion MK1 colour sets too.
I see another of my sets has found a new home. and again nice to see it working ?.
After a few months use as my workshop TV, the boost capacitor gave out with a bang and spilled its guts, I've got replacements but does anyone have details for the correct setting of the boost voltage, LOPT has a label saying set for 570V.
What type of capacitor was it, mixed dielectric were popular in the 70’s for various locations but across the mains and boost capacitors seemed to stress them. Presume the spikes were the problem, on the other hand we didn’t have many other options.
Can’t help with the boost voltage but if the TX states 570v I would go with that.
An Erie cap indeed. A ghost of it's former self.