CTV [Sticky] 1974 HMV 2726 Coloumaster; Thorn 4000

@jayceebee I was about to suggest trying the 3C03's decoder in the HMV, assuming it's compatible.

The signals module out, I notice R161 has now failed. Not related to the decoder troubles, but certainly explains the pops and buzzing I've been getting on sound. I don't think I've got a Thick film 15R 4W, I'll stick in a non TF component.

If it does turn out to be faulty and UDL14 or 15 doesn’t turn up then I’m sure with a few circuit changes a later type could be made to work.

Posted by: @cathovisor

@jayceebee I was about to suggest trying the 3C03's decoder in the HMV, assuming it's compatible.

From the pictures it looks an early version with some differences around IC155, also it is an export board but reworked for UK. It still has an ELC2000 VHF/UHF tuner but I suspect it would be a drop in replacement and work OK.

EDIT. Sorry I thought you were talking about the whole signals stage. All the different chroma boards 428, 430, 438 are compatible with no mods required I believe.

@crustytv I'm looking at that distress mark where it's cracked and am thinking "why?"

No reason other than thick film resistors are s***. The sound circuit supply is oh so simple, it takes 33V from the SMPSU, R161 and W163 (3.6V) zener drop the supply to 28V.

More reliable cement installed, and for added protection I made it a fused one, even though the IC has a max rating of 35V

That wirewound doesn't look out of place either. Audio stages can be all the wrong kinds of fun, of course and great at blowing fuses when you least expect them to.

Beware the bent pin in the adjacent grey chassis plug, Chris.

The 3C03 signals and 2726 signals.

You'll note the 3C03 has the ELC2000 tuner and the additional module "Home Market Special"

Interesting L163 on the HMV

L163 on the 3C03

I'm always very dubious when I see a core wound fully out - that smells of "fault". Anyone who's had to deal with pre-war Ekco and Murphy IFTs will know what I mean!

I think the last time I saw an ELC2000 in captivity was in a Philips N1502?

Do the coils L160/1/3 actually do anything? Might be an idea to check for them continuity not forgetting the centre tap. Remove the DL when checking.

@Cathovisor. L163 is supposed to be like that at the start of the phase adjustments but like you I think it should be further in at the optimum point.

Posted by: @jayceebee

L163 is supposed to be like that at the start of the phase adjustments but like you I think it should be further in at the optimum point.

When I adjusted L163 in, the colour totally went.

And yes, the coils do have an effect when tweaked.

That's it, tools downed in workshop, HMV 4K parked, windows and curtains closed. Fans running to keep things cool. The shop is now closed, see you on the other side of this heatwave.

Posted by: @crustytv

That's it, tools downed in workshop, HMV 4K parked, windows and curtains closed. Fans running to keep things cool. The shop is now closed, see you on the other side of this heatwave.

Yes, maybe we should have a little siesta right now. I’m supposed to be exterior painting 🤣

@jayceebee I'm going to nip to the chemists to pick up a prescription and put some water in the flowers at the cemetery - and just check the A/C in the car... but no work until later today, if at all.

This photo illustrates the phase adjustment cores L162 & L163, as set on my HMV 2726, and Ferguson 3C03, also Jim (Jcdaze) took a photo of his spare signals panel.

Interestingly, It would appear my HMV 2726 and Fergy L162 cores, are set pretty much the same, but differ from Jim's L162, which is flush.

My Fergy L163 and Jim's L163, look to be the same, but obviously the HMV way out. Ignore R190, that was me setting to min resistance when trying to set up the phase.

Based on what I have, L163 has been wound out for some reason. The delay line opened up for some reason, and the 47pF cap found on the wrong end of the delay line. I think when the heatwave allows, I should set the HMV to match the 3C03 and take it from there. Though I'm left wondering why Jim's L162 is flush.

p.s.

I also note on both my Fergy and HMV, the cans have black marker stripes. Surely not a coincidence, and perhaps the same tech working on the TVs.

Posted by: @crustytv

Though I'm left wondering why Jim's L162 is flush.

On a hand-wired chassis it would not perhaps be surprising, but with a PCB and uniform production of coils, you might expect only a turn or two difference between boards.

However this is only my assumption and I may well be ignorant of other factors such as the effects of the delay line tolorance for instance.

Another observation, and rather massive discrepancy I've found, is with regard to L160 and how it has been set.

As you can see, on the HMV the core looks to be about 1-turn down from the top, whereas the same core on the 3C03, is just below halfway down, that's a huge difference! I've no idea if this is due to the differing delay lines, the HMV having a UDL14 and the 3C03 having a UDL15, surely it wouldn't that wide of a difference?

Looking at the circuit, L160 is across the 64us delay line. Once side is fed from the luminance and chroma control IC (TBA396) specifically pin-4 of the chroma diversion gate (Chroma output collector), I've marked that with a blue line. The other side marked with a yellow line, is a little more convoluted, it appears to have a tap from pin-5, supply (vcc) and pin-9 (back porch clamp & brilliance), and ultimately the brightness cct.

L160 setting would affect the R-Y/B-Y luminance output, and that surely must be the odd shading I'm seeing when UDL14 is installed, especially noticeable on colour bars (see below). I seem to recall someone else mentioning the chroma fault, and that it was likely related to R-Y/B-Y. However, I cannot find who said that or where back in this thread. Although that particular fault condition does not appear when UDL11 is installed.

I've also looked through the manual and cannot seem to find any set up info related to L160. I'm probably not seeing it for looking, but it would be useful to know what Thorn had to say about its adjustment. It's not even mentioned in the description of how the luminance and chrominance control of IC155 functions. All I can see is that the waveform of the chrominance out to the delay line, should be 4V p-p. I certainly should check to see if this correct and is being presented to the delay line. If it were low, would that account for the massive adjustment on L160?

What I do also note is that pin 12 from that same diversion gate, is for saturation control R196. I certainly don't have any saturation control. Well, it shifts colour rather than saturation. Is this all pointing perhaps to a faulty TBA396?

Pic-1 UDL14, Pic-2 UDL11

A lot to take in, but is any of this making sense. I wonder where L160 is set on Jim's spare? Any thoughts on any of this, or am I navigating a rabbit hole? I don't think I am, as to me, it all seems to add up to what the HMV is trying to tell via the fault on screen.

p.s.

Yes, up at 6 a.m. trying to grab a little bench time before the flamin heat arrives. It's already 26.6C in the workshop. Hopefully the last day up here, forecast is for a whopping 14 degree drop and rain Tuesday onwards.

Posted by: @crustytv

R-Y/B-Y luminance output

By definition, R-Y and B-Y does not have any luminance component 😉

It's an interesting circuit but as far as I can see the yellow line you've drawn has nothing but DC on it: I can only assume that it provides a supply to the transducers on the delay line (you don't need me to remind you that these things are ultrasonic in nature). If you were to compare the operation of this to other contemporary sets (e.g. a Philips G9), what would their manuals tell you regarding line-up around the delay line?

Edit: reading back to a post made by @jayceebee I see the later 8000 chassis decoders used the same chipset, so there may be a clue there.

As to the odd appearance on chroma transients with the UDL14: I do wonder if this is an acoustic effect caused by the opening up/damage to the device itself. You did say it had been 'got at'.

Oh, well, I was curious as to the wildly different setting of L160, clearly I don't have a clue, and I'm just clutching at straws, the heats not helping me think either.

Posted by: @crustytv

Oh, well, I was curious as to the wildly different setting of L160, clearly I don't have a clue, and I'm just clutching at straws, the heats not helping me think either.

The G9 manual suggests that the input core may be tweaked to get best results when the output core doesn't!

The later 8000 decoder alignment procedure may yield a clue.