1975 PYE CT-219 “Chelsea” 717 Chassis

Second section reformed without issue as well.

Next, the two green grenades. C501 a 330n 1000VDC across the line, it'll be replaced with an X2 .15uF 275VAC. The other C656 a 2n7 1500VDC will be replaced with a 2n7 film 1600VDC.

Posted by: @pye625

Doing some groundwork first pay's dividends.

Why take the risk with often hard to get components?

^^^THIS^^^

I have NEVER understood the mentality of the "oh, just plug it in" brigade. Fine if you've got a lifetime's worth of spares to hand or don't mind bodging your way out of self-inflicted damage I suppose.

Posted by: @cathovisor

I have NEVER understood the mentality of the "oh, just plug it in" brigade

Me neither, I remember when first starting out on the hobby being given more than an unfair share of grief, by certain individuals in a certain place. One, I particularly remember, was "x" numbers of pages and still no sign of power yet! As if it's some sort of testament to the size of your gonads. In that particular case, the wiring was totally perished, but I was still expected to power it on, really!

Go at your own pace and sod 'em. That's what I say.

Posted by: @jayceebee

Posted by: @crustytv

There does seem some evidence above board with one wigwam repair.

I could be wrong but looking at the board markings and components used I suspect it may be original.

Either that, or an after market modification. Even in my limited exposure, I've seen numerous similar sights across a variety of makes.

Posted by: @red_to_black

I wouldn't be so sure Chris! PYE did a lot of things that shall we say was "unorthodox"

I don't think they were alone in that. I remember a tidy few 'first generation' video recorders, mostly from Sharp, as I recall, where a veritable spider's web of components was laid out like bird repellent mesh over a bed of soft fruit.

In any case, if it were mine, I'd leave that "wigwam" well alone until the set has at least seen some 'light' - Get it going as is before reverse engineering any modifications.

Posted by: @katie-bush

Either that, or an after market modification. Even in my limited exposure, I've seen numerous similar sights across a variety of makes.

No, it is neither, I even have a photo from a brochure showing the board, one resistor. This is clearly a field fix, not a mod, a field fix. Three 150K's to try and male the 470K. I'm bored trying to convince folk of it now. Wish I'd never mentioned it.

Posted by: @crustytv

Wish I'd never mentioned it.

I know....... Some days, it doesn't pay to get up in the morning, like me, yesterday, when I thought I'd fix my smart phone - Today I'm looking for another phone! 💩😖🤯

Even so, I'd still be inclined to go for first light before removing that rather complex looking bridge of components. A lot of sets in the early '80s had similar looking networks which had been added by engineers in an effort to produce acceptable pictures from VCRs, amongst other unofficial circuit changes.

Taking out the wigwam may, just possibly, reintroduce a fault that a previous repairer laboured to overcome.

Like me when I mentioned super-glue in the KB Royal Star thread. 🤑 

Be nice to rewind the tape and un-mention some things.

By the way, are you really sure that wigwam is not original Chris? ....

Oh shut up Andrew.

I'll try one last time, then say no more on the matter, they say a picture is worth a thousand words.

The components outlined in green are factory manufactured and correct. The 3 series resistors I've been trying to convince folk about, are outlined in red, they were once one resistor, a 470K R531. Why folk cannot accept this simple fact but will accept some complex repair has taken place that if changed to a 470K will impact the circuit. Its quite bizzarre!

Can you now see?

Nothing complex, no magic mojo technical solution that a 3-series 150K will add to the circuit. At a guess, but not in the realms of insanity, the 470K failed, the engineer attended, sods-law no 470K in the tool box, but he did have a number of 150K. 3-in series, "ah that's close enough". I bet if he could read the intelligence attributed to his simple quick fix being some laboured over technical solution, it would have him wetting himself with laughter.

This repair will continue on the repair blog here https://www.radios-tv.co.uk/pye-chelsea/

I'm 100% with Chris here.

I too have seen manufacturer's mods in VCRs but they're usually neatly executed and nothing like this - but the factory-fitted stuff in your picture will win no prizes for neatness.

Consider also this: there is less than 5% difference between 470k and 450k, so how the blazes is a value change within the manufacturing tolerance of a fitted component - assuming that 5% components were used in the first place - going to make a blind bit of difference?

Whip it out and show it the bin, Chris but out of interest - what does it actually do?

(ETA: appears to be a feedback resistor in the PSU regulator)

Yeah, that's definitely not a factory fitted bodge! I have seen some like that in the Sony monitor that's on the bench, normally covered in white silicone gloop.

There's a capacitor not far from that bodge that looks like it's got a nasty crack in it too.

Regards,

Lloyd

@crustytv 
Has the IF strip in the Chelsea been replaced, I think Ledco had replacements for them, a SWAF would have made the design easier to achieve?

Considering the last time I looked at the blog regarding the Pye you'd written THE END on it, I'm surprised to see it has been resurrected! I'm also surprised that even after receiver board swaps that the picture is so noisy though - unless both boards are duff of course! You've not got a broken/dry-jointed aerial isolator by any chance, have you? I've seen that before...

The move to SAWFs in the UK was driven by Teletext as lining up a conventional IF strip to get acceptable HF and phase performance was pretty trying, to put it mildly. The MC1349 shows a date code of week 34, 1982 and the SAWF four weeks later so this was a very late mod to what was probably an old telly by then - but then we didn't change tellies every few minutes and equally I can imagine these sets were probably still on budget rentals.

My vote? Stick with the Pye for now.

Posted by: @cathovisor

Considering the last time looked at the blog regarding the Pye you'd written THE END on it, I'm surprised to see it has been resurrected!

You and me both, Mike. Considering all the bother I went to adapting an 8K rectifier to provide focus for the 3-wire, only to have that fail, I had just about had enough. Then by chance,  I happened upon another 5-wire doubler and thought I'd give it one last try. Thankfully, it appears to be holding.

Posted by: @cathovisor

I'm also surprised that even after receiver board swaps that the picture is so noisy though - unless both boards are duff of course! You've not got a broken/dry-jointed aerial isolator by any chance, have you? I've seen that before...

All I changed on the IF board was the NSF tuner module, the new unit came with its own aerial socket, certainly don't think I have two faulty units, the fault must lie elsewhere on the IF. From discussions elsewhere, the opinion appears to be that the SAWF module, by LEDCO, is top-notch and highly unlikely to be at fault, this is from an engineer who worked on these back in the day.

I'm now suspecting the TCA270Q module or associated circuitry around the AGC/AFC?

Interesting that removing colour, the grainy signal appears to clear up. In an attempt to do a quick N dirty grey-scale, I also find the A1's and RGB gain pots are pretty much seized, all need replacing. There's a lot more in need of attention and is likely a combination of other problems not helping this, brightness, contrast and colour operation is horrid, crushing the signal. The thick film on the decoder is a top candidate as well, as these are notoriously awful.

Just as you need a stronger signal for FM stereo than you do for mono, the same applies to colour versus B&W.

SAW filters are great - all those horrible tweaks gone, and excellent performance from the devices. Your fault does look like something is trying to run at maximum gain because there's no signal.

If operating the user controls is having such an adverse effect upon the picture, that's telling me the DC conditions are very wrong somewhere. The wavy picture you've got says "smoothing" to me too, unless there's a poor chassis earth; you did say it had been kept somewhere damp, I believe?

Nice to see it going again though 🙂 

A little more progress.

Worth checking the 3 x 39k resistors. 

Already done so 👍 

This is looking like either a timebase fault either in or around the 920, or further back on the IF board and the 270. The IC map shows I have over voltage at pins 7,8 &10, and scope of pin 8 does confirm a bit too much video. Problem is finding a cct that matches my version. It appears to be an early, last version. I have multiple ccts for the 713, also "The teleman" dropped over his manual which has the final revision cct, even that does not match mine. Another typical Philips undocumented revision.

I'll report back my findings once I've delved a little deeper. I have some ideas where to check and if they prove inconclusive then I can always swap the 920, but that's my last resort.