Granada Television Brochure, 1970s
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Memories of a Derwent Field Service Engineer
PYE Australia Circa 1971
Radios-TV VRAT
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Crusty-TV Museum, Analogue TV Network
Philips N1500 Warning!
Rumbelows
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Thorn’s Guide to Servicing a VCR
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Want to tell us a story?
Video Circuits V15 – Tripler Tester
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Remove Teletext Lines & VCR Problems
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Music centre modifications
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B&K 467 Adapters
Mishaps In The Trade
1971 Beovision 3200
1971 Bush CTV1120
Granada Television Brochure, 1970s
Long Gone UK TV Shops
Memories of a Derwent Field Service Engineer
PYE Australia Circa 1971
Radios-TV VRAT
Fabulous Fablon
Thorn TX10 Chassis
Crusty-TV Museum, Analogue TV Network
Philips N1500 Warning!
Rumbelows
Thorn EMI Advertising
Thorn’s Guide to Servicing a VCR
Ferguson 3V24 De-Robed
Want to tell us a story?
Video Circuits V15 – Tripler Tester
Thorn Chassis Guide
Remove Teletext Lines & VCR Problems
Ceefax (Teletext)
Suggestions
Website Refresh
Colour TV Brochures
1970s Lounge Recreation
CrustyTV Vintage Television Museum
Linda Lovelace Experience
Humbars on a Sony KV2702
1972 Ultra 6713
D|E|R Service “The Best”
The one that got away
Technical information
The Line Output Stage
The map
Tales of a newly qualified young engineer.
Tales of a Radio Rentals Van Boy
Sanyo SMD
Disastrous Company Rebranding
1969 Philips G22K511
Memories Of The TV Trade
Crazy house
Dirty TV screens
Dual Standard and Single Standard CTV’s
Radios-TV on YouTube
The Winter of 62/63
A domestic audio installation
1979 Ferguson Videostar Deluxe 3V16
Music centre modifications
Unusual record player modification
B&K 467 Adapters
Mishaps In The Trade
1971 Beovision 3200
1971 Bush CTV1120
What to do with a Philips T-vette...
Cheers, you both gave me some idea's what to look at, I stuck the scope on the collector of the sync separator (T4021) which is also the point for waveform number 3 in the manual, there was the required train of pulses, but with noise overlaid, particularly bad when bright objects appeared on screen, which also distorted the pulses, and when the distortion was present, the sync was interrupted, resulting in the frame dropping on screen. Cathovisor's mention of bias made me remember there is a video bias pot on the main board, and the manual states how to adjust it, meter between chassis and the base of the video amplifier transistor (T1220 on the tube base), set for 11V with no signal, so I did what it said, it needed quite a tweak to get it to 11V, but now I have a rock solid picture, and the waveform (3) looks a lot healthier!
I'll give it a good long test with various video sources just to make sure, but so far it's looking good! I've not checked 405 again yet, so I've probably ruined that to fix 625.. Oh, and it's working now without an attenuator!
I'm guessing that something must have drifted off value somewhere to make it need such a large adjustment, so I'll keep prodding at it.
Thanks again for your help 🙂
Lloyd.
Spoke too soon, it's doing it again!
Well I suppose you could try another transistor. Don't know how critical it is but an RF transistor will probably work OK. Don't forget the electrolytics though...
I've probably got an OC44 somewhere.
When I had a T-vette some years ago, like John, I found it was rather critical of 625 signal strength. I know that if used outside in the back garden with it's own telescopic aerial it gave good stable results. But using the main roof-top aerial, it was quite unstable with similar results you have with your set now.
However, this does not mean that it is meant to be like this, because surely it would have been designed to accept the widely varying signal strength a portable set would encounter.
Are there any tired electrolytics that could be slugging the AGC action perhaps?
To understand the black art of electronics is to understand witchcraft. Andrew.
Sorry for the slight absence over the last few days! Not been feeling too good, spent far too much time sleeping than anything else..
I did get back to this little horror yesterday though, and did some more poking of things. First thing, the cap I replaced back near the start, the 4uF that cured the frame collapse, I’d not noticed it’s supposed to be a non polarised one! I’ve changed it now to 2 back to back caps, not made any difference to the sync issues though.
After lots of messing about I think I’ve found why the sync is lost, it’s more false lock I think, I had the scope on the collector of the sync separator again, and if I slow the scope down and set up the trigger for vertical TV signals, I can see this:
looking closely at the start of the waveform, there is the little negative pulse, which I’m guessing is the frame sync pulse, when the frame does it’s false lock thing that pulse disappears, and the waveform ends up like this:
interestingly I can reproduce the same on 405 sometimes too, but it seems more resilient than 625. I’ve pulled all the electrolytic’s around the AGC video and sync and replaced a few, but most test good on the component checker, I did get some interesting results swapping the sync separator transistor for a silicon PNP, it then would have a blip in both line and frame sync when changing from light to dark! But it would recover a lot quicker.
that’s as far as I’ve got!
Regards
Lloyd
at least the test card is looking better!
Posted by: @lloydSorry for the slight absence over the last few days!
That's nothing... It has taken me nearly two years to get back to the frame fault in the PAM set. 😉
To understand the black art of electronics is to understand witchcraft. Andrew.
I’m tempted to shove this thing back on the shelf for 2 years!! Maybe some of these really were mediocre at best on 625?! I did wonder if it was because I was displaying 16:9 content with black bars top and bottom, so I switched it to 4:3, and it still does the same.
Regards
Lloyd
Posted by: @lloydMaybe some of these really were mediocre at best on 625?
Hard to say, but at the time (1966?) 625 was not common-place so most would have been used on 405. This system is ideal for a portable, especially just using the telescopic aerial from room to room. 625 was a bonus as a selling point perhaps, but may not have been refined enough to what we are used to in later UHF only portables.
I'm guessing of course and tricky to say for sure if there is a definate fault, but it would certainly seem that these set's are fussy on 625.
To understand the black art of electronics is to understand witchcraft. Andrew.
It might be worth posing the "625" question over on UKVRR too, so as to gain an even wider opinion of the set. If they generally really are a bit tricky on 625, it could save you lot's of time.
To understand the black art of electronics is to understand witchcraft. Andrew.
My T-Vette Works reasonably well on 625 although I get the impression that the contrast is lower...not really a problem since you just increase it a bit. I certainly don't have any sync issues but I seem to recall that some could be a bit tricky and have subtle faults. The expert I knew at Philips has long since retired or possibly even departed this world by now since he'd be in his late 80's. When I'm next in the workshop, I'll power mine up and give it a run via a modulator.
Just given mine an airing after several months. The contrast levels on both 405 and 625 are good although a slight readjustment (increase) is required on 625. There is more than enough contrast available on both systems.
Cheers for trying yours out! It sounds about the same as this one here, it certainly doesn't struggle with contrast, although it is a bit up near the top end of the control, there's still a little play in it.
I was reading the Practical Television article from Mikey's old technology website the other day (can't seem to find it on my PC, nor will it let me download it again now?!) and it mentioned a few suspects to try for jittering frame and false lock, all of which I tried, but it still insists on doing it! I am beginning to question my component tester now though, I replaced 2 caps in the frame stages with new ones, even though the old ones test good, and there was a large increase in the height on screen after replacing them, the height control now sits at just below half way, whereas before it was less than a quarter turn from the top end, so I'm now thinking I should just order up a load and replace the lot. Before that though I think I'll stick it back together as it is, and give it a good long run and see how it goes, maybe it'll fix itself! (I can dream....)
Regards,
Lloyd
Posted by: @lloydI was reading the Practical Television article from Mikey's old technology website the other day (can't seem to find it on my PC, nor will it let me download it again now?!)
It is available via our B&W servicing the sets' section here
CrustyTV Television Shop: Take a virtual tour
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Cheers Chris! I'll make sure I transfer it to the iPad this time, before my PC decides to get rid of it again for whatever reason!
Regards,
Lloyd
Hi.
On my Tvette I added a 100 ma fuse in series with the CRT heater and made up zener and diode combination to conduct at 11.2v as the CRT is just 80ma the zener crowbar only needs to pass just a bit over 20ma to blow the fuse, I'm using a wickman type.
Re the CRT I wondered if a CRT from a Sony 110UB could be adapted? Not sure of the deflection angle TBH.
Cheers,
Trevor.
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