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
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
Ok, I've found an AC188K in a jar of junk which measures sensibly on the tester, a quick google shows its similar to the AC128, just slightly lesser ratings, so Ive bunged it in! Back on the 12V bench PSU, and I've set the 11V line to 10.8ishV, its currently 10.87on 625, and switching to 405 it goes to 10.91V. The transistor is getting warm, but not hot, but it does have it's own heatsink block which may be keeping it just right. I'll run it a bit longer and see how it goes, if all is ok then it'll be a new AC128!
Out of interest, I stuck the AC128 on the component tester again, this time it says it's a PNP, and looks sensible, but if you warm it up it then says 'no, unknown or damaged part' and stays like that until it's cooled down again, where it reads normally.
Regards,
Lloyd
Well, it's still running over 20 mins later, and the 11V line is currently 10.88V, so it's not gone up much! It's on 625 lines, the 405 whistle was deafening! I've plugged the speaker in, and I've got good strong sound, I think it's on BBC4 presently.
Regards,
Lloyd
I have found that germanium transistors can become heat- sensitive. I found this out when tackling the Perdio Portarama with excessive height. Just holding between thumb and finger was enough to bring the height down. A new OC81 cured the problem.
Some ACxxx also have the tin whisker problem. I had to replace the driver (AC128) in my Roberts as it had intermittent shorts between the electrodes....if you whacked it hard enough it would read normally but I decided that wasn't best practice so replaced it!
That’s interesting! I wonder what causes it? Maybe I’ll make a thermometer out of it!
I was reading your thread on your T-vette earlier, you certainly had a few problems with it!
I’ve got a few photos of the earlier shenanigans, first up, the dodgy solder joint on the 10 ohm resistor
a few shots of the roasted system switch contacts
the interesting bench setup…
and the temporary replacement for the AC128
maybe tomorrow, if the set behaves itself I might actually get the crowbar in place then we can put the tube in and see what we get!
Regards
Lloyd
I'm currently having a play with the crowbar (!), just wondering what rating of fuse to give it? I was thinking along the lines of around 100mA, since the tube heater only needs around 60mA, Also wondering whether to go for fast blow or slow blow, I was thinking fast would be better, not just for cutting power to the CRT heater quickly, but also the zener diode, as I'd like it to still be useable after a fault!
I did find some AC128's, but they turned out to be faulty, one looked totally unused, still has it's 2" long legs! but the component tester showed it as 2 diodes, and in the set it clearly wasn't working at all, but the AC188K that I bunged in has held up well. I'm going to try the tube in a bit and power it up carefully just to see what I get on screen.
Regards,
Lloyd.
Hi Lloyd, don't forget that the current taken by the heater will be more when switched on from cold. You may be better off with an anti-surge fuse, but in any case it would be worth monitoring the current with a meter upon switch-on to get an idea of cold and then hot values.
A switch-on surge of current could be quite a bit higher than 100mA, especially with capacitor charging etc.
To understand the black art of electronics is to understand witchcraft. Andrew.
We have life!!!
The tube is in, the LT is set to 10.8V, the zener is fitted to the tube base straight across the heater, a fuse has been added, but it’s 500mA slow blow, the smallest fuse I have in stock.
There were new faults to sort out on switch on, I was greeted with frame collapse, I spent a good long while looking for duff solder joints and pinged off wiring, and found none.
I checked around the resistors in the frame stage and also found nothing amiss! During these tests I made a guess that the output stage was working, as the frame would begin to expand when probing around the oscillator transistor. I checked the transformer that contains L4086, L4087 and L4088, this also checked out fine. There are only 2 caps in the oscillator area of the circuit, one a mullard mustard which was most likely fine, and a yellow electrolytic 4uF 16V, which I decided looked suspect, so I swapped it for a new 4.7uF 63V part, I have a bag full of them. This time I got full frame scan! It’s great to see a picture on this set again after all this time!
There is still more to do, there is a sync fault where the frame jitters and sometimes rolls depending on picture content, even though there is a good range of lock on the hold control. It’s looking good so far though!
Regards
Lloyd
Excellent !
To understand the black art of electronics is to understand witchcraft. Andrew.
That's brilliant - if you see what I mean!
Aside from the frame fault you describe, everything else looks okay.
This TV is doing my head in! Just when you think it's OK, it decides it's not!!
I've discovered the frame sync fault is only present on 625 lines, 405 is perfect! So when a bright scene comes along the frame looses sync just slightly, so the picture drops to the bottom of the screen and jiggles about down there, occasionally rolling upwards too, once the bright scene is gone everything reverts to normal. There is a slight bit of pulling on the line too. As you can imagine, a scene with flashing lights sends the poor thing into a frenzy of vertical bouncing! Top of the pops would have been painful to watch on this set...
It's really annoying as the picture is excellent apart from this. I'm no expert when it comes to transistorised TV's, but I've tried looking at the waveforms in the manual, and had a stab round with the scope, waveform '3' seems to vary with picture content, it looses it's defined pulse shapes when a bright scene is encountered, but I've no idea why!
Test card looks bloomin awful on it too..
Regards,
Lloyd
Posted by: @lloydTop of the pops would have been painful to watch on this set...
Some might say on any set! 😋
Have you tried reducing the RF signal input, it could be overloading.
To understand the black art of electronics is to understand witchcraft. Andrew.
Didn’t think of that! I’ll give it a shot, I’ve got some attenuators somewhere 🙂
Regards
Lloyd
Posted by: @lloydDidn’t think of that! I’ll give it a shot, I’ve got some attenuators somewhere 🙂
Regards
Lloyd
Seems like a logical step. If it only affects 625 lines, the issue must lie in the IF or vision detection sections. The frame TB is the same for both standards, so unlikely to be at fault - But I'm happy to be proved wrong.
The easiest to implement, and will show itself up if it is the case, plus, the only real difference in the entire set, is where it gets its RF from. It's very unlikely that the either source will replicate the original broadcast levels, but it's also unlikely that they'd be equivalent to each other.
Be ready for a lot of attenuators! - I've had three or more in series before today, and still needed more. A quick, but very unscientific method would be to withdraw the AE plug from its socket, and very slowly and carefully draw it away from the socket. If you're lucky, you'll find a spot (an air-gap) just right enough to allow a signal to pass, but also to be attenuated.
I thought we'd gotten to the bottom of this problem earlier! I found an attenuator, plugged it in, tuned in the set, and we had a perfect picture! No frame jitter, so I left it playing on the bench whilst I did a few other things, and when the video with a few flashing lights came on sure enough, it decided to start it's old tricks again... Strangely, mis-tuning would fix the frame issue, but then of course the sound was just noise, and the picture was covered in patterning.
Another interesting thing I noticed was that when I first turned the set on the left side of the picture had a bit of a horizontal linearity issue, and as the set warmed it would begin jiggling until eventually it just stayed without the linearity issue! I did manage to replicate the issue by blasting inside the set with a big fan to cool it, once the linearity issue had gone away again there was what looked like ringing on the picture, more noticeable on a blank raster as light and dark areas, with a very noticeable light band at the right side of the raster, not sure what's going on there!
I don't think this set likes me....
Lloyd.
My T-Vette was not particularly stable on 625 either but 405 was rock solid, also had a bit of a soot and whitewash look about. Changing a couple of sub 1uf electrolytics in the AGC/video stage I think improved matters.
John.
Cheers John, I'm just looking at the caps now, there's some right odd values in there! What would be best to replace a 1.6uF cap with? I've got some 1uF caps, or I can order some 2.2uF's, I'm going to have to order some 47uF's to replace the 40uF that I've just found! As for the 0.64uF cap, I've replaced it with a 0.68uF film cap since I have a bag full that I got to build the MiniMod.
Regards,
Lloyd
You could try scoping the supply to the sync stage. Those yellow electrolytics seem to hold up quite well but they are getting on for nearly 60 years old now. Some of those old Philips values do seem a bit odd by todays standards but you can easily use 'nearest' conventional modern values. I never understood why they used .47uF and .68uF electrolytics. They weren't very good and we used to replace them with polyprops. You could find 64uF, 640uF, 4uF etc in there. Just use the nearest modern value and it will be fine.
To me, Lloyd's instances of losing sync on bright scenes implies there's rather more video getting through the sync sep than there should be, or that AC coupling isn't as good as it could be. That says either bias or degraded electrolytics.
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