It's a stunning project, and features a few useful functions not found on my other standards converter, the Aurora SCRF405 (which for those of you who don't fancy the DIY approach, can be found here http://www.tech-retro.com/Aurora_Design/Single_Converter.html)
It consists of a digital video converter (The TVP5150) which converts PAL to an 8-bit ITU−R
BT.656 format. These one's and zero's are fed to an EP2C5 FPGA development board, which mounts to the top of the PCB. The magic happens in here, and the resultant 405 line system A video output emerges from the resistor ladder DAC. This is then passed to a MC44BS373 modulator IC, which is tunable on all Band I and Band III channels. The tuning of the modulator is also taken care of within the FPGA, and is set with a hex switch. There's a second MC44BS373 which is modulating audio at the required 3.5MHZ spacing below the vision carrier.
The unit produces aspect ratios of both 4:3 and 5:4 (5:4 being in use up to 1950)
There's a Pedestal function which lifts black level 50 mV above blanking level. This was abandoned on transmitters post-war, as it reduced the efficiency of the transmitters. It may help with early sets that suffer from flyback lines.
You can select between normal broad pulses or broad pulses with equalising pulses. Equalising pulses were never in the spec, although it may help interlace on some sets (ironically it upsets interlace on some, and causes the top of the picture on some Bush sets to "hook")
The three-line interpolator has three settings: soft, medium and sharp interpolation apertures.
Switchable 1KHz or 400Hz test tones.
There's also a PM5544'esque test pattern, and stair-steps.
These functions are all available via switches on the front panel.
PCBs were ordered from the most-excellent pcbway.com, and arrived within 7 days.
The FPGA board came from eBay.
The MC44BS373's I had to source from AliExpress, as it's now classed as obsolete, however, at the time of writing this, there appears to be plenty of stock from "grey" suppliers. I dislike doing this, as many times I have been caught out with fake parts! Caveat Emptor. I used the AliExpress supplier YT Electronics components co.,ltd
The phono sockets also came from AliExpress (link) and fit with a minor modification.
Assembly is straight forward, don't let the surface mount put you off. Get a decent quality gel flux. If you've seen my videos, you may have realised I suffer with a benign tremor (nothing to worry about, I've had it since I was 14), and I can mount this stuff with ease. I do have the advantage of a microscope.
A bit of blue-tac helps hold the board in place. First off I fit the semi's.
Then the passives...
Programming the FPGA is straight-forward in windows, using the Quartus II (13.0 sp1) software, and the "USB-blaster" supplied with the FPGA board. I failed to get the software to work under Ubuntu (although it would "see" the programmer hardware, the program option remained unavailable). When correctly programmed, there's a binary counter running on three LEDs on the board.
Sockets and switches are mounted.
And the FPGA board fitted.
... and it's switched on!
However, some fault finding was required, as although the test patterns and test tones were OK, there was no converted video. With the help of the designer, Frank and the VRAT forum (here), it was apparent something was wrong with my FPGA board. After some fault-finding, a tiny solder bridge was found on the FPGA board, shorting out two of the lines. Once this was removed, the converter worked faultlessly.
Moire pattern is being caused by the camera, the actual picture quality is superb.
I like the additional functions available from the front panel. Picture quality appears to be on a par with the aurora converter.
What I'd really like is a centre-cut out function for dealing with a 16:9 input.... Frank?
Remember my warnings and concern about the CCT811 video modulator?
This is the offending model in question. Apparently it's also being sold under various guises, one model quoted to me is the RF9000. If it looks like this, I'd be seriously concerned....
I wrote about it here. Please take a moment to read this, if you haven't seen it before.
Well, settling down for an afternoon of vintage TV fun, I switched the video rack on....
Crack, crack, crack, bang! Uh-oh...
"It's bound to be the modulator" I thought.
I was right. It had opened the fuse I'd retro-fitted. (If you have one of these awful modulators, time to stop using it!) Damned glad I fitted one... lord knows what would have happened if it had tried to short out the mains without the protection of a fuse... Fire would have been a REAL possibility.
I opened it up and expected to find a mass of blackened bits, but no. Now I've giving up on this I thought... but it's so useful!
It looks as though the insulation had failed on the transformer, and destroyed the semi-conductors in the drive-side of the supply.
I thought I'd remove the ghastly existing "switched-mode" blocking oscillator, and replace it with something ...
1) Electrically safe. 2) Reliable.
OK. First things first. To find out if it still functions.
I removed the transformer, and connected the workshop power supply between the end of the rectifier diode, and ground....
It seems to want about 6.5 VDC to operate, and has even remembered the settings it had before the power supply failed... good.
It's drawing about 165mA at that voltage, so a supply is not too challenging!
I decided to have a look in the drawer of redundant wall-warts to see if I could find anything suitable, and I spy one of my favourites, an old Nokia phone charger!
Now I always pick these up from boot-sales for a few pence, and are very useful. This one is rated at 3.7 Volts, at 350mA...
"But Andy, you said the modulator needs 6.5 volts to work" ... and so it does, but this particular Nokia charger is unregulated. Off-load it makes about 10 Volts.... Will it make our 6.5 volts at 165mA?
I solder the white +VE lead to the anode of D107, and the black lead to the far right hole (viewed from the rear of the modulator) left behind when I removed the transformer...
... and switch on....
Eureka! It works.
So it's now electrically safe, and I can sit back, and watch some "proper" TV....
My colleague Nathan came into work. He's just moved house.
"There's an old telly in the loft. Do you want it?"
Yeah, why not....
I take the set home, much to the delight of Mrs. Doz
The cabinet has seen much better days, and it looks like it's been damp at some stage in it's life...
No model number, as the sticker's fallen off, but some research shows it to be a 2103, dating from 1971. It's a single standard (625 line PAL) colour set.
... it looks to be complete...
... and un-molested...
Removal of the line output stage screening can, shows the anode lead to the line output valve's insulation has failed, leading to a bit of a burn-up
... and there's a resistor on the side of the line output transformer which falls into pieces as soon as I touch it. This is replaced, and the wiring made good.
The CRT is tested...
... and doesn't look good initially, but after a couple of hours wait, the meters rise into the green as the tube wakes from it's long sleep!
Some mains is gently applied to the set via the variac... nothing. The mains fuse is open circuit, so a new one is fitted... and as the valves warm up....
... a blurry green raster appears ...
.... and after some tweaking, some rugby players appear. The convergence is awful, and the picture isn't in colour, but it proves that the set is viable...
The tuner is seized solid as always, so it's removed...
... and cleaned up...
Being careful not to stress those rusted in plastic nuts!
The tuner is refitted once it's all moving freely, and I start fault finding on the lack of colour.
I prevent the colour from being removed from the picture (for when black and white programmes were broadcast) by disabling a circuit called the colour killer. There's still no colour, so it's likely the reference oscillator isn't running... Just as I'm about to start looking at that fault, the sound and picture disappear! The set is still operating, but there's nothing coming out of the IF (Intermediate frequency) stages after the tuner. Damn.
There are 3 stages of combined IF amplifier. These amplify and filter both the sound and vision the signals together, coming from the tuner. The signals are then split off, and amplified further, the audio being separated and decoded from the video. As both sound and picture went off together, I suspect the fault lies in the combined amplifiers.... I check all three stages, all appears well. Perhaps the tuner has failed? A super chap called Gary has a spare, but it makes no difference....
After some further checks, largely out of desperation, I check through the vision amplfier, and find there's an emitter follower amplifier, and the transistor has failed. It's a BF194 HF bi-polar transistor. A replacement is fitted, and pictures are restored! Still no sound. I look at the first sound IF, and , sure enough there's another failed transistor. A BF194... still no sound!... I check the ratio detector, which is used to demodulate the FM sound, and.... it's another failed BF194! Sound a pictures restored, I look back to the colour decoder.
I check the reference oscillator, and it's running fine, producing a locked 4.43MHz signal. Good. I check through the stages, and find 3 faults. Two of the faults are transistors in the R-Y (Red minus lumenance) and B-Y (blue minus lumenance) ... guess what .... BF194's. Also the colour bust transistor is open circuit... you've guessed this next bit ... it's a BF194...
There have been questions raised on various forums in the past about the reliability of BFxxx and BCxxx lockfit type transistors. It's quite possible that that un-reliability (they are 40+ years old!) is what's been at work here. It's possible that flash over when the insulation failed on the anode lead in the line stage caused a spike which saw off the transistors, but the BF197's and BF196's in the IF stage survived, as did other transistors in the decoder...
After replacing this little lot, and a couple of suspect and corroded looking capacitors, things are shaping up. There's some hum evident on the power supply, and I find a very sad looking cap in the power supply. It's got a nasty bulge in it... It's changed out.
I replace the line output valve and boost rectifier (PL519 and PY500) and the width is better, set up the convergence on the tube, so the three colour guns are lining up correctly, and I'm rewarded with reasonable results.
Note quite sure what I'm going to do about the tatty cabinet though...
Back in about 1981-82, I bought one of these sets from a jumble sale for 50p. I lugged it all the way home, stopping many times along the way (I was only 10 at the time). It didn't work. My mum kindly took it into the local TV shop (Seamen's Television in Carshalton) and they fixed it for me. It's a larger 17" TV, using a hybrid chassis of valves, transistors and 2 IC's, 625 line single standard, black and white.
It's more "trans-luggable" really, you can see that woman in the ad straining, it's got some weight!
The fun continued until about 1985 when the tube failed, curtailing the fun. It was binned.
I'd kept a casual eye on eBay for one for the last few years, and then in late 2014 one surfaced.
I collected it from the south coast and returned home with it.
Cosmetically in good nick, although the tuner was seized solid.
A few repairs have been carried out in the past...
.. but it looks OK.
Callins electrolytics are most likely to be faulty...
TAA700 sync separator and video pre-amplifier chip.
These sets had a reputation for poor caps in the line stage, they've been changed in the past..
Mazda CME1713/ A144-120 tube. Flaky aqua-dag, but that shouldn't effect performance.
So, the mains filter capacitor was snipped out, and some mains applied via the variac.... and, the smell of burning dust and hot valves awaking from their slumber filled the workshop... a few moments later , a picture appeared! Tube looked to have plenty of life left. I went to the kitchen to get a cuppa, and on return was greeted with a VERY hot dropper resistor, and a line output valve glowing cherry red :(
Probably one of those rotten caps stopping the oscillator I thought ... I thought wrong. After an hour or so of testing, I pulled out the line transformer, and performed a ring test ...
No doubt it had developed shorted turns. The TV restorer's worst nightmare.
I asked everywhere to see if anyone had a replacement transformer. I had a few leads, but nothing was forthcoming....
It's probably the EHT overwind, I thought, so the plan was to remove the overwind and ring test that to see if that was at fault. I had some other unknown line output transformers I could take the overwind from.
Unfortunately nothing would shift the glue used to hold the winding to the ferrite core. Disaster struck, it broke up ...
I reassembled the set and stored it in the attic, until a suitable transformer could be obtained.
Time passed, a lot of time......
and then, several weeks ago, a wonderful gentleman emailed me from one of the forums, who had seen my request for a transformer. He suggested a Philips 210/300 chassis transformer may be a suitable substitute. He had a Konig replacement, a ZTR371, which had the benefit of having a solid state EHT rectifier built in. It duly arrived in the post...
The set was removed from storage, and prepared for the transplant!
Both the Philips and Pye circuits were examined... there were differences. Mainly in how the line linearity is handled.
I initially decided to modify the Pye circuit, to accommodate the Philips positioning of the line linearity coil... stood well back and slowly increased the mains on the variac. Almost no width, but there's something....
I then changed the circuit back, and changed the wiring on the transformer to suit the Pye line linearity cicruit... results were much improved, although "boost" HT was woefully inadequate at about 320V, 850V would be better...
The reason for the lack of boost HT was quickly spotted.... another wiring change...
It's all a bit of a lash up of bits of wire and croc clips, but it IS working.
During this time I noticed there was now a precious lack of "snow" on the screen. I decided to stop here, and evict those awful Callins electrolytics, and anything else which looked suspect.
... and un-seize the tuner.
... lots of surface rust on the tuning spindles, which is cleaned off using a little WD40 on a cotton wool bud.
The cam-gear on the other side is also stiff, but eases with a little WD40.
After it's all moving again, I cleaned off the WD40, just in case it attacks the plastic nuts on the spindles. A good coating of spray grease should keep everything lubricated.
So, the tuner is reassembled and fitted back to the set. I can now tune in the set, and can *just* see a picture, but it's totally lacking in contrast. Time to evict all those nasty electrolytics. Many are either physically leaking, cracked or electrically leaking or low in value. Sadly, this doesn't fix the issue. On a brighter note, the height and width are improving, probably due to the valves waking up after a long slumber! I add a 100pF capacitor across the line harmonic tuning cap, which improves the amount of adjustment available on the width control.
I mount the line output transformer permanently, and tidy up the wiring.
So, back to the lack of contrast. The video is demodulated by the TAA700 IC. Expect for in this case, there was precious little video coming from the IC. I find a few resistors outside of spec, but changing these makes no difference. I fit a new IC. No change.
Scoping up some of the waveforms around the IC shows it not quite getting the right information back from the line output stage to correctly operate. Unsuprising considering the wrong line output transformer is fitted. It's probably stuck in blanking...
I turn my attention to the line stage, and R 92 in particular.
I connect a 1 megohm pot and a 100K resistor in series, and connect it across R92, in an attempt to increase the drive to the IC.
Tune for maximum smoke. Only it doesn't work, as I get the required pulses at the IC , the picture gets worse! ... So I re-wire the pot so as to decrease the pulses to the IC!
Bingo! Pots of contrast. I disconnect the pot and take a measurement of the value. It's near enough to 1 megohm, so R92 is replaced with a fixed resistor.
Now just to centre up the picture and soak-test it...
... if only...
You might glaze over at this bit ....
After being on for about half an hour, the picture faded out rapidly. I cut the power quickly. Is this the return of the fault that had killed the original transformer??? The new transformer is running a little hot. Perhaps a bit hotter than I'd like. The boost capacitor, and the first anode decoupling capacitor have both been replaced in the past, it was probably in the 80's at the latest, so I order some up. Replacing these makes no difference, and half an hour later the set cuts out abruptly again, as the line output stage shuts down. I wait for a few minutes, and scope up the line drive signal to the PL504 output valve. It remains strong, even in the fault condition, so something is loading down the line output stage. I change the PL504 and PY88 boost rectifier, and I'm rewarded by more width, so I remove the 100pF cap I'd previously fitted to improve the width. Sadly after a few mins, the line stage once again shuts down. I move the width stabilisation feedback from the direct tap on the transformer, to the capacitively coupled tap. This improves the range of the width control further, but doesn't sort the fault... phut! The set goes off.... I give any remaining suspect components in the line output stage a liberal squirting of freezer (on the cheap). Sadly it appears the line output transformer can't cut the mustard. It's failing when warm. I'm about to give up. It has taken hours and hours of work to get this far, and I hate to be beaten, but enough is enough.
I made some tea, and studied the circuit diagram again. Nothing is really forthcoming. I decide to cut apart the original Pye transformer to see if I can learn anything from the windings. I make some simple resistance measurements and compare them to the Philips transformer. The winding I'm supplying the HT to is a lot lower resistance than the Pye transformer. It should therefore be drawing more current. I scope up the current flowing into the transformer using a totally inappropriate hall-effect amp-clamp, which appears to tell me there's 2A flowing into the lopt. I suspect there's a lot less than this in reality. I can see there's an unused tap on the primary of the Philips transformer, so I hook up the HT feed to this tap. Now my (lying) current probe tells me there's an amp flowing into the transformer, well that's a change in the right direction. The picture comes up, and stabilises, the width is still good, and stays there .... for hours .... Success at last!
So for future reference, here's a quick sketch on how to fit a Philips 300 transformer to a Pye 169!
Some of the guilty & redundant parties...
Obligatory arty valve shots (seem to be getting the hang of this Nikon camera now!)
...and here's a video of the thing in action (maybe not so good with the new camera!)...
PCBs were ordered from the most-excellent pcbway.com, and arrived within 7 days.
