When Restoring old TV sets, remember that just because it worked when it was last used in 1968, does not mean that it will work now. Indeed, if it is simply plugged into the mains and switched on, there is a good chance that there will be a very loud BANG!!!! .Old Sets fall into a number of catergories:
Here are a few things to look at and questions to ask yourself...
GENERAL POINTERS ON ALL SETS.
Look carefully at the set before taking on the project of restoration. Look for previous repair work, this could give some clues as to the set's history. Don't let dust or cobwebs put you off! Things do clean up. Rust could be a worry though as it could suggest moisture.
Pay specific attention also to lettering and logos. These, if severely scratched, can be very hard to restore. If a set has had an amateur paint job, this can be especally tricky to restore. I have to confess that I tend to pass woodwork and cabinet restoration to my local joiner and french polisher. There are ways of doing this sort of work yourself, but I am primarily concerned with electronics. Andy Emmerson has written an excellent book, details of which are under the 'Good Books' section. I am not going to simply regurgitate his excellent tips, but I strongly advise that you buy this book!! (OK Andy!)
Electronically speaking, look carefully for any signs of previous work, moisture damage, burn ups, missing components or 'modifications'. These can tell you an awful lot about the set's history. Sad to relate, the Cowboy is nothing new!
There are some parts that may prove difficult to replace, but not impossible. If you need, for example, a Line Output Transformer for a Bush TV22, then patience is required. Advertising in magazines such as 405 Alive, edited by the above mentioned genius Andy Emmerson, can get results. There are ways round these sort of problems, but they involve circuit redesign, sometimes on a Grand Scale. Decide if you want a Museum Piece, a Working Set, or if you're feeling ambitious, a Working Museum Piece!!
So, you've decided to go ahead. Congratulations and good luck! But don't do anything until you have the Servive Manual, or at the very least the circuit diagram and the layout! The Workshop Manual is very much a necessity for me. These can be obtained. Look Under 'Bits and Pieces' for advice on sources for manuals. Incidentally, for advice regarding spares, look under 'Bits and Pieces'
Now you've got the manual, the bench, the space and the long winter nights. Look under Test Gear for tips on what equipment you need. Get as much as you can realistically afford, obtain, beg, borrow or liberate.
DON'T PLUG IT INTO THE MAINS YET!
Look around again, look at the circuit. Check any fuses, if they have been bridged by wire, very common I'm afraid, replace and use your ohm meter to check for shorts. If there is a reversible mains lead, check which way round is the safer, using your ohm meter in between the pins and chassis. Check that all the mains dropper resistors are Ok, replacing any sections that are open circuit or high. Remove the valves, making sure you know where they all go, and check that the right ones are fitted. Remove the tube base connection, gently!!, and check for any signs of distress here. Look at the capacitors; Replace HT smoothing cans, any wax paper capacitors, all the grid coupling capacitors and any other worried looking electrolytics. Check that any HT diodes are OK. Replace if necessary. When replacing components, always replace safety components such as fusible resistors with the correct replacement parts. Never replace a safety component with a standard one and never replace sprung fuses with a bit of wire! MAKE SURE THAT THE BODY OF THE TUBE IS PROPERLY EARTHED AND THAT THE AQUADAG IS INTACT AND IN GOOD CONDITION. IF THE BODY OF THE CRT IS NOT EARTHED, THE SET IS A SAFETY HAZARD.
NB: In some very early sets. CRT's do not have an Anode Connection, but the body of the tube itself. The body of the tube will be VERY dangerously 'Live'. This connection can get dirty and arcing may be visible. Switch off the set and discharge the BODY of the tube to the chassis earth fully before work. Always check with the manual before working on such a set.
Check thoroughly for dry joints as well, especially around valve bases and components that get hot. If the set has Printed Circuit boards, check the tracks and connections thoroughly for cracks and dry joints. For carbonised, or blackened board, which can cause leakage, scrape the carbon away with a fine or artists knife. Broken or burned tracks can be bridged with wire.
With all the valves out, having made sure that you know where they all go!!, apply the mains Gently using a variac. Look for any signs of overheating, smoke or distress. Any causes should be investigated. Refit all the valves EXCEPT for the EHT rectifier valve. Variac the set up again and watch closely, keeping your hand on the on-off switch. If not all of the valves light up and some very brightly, switch off and check for s/c capacitors on the heater chain, also for internal shorts in valves. If the valves do not light at all, check the mains dropper again, any associated diode, and then check for an open circuit heater. On most B9A valves, the heater is between pins 4 and 5. Don't be fooled by a PFL200. It's heater is on pins 5 and 6!! Yes, I've done it. Also check the tube heaters. If these are open circuit, you need a new CRT. Luckily this is rare. If all is well, you should hear some sound, and when the tuning control is operated, clicks should be heard on the sound. Listen for a high pitched line whistle. Try rocking the Line or Horizontal Hold control back and forth. If the Line Output Valve, usually a PL something, is overheating, check quickly for a healthy Negative voltage on the control grid. If this is absent, look closely at the line oscillator stage.
One of the happier habits of a Neon Screwdriver is that it will glow when positioned adjacent to a Line Ouptut Valve, Efficiency Diode, LOPT, Tripler or Top Cap of EHT rectifier valve. If it fails to do so, or is dim, then the line output stage is being damped or is inoperative. Check the boost capacitor and various other associated components, but make sure that any replacement parts that you fit, especially capacitors, can handle frequencies of up to 15.625 kHz and can handle the hard life that these components lead. Any replacement diodes should have a suitably high switching speed to handle line frequency operations.
If there seems to be life, refit the EHT rectifier valve or tripler and see if you get any sort of life on the screen! If this valve does NOT light up, stop and think. The heater voltage for this valve is generated from a winding on the Line Output Transformer. Insufficient life in this stage, or lack of line drive, as described above, will leave this valve extinguished. Another thing to look for is an overheating efficiency diode. This is the other valve with its top cap linked to the LOPT. Try replacing these two valves, and make sure the top caps are the right way around! Check in the manual!! This is another mistake that I confess to have made. Oh yes, also check those little coils on the top caps.
If you get blue arcing on the EHT connection to the tube, that's the round thing on the body of the CRT, switch off immediately and follow the procedure below.
1: Using two screwdrivers BOTH with WELL INSULATED HANDLES, discharge the CRT. This is done as follows...Carefully push one screwdriver underneath the EHT cap until it makes connection with the Tube Final Anode undernreath. When it does, use the other screwdriver to short this to earth for a few seconds. Be prepared for a good spark. Do this several times until no spark appears. The CRT, which acts as a large capacitor, will now be discharged. Remove the EHT cap and touch it to chassis. Short the CRT anode to the body again, just to make sure.
You now need to inspect the EHT connector for burn marks and signs of streaking. If there are, the cap must be replaced. In most cases, all you need to do is to pull the metal connector out of the cap, levering out with a screwdriver if necessary, and desolder it. The rubber cap will now slide off. To fit a replacement, simply reverse this procedure.
The next task is to clean the CRT connector and the cap thoroughly. Usung a dry non abrasive cloth, remove all the dust from both. Then, using Isopropyl Alcohol and the aforementioned non abrasive cloth, or if you're careful not to leave bits of it behind, cotton wool. Clean repeatedly until no more muck comes off onto the cloth. Make sure that the area of the tube body around the Anode Connection is also thoroughly clean, I go for about a 6 inch radius around the anode connection.
Once the connection and cap are clean, refit the EHT cap and all should be well. However, a quick word of warning about tripers. If there is evidence of arcing or smoke coming from the tripler itself, you'll need a replacement. In many cases as far as colour sets are concerned, a universal tripler may well do. But check that the focus voltage is correct. NEVER TRY TO MEASURE FOCUS OR EHT VOLTAGE DIRECTLY!!!!
Another quick check, but be VERY CAREFUL INDEED, is to use a WELL INSULATED HANDLED SCREWDRIVER and try to draw a spark from the top cap of the EHT Rectifier valve. If there is no spark, or a small spark, there is insufficient EHT. If this is the case, remove the top cap of the efficiency diode. If the EHT is partially restored, check the boost capacitor. This links the LOPT winding to the EHT overwinding. If this is not at fault, I'm afraid you'll probably need a new Line Transformer. This is where the benefits of 405 Alive come in. Place an advert and be patient. Also, an advert in TELEVISION magazine can bear fruit
I'm afraid LOPT problems on vintage TV sets are all too common. These components led a hard life. One manufacturer of one model of set, no names mentioned, made three times as many LOPTs as sets! Sometimes a set can come on OK, but the picture can get larger and dimmer as the set warms up. If this happens, switch off and feel the EHT winding on the LOPT. There's a good chance it will be warm and possibly sticky. If it is, the LOPT will almost certainly require replacement.
Another possible cause of problems is loss of HT to a specific stage. Check ALL anode feed resisitors. If any are high, replace with new components of suitable rating.
A bright horizontal line means that the Frame Stages are more than likely to be inoperative. Check the frame oscillator onwards to the scan coils. It is often worth trying a replacement Frame Output Valve, Generally a PCL85 or PCL805. The classic PCL85 / 805 symptom is 'Line across screen, no sound.' Unlike the Line Output Transformer, the frame output transformer is generally very reliable. Complete failire of the scanning coils is uncommon, but can happen. Check carefully for broken wires on the scanning yoke, on the CRT, before condemming the coils.
For Lack of Height, check the anode voltages on the Frame Stage valves. Also check the height control and its associated components. Low HT to the frame output pentode (tends to be a PCL85) is the most common cause.
Another common frame problem is poor linearity or Cramping. This is usually down to low value capaciitors in the frame oscillator or output stages. The most severe fault to be found is severely stretched raster at the top and the bottom half of the picture or raster cramped into a bright white line. This too is down to capacitors in the frame oscillator stages and the CR circuit that generates the sawtooth waveform that is fed to the frame output stages.
One other condition you'll come across is no line or frame lock. Check the Demodulator stages and sync seperators. Also the Line / Frame oscillators could be so far off frequency that they can't lock.
Less common is a vertical white line. Most TV sets that you will come across generate their EHT through Line Flyback. If there is a bright white vertical line on the screen, knonw as line collapse, check the connections to the scanning coils, the scan yoke and the coils themselves.
Lack of width can be tricky. First of all, replace the Line Output Valve. Adjust the width control. Unfortunately, lack of width can also be down to the LOPT. Take great care when adjusting controls in the line output stage!
A blank raster and weak sound suggests IF stage problems, lack of signal but plenty of on screen noise suggests that the IF sections are probably alive. Channel Changing should produce some noise on sound and vision channels. On 405 sets, a screwdriver on the Antenna socket can prove the life at least of the IF stages.
SINGLE STANDARD 405 LINE ONLY SETS.
Very old 405 line sets may be TRF, i.e Tuned Radio Frequency, this means that they have no IF stages, but the sound and picture are directly demodulated at RF. This means that they employ the same principles of very early radio sets.
Another thing to watch out for is Live CRT body connections and earthing. Sometimes, the earth on the tube is just a metal strip connected to chassis and pressed against the CRT. Make sure its clean as detailed above.
EHT Generation is not necessarily generated on Line Flyback. In some cases, an extra winding on the Mains Transformer steps the voltage up to 8kV or so to drive the CRT. This winding can be troublesome. If it fails, a suitable transformer can be very hard to find. An extra R.F. EHT Generator unit could be fitted. Another possibility is to use a tripler from the Anode of the Line Output Valve, but this does leave a bit to be desired.
I must also point out that some sets will be pretuned to one channel, in Band 1. Use your signal generator to find out the frequency and check against the FREQUENCY TABLE. To run any 405 line set, you will need a MODULATOR and a source of programmes. Look under TEST GEAR. For single channel sets, you will need the modulator to be on that set's channel, Often Channel 1 London.
DUAL STANDARD MONOCHROME SETS.
Dual Standard sets pose an additional complication or two. The main one is the System Switch, which switches Tuner, IF, Sound and Line Timebase characteristics. Often, this needs little more than a spray of switch cleaner, but if a probem occurs, the Manual is ESSENTIAL. In the case of an inoperative system switch, hard wiring this for one standard is an option. Of coure, 625 Line reception allows the set to be used on a domestic roof antenna, with a VCR, etc. Some dual standard sets, such as the BRC1400 series and its predecessor, the 950 series, incorporate the System switch onto the VHF tuning knob. This is then solenoid operated. If problems occur, check the solenoid and the volts to it.
Later dual standard sets have an integrated tuner, where each of six buttons can be set up for Band 1, Band 3 or UHF, 405 or 625 operation. Switches are often on the side of the tuner module. A good example of this is the Philips 210 series. This principle is also used on some Dual Standard Colour models, see below.
Another word: The LOPT always leads a hard life, even more so at 625. Often a LOPT can fail when the system switch is operated. Also, some weakened LOPTs can operate OK on 405, but struggle on 625. Often, the problem is on the EHT Overwind. Bush sets of this era in particular are prone to LOPT problem! I collect Bush Sets and have personal experience of this!!!!!
There is a case for switching the set off to change system, then turning the set back on again, rather than operating the system switch with the set running. Remember, a LOPT can be hard to get...
DUAL AND SINGLE STANDARD COLOUR SETS.
The Advent of colour made life harder but much more interesting. There were few Dual Standard Colour sets made, as the BBC1 and ITV services were duiplicated on UHF 625 lines in 1969. However, these interesting sets are popular among some of the more masochistic collectors (like me!) and always good for a challenge. Also, the first ever entirely Solid State Colour TV set in the UK, the BRC 2000 series, was a dual standard, back in 1967. I have one as a main TV set!
The approach with all Colour TV sets when doing repair or restoration is to Get it right in Black and White. Mnay of the problems which afflict Monochrome sets also afflicted colour ones, often to a greater degree as the voltage requiements were much higher. DANGER: THE EHT ON A SET OF THIS ERA WAS OFTEN ABOUT 25kV. THIS IS NOT GOOD FOR YOU!!
If you have a Tube Tester, check the condition of the CRT now. But don't rush out and buy a replacment until you have a decent picture of sorts on the set. In the case of very old Colour CRTs, you may need to get the original regunned. I am reliably imformed that A63 11X guns are still available...
Extra issues on Colour sets were convergence and decoding. A colour TV set generates a colour image by superimposing three images, RED, GREEN and BLUE, Herein referred to as R. G. B, on top of one another. Please read the THEORY page if you are not already familiar with the principles of Colour TV.
Using your Crosshatch Generator and also a white raster signal source also a good large mirror to enable you to see the screen from behind the set, follow exactly the workshop manuals preocedures for convergence. In most sets it is possible to switch guns off in turn for checking of purity and convergence. Basically these procedures are as follows:
1: Check that the degaussing circuit is operational. The degaussing coils are on the back of the CRT, often underneath a metal cover. When the set is switched on from cold, you should hear a brief buzzing noise as they operate. If they do not seem to be working, there will be severe impurity on the screen caused by magnetism of the CRT shadowmask. The few components that are associated with the degaussing should be easy to find and check. In cases of severe magnetism, an external degaussing wand may be necessary. Always make sure that this is well away from the set when being switched on or off. Never leave this on when not in use!!
2: PURITY: When the set is on and warmed up, apply a pure white raster and switch off G and B guns, leaving RED ONLY. This should be a constant red display all over the screen. Adjust the purity magnets for this as described in the workshop manual that you shouldn't be without! And MIND YOUR FINGERS! Check also for pure Green and Blue. Then turn all guns on and you should get a constant coloured raster. If it isn't pure white, don't worry yet, we'll come on to Grey Scaling. You just need it to be constant over the whole screen.
3: STATIC CONVERGENCE. This is the convergence in the centre of the screen. Again, use your worksop manual that has been worth every penny hasn't it !!?? Usual procedure is to switch off the blue, converge Red and Green and then match up the blue. The Blue gun has an extra adjustment, Blue Lateral. Do not forget this. After you have got this as good as possible, recheck your purity. It should be OK, but if not, go back and repeat these two steps.
4: DYNAMIC CONVERGENCE. This is where all those controls on that convergence panel come in, please resist the temptation to try judicious tweaking, especially if you find impossible puzzles irritating, as you will correct one aspect at the cost of another, and so on and so on! Use your manual again, and remember to regularly recheck your Static Convergence. Usual Procedure again is to Turn off the Blue, Match up Red and Green and then marry up the Blue. You may have to go back and repeat adjustments several times while setting this up. Patience is needed! Fortunately, the circuitry on a convergence board is very simple so if a specific adjustment will not set, check the components associated with that section. For severe misconvergence, I have on one occasion found that open circuit tracks were the cause! Blue was about 4 inches higher at one side. Another thing to look at is Reversible Electrolytic Capacitors. These are still readily available and they do fail!
The next issue is Grey Scaling. This varies from set to set. Use the manual. The basic principle is to set up the set for the correct balance of Red, Green and Blue to create black, grey and white. If one gun of the CRT does not set up correctly, check the Video and A1 presets before condemning the tube. This should give you at least a good black and white picture.
And FINALLY, when there is a good Black and White Picture, turn up the colour. In most cases, it should come up OK. If not, check first of all the tuning. If this does not create colour, look at the circuit of the decoder. Most decoders have a colour killer circuit which comes in where there is no colour imformation. The book will tell you how to disable this. When you have, you will get either Perfect Colour, No Colour, Incorrect, i.e Negative Colour or pretty coloured stripes. This will tell you where the fault is most likely to lie. Follow the setting up procedures in the manual, this will hopefully show you where to look more closely. In order to fault find the decoder, use the circuit diagram, check DC conditions and follow the setting up procedure. Do this off a Terrestrial transmission and use good signal strength. For more details on how a PAL decoder operates, pay a visit to the THEORY page.
CRT Replacement, should it be necessary, is not as hard as it first seems. Remove the chassis fully and place the set face down, protected, on a low bench such as the floor. Remove the scanning and convergence assemblies from the tube neck. Now put your gloves and goggles on. The CRT normally is held in by four bolts one at each corner and will lift out. Steady the neck of the old CRT as you lift it out, and place it in a safe place. Unpack the new CRT and reverse the procedure. Make sure you put it in the right way up. Use the EHT connection as a guide. Rebuild the set and set up the purity etc. as described above. When you know for sure that the old CRT is definitely faulty, you can either get it regunned or make sure it is disposed of safetly. Imploding glass is not a good christmas tip for the dustman...
A fully restored set should be used and enjoyed, indeed regular use is a necessity to keep the set in the tip top condition to which you have restored it. Never tinker without good reason, and always turn off and unplug the set when unattended. Apart from that, happy viewing!!