Hi there I now have my HMV F5 working well, though a couple of queries remain. I have ion burn magnet but dont know how it should be installed and can see no markings on the tube neck. There are also 3 bits of metal supporting a metal ring with tabs on it that I have not put back and have no idea what they are supposed to be there for. This was on the tube neck also. Can anyone shed some light on this for me?

thanks

The ion trap magnet sits on the CRT neck in the area of the electron gun where it changes from bent to straight. It is adjusted for maximum brightness on the CRT. I'll send a picture to Brad to insert into this post showing where it goes.

The metal ring sounds to me like the metal cone that fits over the deflection yoke. The other possibility is that it is a picture centering ring. The picture I'm sending will show the details of the yoke cover bits as well.

Thanks for that, I have since worked it out (partially anyway) it turns out my TV has had a replacement tube of a type that does not need an ion deflection magnet. the rings are small magnets that centre the picture. I have refitted them but they are very hard to adjust and I'm not quite sure how. Is there some sort of procedure to follow to adjust these correctly?
The latest issue( theres always something!) is black incurving edges down each side of the picture. Maybe placing of the deflection yoke?

The black concave edges on the raster sound more like an issue in the deflection circuits, not the yoke itself. The yoke could be bad, but I usually find such issues with my set are due to bad components in the deflection circuits (namely leaky wax, electrolytic and polyester caps, and out of tolerance carbon resistors).

Another possible cause could be an issue with the magnetic rings on the neck of the tube, as the way they are adjusted affects the geometry of the raster. I'm restoring a 1965 HMV Windsor, and had to replace the focus ring assembly as the housing was brittle and crumbled away. I had to replace the entire assembly with a focus/convergence assembly from a CRT monitor, which affected the vertical linearity and size of the raster. I just stuck some magnets on the tube near the yoke, to help bring the picture back to its proper parameters.

Chris

The centering rings are are normally adjusted together. i.e. adjust both rings together to shift the picture. To increase or decrease the strength of the magnetic field you move only one of the rings in relation to the other.

The inwards curving black edges sounds like pin-cushion distortion and is corrected on black and white TV's by small magnets placed on the left and right side of the deflection yoke. Yours may be either mis-adjusted or missing.

Is your replacement yoke an original HMV yoke or something else adapted to suit?

Thanks both for response. The incurving black edges only appear after the set has warmed up for a while, so I am figuring it may be the only capacitor I have not replaced in the horizontal circuits, C104 . 0.0047 μF. Interestingly there is a 10 ohm resistor connected in seies with it which is not on the circuit diagram. There are also a couple of small capacitors connected to the LOPT which are not on the diagram,with no markings so I dont know what to replace them with or even if they are needed, and C108 on the diagram was clearly never there. Not being too clear on the function of C 108 I thought I'd put one in anyway, didnt seem to change anything. Any ideas why there are differences in the circuit?

Thats useful to know about the adjustment of the magnets, I will now have some idea how to go about it!

The new yoke was taken from another set, it looks just the same as the old one but I'm not entirely sure.

I dont see any magnets other than the focusing ring magnets.

Other issues - I have never been able to get the verticle linearity quite right, all caps changed and resistors checked. a part of the verticle scan near the top(but not right at the top) of the raster is a little squashed up,increasing the height control worsens it, as setting the verticle hold to the lower frequency end. I suspect it might be the output transformer, any other suggestions?

The BHT is higher than it should be (by 100v or so) could that be the cause? I dont know why it is high or what if anything to do about it. Only thing I can think of is that the HT voltages are also very slightly high. This may be because ive pulled out V3-6,10,12-14 as I dont need those circuits as I feed the video signal to the grid of v7 via a preamp I found the circuit for on a French website (see Krieslerals forum if interested.) it gives a beautiful result!

Stu

The only capacitors that need to be changed around the LOPT are any waxed paper ones. If C104 is a waxed paper type then it could very well be the cause of your problems. The other small value capacitors are most likely ceramic types and should be fine still.

The differences between the circuit and the actual TV is not that unusual. If the extra parts look original then they may be production modifications. Not all of the service bulletins have survived (as far as I'm aware) so there is no way of verifying what is a factory mod and someone making up their own mods.

There is a vertical linearity adjustment. I assume you have tried it? If not it may solve your linearity issue.

Just how much higher are the HT1 and HT2 voltages? Anything more than 10v higher than the factory figures may cause unintended problems. The 100v higher than normal boost HT voltage is also a worry. It may mean the line output stage is running well beyond it's designed output and EHT to the CRT may be excessive as well.

I replaced C104 on the weekend, when I switched on smoke came out. It turned out to be the resistor( actually 100 ohm not 10) in series with it heating up. I wasnt really sure what to do, replace it or take it out as per circuit diagram, I figured in case there is some other modification which necessitates this I would replace it. So there must be appreciable current flowing through it, and it appears the old capacitor was virtually open circuit ( though almost impossible to verify its behaviour in high voltages and frequencies) .

The whole set seems to be behaving differently now . Does anyone know what the function of that capacitor is exactly? The BHT is still high, though not quite as high. What could cause it to be high? I'm reading up on these circuits but its hard to understand it all completely. The HT voltages are 10-20v high - but I will measure everything again sometime.

The vertical linearity seems better now, though I dont quite understand how unless the BHT voltage.
Now theres another vertical problem - was there before but worse now, intermittently it seems to sort of momentarily stall giving flashing bright scanning lines part way down the screen. This will be difficult considering its intermittent. Hoping not the VOPT !

There is also an issue in that when the brightness is turned up to a certain point the picture enlarges, dims and then fades. I read somewhere that might be an EHT problem?Its worse since replcing C104. I also read somewhere that the C104 may be something to do with EHT regulation, but not sure its that one.

Another question I have which has been bugging me some time, if anyone can answer, I understand the sync pulses are derived from the video amp output, , however the video output leads to the noise inverter, and there is another lead from the grid of the video amp to the sync seperator. What do these two connections do?

Oooh, that's bad!

The 100 ohm resistor sounds like it may be a bodge to fix another fault. I may be wrong but to me, C104 forms a part of a parallel resonant circuit with L28 (width coil) and a portion of the line output transformer. Reasonably high circulating currents would be expected in this area so I'm not too surprised that the 100 ohm resistor smoked. It would only need 100mA of current to do so.
I'd be inclined to leave out the 100 ohm resistor and double check that your replacement C104 is a 0.0047μF (4n7) capacitor and that it is not faulty. Even though it's new it may be shorted. Make sure it has a 600v or more rating.

Remember everything is running at 15.625 kHz AC so the behaviour of the circuit is very different to the DC behaviour. The reactance (capacitive resistance) of C104 at 15.625 kHz is around 2200 ohms so it won't behave as a short circuit.

The picture problem at high brightness sounds typical of "blooming". It's due to low EHT voltage when beam current is increased (i.e. high brightness). Normally due to a weak EHT rectifier which in your case is a 1S2 diode.

The vertical problem is hard to pin down. Your high HT voltages won't be helping, the circuits are under more stress. You may want to consider adding a high wattage resistor just after the first choke in the power supply to correct the voltages to the TV.

I'm attaching a scan from the service manual explaining the noise inverter and sync separator stage. Hopefully it will make sense to you.

HMV F5 Extract.

Thanks very much for that. Ive been busy with other things for a while but I did replace the 1s2 with another , fixed the EHT problem , easy! If only it was all that easy( it would probably be boring then!)

The set has been behaving quite well lately, but there must still be something not right with the horizontal , the width control never did anything, that I can see anyway, which must be tied up with the C104 issues. Now its started flickering very slightly from side to side. But the vertical seems ok now. Theres always something!

Ill check all the voltages properly sometime soon.

thanks for the extract, id be really greatful for a copy of the whole document , happy to pay postage or whatever is easiest for you. I have been reading G.M.PATCHETTS TELEVISION SERVICING , VOLUMES 1-4 , highly recommended , really increases my understanding, but its hard going. The trouble is its British, and there were design differences between the countries, mainly the fact that most TVs in the UK had no mains transformer. Still much of it is relevant, but it would be great to have the specific explanation of my particular set.

It will take a few days to sort the scans into a decent pdf document before I can get it hosted here. If you want it sooner, email me and I can send you the raw page scans.

HMV F5 Service Manual

Uploaded.

Thanks so much for that, I'm looking forward to studying it. it should answer a lot of questions I had and more! The previous page you sent already answered some questions such as the function of T5.
my latest issue with the set, an interesting one, where copy protection is included on a DVD it shows up on the screen as a series of broken lines accross the top of the screen sloping downward left to right about 10 degrees. I remove it with a video stabiliser but in all cases there is still one feint line as described. These lines roll around when vertical hold is adjusted. I'm going to research the copy protection to see what it translates to in the composite wave form, but it still seems something else is not quite right.....

Further to my last entry about the sloping lines, could it be that these are flyback lines (and the copy protection I understand occurs during the flyback period) and flyback is occurring too slowly showing some horizontal scans rather than a diagonal line as would be expected? And that these are not being supressed properly, or that the flyback process is lasting longer than it should therefore persisting after the blanking period.

If that is the case then I need to see why, but in studying this I dont understnd the wave forms on the vertical output circuit. The coils must have a linearly increasing current from a negative value to an equal positive value then immediately falling back to the negative value. Then the transformer primary must have a current increasing at a constant rate of increase. However the wave forms shown look like a series of sharp peaks. Can anyone shed any light on any of this?

Macrovision messes with the sync pulse levels and cause severe disturbance in the sync circuits. It will produce the effects you see and trying to restore the video so that it has the correct sync levels can be difficult. You really need to use a clean video source to get an idea of the true operating state of the TV before deciding that there may be a fault.

The waveforms shown on the circuit are voltage waveforms. Inductive circuits react to changes in current and as you have correctly surmised a constant (ramped) change in current is required to produce a linear scan. Applying a voltage pulse to an inductor will produce a steady increase in current as it converts change in voltage to magnetic flux to oppose the voltage change. The opposite occurs as the voltage decreases.

Yes I see that now about the voltage and current.
I use a video stabiliser to take away the copy protection so I get a clear picture, but there is stilll one feint line near the top actually sloping upward left to right not downward. Its no great issue, I'm just curious how this is possible!