I've had a peep inside the Plymouth, and it looks in good condition. The chassis unplugs easily, but the leads are very short and it can't be tilted for servicing. There's a panel underneath the chassis that can be removed, but the platform underneath gets in the way of inspection. I don't know how you were supposed to make voltage measurements; take the platform off and turn the whole set upside down? Any suggestions?

Aside from putting the TV on its side, I can't really say what else to try. Later Astors normally let you sit the chassis at an angle for servicing. Without seeing how yours is mounted, I can't make any suggestions.

I've got the hang of pulling the chassis out quickly, so I'm repairing it using "static" tests of individual components, and voltage measurement on accessible wires. I've got a raster, but the vertical output is weak. The main problem is low boost voltage - it supplies the vertical oscillator and should be 475V, but it's around 400V even with the boost caps replaced and the resistors adjusted (shunted) to their correct values. A fault in the horizontal transformer, or perhaps weak horizontal output valves? The picture width is OK though.

If you have good width I would not be too concerned at this stage with the lowish boost voltage. If the height is really struggling check the height control is not dirty or faulty and make sure the resistor in series with it (3.3 M I think) is OK as well.

It may be a tired Vertical Output valve.

I have an Astor with a slightly later chassis but using much the same circuit. I can check its boost voltage sometime if you want for comparison.

Thanks. I got a bit of improvement with a new vertical output valve (6GV8), and the height is just about OK now. The problem with the boost voltage was a weak horizontal oscillator valve(6BL8). Now to see how the set handles pictures!

The Astor's producing fairly good pictures, but they're a bit stretched on the left-hand side. Adjusting the horizontal linearity coil doesn't have much effect on this fault. I've measured the inductance of the coil, and it can be varied between 6 and 8mH, but perhaps it's got a shorted turn.

The grid voltage on the vertical oscillator section of the 6GV8 is -4.5V, much lower than the proper -11V. So there's still a problem in this area, too, unless my digital multimeter is loading it too much. The diagram shows voltages measured by a VTVM.

Most if not all digital multimeters will have an input impedence of 1M or more which is similar to the old VTVM's, so I doubt you're meter is giving low readings.

The linearity coil may be ok, there are some more checks that can be done before concentrating on the coil. As long as it does not look burnt chances are good that it's ok.

Starting with the H Linearity issue, there are several things to check. Make sure C104, C106, and the width capacitor that is being used (either C108, C109 or C111) all measure the correct value and have no leakage. Also check that R124, R126, R127 and R129 test ok (all can be checked without unsoldering connections). It is important that the capacitors have no appreciable leakage as this can cause linearity issues. If possible check capacitor leakage with at least 200 volts on the capacitor.

The height problem may be related to the H Lin fault. The boost HT voltage may still be a bit low. Whats the voltage at pin 1 of the 6GV8 (V OSC anode)? Should be approx 50 volts. Check that capacitors C73, C74 and C112 have no leakage.

Thanks for that, Andrew. I'm building a capacitor tester now. I suppose I could "throw some polys at it", but I'd like to know exactly what's wrong.

Glad to help. Hopefully you can narrow down the fault to one of the parts I mentioned.

Try having a look at the yoke. If it has two round ferrite pieces, one either side of the yoke, try to adjust the one on the side of the yoke where the picture is affected. The drive hole is usually square and the ferrite will probably be tight..Remove the ferrite, rub a little grease onto the surface of the ferrite and replace it. The adjustment of this item can make a big difference to the linearity.

Vertical stages always seem to be critical with regards to component values. One thing to check is that there is no leakage to the chassis from the height control. This was common in G.E. televisions. Any leakage will probably not be able to be measured. Undo the height control tabs and disconnect it from the chassis. It is worth a try and only takes a moment to do.

Wayne.

It's taken me two years to get back to work on the Astor Plymouth, but I've fixed all the vision problems now. The chassis in this is the 4A, the last one with point-to-point wiring.

The horizontal fault was actually caused by me "throwing polys at it"; I had replaced the horizontal linearity papercap (C104) with a poly marked .022μF. Even though the poly was brand new, it was faulty, with a value of about 20pF. This is why there was no improvement when I adjusted the linearity coil L22. Relaced it again, and got a straight picture.

The lack of boost voltage and vertical height (not awful but still not quite enough for the widest horizontal setting) was caused by the focus pot R132; the track resistance was 1.7M instead of 2M. The boost voltage is mainly determined by this component, which has a very loose tolerance and can vary from 1.5M to 2.5M. I think it's fair to call this a design fault! R132 can be replaced by a 3M or 5M pot without upsetting focus control. I used a 3M.

Now for the "caption buzz". I've tuned the sound detector coil, with a slight improvement, but it also helps to set the DVD player output to "low sharpness". I'm also going to try a higher level of sound modulation if I can.

(Thanks to Andrew and Wayne for their advice.)