Mighty Monarch of The Air

[Phil Nelson]

You know that your power supply is working somewhat, since you have a raster on the screen and full vertical & horizontal deflection. To put roundscreen's suggestion another way, it would be useful to find out if the right voltages are being supplied to other parts of the TV (such as IF sections). The 200-something voltage supply is often called "B+," as Bill says.

If you look at your basic power supply, it delivers two such voltages, +255vdc and +210vdc:



If you look around the full schematic, there are a number of spots where a little arrow from a section points to either +255vdc or +210vdc.

http://antiqueradio.org/art/temp/Majestic1600A.jpg
http://antiqueradio.org/art/temp/Majestic1600.jpg

The arrow means that a particular circuit draws from that part of the power supply.

If you want to be very systematic, you could start from the ground up, first checking to see if those two voltages are present at the two output points from the basic power supply. (I'm guessing the answer is Yes, else you wouldn't have a full raster.)

Next, you could go around the schematic, checking each place where you see the little arrow to one of those supplies. If you find the right voltages at every spot, that's great! Power is reaching all of those main take-off points.

Finally, you could go to page 8 of the Sams manual, which has the voltage chart, and zero in on the voltages for each tube.

The highest voltage usually goes to the tube's plate. On V14, for instance, that is pin 3.

Since the video IF was suggested, you can check the video IF tubes: V3-V4-V5. On those tubes, the highest voltage is at pin 5 (also 6). For the video section, this will answer roundscreen's question whether the correct B+ voltage is getting to those tubes. For the audio section, the IF tube is V8 and its plate is also pin 5.

Voltage checking is tedious and you must be careful to avoid shocks. Put one hand in your pocket when touching the voltmeter probe to any point in the live chassis.

In the old days, a repair shop would have a set of "tube extenders" that plug between the tube and the chassis, exposing test points for each pin above the chassis. If you don't have tube extenders, you can set the chassis on its side and measure from underneath. If neither of those is possible, you can wrap a short piece of wire around the pin in question, re-insert the tube, and measure from that wire (slip a bit of plastic or paper between the wire and the chassis to avoid a short circuit).

An experienced repairman with a shop full of specialized equipment (signal tracer, oscilloscope, etc.) could isolate your problems much more quickly, but if you're armed with nothing but a multimeter, this slow approach can be useful.

Read the little notes below the voltage chart before you start, and note the line voltage setting (often 117vac). For initial checks like this, I want to see whether a voltage is in the right ballpark. If the chart says 105vdc and I measure, say, 93vdc or 111vdc, I figure that's close enough for the tube to basically operate, and I move on to the next one.

Sometimes, a bad reading will jump out at you, and then you can look for a burned resistor, miswired component, etc., in that tube's circuit.

If you go through all of these measurements and don't find any bad readings, you have not wasted your time. It's useful to know all of the places where your TV does have correct voltages, and that would confirm that a lot of your recapping work was successful.

If measuring voltages on the live chassis isn't practical, for whatever reason, you could fall back on the resistance chart, measuring resistances on the same pins. I normally do this from under the chassis, with the tubes in place.

Sorry for the long-winded reply. This is my way of avoiding work on my Capehart set, where I'm unearthing ugliness like a burned-up width control

Phil Nelson