You can get an idea of which major circuit block the problem is in with a
few voltage measurements. First, a caution about this instrument; there are
very high voltages running around inside, and they can be lethal (that means
that they can kill you).
First, the obvious thing to check is the power supply voltages. Start with
the AC line fuse. There will probably be test points in the vicinity of the
power supply. Check these first, and fix any outputs that appear dead or
show wrong voltages. Also, while you're taking a first look around, make
sure that the CRT filament is lit up. If it isn't, then the CRT and the
power transformer are suspect (don't forget to check the power switch).
I assume that you have no schematic for the unit. That means that you don't
know which pins on the CRT the deflection plates are connected. Usually,
they are fed by very well insulated wires that stand out in the open, not
dressed close to the chassis. Check voltages at the wires coming from the
vertical amp. These voltages should be very close to the same. They will
likely be at a high potential (200-400 volts). If they are not very close
(within a few volts), then the problem is likely in the vertical circuit.
Do the same check with the horizontal amp. Again, voltages should be pretty
close. You will have to disable the sweep to make sense of this
measurement; set the Time/Div switch to X-Y, or whatever function it has
that disables the sweep.
If these voltages are OK, see if you can find a test point for the high
voltage. It should be available as a divided voltage, so you can check it
with a multimeter. If there is no test point, you will need a high voltage
probe to check the CRT anode voltage at the HV button. Be very careful
here. Turn the scope off, connect the HV probe, then turn the scope on.
After checking, turn the scope off before removing the probe. Obviously, if
the HV test point, or the HV probe reads 0V, then the problem is in the HV
section.
If all of the above show no discrepancies, then the problem may be in the
sweep circuit. Probably an easy way to check the sweep circuit is by
setting the sweep time switch to a low sweep speed, such as 1 sec/div. Then
you can watch the sweep building on your voltmeter.
Without a schematic, that's about as specific as I can get. You should be
able to get the service manual from Leader.
--
Tweetldee
Tweetldee at att dot net (Just subsitute the appropriate characters in the
address)
Time is what keeps everything from happening all at once.
