I have this tek 465m for many years and it has always had the
following problem.

There is no horizontal sweep (either A or B) when the "var" knob
is in the calibrated position (i.e. uncal LED off). other than
that the scope works really well and other than being an annoyance
it hasn't bothered much.

However, last week last week the high voltage supply when out (the
fuse blew) and after fixing that, I wanted to dig into the horizontal
problem. I don't think the HV problem and the clibration problem are
related at all.

What I have found is this.... the switch and variable pot are OK. There
are two switch circuits, one shorts the variable potentiometer wipe to
the low contact and the other switche the uncalibrate LED. Just shorting
the wiper on the potentiometer using a jumper wire, while the variable
pot is at 25% will "calibrate" the sweep timing. It turns out that the
sweep will only work when the LED is "on". There are three LEDs which are
driven off the same power supply, which look like they are derived from
the +32V using a voltage divider, trigger, MAG10 and the Uncalibrate
LED. It turns out that if either of the MAG10 or the Uncalibrate LEDs
are on, the sweep will work. There is a small dip in the LED power
supply rail (5mV) when either these LED are on. I suspect that this
also effects something in the sweep generator.

Has anyone run into this ? I do have a maintenance manual. Unfortunately,
this manual does not have the foldout schematics and the simplified
schematics aren't relevent. Anyone know were I can get a copy of the
schematics for the relevent sections (i.e. sweep, LEDs, etc...).

Thanks, -ingo

--
/* Ingo Cyliax, , Tel: 812-391-0895 */