Analog scope trace ref height

[Lance Morgan]

I'm borrowing an old 2 chan 20MHz analog scope - a Hitachi V-212

After I set the trace height to zero (or whatever reference point) -
there's a big height change (sometimes by 2 or 3 grids) when I change
the (vert) Volts/DIV to the next setting. This is with no input
signal. This is abnormal(?), as it should remain fairly stable, right?

Is also weird that the recessed DC balance pots appear bent - facing
down - and are not readily accessable

Thank you,
Lance

 

[Jim Adney]

On 31 Mar 2004 15:33:34 -0800 alancemor@yahoo.com (Lance Morgan)
wrote:

I'm borrowing an old 2 chan 20MHz analog scope - a Hitachi V-212

Those are actually nice little scopes. Nothing like Tek quality, but
still reasonable for a cheap scope.

After I set the trace height to zero (or whatever reference point) -
there's a big height change (sometimes by 2 or 3 grids) when I change
the (vert) Volts/DIV to the next setting. This is with no input
signal. This is abnormal(?), as it should remain fairly stable, right?

Is also weird that the recessed DC balance pots appear bent - facing
down - and are not readily accessable

You adjust the DC balance pots to get the trace not to move up or down
when you change ranges, the fault you mentioned above. It is most
likely that the PC board inside has just shifted somewhat, or that it
never was quite right so that it's hard to get to these pots.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

 

[Walter Harley]

"Lance Morgan" <alancemor@yahoo.com> wrote in message
news:2a52f3e9.0403311533.1ae5e67@posting.google.com...

I'm borrowing an old 2 chan 20MHz analog scope - a Hitachi V-212

After I set the trace height to zero (or whatever reference point) -
there's a big height change (sometimes by 2 or 3 grids) when I change
the (vert) Volts/DIV to the next setting. This is with no input
signal. This is abnormal(?), as it should remain fairly stable, right?

If you ground the input, rather than leaving it dangling, is it still the
case?

 

[Jim Yanik]

Jim Adney <jadney@vwtype3.org> wrote in
news:q0um60djf0g98qgtm85vr8ja5rfabcnv81@4ax.com:

On 31 Mar 2004 15:33:34 -0800 alancemor@yahoo.com (Lance Morgan)
wrote:

I'm borrowing an old 2 chan 20MHz analog scope - a Hitachi V-212

Those are actually nice little scopes. Nothing like Tek quality, but
still reasonable for a cheap scope.

After I set the trace height to zero (or whatever reference point) -
there's a big height change (sometimes by 2 or 3 grids) when I change
the (vert) Volts/DIV to the next setting. This is with no input
signal. This is abnormal(?), as it should remain fairly stable, right?

Is also weird that the recessed DC balance pots appear bent - facing
down - and are not readily accessable

You adjust the DC balance pots to get the trace not to move up or down
when you change ranges, the fault you mentioned above. It is most
likely that the PC board inside has just shifted somewhat, or that it
never was quite right so that it's hard to get to these pots.

-
-----------------------------------------------
Jim Adney jadney@vwtype3.org
Madison, WI 53711 USA
-----------------------------------------------

Most likely,someone slid the cabinet on wrong(carelessly) and snagged the
pots.I've seen people cut coaxes,and break switch wafers this way,too.

--
Jim Yanik
jyanik-at-kua.net

 

[Lance Morgan]

Jim Adney <jadney@vwtype3.org> wrote in message news:<q0um60djf0g98qgtm85vr8ja5rfabcnv81@4ax.com>...

On 31 Mar 2004 15:33:34 -0800 alancemor@yahoo.com (Lance Morgan)
wrote:

I'm borrowing an old 2 chan 20MHz analog scope - a Hitachi V-212

Those are actually nice little scopes. Nothing like Tek quality, but
still reasonable for a cheap scope.

After I set the trace height to zero (or whatever reference point) -
there's a big height change (sometimes by 2 or 3 grids) when I change
the (vert) Volts/DIV to the next setting. This is with no input
signal. This is abnormal(?), as it should remain fairly stable, right?

Is also weird that the recessed DC balance pots appear bent - facing
down - and are not readily accessable

You adjust the DC balance pots to get the trace not to move up or down
when you change ranges, the fault you mentioned above. It is most
likely that the PC board inside has just shifted somewhat, or that it
never was quite right so that it's hard to get to these pots.

-

Thanks for all of the responses. You guys were right - I can see where
one of the front base foot pads has been pushed up, into the bottom of
the chassis shell by + 1/4", bending the bottom panel up, most likely
shifting the PC board & pots

Lance