Tektronix 2225 oscilloscope showing only two Dots instead of two lines

[megadeth]

Hi everyone,

Just got a secondhand Tektronix 2225 oscilloscope as my first oscilloscope, when I switch it on only showing two dots on the screen which representing the two channels, they are responsive to vertical and horizontal position knobs, unfortunately, I got the oscilloscope without the probes  so I will not be able to test if these dots are responding to the measured waves unless I buy the probes, could anyone advise how to start troubleshooting this problem.

Thanks in advance.

[Circlotron]

Is the SEC/DIV knob set to XY? That will produce a stationary dot.

[megadeth]

Is the SEC/DIV knob set to XY? That will produce a stationary dot.

No, it is not on XY, I will take a photo to it once I reach home and posted here.
Thanks,

[David Hess]

Having the beam unblanked but the sweep stuck often means that the sweep generator has failed.  Sometimes it is as easy as the JFET buffer being bad.

[CaptDon]

Try the AUTO TRIG mode. If no input then the thing probably isn't even triggered!!

[megadeth]

Try the AUTO TRIG mode. If no input then the thing probably isn't even triggered!!

OMG, Thanks a lot i got it work perfectly now.
Appreciate your help, and thanks to everyone who tried to help.

[TimFox]

"Auto trigger" means that the CRO horizontal sweep waits for a finite time without receiving a trigger, and then triggers itself regardless of the trigger level setting.

[artag]

Just poke a bit of wire (or a resistor) into the centre of the input BNCs. Your fingers will pick up lots of 50/60Hz mains noise and give you a display.

[donlisms]

Or maybe not...

BNC connectors actually have specs and precision tolerances and that sort of thing.  It's generally a bad idea to risk loosening up the contacts with a random piece of wire, if you want to keep your connections in good shape forever.

(Not that I would ever do that...  :-) )

[David Hess]

On vintage oscilloscopes the BNC for channel 1 is often worn out through normal use anyway.

There is nothing special about the BNCs on a 50 MHz oscilloscope, so they can be easily replaced.  Check out the wire dressing going to the BNCs on the 50 MHz 2225, or any of the 100 MHz 22xx oscilloscopes.  It is usually a low value air wired 1/8 watt carbon composition resistor.