Tektronic 2225 Oscilloscope Trigger Fault

Thread Starter

wood77fly

Joined Jul 20, 2020
8
Good Evening I have a tektronix 2225 oscilloscope that I have not used for a number of years. I needed it to measure the output from a 26mhz oscillator but I cannot see a sensible waveform. It just looks like a blurr. The waveform for the 1mhz test point can be held still with a little fine tuning but any higher frequency cannot be displayed properly. The trigger LED only comes on briefly on the 1mhz test point on higher frequency the trigger LED does no come on at all. Does anyone have any ideas on where to look on the pc board for the trigger fault. Kind Regards
 

MrChips

Joined Oct 2, 2009
21,689
Tektronix 2225 Oscilloscope is a 50MHz scope. You are going to have a difficult time trying to measure a 26MHz signal.
Are you using an oscilloscope probe set to the x10 attenuation position? Without a probe your bandwidth is 2MHz.
Do not set the VERT channel amplitude to x10. The bandwidth at that setting is 2MHz.
 

Thread Starter

wood77fly

Joined Jul 20, 2020
8
Tektronix 2225 Oscilloscope is a 50MHz scope. You are going to have a difficult time trying to measure a 26MHz signal.
Are you using an oscilloscope probe set to the x10 attenuation position? Without a probe your bandwidth is 2MHz.
Do not set the VERT channel amplitude to x10. The bandwidth at that setting is 2MHz.
 

Thread Starter

wood77fly

Joined Jul 20, 2020
8
Thanks for the information. Yes the probe is set to x10 but I will check the vert channel amplitude. I am however concerned that the trigger LED is not showing. On all Youtube video when the trace is locked the LED is on showing triggering is active. Kind Regards
 

Thread Starter

wood77fly

Joined Jul 20, 2020
8
Thanks for the information. Yes the probe is set to x10 but I will check the vert channel amplitude. I am however concerned that the trigger LED is not showing. On all Youtube video when the trace is locked the LED is on showing triggering is active. Kind Regards
 

Thread Starter

wood77fly

Joined Jul 20, 2020
8
Regarding the trigger source, coupling, and mode , I assumed that I had got this correct as the 1Mhz test trace could be held steady. Regards
 

AlbertHall

Joined Jun 4, 2014
10,258
Set the trigger to DC coupling, normal mode, and connect a low frequency signal (e.g. 1kHz), set the timebase to show 2 or 3 cycles of the signal. Now adjust the trigger level control and you should see that the trigger point moves from the bottom to the top of the waveform.
If that is OK then connect your 26MHz signal and adjust the timebase appropriately, and see how the trigger works.
 
#1. test scope with calibrate signal x10 probe
#2. Compensate the probe, adjust pot on probe fro square wave, x10 probe
#3. make sure there is no appreciable voltage between the ground of the scope and what your measuring.
#4. This is probably an appropriate time to use the ground clip of the scope probe.
#5. use external trigger if you can.
 

Thread Starter

wood77fly

Joined Jul 20, 2020
8
With 1 khz standard signal connected x10 probe set for square wave coupling DC 0.5 m/s per div Source EXT=Z Volts 0.5v per division . I get a square wave trace 3 divisions high X 7 Divisions wide which I can hold still with great difficulty with the hold off control. Switching level from + to - does nothing to the trace at all. Slope seems to inverts the trace but difficult to see as the trace starts moving. At all times the triggerLED does not come on. If I move the mode to 'norm' the trace dissapears and pressing the beam find then results in a verticle line 'no waveform. The square wave only appears if I move mode to TV line/ p-p auto. I feel cirtain that the trigger circuit is faulty but then I am no electronics engineer. Regards
 

Thread Starter

wood77fly

Joined Jul 20, 2020
8
Unfortunately not. A shematic I believe is available on line but although I have reasonable experiece with electronics I doubt that I would be able to diagnose from a schematic unless there is a fault finding proceedure for the trigger board. I dont have a second scope. I could have a look around for a puffed up cap or a burned track but it would be good if someone could give me a few pointers first. Regards
 

AlbertHall

Joined Jun 4, 2014
10,258
It would next to impossible to find the fault without a 'scope to follow the trigger signal.
By all means look round for anything suspicious.
You should be able to find where the trigger circuitry is by looking for where the trigger level control is connected.
 

Thread Starter

wood77fly

Joined Jul 20, 2020
8
I have managed to find a pdf of the maintenance manual. On page 4-14 it starts by saying ' check that the display can be
un-triggered at either extreme or rotation of the trigger level control. If the trigger level pot were faulty i.e. shorted to either end of the track would that not stop the triggering
 

AlbertHall

Joined Jun 4, 2014
10,258
That's an unlikely fault for a pot. More likely is that the wiper doesn't connect to the track or that the track is not connected at one end. Either of those could stop it triggering - but there are lots of other reasons too.
 
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