Oscilloscope METRIX OX734 - Page 1
Forum section: electronics / repair

author: Oliv_Bricol-2
author_rank: Contributor
timestamp: October 13, 2025, 07:17:59 am
content: Hello everyone.I'm trying to get an old METRIX OX734 oscilloscope back up and running. The display is surprising, and I don't know the cause of this type of fault, or especially how or where to fix it. I'm including the image; it will be simpler than trying to explain. The image represents the signal from the device's calibration output, a simple square wave signal.

author: ondraN
author_rank: Regular Contributor
timestamp: October 13, 2025, 10:53:53 am
content: This can be caused by a bad Astigmatism setting, or synchronization instability. Astig and Focus are best set on a sine wave.Trigger instability is often caused by faulty capacitors1. in the source and thus poorly filtered supply voltage2. faulty decoupling capacitors.Send a photo with a sine and triangle signal, it will be clearer there.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 13, 2025, 05:26:44 pm
content: The electrons spot is not focused, has a very elongated horizontal shape (astigmatism distortion), instead of being a small round dot. Try rotating the AST. knob, and the focus FOC. knob too, if needed.Does the spot shape respond to those knobs?

author: Oliv_Bricol-2
author_rank: Contributor
timestamp: October 14, 2025, 01:53:05 pm
content: Hello,Thank you for your clarification. I've adjusted the focus, but I don't know about the astigmatism anymore. I'm going to inject other signals, but indeed, there's a kind of trail, or the trace bleeds, the middle of the trace is lighter than the ends. Yes, the settings work well and respond normally, I think.

author: ondraN
author_rank: Regular Contributor
timestamp: October 14, 2025, 05:06:49 pm
content: If the astigmatism and focus are not set correctly, then the brighter center of the upper and lower level display is normal. Use a sine signal, that's the best way to set it.

author: RoGeorge
author_rank: Super Contributor
timestamp: October 14, 2025, 05:43:20 pm
content: If you don't have a signal generator, touch your finger to the tip of the probe (or connect the probe to a long wire/cable of 1/2meters, with no power on it, just the wire), that should make the induced hum visible on the screen. The mains hum on the screen should look about the same as a sinusoidal signal, but with a lot of wiggling. Sinchronize the oscilloscope on this signal, or synchronize the scope on "Line" if it has such a setting.While touching the probe tip, first, set the volts/div to see the entire amplitude of the sinusoid in one screen. Then set the time/div to 10ms/div or so, so you will see some wiggled signal resembling a sinusoid. Doesn't have to be perfect, the exact shape is irrelevant. Now turn the AST button until you get the same width of the trace everywhere. Then adjust the focus, then again the AST, then the FOC, until you get a trace of constant width, and in focus no matter if the waveform is increasing, decreasing, or horizontal.Luminosity of the spot has to be just enough to see the spot clearly in a shaded room.If, after adjusting the AST and FOC, you still can not get can not get a round spot of 1mm or less (so a sinusoid with equal width of the spot trace everywhere), then you might need to open the oscilloscope and fix the focus/astigamitism circuitry.

author: Roehrenonkel
author_rank: Frequent Contributor
timestamp: October 14, 2025, 06:58:47 pm
content: Hi Oliv_Bricol-2,i'm not sure on what channel you are triggering,show us the settings.Best

author: Oliv_Bricol-2
author_rank: Contributor
timestamp: October 15, 2025, 08:59:52 am
content: Hello, I have adjusted to obtain a correct visualization of the signal, it is identical on both channels. I will inject sine and triangle on each as indicated, I have never had glasses with astigmatism before.

author: Oliv_Bricol-2
author_rank: Contributor
timestamp: October 16, 2025, 07:46:26 am
content: Hello, strangely, the display is better. On the different signals, the AST is at its limit. It's impossible to get better. The trigger is very difficult to obtain; there's always a slight shift in the trace in one direction or the other.It's not a big deal; I'd like to convert it into a gadget to display LISAJOU curves. Thanks everyone for your advice.