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I recently picked up a faulty Hitachi V-1150 'scope and after fixing a problem in the power supply it now starts up. However, it only uses the very middle of the screen vertically, and goes wild if I try to lower the volts/div.

My theory that the oscilloscope "thinks" that the screen is smaller than it is is also backed by the fact that turning the vertical position knobs to their extremes only moves the trace up and down a tiny amount.

As you can see from the pictures, the entire trace is also shifted to the right.

The largest I can get the trace so the waveform is displayed accurately:

The largest I can get the trace so the waveform is displayed accurately:

When I decrease the volts/div:

When I decrease the volts/div

Does anyone have any ideas about the cause(s) of these problems?

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  • \$\begingroup\$ something is off with the vertical deflection circuitry \$\endgroup\$ – Trevor_G Jun 6 '17 at 19:45
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    \$\begingroup\$ You can get a copy of the service manual here. It includes schematics. \$\endgroup\$ – JRE Jun 6 '17 at 20:08
  • \$\begingroup\$ Shifted to the right could be that it just needs adjusted. The vertical problem looks more like a capacitor somewhere is shot. I'd take a look at all the electrolytic capacitors. If there are any paper and oil or wax capacitors in there then I'd suspect them, too - but I think that scope is modern enough not to have any paper capacitors. \$\endgroup\$ – JRE Jun 6 '17 at 20:16
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    \$\begingroup\$ Looks like you haven't really fixed the power supply. Low vertical deflection suggests insufficient supply voltage on the Y amp (most scope tubes need several hundred volts across the plates for full deflection). The 'going wild' at lower V/div could be ringing in the peaking coils. \$\endgroup\$ – Bruce Abbott Jun 6 '17 at 21:21
  • \$\begingroup\$ Ok thanks everyone. I'll check all of those things out \$\endgroup\$ – Ben Stobbs Jun 7 '17 at 16:10

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