Hitachi V-252 Oscilloscope Repair

Thread Starter


Joined Feb 10, 2017
My trusty Hitachi Oscilloscope suddenly ceased scanning and I was left with a dot in the centre of the screen when switched to the X_Y mode.

I have have spent ages trying to google the problem with little success, but as I have finally solved it I thought it might be helpful to others to pass on my findings!

Reseach told me that a dot indicated a Horizontal failure, and I was unable to obtain a copy of the V-252 Service Manual. However, I was able to get a service manual for the earlier models V-211/V-212/V-222 & V-422, and after looking carefully at this manual, it became clear that the PCB layout & components in my V-252 were almost identical.

I checked all the voltages and noticed that the 5 Volt line was only reading 0.92 volts, but all the other voltages were fine. I checked the 5 volt 7805A regulator out of circuit and it gave me a 5.15 volt output voltage reading so I assumed that it was OK, and looked elsewhere for the fault. Despite checking various electrolytic capacitors and resistors, including fusing resistors I was still unable to identify the problem. As a last resort I decided to use my Maplins digital bench supply, with current limiting to produce 5 volts at the output connector of the 7805, with the scope switched off and the voltage held up!. I then powered up the scope and everything started working normally again. I replaced the regulator with a new one in my spares box (L7805CV and hey preso my scope sprung back to life.

I always believed that regulators were virtulally indistructable but this obviously not the case!

I am attaching a copy of the Service Manual in case it is useful to anyone



Joined Oct 2, 2009
Thanks for the tip.
Yes, checking system power supplies is one of the first tests to perform, after a good visual and smell check.


Joined Jan 8, 2017
If it is set to X Y mode you would only expect a dot with no signal on either channel. Does it work with the timebase driving the X axis. (This is the most common way an oscilloscope is used.)