Having issues with a Hitachi V212 Scope. Power LED is on, but screen is completely dead. The usual low voltages are all present, including CRT heater, but I'm guessing there is no power to the CRT grid. As I don't have High voltage test gear, is there a safe way to test and track down the fault.
Many thanks😱
John O
Many thanks😱
John O
Do you have a schematic? What is the highest voltage there? A basic DVM should handle 1000V DC with no danger.
Service manual can be found here.
https://xdevs.com/doc/Hitachi/Hitac...ervice_Manual-Hitachi_V212_Service_Manual.pdf
https://xdevs.com/doc/Hitachi/Hitac...ervice_Manual-Hitachi_V212_Service_Manual.pdf
Check F1001 first , this is on the primary of T1001 that feeds the HV section (This is merely at ~30VDC at this stage)
On my old scope that I found on the skip, the Y axis did not work. All I did was a good rinse on all the switches and pots at the front. Like on an old amp. Works like a charm🙂
If its old, try the simple things first.
If its old, try the simple things first.
'A' scope or 'My' scope.
Has this worked in the past or is it one you came by with an unknown history?
Can you actually see the heaters lit or are you just going off measuring voltage?
If you turn the scope on for a little while and then off and back on do you see anything at all on the CRT?
The possibilities range from no EHT through to a missing or failed deflection or vertical amp (including all supplies) which is driving the spot or trace offscreen or even a gassed tube (which is why a visual check on heaters is needed).
Has this worked in the past or is it one you came by with an unknown history?
Can you actually see the heaters lit or are you just going off measuring voltage?
If you turn the scope on for a little while and then off and back on do you see anything at all on the CRT?
The possibilities range from no EHT through to a missing or failed deflection or vertical amp (including all supplies) which is driving the spot or trace offscreen or even a gassed tube (which is why a visual check on heaters is needed).
There is no EHT, just the -1.9 kV cathode voltage in the V212. If F1001 has blown TR1006 is prolly borked too. Replace. Check secondary for shorts. If there are none and the capacitors look OK (no leaks) you can switch on. If TR1006 oscillates but still no light check HV with a 1:10 probe. Easily made with 9 10M resistors in a BIC pen housing and a DMM with 10M input resistance (they all are AFAIK). You should get -190 V on it at P1001.
Hello everyone. I have been given a Hitachi V212 oscilloscope.
When I turned it on for the first time it worked. I even tested it with a signal generator and it worked correctly.
But the next day while I was again testing with the generator, the screen suddenly went blank.
I have checked all the components in the oscillator and high voltage transformer section (TR1001; TR1002; TR1006, capacitors) and everything seems to be fine, but it does not oscillate.
The voltages are all correct as indicated in the service manual.
I have even removed the small transformer and I do not see any cut windings.
I ask you before I give up, can I make a voltage multiplier with diodes and capacitors, from 220 volts alternating current to 1900 volts continuous current?
And then apply this high voltage at the point where the diode D1024, R1024 and the neon NL1024 meet.
Thank you
When I turned it on for the first time it worked. I even tested it with a signal generator and it worked correctly.
But the next day while I was again testing with the generator, the screen suddenly went blank.
I have checked all the components in the oscillator and high voltage transformer section (TR1001; TR1002; TR1006, capacitors) and everything seems to be fine, but it does not oscillate.
The voltages are all correct as indicated in the service manual.
I have even removed the small transformer and I do not see any cut windings.
I ask you before I give up, can I make a voltage multiplier with diodes and capacitors, from 220 volts alternating current to 1900 volts continuous current?
And then apply this high voltage at the point where the diode D1024, R1024 and the neon NL1024 meet.
Thank you
I would have to say no because there would be no isolation from the mains.
How do you know its not oscillating?
Hi Mooly. I used an oscilloscope that I was loaned (Rigol DS 1054).
There is no oscillation at the base and emitter of the TR1006 and it seems to oscillate at the junction of D901 and D902 but with a lot of interference.
I'm about to give up. All I have left is to change all the components in that part and see if that fixes it.
What else could be the reason why there is no image on the screen since the filament can be seen to be on?
Thanks for answering.
https://www.aliexpress.us/item/3256803182563889.html?gatewayAdapt=glo2usa4itemAdapt
I could use this ???
I could use this ???
D901/902 look to be part of the flyback blanking.
TR1006 should be running and you should see a rough looking sine/square-ish voltage on the collector. It is a self running oscillator with feedback for voltage regulation via the 22.1 meg and 470k resistors.
Be very careful measuring around the transformer because if it does run the secondary voltages will annihilate the input circuitry on the Rigol. You are fine measuring the primary side.
Is C1002 negative returned to ground or is it actually return to the 8 volt rail and the diagram is missing a link where it says 8 volts. Even things like the switching transistor could be faulty, it does happen but don't randomly swap stuff in hope.
Is the 120 volt OK?
Worth checking the high value resistors in the oscillator such as R1001 and R1003. You would be unlucky if the transformer were duff but looking at the circuit and everything else should be fixable I would have thought.
Anything else... well you obviously need the EHT present from that circuit but other things can be a failure in either or both the X and Y amps driving the trace off screen. The X and Y plates voltages should typically be equal and around half the supply voltage of the rail feeding the amps.
Can't see your link...
Mooly, thank you very much for helping me.
Fuse F1001 is correct; there is 120v on R1001; there is 8v on R1005; R1016 and R1017 are correct.
I will keep looking, but I am about to abandon the repair project.
What it showed on Aliexpress is this "DC-AC 12V-24V To 820V-2000V 1KV 2KV High Voltage High Frequency Boost Power Supply Module Electronic Inverter Doubler Drive"
Fuse F1001 is correct; there is 120v on R1001; there is 8v on R1005; R1016 and R1017 are correct.
I will keep looking, but I am about to abandon the repair project.
What it showed on Aliexpress is this "DC-AC 12V-24V To 820V-2000V 1KV 2KV High Voltage High Frequency Boost Power Supply Module Electronic Inverter Doubler Drive"
Attachments
That little board is interesting... would it work... I really don't know. The scope oscillator has the voltage feedback regulation to maintain EHT under varying load (brightness). Changes in EHT affect the how easy the beam is to deflect and if it varies the image on the screen varies in size which on a scope means the calibration is altered.
Also the frequency of the AC is important in relation to the components on the secondary side. The scope looks to run at around 50kHz.
It may or may not all be suitable 🙂 No way of knowing,
Have you looked for problems on the secondary side such as the diode and small high voltage caps used for smoothing?
Also the frequency of the AC is important in relation to the components on the secondary side. The scope looks to run at around 50kHz.
It may or may not all be suitable 🙂 No way of knowing,
Have you looked for problems on the secondary side such as the diode and small high voltage caps used for smoothing?