EEVblog Electronics Community Forum
Products => Test Equipment => Topic started by: sad123 on October 23, 2021, 02:25:55 am
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I couldn't get an answer in the repair section, so maybe someone here knows?
I got an older Hitachi V-152 oscilloscope that needs a few issues sorted.
Before I can do this, does anyone have the procedure to discharge the CRTs in these ones? They don't have an anode cap on top like TVs, or a separate connection like a tektronix.
Also, does anyone have the service manual for this model (V-152 not V152F).
Images of the innards:
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Old LF CRO's usually didn't have PDA treblers/quadruplers to store a good belt for the unexpecting so just good safe practice around the PSU and EHT stepup (if it has one) will keep you safe. You could if you're nervous cobble together a cap discharge lead of say 100 ohms if a poke around with a DMM shows any stored voltages after it's been OFF for a few minutes.
After some familiarity you will get to know where charges are stored and head there first to make it safe to work on.
Just be wary of the EHT as they're generally 1KV or more.
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Out of curiosity, what happens if you connect a typical filament light bulb to +1kV ?? Will it just burnout like a fuse ? A 100nF cap at 1000V is only 50mJ though
What about a stove-top heating element ?
Some people just use a screwdriver, it better be well insulated !!
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It doesn't have post-deflection acceleration, so there's no HV anode to discharge. It should discharge itself as soon as you turn in it off, but you can poke all the CRT pins at the back with a grounded probe if you like.
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The OP is now much further down the track in this Repair board thread:
https://www.eevblog.com/forum/repair/hitachi-v-152-oscilloscope-how-to-discharge-the-crt/msg3763652/#msg3763652 (https://www.eevblog.com/forum/repair/hitachi-v-152-oscilloscope-how-to-discharge-the-crt/msg3763652/#msg3763652)
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Yes, thank you for that. This matter is now sorted and the thread can be closed.
I'll open an new one for a couple of issues with the scope.
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Out of curiosity, what happens if you connect a typical filament light bulb to +1kV ?? Will it just burnout like a fuse ? A 100nF cap at 1000V is only 50mJ though
What about a stove-top heating element ?
Some people just use a screwdriver, it better be well insulated !!
It's all down to the amount of energy available. The HV from a typical CRT is not even going to make the bulb flash. The bulk filter capacitor in a SMPS will make a flash of light. A suitcase sized capacitor charged up to 15kV will likely make the bulb explode.