Hitachi V-212 Oscilloscope

[Mike_M]

Hello There,

Just a quick question and opinion requested.     I've been wanting to get an Oscilloscope for the longest time.   So just stopped off at a store nearby and they had used "Hitachi V-212 Oscilloscipe" for fairly cheap but AS-IS.   Well I gambled an bought it thinking would be a good project if didn't work to try and make work.   Well I powers up and seems to read but only in the middle of the screen (seems squished) horizontal seems to have shrunk.   Just wondering if there is any hope for this or the tv tube could be the culprit.     Guess just kinda looking for a nudge in the right direction.  =0)

Thanks,

Mike.

[jimmc]

First the good news, it's not the tube.

Sounds as if there is a problem with the horizontal amplifier or the power supply feeding it,see p 41 & 43 of the manual.

Remember here are dangerous voltages around, up to 1900v, so take care.

There is a copy of the manual here http://mpe.berklee.edu/documents/studio/manuals//testingmet/Hitachi%20V212/V-211%20V-212%20Operation%20Manual.pdf

Jim

[Lightages]

If nothing else, 2000VDC hurts a lot. I know all too well. It can also kill. Keep one hand behind your back if you are poking around inside if you do not know high voltage safety practices and wear safety glasses. Actually, keeping one hand behind your back IS one of the high voltage safety practices as far as I am concerned.

[Mike_M]

Update:  Just did some "poking" around  (one handed) as I am nervous with the whole 1900V+ idea.    Does definitely seem to be the H.AMP at fault.   In the service manual I tried to read 2 test points  X and X+ suppose to have +58V or so but only seeing +4V.   But in reality if I was playing with some low voltages and current I wouldn't have a prob.   But don't think I'm ready to play in the high voltage area.  Maybe try and find a local shop that would have the ability to repair it.

THanks again,

Mike.

[Gonzini]

Check for resistors that have gone high in value or open around the H amp, dry joints as well.
If you do make sure its been switched off for a while and double check the H.T rails have drained before you probe about!
It will be fixable im sure

[c4757p]

I will offer one warning - not all oscilloscopes mark the high voltage properly. I had a GoldStar (LG) that had 600V exposed outside the "high voltage" shields - of course, I found that with a very "natural" voltage probe...  On the other hand, you could take the cover off of my Tektronix and rub your hands all over it and not come near anything above 80V.

That said, if you use proper technique, assume everything is HV until proven otherwise, and don't go sticking your hands where they don't belong, you will be fine. People have worked on CRT-based equipment for decades and problems are rare. Just try to do as much work with it shut down as possible, and discharge all the rails before you go digging around. I like to leave shorting links across all of the particularly nasty rails while I work on it - I just count them as I put them on and take them off so I don't power it up with them attached.

[Gonzini]

Check R859, 470R fuseable resistor. Drops down from a +220V rail.
If its open then check all transistor junctions in the output stage.
I see there's some other rails too, +/-8V

[Mike_M]

I might have found something.   TR854 looks (need magnifying glass) but looks like the top is "bubbled" no other transistor has this "mark".   Just measured the resistors around it and I am getting the proper 22k readings.   Might need to see about testing the transistor.

Thanks,

Mike

[Mike_M]

Check R859, 470R fuseable resistor. Drops down from a +220V rail.
If its open then check all transistor junctions in the output stage.
I see there's some other rails too, +/-8V

Thanks,   I just probed that resistor and I get open circuit across it.   

Also curious there are 2 "light bulbs" I'm assuming (well not assuming with fingers in wrong place) they glow for a second when you turn off the unit that they are discharging bulbs of some sort?

[Gonzini]

Doesn't look to complicated, classic design really.
Defo check that 470R resistor if TR854 is fried.

Stay safe! self preservation is the most important thing.
Like everyone has said, those high voltages in there are pretty nasty. If your not 110% sure don't go there, don't let it scare you though. A healthy respect for it should keep you alive!
That's it for me tonight    

just seen your last post..
Maybe they are neons? Can't them on the schematic here..

[PA0PBZ]

Maybe they are neons? Can't them on the schematic here..

Neons, between K and G1 of the tube. Page 52 (55 in the PDF).

[Mike_M]

Update #2:   

Got the Fusing Resistors (ordered some extras) today.  Replaced it and VOILA!!  full trace!   Only issue at hand now is the trace is tilted and the adjustment for it is maxed so can't straighten it.  So going to check the resistors etc.  I think the POT might be faulty.

Thanks for all the help!

Mike.

[c4757p]

Maybe they are neons? Can't them on the schematic here..

Neons, between K and G1 of the tube. Page 52 (55 in the PDF).

If you haven't figured out their purpose yet, Mike, you're correct that they are "discharging bulbs" of a sort. They begin to conduct at their threshold (I'm assuming they are in series, though I haven't seen the schematic, so around 180V), preventing the voltage at that point from rising above that. They're being used like robust, high voltage Zener diodes.

I used to have an oscilloscope with a similar configuration, but interestingly, the lamps had a constant glow, not just a flash at shutdown. Not sure if there was something wrong with that, but the instrument did work...

[Mike_M]

Ok,  still having the rotation issue.   Found in the schematics the Rotational Coil (Part of the HV & Z Amp RV1348).   Seems something is wrong in that circuit.   The potentiometer tests fine (removed it and read it 22k3).   If I unplug the rotational coil the trace onscreen is almost correct out by just a little bit.     I've measured the resistance on the coil itself in the circuit there is writing by it saying its a 230 (110%) 1500T   I get a reading of 216.9 across it.      Just wondering if I put a higher resistance pot in would be able to get more adjustment or would it more likely mess it up. 

Thanks Again,

Mike.

PS> Just read the voltage from either side of the POT and I'm getting -8V on both sides.   Yet in the circuit diagram one side should be +8 and other should be -8V.

[The_Penguin]

I have no advice to offer other than keep at it. It's a nice scope, and worth the effort.

[Mike_M]

Update:   Just did a prototype of  the Trace Rotation circuit and hooked it into the coil for the CRT and voila!  I have full control of the rotation to point I can straighten it.   Just don't know why I'm not getting the +8V at the POT only see -8V on either side of the POT.   Turns out I just need -0.9V to straighten.    So was just thinking of making a small circuit to just put inside that will do the trace rotation and tap the +8 and -8 directly from the points on the connector as I'm getting those values there.

Thanks,

Mike.

[Mike_M]

Did some more digging.   I found the rails for the +8V and -8V but there is a wierd component unmarked on the board not in the circuit diagram and it is inverting the +8V into -8V but according the the service manual and circuit it should be feeding +8V  which when on if I take a meter reading I get 8V on one side and then the side heading to the POT and transistor its -8V  the component has F10Y stamped on it but its the only marking and its a little black rectangle.  I've attached a picture of it hoping someone might recognize it.  Just behind it is a jumper wire and that reads -8V and does go to the other side of the POT and transistor as per spec.

Any ideas?

Thanks,

Mike.

[david77]

How many legs does it have? If three, I'd say it's a transistor in one of those weird Japanese packages.

[w2aew]

PS> Just read the voltage from either side of the POT and I'm getting -8V on both sides.   Yet in the circuit diagram one side should be +8 and other should be -8V.

Sounds like you need to trace back the +8V supply on the topside of that pot...

[Mike_M]

How many legs does it have? If three, I'd say it's a transistor in one of those weird Japanese packages.

Just 2 legs.  I'm going to pull it and see if I can take resistance readings from it.  In circuit I get 22k across it but.   Just debating jumpering it as it does have the 8V I need on the other side of it.  Just wondering if its blown and the -8V I'm reading is just from the other rail.    And just note the silver wire ontop of that black rectangle is not part of it.  its a jumper wire on the board that if I follow its trace is and does measure the -8V rail.

Worst case scenario is I build a small circuit that mimics it (which I already did) and tap the +8 and -8V from the connectors labelled as such and just adjust and hide inside it.

Update:  I just extracted it and I can't read anything across it resistance or capacitance (either direction)  I'm assuming  its dependent on direction as it does have a mark I assume is a marker for pin 1.
Thanks again all,

Mike.

[SeanB]

It is a 400mA fast blow PCB mount fuse. Looks like a transistor, but has only 2 legs. You can replace it with a regular 400mA fuse or use a 400mA polyfuse as it is an 8V rail.

[Mike_M]

It is a 400mA fast blow PCB mount fuse. Looks like a transistor, but has only 2 legs. You can replace it with a regular 400mA fuse or use a 400mA polyfuse as it is an 8V rail.

Hoot!   Thanks!  Off to obtain one.  =0)

Thanks all!!   

Mike.

[Kipling]

Somewhat late to the party here. Just stumbled across the forum looking for an operation and/or service manual.

I have a V-212 and it too has the rotation issue and has done since I got it 20+ years ago. I remember playing around with the rotation pot and I'm sure I put in a higher value pot which got the trace almost level. Didn't have the benefit of the internet or a service manual in those days so the info on here should help fix it - not that it bothers me that much anyway.

Thanks guys, if anyone's still reading this thread.

[Kipling]

It was the fuse marked F10Y for me too. Cheated and replaced it with the finest strand of tinned copper I could find (0.1mm) and all working now.

I found that I had changed the original pot from 22k to 500k. No idea where I got the pot and knob or where the original went as it was decades ago, but it works just fine with the 500k so I'm happy.

Cheers all

[E;fnetdesigns]

I have this same scope (Hatachi V-212)that was given to me by a neighbor. They said it didnt work but what i found was to mains selector in the rear was set up for 240 VAC so I set it back down to 120 VAC and tada she works now. Though I did have some rotation issues but I found that was due to i guess the natural magnetic of the earth because when i stood it up on end it tilted but putting it back flat on the bench it was fine.
i also got a Motorola R-2670 RF service monitor that had a blown line fuse for $50 at the local swap meet. it seems to be just fine and is quite a big step up from the old Cushman I have