Hitachi V212. works fine but...

[dc740]

Hello everyone. I got my first oscilloscope, an old Hitachi V212. Everything works except for the voltage selector switch for channel 1. I can't select 5v and .5V.
.5V works only if I touch the knob a little. It seems that the selector knob is dirty.
5V shows a full line in the screen (similar to a constant voltage)

The knob has 9 pins! The selector switches are composed by the white parts in the screenshots.
Part id:
NOBLE ADR255S v8512

Does anyone know, or have ANY idea of how could I fix it? (or clean it!) Channel 2 works perfect in every setting.
I'm also open to suggestions on replacement parts.

[nanofrog]

Take the switch out, tear it down, clean it (wipe it out & use alcohol first to save on contact cleaner), and lubricate it. Fair bit of work, but worth it.

Might want to take a look at Deoxit products for cleaning, protecting, and lubrication products. Lots of choices due to application method (brush, spray can, oiler bottle & pens, ...), volume, and concentrations (5% or 100%). The least expensive in regard to total cost, would be the 2cc tubes of D100L contact cleaner (100% concentration, P/N = D100L-2C), G100L-2C protectant, and F100L-L2C lubricant. Runs ~$6 - 7 per tube.

For lubricant however, you'd be better off with FaderGrease IMHO (can't run out/off the contacts like a liquid can).

D Series: http://store.caig.com/s.nl/sc.2/category.188/.f
G Series: http://store.caig.com/s.nl/sc.2/category.292/.f
FaderLube: http://store.caig.com/s.nl/sc.2/category.293/.f
FaderGrease: http://store.caig.com/s.nl/sc.2/category.305/.f More expensive than the liquid, but there's more in the containers (micro-tools has a 28g jar for ~$18).

Good source for purchase would be http://www.micro-tools.com/store/home.aspx (had good experiences with them in the past; shipping is reasonable, as are prices). You can also try Amazon.

Hope this helps. 

[dc740]

Thanks for the suggestions. After using it for about half an hour the 0.5V/div selector started working normally. It seems like it was really dirty.

I ended up leaving the 5V/div broken as it was when I got it. I don't want to unsolder so many pins and disassemble the potentiometers, since the odds are completely against me. I will probably end up breaking the entire selector and that would break the entire channel 1. It doesn't make sense to do that to fix something I don't use, since I work mostly with 3.3v and 5v (DC) and I never used the 5v/div selector, I just found out it was broken by learning how to use the oscilloscope.

I'm not even sure the potentiometers are the cause! I only see straight line in the screen, around 6 or 7volts (considering each div is 5V). Decreasing the time/div shows that the line it's not completely straight. I'll compare the resistance values between channel 1 and channel 2 selectors just to satisfy my curiosity later

But thanks again!

[neggles]

Take the switch out, tear it down, clean it (wipe it out & use alcohol first to save on contact cleaner), and lubricate it. Fair bit of work, but worth it.

A much simpler initial solution is to just wipe the switch back and forth repeatedly to use its own contacts to clean themselves.

If that doesn't fix it, then you probably have to actually disassemble it like nanofrog said.

[RobbieC]

I have an old 212 that I've used at work occasionally as a "go/no-go" for signal presence for board testing (my work had quarantined it for being out of cal around 12 years ago).
It always had some serious jumps from the ground reference at each v/div setting, which I attributed to "dirty pots". Last month after downloading the service manual and doing a complete readjustment of the biasing, among other things, it works great (the trace rotation usually needs tweaking each use, but it is in a high RF/EMR area).
If you have the equipment, I'd recommend giving it the full meal deal.

Here's a link:
http://oldradio.tesla.hu/rajzok/muszerek/hitachi%20v-211-212-222-422%20oscilloszkop.pdf

Let me know if you have any questions!

[dc740]

Well... to be honest, I think it would be nice to do that, since I believe no one has ever calibrated it. yet the timing frequencies  seem incredible accurate when I measure a pwm signal from arduino.
The bad thing is... I don't have the required equipment to do it. I'm not even close, I only have the digital voltmeter . (page 10 of the service manual)

[RobbieC]

Well, if you just have a DMM you can at least work on the following sections:
1,3,4,6,13,14,24

If you can coerce someone to let you borrow a descent function generator (I'm sure a "constant amplitude signal generator" and "time mark generator" are standard equipment for the industry, but a good ol' function gen should work for your, and my, needs) you can do these sections:
7,8,9,10,11,12,15,16,18,19,21,22,23

You can always put out a shout on the forum to see if anyone in your area has one to borrow for an afternoon.

Tuning up your scope is the EE equivalent of adjusting the timing on your old Honda CT-110 on a Sunday morning. Okay, that might be stretching it. (Though now I'm thinking of tuning the CT using my old scope...)

[madshaman]

Well, if you just have a DMM you can at least work on the following sections:
1,3,4,6,13,14,24

If you can coerce someone to let you borrow a descent function generator (I'm sure a "constant amplitude signal generator" and "time mark generator" are standard equipment for the industry, but a good ol' function gen should work for your, and my, needs) you can do these sections:
7,8,9,10,11,12,15,16,18,19,21,22,23

You can always put out a shout on the forum to see if anyone in your area has one to borrow for an afternoon.

Tuning up your scope is the EE equivalent of adjusting the timing on your old Honda CT-110 on a Sunday morning. Okay, that might be stretching it. (Though now I'm thinking of tuning the CT using my old scope...)

Here's a related pdf on the topic: http://assets.fluke.com/appnotes/Calibration/lpmsc98.pdf

[RobbieC]

Nice! I need to read through more of the Fluke app notes and white papers.
I used my older Tek AWG and it worked for the majority of what I needed.

Thanks!