Analog oscilloscope restoration process

[fredboivin]

Hi all,

I've scored a FREE (!) Hitachi V-202F oscilloscope from a former teacher. It works and is in reasonably good condition, but I would like to restore it as a project. I've already got the service manual from this thread: https://www.eevblog.com/forum/repair/hitachi-v-202f-oscilloscope-schematics/.

What are the steps when restoring a old scope (cleaning, replacing, calibrating, etc)?

Thank you!

[tautech]

There is some wonderful work by members in this thread.
https://www.eevblog.com/forum/repair/vintageclassic-renovation-techniques/
I'd suggest you document your process well and link it in there when complete.

Dave did a good hour long video on minor calibration check to a Hameg.
Think it was this one:
http://www.eevblog.com/2013/08/03/eevblog-502-19-hameg-analog-oscilloscope/


Initially a check of the PSU specs is all that is required if it seems to be operative.
Drifting PSU voltages and power rail ripple are of greatest concern to calibration long term accuracy.

Any ripple outside spec's points to E caps in the PSU.

[oldway]

If it is working, nothing to do....Use it and enjoy.
Trying to restore something working, you are only looking for troubles.

[SkyMaster]

Hi Fred,

Does your new free scope really need to be restored?

I would suggest to start by removing all the knobs and clean them with IPA (IsoPropanol Alcohol, 99% IPA is normally available at your local drugstore; at least in the province of Québec). If some knobs are difficult to remove; do not force them, clean them in place until you figure how to remove them. I see that the "Mode" knob is missing, you will have to source an original looking replacement, or get three to have identical looking "sliding" knobs. It is easier to clean the front panel once the knobs are removed.

If the scope is working correctly, I would limit the restoration to a cosmetic one 

I've scored a FREE (!) Hitachi V-202F oscilloscope from a former teacher. It works and is in reasonably good condition, but I would like to restore it as a project. I've already got the service manual from this thread: https://www.eevblog.com/forum/repair/hitachi-v-202f-oscilloscope-schematics/.

What are the steps when restoring a old scope (cleaning, replacing, calibrating, etc)?

[PaulAm]

Clean the front panel with IPA.  You may want to test this in a small area.  Panel markings are generally safe with IPA, but there's always the chance.  It is very annoying to find you have removed the legends.

If you can get the knobs off without trouble, soak them in simple green and clean them up with a toothbrush.

Simple steps can make the scope look new and make it more of a pleasure to work with.

Since it's working, I wouldn't tear into the scope, but you can learn a lot by verifying the calibration.

A little project that is fun is to build a time/mark generator to check the sweep calibration.  Get yourself one of those little canned crystal oscillators (10 MHz is a convenient number), add on a number of decade dividers and you have a calibrated signal source good enough to verify the sweep settings.

You can check the DC settings with a variable power supply checked against a DMM.  AC is a little tougher since the display will be p-p while most meters will display rms.  You can always calculate the expected values; it will be close enough.

You can verify the trigger level works by feeding in a low level sine wave (the output of a low voltage power supply transformer (~ 5-10V) works fine for this.  You should be able to get the scope to trigger at any part of the waveform.

have fun

[fredboivin]

Hi,

Thanks everybody for the advices! The scope is working, but is definitely out of calibration. I was planning to do it myself (I've got the manual and the equipment at my job), but figured as I'll open it anyway, I should also replace some caps, etc.

The time/mark generator project is a great idea, I'll look into that!

[RJFreeman]

I would pre test Isopropyl Alcohol  before using it to clean the knobs and markings as I have had alcohol based solvents soften plastic knobs, and fade coloured plastics used for the knobs and soften screen printing on front panels.

Personally I would remove the knobs and give them a good soak in hot water with dish washing detergent, wrap them in a tea-towel and then swing the towel around a few times to dislodge the water (which gets down the holes for the shafts). then allow to dry for 24 hours or so.
- note I suggest you do this in the bathroom with the lid of the toilet down as it does spray a bit of water around and if any knobs escape from the tea-towel and you are outdoors, they may be a bit difficult to locate afterwards....

There does seem to be some dirt on the front panel, I have found Eucalyptus oil is usually the most benign effective cleaner for front panels - although cheaper Eucalyptus oil is often mixed with Isopropyl Alcohol so check before buying that it is pure Eucalyptus oil and as always, test on an inconspicuous section of the front panel before cleaning the whole thing.

I use Eucalyptus oil (and the above method for cleaning knobs), on mixing consoles where you do not usually have the luxury of spending several minutes lovingly scrubbing each of one or two hundred knobs....
They do end up smelling of Eucalyptus though 

[SkyMaster]

replace some caps, etc.

The issue of electrolytic capacitors dying early in their life is a fairly recent one. I have several pieces of older test equipment, some dating back from the late 60's, and they all have their original capacitors.

Your Hitachi oscilloscope was probably made in Japan in the late 80's, or early 90's, and the capacitors are probably of high quality 

Did you also get the original probes that came with this oscilloscope?

[fredboivin]

As for the scope, it has some gripes: the vertical axis drifts slowly upward and sometimes when changing the timebase, the sweeping stops. The sweeping problem seems to be correlated with a dirty knob though. The focus is also not very good.

Unfortunately, the probes it came with don't seem to be original: BNC to dual banana. I am planning to replace them, do you have any recommendation?

I opened the case and all electrolytics are Nippon Chemi-Con, so as you are saying, I think I'm covered there. The internals are very neat, I'm always amazed at how it takes so little to make such a useful tool!

[SkyMaster]

To clean contacts;

Super Contact Cleaner with polyphenylether, MG Chemicals, Cat. No. 801B-125 - Made in Canada
Electrosolve Contact Cleaner for electronics, MG Chemicals, Cat. No. 409B-340G - Made in Canada


Over the years, I was able to find discontinued but still new in sealed bag Tektronix and HP probes, but it can take years before you find what you want at an affordable price, and you want two identical to have a nice pair.

Probe Master is making replacement oscilloscope probes at very affordable prices; $40 US for  a X10 100 MHz probe, and they are made in USA (well it seems, but maybe it is only true for their more expensive models).

Model 3904-2 http://www.probemaster.com/product_info.php?cPath=1_8&products_id=34&osCsid=3984dafe681c3ac0c8501efbcdbb5d37

If I was looking to buy probes, I would contact them and ask if they can ship though USPS, because from their website they use UPS, and UPS always hit you with outrageous custom fees.

[Paul Moir]

Also for something like $18 including shipping you can get a pair of el-cheapo probes from Amazon.ca.   If you suspect you may have to abuse your probes, having some cheapies is definitely a good idea.

UPS likes calling me at 7:00am to approve their outrageous brokerage fees. 

EDIT:  Oh, hey I have an old Textronix P6149 50MHz probe if you want it.  No accessories other than the ground lead and a wrecked P6149 for parts.  Send me a PM if you want them.

[fredboivin]

Thanks!

Yep, those are the chemicals I was planning to use.

I don't plan to beat up my probes, but I also don't have a lot to spend (damn you, student loans!) and I plan to upgrade to the Rigol DS1054z when I'll get the space. Do quality probes like (I assume) the Probe Master's are worth it or the el-cheapo one do the job?

And I ALWAYS ask USPS when shipping, got caught once and it's already too much!

[tautech]

The P6** probes on eBay or Aliexpress will be fine for your use.
You should be able to get a pair of P6100 1x,10x for US$15-20 delivered.