Ronan calibrators.

[jchw4]

Somebody recommended them as a cheap voltage source, but there is absolutely no information on them.

[jchw4]

Some time ago I bought a Ronan X85 Calibrator as a nice weekend project.

The only data I could find was a brochure basically saying that it exists. No manual, nothing else. 

The unit was sold as "Used, fully working".

As received: nothing worked. Display lit with all zeroes, none controls worked, output was fixed at around 4 volts....
I kind of expected that something could not work, but not all. 

The first thing I noticed was that it had a charger, so it probably had a battery.
A bad sign, since the 80s it could corrode through.

But as it was a "weekend project" I decided not to return it.

As you can see, corrosion was not that bad. It was probably stored vertically and the acid did not reach the boards.

[jchw4]

More photos

[jchw4]

It's interesting that different boards were probably designed by different people. Just look at these traces. 

[jchw4]

I have never seen this battery type.
Does anybody know if it was a custom or just abandoned type?

[jchw4]

The charger is very "60s" (?) style. But it works.
It would be nice to make it a little bit better and keep the old look. But it works as it is.

[jchw4]

The only thing that had some signs of life was ohms source, but the potentiometers were definitely in bad state.
Since two new pots with shipping were more expensive than the whole thing, I decided to rebuild the old ones.

Opening:
- Desolder the wire from the sliding contact and carefully remove all solder from the contact with the braid. The cleaner you do this step, the easier would be the next steps.
- Carefully cut out the molten pieces, pop the back cover and pull the contact through the side wall.

The old lubricant turned into a glue, but soaking in IPA helped.
The greenish layer did not want to come off, so I used a "wet deoxit sanding" method with 1000 grit paper. Worked well.

It needed a new lubricant, and I tried a few random ones that I had. Finally PTFE worked well. (I was looking for less than 1 Ohm minimal resistance after assembly.)
I am not an expert though, but hope that it will work for long.

A few drops of hot glue made it strong enough.

An important note: some potentiometers serve as PCB mechanical stands. You must first attach them to the front panel, and only then solder to the board. Otherwise you’ll damage the board when tightening the front nuts.

[jchw4]

All the boards looked covered with some protective lacquer. Likely it was enough to protect from the battery vapours.
(The device was probably stored vertically, so liquid electrolyte did not get onto the boards.)

After cleaning with IPA all the boards became milky, so they likely used shellac as a protective layer.
As the thing did not work at all, I decided to wash it completely away to simplify probing.
So after 500ml of IPA it was fully clean.

Probing components revealed a dead diode in the negative voltage source.
After replacement the voltage source came back to life.

But the DMM was still displaying all zeroes. I still don't know why it did not work, I even ordered a few components, but at some point it just started working. 

So there is still probably unstable contact somewhere. Though I did not have any issues with the DMM since.

[jchw4]

New battery.

It took me a long time to come up with the solution to the battery problem. But as everyone now has a lot of sanitizers, I found one of a similar size and put 5 AA Ni-Cad batteries inside.

I also found 5.5mm socket that I desoldered from some toy and basically made new "Ronan-style" battery. Photos of the new X86 show similar battery with the similar connection 

[jchw4]

Adjustments.

Device is using three LM336 voltage references.
- One for output.
- One for DMM.
- One for DMM current source for resistance measurements.
So there are three 20 turn potentiometers to adjust references.
Plus there are three more for DMM zero, DMM 1V, DMM 10V ranges.

I don't have any documents about the device, but luckily there is an X86 manual available.
After reading it I feel that they are extremely similar, so I guess that the steps are the same.

The manual (X86) suggests using precision external sources to calibrate the DMM, but I feel that any modern benchtop DMM is sufficient.

I highlighted adjustment potentiometers.
- The top board: Ohms current source.
- The middle board: DMM zero, DMM 10V range, DMM 1V range.
- The right board: DMM 100mV range.
- The bottom left board: source adjustment.

The source part of the calibrator and the DMM part are fully independent.
There is only one adjustment on the source side.
My guessis that the DMM adjustment sequence should be "DMM Zero", "DMM 100mV", "DMM 1V", "DMM 10V", "Ohms current source".

Upd: updated photo.

[jchw4]

Stability.

The final issue that I had was switching from the 1V range to 100mV range yielded permanent 13V on the output.
With the help of the other forum members (see https://www.eevblog.com/forum/beginners/strange-lm312h-behavior/), it seems that the easiest solution was to replace the opamp with the modern one.
But even with the original one, the device is stable within the DMM range, and noise is beyond what is displayed.

The current source does not have feedback and depends on the 0.01% 10 Ohm resistor, which dissipates 0.1W of power and nearby transistor drops 12V at 0.1A and heats up too.
Which is unfortunate, as the voltage source is very good.

[jchw4]

Improvements.

The interesting question was whether we can increase voltage stability even more for cheap, because precision voltage source is very useful, even if not very accurate.
With the help of the forum members in the same thread (see https://www.eevblog.com/forum/beginners/strange-lm312h-behavior/) I replaced source zener with MAX6225 and the result is much much better now.

[jchw4]

Final impressions on the X85:

X85 Calibrator
- Good: Will give you stable 4.1 digits of output voltage and resistance.
- Good: Should give you stable 4.1 digits of output current, but there is no feedback.
- Good: Can be bought for cheap.
- Good: Easy to fix. (But may need a lot of work.)
- Bad: Looking at Ebay photos I assume they all have leaked batteries. Depending on how it was stored (vertically, horizontally, on which side) and your luck, the battery could corrode it through into total garbage.
- Bad: PCBs are very old and they are easily damaged. Don’t ask how I know it.


You can see my final repair result on the photos.

[alm]

Thanks for posting this nice teardown, repair log and review of this unit! I like your creative solution for the battery replacement.

Just one tiny thing suggestion for the future: I would prefer to see noise measurements reported as ppm of output. This makes it easier to relate to DMM digits and specifications, and also allows you to compare different ranges better.

[coromonadalix]

Thks for the teardown,  never saw that brand   

[77Ribetts]

Hi so i found this hope its handy for someone also thanks for all the photos and info



https://www.ronansystems.com/assets/docs/X85%20I&O.pdf

[coromonadalix]

Send the pdf  to known host sites  to keep it ...

[jchw4]

Hi so i found this hope its handy for someone also thanks for all the photos and info

https://www.ronansystems.com/assets/docs/X85%20I&O.pdf

Wow, I was pretty sure it was not there when I was looking for it.
Before we only had a low-quality scan that somebody uploaded to KO4BB  with hard to read schematics scan quality. But the older scan has more pages and an addendum, so it is worth checking too.

I actually reversed the whole schematics while working on the unit. I shoud probably clean it up and upload some day.

[J-R]

Just in case the link goes bad in the future, here is the X85 manual and a document about the X85-RJ optional accessory:

[alm]

Thanks for preserving this! You could also consider uploading the documents to one or more of the following manual repositories if they are not yet there:

• KO4BB
• BAMA
• xDevs
  

[Chris56000]

You all do realise the price of these things will now start going bloody silly because the manual with circuits has been uploaded, do you?!

Chris Williams

[JohanH]

Just in case the link goes bad in the future, here is the X85 manual and a document about the X85-RJ optional accessory:

Everyone should get into the habit of adding such web pages and documents also to the Internet Archive Wayback machine https://web.archive.org. This is probably the largest archive on the Internet.

For your convenience, the documents are now also available there:

https://web.archive.org/web/20230221121355/https://www.ronansystems.com/assets/docs/X85%20I&O.pdf
https://web.archive.org/web/20230221122147/https://www.ronansystems.com/assets/docs/X85-RJ%20Datasheet.pdf

[J-R]

You all do realise the price of these things will now start going bloody silly because the manual with circuits has been uploaded, do you?!

Chris Williams

Haha, maybe so, although these are perhaps a bit clunky and of limited use.  I snagged an X88 a while back to play around with, hence my interest in this thread.

[J-R]

Update on the X88 I recently purchased:

It was manufactured in 2000.  It reminds me of something from the 80s, though.  The buttons and general operation can be a bit obnoxious, especially having to move the test leads around constantly for the different functions.

I went through the full calibration procedure and adjusted everything, about 20 different potentiometers, half for the input, half for the output.

For the input, it's essentially a 15,000 count DMM, but has very limited capabilities compared to a typical DMM, both in functions and ranges.  Input protection is nearly non-existent.

Compared to the PDVS2mini, the DCV output is nothing special, of course.  What you set on the display is what you get, but the "imaginary" digit past that is a little bit jumpy.  Same goes for the 100mA DC output.  Strangely, you can't actually select 100mA, only 99.99mA.  This variable DC constant current output is probably the main thing I can see using this for at the moment, as it's more stable/precise than any of the bench power supplies I have.

The 'interesting' feature I like on this is the extensive RTD/Thermocouple simulation capabilities (it can read via the inputs as well).  You can pick a specific temperature in C/F and simulate this to a DMM.  So for example, I can choose K-type thermocouple, set the output to 900F and connect it to a typical DMM and bam, 900F on the DMM.  Fun.

It also can do some 4-20mA loop functions, but I don't have any use for that at the moment.  The previous owner was an HVAC tech, so they probably did use that.

So ultimately a cute/interesting relic, but how useful it is to you will depend on your situation.