A story of one Datron Wavetek 4708

[doktor pyta]

In my lab I often repair precision test eqipment. There are cases when repaired DMM needs to receive comprehensive calibration.
Keithley 2000 is a good example. You just can't calibrate one range, You have to follow full AC or DC calibration procedures.
While ago I started looking for a way to expand my lab's capabilities. Best affordable option would be Datron Wavetek 4708.
4708 met my criteria, the parameters were similar to newer Datron 4808.
Panaplex neon displays of 4708 are relatively easy to get by extracting from old Datron 1061...71 DMM (the VFD for Datron 4808 is unobtainium AFAIK).
Keep in mind that these displays may break while shippping.

Back in 2016 there was an event on bidspotter.com called 'HUGE TWO DAY TEST & MEASUREMENT AUCTION ...'. Location: Las Vegas, Nevada. Among many beautiful instruments I felt in love with Datron 4708 equipped in full option.


No further information was available. Until August 2018 when it appeared on ebay. The items description was however inconsistent: 'DATRON 4708 ULTRA PRECISION ACV ACI CALIBRATOR - REV' while photos clearly showed opt. 10, 20, 30, 80. I asked the seller to take a picture of the internals. After few weeks and second email the seller agreed and here is what I received. It looks like we have full option here.

There was one problem: the item is big and heavy (~40kg) so shipping cost to my location in Poland, EU was higher than the price of the item. I started searching for a cheaper option and found a reliable company in U.S. which ships to EU at reasonable prices. Finally I was told that total shipping cost will be approx. 550USD (200USD inside U.S. plus 350USD from U.S to EU). Finally I decided to buy the calibrator.

[doktor pyta]

Soon the unit arrived with no damages during transport. I was aware of the seller's note  'Unit has a faint odor when power applied'.
It also reported Fail 9 which indicated failure in power supply. Thus I didn't wanted to power it without finding the cause.
I opened the instrument and found one discoloured tantalum capacitor and burned resistor. I replaced them with good ones.

I also found two quality controll issues.
Bent pin 1 of MC14049 was easy to fix. 
One leg of 10R resistor was lifted. I have no doubt that it was overlooked during PCB inspection. I was worried how repairing this point will affect AC calibration but finally I did it.
There were also two burned fuses.
When I was sure that nothing is shorting power lines (checked with ohmmeter) I was very curious if it will run.

Next, I set correctly mains voltage selector to match EU standards.
Then I removed boards related to AC function and set DIP switch to detect only DC U, I, R.
I was ready to go.
After pressing power switch Fail 9 and Fail 1 appeared on the display.
Fail 9 meant another shorted tantalum cap and Fail 1 is related to overheating of power amplifier. But the heatsinks were cold.
I tracked mentioned shorted cap and replaced it. Then I checked resistance of NTC thermistors mounted on heat sinks. It was correct.
I replaced 4 tant caps connected to the thermistors and I tried powering one more time.
This time I was happy: the instrument started without any error and worked for five minutes.
Then magic smoke and fire escaped.
It was another 10uF/25V tant cap. At this point I decided to replace every tant and electrolytic cap in the instrument.
It was easy with desoldering station.
Then noisy fan was replaced with SUNON SP100A1123XST. Original Redpoint fan is shown as a reference.
I was ready to troubleshoot new issues.

[doktor pyta]

For servicing purpose I set internal switch to a position marked '50V'. I turned on the instrument and watched what will happen.
Fortunately there was only the noise of the fan and no fireworks.
I set 1V range and set 1V, the voltmeter showed 1V. 10V on 10V range also went fine. 19.9V on 10V range was successful as well.
Both polarities were tested that way.
Then I set 100V range. I increased the voltage and was able to get stable reading of +18V (and nothing higher) and -44V (which was reasonable). This asymmetry looked strange to me and I started checking supply voltages of the P.A. board.
They were close to +/-55V. Components on the heatsinks seemed to be OK. I started thinking that it could be normal for this amplifier as one of the stages operates in A class with a MOSFET current source to positive supply. I decided to give it a try setting internal switch to '400V' position. The circuit started to work as expected. I was able to generate stable voltages between -199.99999V and +199.99999V.
After this success I checked current and resistance functions. They worked correctly. I left the calibrator operating for some time keeping in mind that if top metall cover is removed  there is almost no airflow over power supplies' heatsinks.
I used external 12V fan to cool them.
Once or twice over few hours I saw Fail 3 message meaning 'control data corrupted'.
There were also situations when 1V ranges and below as well as 100V range indicated proper values but on 10V sometimes I measured 9.93V.
It was weekend so I thought I wil leave checking 1000V AC and 1000V DC ranges to other occasion.
Instead I fitted two AC boards to see how they behave. Well, they didn't. 1V at 1kHz gave the signal 0.53V at 0.7kHz. The voltage didn't change despite pressing voltage buttons.
Other AC ranges answered in similar way.
I expected optocouplers as they often fail in older Datron instruments. I ordered 7pcs of Isocom ICPL2601. I also replaced MCT6 with new Fairchild part.
After this step the issues described above were gone! The internal synthesizer was also OK as at all settings the output frequency was accurate to 8ppm!

[doktor pyta]

Next issue was Fail 2 appearing anytime I wanted to activate 1000V range, DC or AC.
After investigation I figured out that relay RL5 was responsible for that (red rectangle on the picture).
Voltage detection circuitry was expecting high output voltage but the voltage was low due to burned out contacts.
It was replaced together with RL1 (yellow rectangle) as they were both available in TME for reasonable price.
Three large black relays were inspected both electrically and visually as they can easily be opened. They were in very good shape.
The calibrator was alive and ready for long term testing.

[doktor pyta]

Little hint how to replace battery without using special extenders. Keep in mind this is one of possible solutions.

1. prepare suitable lithium 3.6V AA battery. Example model: SAFT-LS14500CNA.
2. prepare Schottky diode with voltage drop below 200mV @1mA. I found SB120 as suitable (and found on my desk). Prepare two insulated wires ~30cm of length.
3. solder the wires as shown on the picture attached. Use test points marked '+5' and '13'.
4. make sure once again if everything is OK.
5. cut the old battery wires in places marked by red X and blue X.
6. remove old battery from the plastic holder and make sure it won't be shorted while doing further steps. Small plastic bag can be used.
7. trim the leads of new battery and place new battery in the holder.
8. solder new battery to the points where old battery was soldered.
9. make sure once again if everything is OK.
10. unsolder wires from test points marked '+5' and '13'. Work finished.
11. put in a visible place a label with replacement date. Next replacement should be done after 5 years (refer manual). From my experience they can live as long as 10 or even 15 years.

More obvious solution is to provide +5V from bench power supply between points marked '+5' and 'GD' but there are some cons.

-gold plated edge connector is not connected to anything. Power supply for logic is applied. This can create random logic states in the circuit.
-power break may occur, banna plugs may slip out of PSU terminals
-soldering iron's tip may be grounded (as in my Weller PU81). If the power supply's LO is also grounded short circuit (and loss of SRAM data) is possible.

[doktor pyta]

spoiler (yes, with wrong cables and omitting guarding, grounding posts)

[TiN]

Sweet. I'm in process of trying to resolve shipping issues for similar piece of metrology gear, with 41kg weight. So far direct shipping (even expensive) didn't work out, hopefully try two will be more successful..

Looking forward for your test results. If there are particular focus, I can remotely access D4808 with some DMMs to capture data. Will be possible to do some compares with data, if you interested.

[capt bullshot]

 
subscribed

[doktor pyta]

Below series of photos showing how I build replica of 'Lead kit'. First two photos taken from www.hitechfacility.co.jp.
The enclosure I'm using is G110-IP67 from Gainta. It seems that TiN used very similar box for his HULK setup.
Banana plugs are made by STÄUBLI (SLS410) and still have MC marking just as original ones.

#1

[doktor pyta]

#2

[doktor pyta]

#3 la grande finale

[branadic]

Wouldn't a sheet of teflon be better instead of FR4?

-branadic-

[doktor pyta]

Yes, but:

1. Datron inside the box used their own custom PCB based on FR4.
2. I wanted to keep the price low so I used 2mm FR4 without the copper as construction material.
3. The force needed to insert or remove these 6 bananas from calibrator's terminals is quite high. I was affraid that 4mm thick PTFE that I own is to weak to survive dozens of such repetitions.

[ap]

I am not sure this is a good idea. The sls410 is based on brass. I performed measurements some time ago and, as expected, brass really added a lot of EMF in my test setup compared to CuBe or CuTe (>1uV). So in the 100mV or 1V range the resulting error contribution may be considerable.

[doktor pyta]

True.
I must have got lost in the catalogue details. SLS410-TS (22.1013) was my goal. However this part is discontinued.
Do You think LS4 would be better for this application?

[ap]

Definitely, not sure if you can mechanically solve that. Thicker PCB comes in mind.

[MiDi]

True.
I must have got lost in the catalogue details. SLS410-TS (22.1013) was my goal. However this part is discontinued.
Do You think LS4 would be better for this application?

Stäubli discontinued the -TS (CuTe) series (response from Stäubli), in the newer catalogues the -TS disappeared.
For some connectors they offer "Hartkupferlegierung" and these are CuBe (+another metal?).

I checked plugs from other manufacturer that claim gold plated CuBe and it turned out, that it is really hard and breaks soon - under the gold plating it looked like brass.
I would expect that pure CuBe - like CuTe - looks and behaves nearly like pure copper - with better machineability.

Not shure if the Stäubli are pure CuBe (do not want to test on my SLS4), the claim "Hartkupferlegierung" and the fact they do not claim CuBe gives me indication that it may be not

@ap: did you compare SLS4 as CuBe?

[ap]

CuBe is a copper material that is springy and is therefore used for the LS4. CuTe can be milled, and was therefore used for the SLS410-TS.
CuBe type bananas are ok EMF-wise. I have tested the Stäubli ones.

[doktor pyta]

I found a photo of another version of Datron lead kit.
Does anyone know the manufacturer of these banana plugs?

[serg-el]

https://www.dem-uk.com/deltron-components/products/4mm_single_pole_connectors/4mm_bunch_pin_side_stackable_plug/

[lukier]

I found a photo of another version of Datron lead kit.
Does anyone know the manufacturer of these banana plugs?

It seems to say DELTRON UK on the photo, so maybe that's it:
https://www.dem-uk.com/deltron-components/products/4mm_single_pole_connectors/

BTW Congrats on the Datron, nice bit of kit

[serg-el]

And Chinese counterparts 

 https://s.click.aliexpress.com/e/9VerPbc
 https://s.click.aliexpress.com/e/bLgIT7ii

[Testtech]

Looks good!
Where did you source the teflon shielded wire?

[doktor pyta]

wire bought from ebay user empiredon:

https://www.ebay.com/sch/empiredon/m.html?_nkw=&_armrs=1&_ipg=&_from=

[Johnny10]

I feel for you... I have a Datron 4000A that blows a tantalum every time I get it out to use it!!!!!!!!!!!!!!

Just changed all the small tants and even those can fail.
I started running unit off Variac and keep the voltage lower than needed for about 1 minute.

I was reading about the fan replacement... did it make a noticeable difference in loudness?

Thanks and looks like a successful project.