Datron 4000A Questions

[Johnny10]

I know there is so much information available on this forum I need some help with a new  purchase.

This morning I had the chance to pick up a Datron 4000A not working and showing a Fail 3 error code.
A few moments after turning unit on a very bad smell originated from unit so I immediately turned off power and started looking  for the culprit.
After pulling each board examining and re-seating didn't see anything unusual.

With cover off I turned unit back on Fail 7 error code and smoke began rising off the power supply board.

2 tantalum capacitors are a chocolate brown with oozing.
Not the pretty yellow of their neighbors.

While preparing to order parts I need to find some schematics for this unit.
And maybe operation manual.

Any assistance would be appreciated.
One other thought... I am reading the Options as 20 and 80.
Does this mean the unit only does AC or does it have Ohms and DC Calibration also.
Not sure I understand how options relate to features.

[Johnny10]

Front Panel

[Mickle T.]

Datron 4000A is DC only calibrator. Option 20 = DCI and Ohms functions. Option 80 = 115V 60 Hz Line operation.

[manganin]

very bad smell

Classic problem. Looks and smells worse than it actually is. Changing the tantalums usually returns the analog supplies which are down.

[ap]

General issue with Tantalums is that they often were used beyond spec. They were supposed to do PSU rail filtering, and saw a high ripple current, especially when electrolytic caps decreased their capacitance due to aging effects. Many companies did not observe this.
I would recommend not to replace by Tantalums but by organic cap such as Oscon. Better AC behaviour and not that sensitive against ripple.

[chris_11]

Tantalum capacitors, if left alone (read without voltage applied) for a long time can exhibit dendrite growth through their isolation barrier. You can cure that with a current limited switch on. However with a hard switch on without current limit they go up in smoke.They can even exhibit a nice fire.
Replacing them all with OSCON or similar is a good choose.
You have some corrosion on the nuts and screws. Might be a good idea to check the complete instrument and clean the PCBs since it has run or being stored in a very humid environment.

[Johnny10]

I am in Florida and I believe storing items with no de-humidification or AC causes this corrosion.
Yes, I see the corrosion but the boards and traces look quite good.
Closer examination will be necessary.

Changed the tantulums,  but on start-up still get Fail 7 error.
Cannot change switches front panel switches.

This error must lock out keyboard.

[Mickle T.]

FAIL 7 - 400 V PS failure.

[ManateeMafia]

I will look later tonight if I have the 4000A manual.

Where in Florida do you live?

[manganin]

Still a good idea to check the low voltage power rails (ramp up and stability). Especially those feeding the fault detect comparators can generate random fault indications.

[ManateeMafia]

I have the manual set for the 4000/4000A. A quick comparison between it and the digital copy of the 4708 SM shows the failure codes have different descriptions. Manganin may be correct with the direction for t/s this error.

Attached is a copy of the error description. The quality is not great but it is readable. I can get copies of particular sections once I clear off my scanner.

I have a 4700 and 4808. The 4700 had several tantalums fail with other failures on the inguard supply board. The 4808 also had a couple bad parts on the inguard supply. You could bench test the board by connecting to a power supply.

Let me know what you need and I will scan some copies for you.

[Johnny10]

I have been looking for a problem with the 400V supply for the past few hours.   
But I have to say I have also been reading the 4708 manual thinking the boards were the same.
After pulling out the inguard supply and comparing the actual board with the schematic not quite the same and other boards are even more different than 4708
.
That +-50v is interesting since I have not found 50V anywhere in my testing.

Well it is only the first day !
Many more to come.

[ManateeMafia]

I scanned in all the pages referenced by the manual. It is a large file at 40M. I can be upload it to xDevs for now until it can be converted to a more manageable size.

[Mickle T.]

It's better to upload it to the Didier's KO4BB site too.

[ManateeMafia]

The file is uploaded to xDevs here  https://xdevs.com/doc/Datron/4000A/Datron_4000_Fail_7.pdf

I have also uploaded it to KO4BB.

The outguard supply was also included for reference.

[Johnny10]

Great!!

Really Appreciate the effort and the quality.

And it proved that no 50V is present.
I do have 86V from transformer and through to test points.
But no 50 V, will have to study description this evening.
 
Again, Appreciate the effort.

[Johnny10]

OK,

Quick update.
I repaired the Inguard Board.
Problem was  no + 15 V which created no 50V replaced the 7815 and surrounding burnt Capacitors.

I now have +- 15, +- 50, 2.5 Reference

Now no more Fail message.

However I still can't operate front  panel controls.

[ManateeMafia]

Good news that it is now working in a smoke free zone. The 7815 was also dead on my 4808.

The 4700 manual states that the keyboard won't work if the letter B is on the MODE and OUTPUT displays. This means that the processor is busy.
I also had a problem with sticking keys. They were catching on the overlay for the front panel. I had to trim the overlay freeing them up.

[Johnny10]

My Mode screen is completely blank.
I set the internal reset switch received a Fail 5 error and then pressed the Front Panel Reset.
Key worked quickly and released Fail Mode.
So I don't think it is all bad or sticky switches.

Have you read where any other errors set lock the keyboard?

[ManateeMafia]

Ok.

Does your MODE display show anything on power up?
The RESET key is separate from all the other keys. It basically resets the watchdog circuit. The only information I have found for an inactive keyboard is if the calibrator is in REMOTE mode through the GPIB.

I wonder if the CPU is going into reset? You could always try communicating with it remotely to see if it responds. You may have to scope out the front panel and look for signs of life and also check the CPU reset line. That can be seen on TP7 of the digital PCB. It is tied in with the power supply fail detector.

The schematic for the 4708 is pretty close. The quality isn't the greatest but I can scan that section for you if needed in the morning.

[Mickle T.]

Is it possible that internal "Clear" key was pressed too? If so, 4000A losts all of NVRAM content, including the calibration constants and factory precal constants. FAIL 5, blocked MODE display - these are typical signs of precalibration lost.

[Johnny10]

I am going back in to check all voltages today.
My feeling was Digital board was working since the 0 and -15V error flags are sent to CPU.

I may be missing supplies to digital components.


Mickle T.
Where is the internal Clear Key?

[Johnny10]

OK
Checked lots of voltages this morning, all seemed within spec.
So I took Manatee Mafias advice and connected unit to GPIB.
Sent some messages to the unit and for now I tested DC voltages 1 through 100 volts.
I have control of DC output I guess I will read up on program commands to see if I can get keyboard access again.
Using the programming commands found in the Datron 4708 manual.


I only have 6 1/2 digit DMM HP 3457 that I repaired a  number of months ago.

Thanks Manatee Mafia and manganin and Mickle T.

Time to go learn about my unit, do some clean-up and put it back together.

[Vgkid]

That is good news. That front panel lockout reminds me of what happened to my solartron dmm. Powered it on one day all buttons were un responsive. Power cycle did nothing (remote led was continuously on). Ended up having to pull the remote card.

[ManateeMafia]

I might have some spare parts here if you can't find it. My 4000A has been sitting around and I have no urge to fix it up. Both displays are broken on it and I used it for t/s the 4700.