[SOLVED] HP 34401a - Error 612, 613, 615, 617, 618, 619, 621

[Zucca]

Hi there,

Check this last mail email from a cal lab (see full story here https://www.eevblog.com/forum/testgear/34401a-cal-error-707/):

We recently received another 34401A in that has the same issue with the ohms function as your did. Would you be insterested in trying to fix it for us. If you do we can work out some kind of deal with the calibration. Let me know if this is something you'd be interested in? If not, I understand, I will just send your unit back.

After a quick check on this unit, it seems there is a lot to do here, see below the self test results:

Code: [Select]

-> SYST:ERR?
<- +612,"Ohms 500 nA source failed"
-> SYST:ERR?
<- +613,"Ohms 5 uA source failed"
-> SYST:ERR?
<- +615,"Ohms 10 uA source failed"
-> SYST:ERR?
<- +617,"Ohms 100 uA source failed"
-> SYST:ERR?
<- +618,"DC high voltage attenuator failed"
-> SYST:ERR?
<- +619,"Ohms 1 mA source failed"
-> SYST:ERR?
<- +621,"AC rms full scale failed"
Now I have to start the investigation and post my findings here...

Z

[free_electron]

That looks like the thick film resistor network is shot. check the 9 megaohm resistor in it. most likely it is open.

[Zucca]

Now I have time to follow this up, so let´s understand what those code means:

612 Ohms 500 nA source failed
This test configures to the 10 V dc range
with the internal 10 M 100:1 divider  U102A connected across the input.
The 500 nA ohms current source is connected to produce a nominal 5 V
signal. A 20 ms ADC measurement is performed and the result is
checked against a limit of 5 V  ± 1 V.

613 Ohms 5 uA source failed
This test configures to the 10 V dc range
with the internal 10 M 100:1 divider  U102A connected across the input.
The 5  µ A ohms current source is connected. The compliance limit of the
current source is measured. A 20 ms  ADC measurement is performed
and the result is checked against a limit of 7.5 V  ± 3 V.

615 Ohms 10 uA source failed
This test configures to the 10 V dc range
with the internal 10 M 100:1 divider  U102A connected across the input.
The 10  µ A ohms current source is connected. The compliance limit of the
current source is measured. A 20 ms  ADC measurement is performed
and the result is checked against a limit of 7.5 V  ± 3 V.

617 Ohms 100 uA source failed
This test configures to the 10 V dc range with the internal 10 M 100:1 divider  U102A connected across the input.
The 100  µ A ohms current source is connected. The compliance limit of
the current source is measured. A 20 ms  ADC measurement is
performed and the result is checked against a limit of 7.5 V  ± 3 V.

618 DC high voltage attenuator failed
This test configures to the 1000V dc range. The 500 nA ohms current source is connected to produce a
nominal 5 V signal. A 20 ms  ADC measurement is performed and the
result is checked against a limit of 5 V  ± 1 V.

619 Ohms 1 mA source failed
This test configures to the 10 V dc range
with the internal 10 M 100:1 divider  U102A connected across the input.
The 1 mA ohms current source is connected. The compliance limit of the
current source is measured. A 20 ms  ADC measurement is performed
and the result is checked against a limit of 7 V  ±  3.5 V.

621 AC rms full scale failed
This test configures for the 100 mV ac range.
The 1 mA ohms current source is switched on to charge the ac input
capacitor  C301 . This produces a pulse on the output of the rms-to-dc
converter which is sampled 100 ms after the current is applied. A 20 ms
A/D measurement is performed and checked against a limit of 10 V  ± 8 V
into the  ADC

618 and 621 are respectively due to 612 and 619, so we can ignore those two.

Yes free_electron, the U102A is the first suspected, but in R I have no ohm current source.

What if the ohm current source is fried?

mmmmm... I will find out... 



 

[free_electron]

like i said : check the 10 meg divider. pin 1 to pin 12 i believe of that ceramic hybrid. imost likely it is open.
i have seen those fail two times. that hybrid is very expensive... like 250$ ..

[Zucca]

Thanks free_electron to stay with me!

I did after I posted the previous one and it was not open.

I connected the bad 34401a HI to the I 3A current on a 34461a, and then I connected the two LO between 34401a and 34461a.
With 2WR set on the 34401a I got no current flowing in the 34461a.

In this set up the 10MR divider doesn't play any role, please tell me if I overlooked something.

Thanks a lot!

[Zucca]

I activate the 2WR with a shortcut between HI and LO.

Yep... something is wrong here [everything in V]



I need to replace the U201, IC-Op Amp LP Dual 8-Pin AD706JR

http://www.mouser.com/ProductDetail/Analog-Devices/AD706JRZ/?qs=sGAEpiMZZMvtNjJQt4UgLalm6EXZly%2fyYoythdEg1pg%3d

How can I understand if also Q201 is bad?

[Dr. Frank]

U201-A and Q201 should be ok.

Both stabilize the 7.012V reference over R202 correctly, and the gate voltage on Q201 is 3.637V only, i.e. lower than source voltage, therefore the necessary current of 175µA must be delivered correctly over the drain, from the 11.444V node. All voltages around Q201 are quite reasonable.

It is strange, that you measure 4.920V over R201, as both FETs in U101-D should be shut. Maybe U101 is corrupt. But I could remeasure on my unit..
Edit: No, that's also fine, mine shows 4.9115V there. Obviously the third FET inside U101-D biases that point to VDD = Vcc ~ 4.937V
Also, all other voltages around Q201 and U201-A are equivalently set in my unit.. besides Drain voltage, which is 9.725V vs. 14.812V above 28.75k inside U102-D, which gives correctly around 5V in my unit.

These 11.444V are too high, should be 13.853V-5V = 8.853V instead.
So, U201-B may be defect, as it may source current into that node.
Also, as pin5 (+) = 11.444V, pin6 (-) = 12.292V, therefore output pin7 should go towards AGND, and not to 14.297V.

Therefore, U201 is the most probable error, and I would start with its replacement, which should fix the problem.

Frank

[Zucca]

Thanks Frank to double check with your device   !

...and the gate voltage on Q201 is 3.637V only, i.e. lower than source voltage, therefore the necessary current of 175µA must be delivered correctly over the drain, from the 11.444V node...

In University they told me in a n-ch FET if (V Gate - V Th) <= V Source the FET is open. In this case is acting as a 24.5KR resistor. That´s why I was a little confused. Anyway I should have read the Q201 datasheet.

So, U201-B may be defect, as it may source current into that node.
Also, as pin5 (+) = 11.444V, pin6 (-) = 12.292V, therefore output pin7 should go towards AGND, and not to 14.297V.

I love when another person thinks the same way I do  .

Let´s oder some of them now...

Not sure why it failed like that. When I saw the ohm current source was dead I thought most likely the protection diode or BJT transistors did their job... and some smart user was testing R live on a very high voltage circuit...

[Zucca]

U201 Replaced. Solved.

[mzzj]

Year ago I had a 34401a also with several error codes. Same problem, after checkin input and outputs of the u201 i came to conclusion that it has to the problem. Replaced and good to go.

[Phiveaces]

Just wanted to say that thanks to Zucca, I now have a working 34401A

Mine only had errors 613, 615, 617, 619 and 621.

Setting the Ohms range to Ohms, and checking the output of U201 compared with its inputs showed  ~14V when it should have been closer to AGND.

Replaced with a new one from Digikey and now all tests passed! 

[Zucca]

That was my Xmas present to you! Enjoy!!!

[chihaxinh]

I have same problem but replace U201 not help ! 

[Dr. Frank]

I have same problem but replace U201 not help ! 

You mean, you have the same Error messages?

To change this OpAmp simply on this, was obviously the wrong action.

You also have to check the voltages in the Ohm circuitry, as zucca, Phiveaces, and me have done. This is urgently necessary to identify the really corrupt component.
A useful help is a diagram with the correct voltages vs. the erroneous ones, you have to measure on your own.

Please come back when you have made these measurements!

Frank

[Zucca]

Please come back when you have made these measurements!

+1

[chihaxinh]

Hi All

I have some free day for prepare new lunar year , i making measurement and give you information. I replace 3 opamp 706 but not help , again and try again . So i have only one new opamp 706 , pls help me

I checking Q202 and Q211, Q211 part exactly in service guide but Q202 have marking 1671 .
In service guide, Q202 it's N chanel JFET 2N5461 , i cheking pinout:
Q202 - 1671 marking have  D S G
2N5461 have S D G
i think 1671 like japan jfet . I change pin 1 2 for matching like schematics but not help !

Can you guide me how to check opamp live or die !

Thank you so much !

[TiN]

Did you measure output current from ohm source?
Use external DMM to measure current from marked node to 34401's LO terminal.

[chihaxinh]

Hi Tin

i have 3 another 34401a, but i not pro. can you guide setup for measurement ! you mean checking voltage or current?

[TiN]

Current. You should read correct currents with red lead connected to CR202 anode, and black lead connected to 34401 meter's LO (black input jack is ok).

[chihaxinh]

Hi Tin

I have some mistake , Q202 it's P chanel JFET - so i checking picture in internet for sure pin out connect in diagram .

You can see picture below for setup measurement current like you said ?

[TiN]

Yes, that's correct connection.
Use manual ranges for ohms on bad DMM, and measure current. Change to every range and check all current source levels.

[chihaxinh]

Hi Tin

I checking and give new information, vol dc and ohm function not woking in 2W and 4W mode

I check current like your said and have

000.000 Ohm - 1mA
0.00000 KOhm - 1.006mA
00.0000 KOhm - 1.002mA
000.000 KOhm - 0.010mA
0.00000 MOhm - 0.005mA
00.0000 MOhm - 0.000,6mA
000.000 MOHm - 0.000,6mA

And voltage measurement after replace U201 and swap pin Q202 for correct pinout in schematics.

[TiN]

Then your ohms current source working fine, and problem is somewhere else.
Did you check all zener voltages and power rails? I think you saw my 34401 repair? Maybe yours have similar problem.

[chihaxinh]

Hi Tin, i checking power supply rails , everything ok !

Voltage DC and Ohm function not work ( 2W or 4W mode )

[TiN]

Did you check all the zeners? There are many of them.