Electronics > Repair

HP 3458A - Fails Slave Test - Convergence

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Ade911:
Todays status

IanJ very kindly checked my CAL file device but it only had H0 Data for some strange reason so alas thats gone. The only positive would be that the meter has not been calibrated since 2001 I believe or so the CAL label said, would someone else's CAL file assist in my recovery , if yes can any one share it please.

Todays status - Still fails all calibration , HW, fails same issue as before.

For some strange reason when you inject 10V and manually cycle through  the X1, X10 , initially when you selected mv the meter wouldn't do anything now it states overload and samples , no idea why.

Monitoring A1 TP100

X1 10V I/P 10V TP100
X10 10V I/P 1V TP100
x100 10V I/P 0.1V TP100

Below X1 [mV ?] 10V I/P Overload [ sampling] TP100 = 17.39V

I thought the input to the A3 would never exceed 10V , is this incorrect.

Ive also noticed that if you remove the 10V I/P and set to X1 TP100 starts to drive up towards 17.39V, is this normal.

Also removed Jumper P100 and there is no input via P102 and still does it.

Any idea where to check next please, I hope that because the voltage from A1 if above 10V the A-D will not sample and there is some limit circuit stopping 17V damaging the device.

 Trying to be logical and methodical in finding what is wrong.


IanJ:
Yep, Ade sent me his DS1220Y after I offered to double check it was indeed corrupted/data loss via my programmer......which, alas, it is.

Ian.

Ade911:
Hi 3458A knowledge group, so after ordering spare parts and fitting things still look bad. I really don't know what happened to the unit, be it a surge or something I really don't know;

Status

Repositioned JMP600 to pin 1-2 [Right side] Front of meter facing me - Calibration security code

Fitted NEW U105 --> LT1008CN8 out put was floating/drifting

Replaced Q106 - Damaged CAN
Replaced Q107 with  J112 [Found the resistance between the Gate and Drain on a meter changes over time] - Causing TP100 to rise in voltage to 17V or so.
Replaced Q108 with J112 [ Not 100% sure before removing both which was causing the voltage on TP100 to rise.

Now

Original error still there.
Input connected to +10V, +10V now read on TP100 [x10 = 1v , x100 = 0.1].
Short input pins TP100 = 0V

Set DC to mV [No short input floating] X1 or X 10 - DC TP100 now ready +17V !

DC X1 ~ +1.5V , X10 +0.042, X100 +0.004V

Not sure where the +17V is being generated from [High voltage relays not used I assume]

If I try and do a CAL 0 the meter does something then beeps

If I try and do and CAL from the manual nothing changes

If I try AUTOCAL DCV nothing changes

Im therefor not sure where to check next.

Any advice would be so very much received please as I have no idea what to check next.

New error message

Select mV
Enable TARM
System now samples with overvoltage error - TP100 = +17V
Select X1 - TP100 = +10V , no sample [ ERRSTR 101,"CALIBRATION ERROR"







Ade911:
Update after waiting for some parts to arrive, I was not aware how difficult and impossible to get some devices fitted it is.

Same fault as from day one, now down to fault finding on the A3 bd. I confess my knowledge of the A3 bd is very limited so support will be very much appreciated. Again input gives 10v on the DC_AD pin of A3 unless you select mV which drives the voltage to ~17v.

Not planned I touched U112 [AD848] and its very hot and U111 and U140 are warm. Removed all three chips and bread boarded,

U111 [LM6361] drawing 3mA so within spec even when the inputs are grounded [ output toggles].

U112 [AD848] +15V = 5mA , -15V = 3mA , again when the input is grounded the output toggled correctly.

U140 [LM6361] drawing more than 10mA and output not toggling [+15V=5mA, -15V=3mA no connection. Pin 2 GND 2ma/ 2mA OP OC, Pin 3 GND 10mA/8mA OP OC]

I was able to find in the UK a supply or RS LM6361 chips , I replaced both, tried again, same issue , U112 is still getting very hot. I need i guess to purchase a replacement although the chip seems to work fine on a bread board.

From what I have read on line DC_AD is the main input voltage to A3. What does ZR_LO and ZR_HI do. ZR_HI reads 7.2V and ZR_LOW always reads 0V even when switched to Hz to activate the FET on A1.

Voltages taken
DC_AD = +10V
U112 Pin2 = +1.539V Pin3 = -14.96V
U110 Pin2 = +0.012V Pin3 = 0.00V Pin8 = +15.63V

ADC References are all correct so Im now thinking A3 has died , thoughts ?

Kleinstein:
It is normal that some of the OP-amps rund a bit hot. That is prie paid for high speed. With such a precision board it is not such a good idea to unsolder that many parts just based on a faint hint. Any step of soldering adds stress to the parts and other parts on the PCB and can add additional faults.

So the advice is to do a little more measuring up front and thinking before soldering. The main suspects on the A3 board are U180, the obsolete Elantec comparators and maybe if lucky the fiber optic link.
This does not mean to unsolder these, but more like check there supply and the comparator output signals. Have a look at TP112, TP140 and TP142.

The ZR_hi / lo are the links to the reference. There is no switching so hopefully a very stable voltage on those signals.

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