Electronics > Repair
HP 3458A - Fails Slave Test - Convergence
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Dr. Frank:

--- Quote from: Ade911 on May 24, 2023, 07:37:11 pm ---
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.

--- End quote ---

TP100 (w/o AZ) is the input signal times the range amplification, i.e. x1, for 10V range, x10 for 1V range and x100 for the 100mV range.
Where did you inject the 10V?
At the input jacks only, hopefully.
If you overload the amplifier, then of course you get +/-17V something out of U100.
The input to the ADC can of course be +/-12V for full scale.
Dr. Frank:

--- Quote from: Ade911 on June 01, 2023, 07:43:41 pm ---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  |O

Replaced Q106 - Damaged CAN
Replaced Q107 with  J112    |O  [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    |O   [ 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"

--- End quote ---

why have you changed A1Q107 / Q108?
Put in the original transistors, please.
Hopefully you now understand, how this circuit part works?
Dr. Frank:

--- Quote from: Ade911 on July 02, 2023, 07:21:15 am ---Hello Frank,

Not sure if you can answer ; if i have access to another unit , would board swapping cause issues with the other unit, not ideal but run out of ideas before asking for a quote from the OEM.

Im stuck, I don't seem to be able to find out anywhere where it states the system will still sample even if U180 is dead. It will sample if TRAM is activated , no input and DCV dropped to mV but im not sure why this happens but not in volt range.

OVLD signal on U228 is working fine.

--- End quote ---


You have probably damaged A1 with all your component changes and measuring / injecting signals (I'm partly confused about your descriptions so far.).

U180 rarely fails completely. That didn't seem to be the problem, initially.

As the comparators A3U110, U11, U112, 140 are fully overloaded, is A1P100 set correctly?
Have you touched the LTZ1000 reference board, and are its voltages and potential applied correctly, especially reference zero?

Is the input amplifier with U100 / TP100 now working correctly, as described above?

If you apply input signal of 10V in 10V range, w/o AZ,does that appear correctly @ DC_AD on A3 board?

What are the voltages on A3U110, pin 2 +3?

As long as you can't confirm that A1 is working properly, I would not swap any boards any more.

In your situation, I would not jeopardize the other working boards by swapping, to write it in a polite manner.

Frank
Ade911:
Hello Kleinstein, yes its my sons so i dont think he would be very happy if something broke, I will not do any board swapping , just a thought before doing some thing drastic like sending to keysight.
Ade911:

--- Quote from: Dr. Frank on July 02, 2023, 09:23:29 pm ---
--- Quote from: Ade911 on May 07, 2023, 12:37:13 pm ---

Managed to purchase maybe 5 years ago , upon trying to power on at that time I found the inguard board was burnt around CR11,CR12 maybe caused by the incorrect power setting from the previous owners. These were replaced and the system powered on, but due to travelling allot at the time it was switched off and left for 2-3 years.


Many tx Ade.

--- End quote ---

Hello Ade,
I'm trying to get some light in your recent descriptions..

CR11 and CR 12 are on A1, SENTRY, Input Signal Conditioning, and on A4, inguard power supply (an "Inguard board" is not existent).
That's very confusing.

Please name all components correctly,  best would be using the BOM designator, like A1CR11 and A1CR12, or A4CR11, A4CR12, and so on.
Please describe in detail, which components were damaged at that time, A4CR11 + CR12 only?

Frank (to be continued)

--- End quote ---

Sorry for the confusion.

A4 Inguard power supply - A4CR11 + A4CR12 were replaced as they were damaged [PCB is slightly damaged as well but repaired and working.
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