Monitoring TP11 on A1 I can see a signal jumping from zero to around 7 volts, the screen also shows its sampling, then it beeps and stops , or some times it will sample , a relay will click and TP11 will jump to 10V before failing again.
Ive checked the Convergence circuit with my very limited understanding of the circuit.
FETs are on and off , ive cycled functions to see if the FET will change state just to see if its working.
As the test sometimes goes further than other times I took the decision to replace U7,8,9,20,17, 14,11 [I know some chips don't need changing but desperation cut in] ![Banging Head |O](https://www.eevblog.com/forum/Smileys/default/bangheadonwall.gif)
@ TP11 / A1 you measure behind the input multiplexer, which applies DCV input, then zero for the AZ cycle.
Therefore it's completely normal, that you see varying voltages on that pin.
If you apply 10V to the input jacks in the 10V range, you should see 10V / 0V , with about 200ms time for each cycle.
If you switch off AZ, then the 10V should be visible continuously @ TP11.
Please try that out
when I apply +10V to the input with Auto Zero ON or OFF i only see a constant +10V on A1 TP11, its not dropping to zero volts.
Which NPLC length do you use?
Ade > Default value at switch ON.
For AZERO ON and NPLC 10, NPLC 100, you should always see a switching signal @ A1TP11, between 0V and 10V, for 50Hz => 200ms Lo, 200ms Hi.
I set AZERO ON and NPLC to 10, 100 , measuring at A1TP11 I jut see +10VDC, no oscillation as you say it should be.
Sorry, I can't check that in situ, but that's exactly how Auto Zero is working, if the DMM is running correctly.
Under these conditions, that same signal should be visible @ TP100.
Ade> TP100 = +10VDC
If the whole system is stalled somehow, as it might the case, then you should read out the ERR? message.
Maybe you try NPLC 0.001,, or so, i.e much shorter than NPLC 1.
Or try sampling with APER 1.
NPLC set to 0.001 still +10VDC on A1 TP10
APER =1 still +10VDC on A1 TP10
Frank
Evening Frank,
The error messages I get at present when turning the unit on are
202 Hardware failure - Slave test convergence
110 Calibration Required - SCAL
0 No Error
I too think the system is frozen somehow, this is why I also checked A1 U10 Pin3 , this is sitting at +5V, I thought this may have caused measurements to stop but guess not.
If I enable TARM [beeps as well]
Inject +10VDC to the front of the unit
Scroll to mV I then get +0.VLD but the system is sampling on the front screen A1 TP10 still at +10VDC
Error message
114 System Error - balanced rundown convergence
0 No Error
If I enable TARM [beeps as well]
Inject +1mVDC to the front of the unit
Scroll to mV I then get NO +0.VLD and the system is NOT sampling on the front screen A1 TP10 noise but no smooth voltage> 20mV [Noise could be from the power supply I am using ?]
The unit only samples when the voltage is too high for the from screen, in auto nothing works.
Is there another A->D that says the input is too high or ??
No. There is an analog overload detection / clamp circuit on sheet 4 / 5 for protection of the fast input DCV path, A1R17/18.
This is centered around A1U10, Q26/Q27 as low leakage diodes.
This circuit has to switch off the input relays very fast to unload the DCV input.
Have you already tried to use a very short NPLC number, like NPLC 0.01, 0.001, or so?
There was a difference between the slow and fast sampling.
All these rundown convergence error point towards A3, most probably the EL2018, maybe U180.
But anyhow, as the input amplifier and the MUX might not work at all/incorrectly, maybe the control shift register chain is defect. Please check those on input / output DATA, like A1U105, sheet 3/5, and U6, U17, U9, U201, 203, U1, U4.. sorry, you have to search for the whole chain by yourself.. I don't know where this begins, and how it ends.
I would trace from behind, maybe there is already a break in between..
Frank