Electronics > Repair
HP 3458A - Fails Slave Test - Convergence
Dr. Frank:
you may read date codes from the nvRAMs and from any IC on A1, A5, etc.
First will give you a hint about the sanity of the calibration constants, 2nd will give the age of the whole instrument. there also some stickers on stamps inside. The serial number as well gives a hint.. I have a table somewhere, to match production date and ser. no.
If its really from 2001, like my unit, then 20 year old nvRAMs should be replaced.. save content of calram at first
There's been a lot of recent damage inside the instrument... so that's unpredictable, what has happened.
if the unit worked until recently, then I tight not have affected the comparators, which are unobtainium.
these usually fail for very old units with high use in high temperature environment, due to heat death.
check all the fibre optics. maybe the shift register chain is broken, I remember one instance.
try to change NPLC to small numbers <1 , hopefully the instrument reacts to commands.
BTW.: TiN / xdevs has most experience on the 3458A and really disassembled each and every part of this DMM.
Anyhow, thank you for the compliments
Ade911:
I checked U181 and this looks fine,
All signals are fine except pin 3 where it toggles only to 7v during a DCV cal then fails / stops sampling, or 10v when it does a little more sampling and the output jumps to 5v [plus relay clicks on].
U142 , again I believe is ok, the output is toggling between 0 and 5v, however if I scope the input pin 3 the sampling fails [TP140] , its as if the system doesn't like the extra load, which is strange as its only a normal scope probe.
You mentioned the shift registers , where or is there a guide explaining how they work [plus other sections, signal routs etc], i confess i didn't read all the HP Journal shared by Grandchick because it seems to focus only on the logic behind the A-D conversion process.
OK , of to test the other items you mentioned,
thanks again
Ade.
Ade911:
Dr Frank,
Details on the Dallas chips
DS1230Y-150
9538U 067285
DS1220Y-150
9547D 070606
Not sure if that is the information needed to confirm the age.
BTW , is there a procedure I can follow to download the stored data / replacement please.
Many tx
Ade
Ade911:
update
So I guess the dallas chips are from 1995 week 38 / 47 after watching videos about them, ill order replacements and hope you can clarify how i can download and replace.
I also found an old communication from TiN re the TARM command, OMW , after doing this the meter came to life and did a few samples before stopping again [but it is repeatable]. With nothing connected im getting various voltages between +5.xxx and +10.xxx , If you do an autozero i then get +10.xxxxv.
Ade911:
Todays update
only samples if i manually trigger TARM command, no idea why.
when i initially started to look inside i found the voltage on U100 pin 6 is slowly drifting up , its still doing it now. Unfortunately I damaged Q106 but was able to replace so didnt think any more about it, but today I find myself again back here as the signal DC_AD is slowly rising and is reflected on the screen [least I know the DAC is ok]
screen readings
DCV volts ? +0.689 max then freezes - error message time out read A/D 108 [but it cant be the DAC]
ACV mv samples for ever 1.945mv AC
ACV 000.081 and rising VAC
OHMS +0.VLD GOHM
OHMS +OVL.D MOHM stops sampling
OHMS +OV.LD KOHM
OHMS +OV.LD OHM
DCI nA 000.173
DCI uA 0.000159 stops sampling
DCI mA 0.0000248
DCI A 0.0000135
ACI uA 000.0434
ACI mA 0.000286
ACI A 0.000268
FREQ 50.xxx HZ
Data error matches system asking for DCV and OHMS calibration
Any support most welcome please
Tx Ade
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