| Electronics > Repair |
| HP 3458A - Fails Slave Test - Convergence |
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| Dr. Frank:
--- 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) |
| Dr. Frank:
--- Quote from: Ade911 on May 05, 2023, 11:47:16 am --- 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. :palm: 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] |O --- End quote --- @ 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 |
| Dr. Frank:
--- Quote from: Ade911 on May 08, 2023, 01:18:11 pm ---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. --- End quote --- What PCB / TP are you talking about? Where do you measure these signals? |
| Dr. Frank:
--- Quote from: Ade911 on May 08, 2023, 07:45:28 am ---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. --- End quote --- How did you confirm / measure, that the EL2018 are working ok? Did you scope on their outputs? |
| Dr. Frank:
--- Quote from: Ade911 on May 08, 2023, 04:57:50 pm ---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] --- End quote --- Have you applied a fixed input voltage (only at the input jacks, of course!) for that test? Use TP100, instead of A1U100 - pin6. switch AZ off for that test. If you apply fixed 10V in 10V range, then you should see that 10V at TP100. apply 1V in 1V range, you should see 10V as well, repeat that for 100mV in 100mV range, please --- Quote from: Ade911 on May 08, 2023, 04:57:50 pm ---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 --- End quote --- Please explain, what are you doing here, I do not know (or can't guess) what you mean with screen display, which sources you apply, and what mode / range you select in each case |
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