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Repair : HP 3245A precision DC/AC source

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PartialDischarge:

--- Quote from: nikonoid on October 17, 2017, 02:33:49 pm ---

Any recommendations for replacement EMI filter brand/type for 3245a and 3458a? Does it make any difference? Thanks.

--- End quote ---

Anyone you like, I hope schaffner has learned from the past by now, I used this one from mouser FN9222UZ-3-06 with surge protection, cause I live in a thunderstorm-prone area.

View[+]Finder:
Based on the excellent writeup and video by TiN xdevs, I found a used HP3245A on eBay (where else?) for about the same $$ as was mentioned in the post. It arrived in better physical condition than expected, but was way out of calibration. Having to calibrate the old way with a DMM and manual input of voltage makes one appreciate the value-added in the 3458A calibration method. After my usual internal inspection and dust removal (no IPA this time) the 3245 was ready for warm-up and calibration.

The end result is that my 3245A has passed all the 'tests' and is in line with all the performance measures. One troublsome spot--perhaps due to the state of earlier cals (there had been 14)--there was a glitch related to Step 45. My first time the 'voltage' indicated -.004 so that's what I entered, but after that Step 46 and 47 were out of line with the example in the book and the calibration was not accepted. (What a PITA: I can go for coffee while the 3458 chugs along on the volts cal)

Without wasting too much time on precision, I started another cal and used the 'book value' for Step 45. It worked, but not as well as possible. My next cal was done with care on volts only and I recorded the entries on paper. I used .0001 for the Step 45 in lieu of the slightly negative 'suggestion' from the 3245, just wanting to see if that would give better results. It did; much better.

The final was a full cal and all voltages were fed to the 3458 (NPLC 200) and to my 34465 DMM set up to collect a histogram of readings at 1 PLC. Both meters were reading the same voltage from the 3245 and the 34465 was set on 'High Z' so as not to load things down. Each run of the histograms captured over 1000 obs and sometime several times that. By observation, each histogram was checked for skewness, kurtosis and bi-modality and restarted if needed. With a stable and reliable histogram, the consistency of mean and standard deviation were used to indicate the end of the run. The mean value of voltage was used as the input to the 'CAL VALUE' on the 3245. This was usually close to the value displayed on the 3458, but when different, the 34465 'mean' was used. Current calibration was done with the 34465 alone using the same process as above.

The 'histogram' method improved a bit on the 'straight from 3458' as suggested in the 3245 cal manual. Performance results that were near the edge of the range were now close to the center in all cases.

View[+]Finder:
Has anyone done any investigation /experimentation around the 3245's frequency generator? There doesn't seem to be any way to calibrate, so I assume there is a crystal oscillator running the show. For example at 300kHz dialed in on the 3245 and measured on a HP5316B counter (with 10kHz Rh reference) it shows 300.0035E3. The 3458A shows the same. On the o'scope there seems to be an occasional glitch maybe from a higher frequency.

Not a big deal, but if anyone has more info . . ..

Probably well within the specs for an instrument of that age.

Thanks

Samogon:
Are you accepting new members?

I have got 3245A with startup error "92 Bus Source issue"
Measured all voltages on A6 (PSU) all voltages are good except 15V at J15 shows 21V. Measured P2 connector pins 1 and 2 give 17VAC as i understand transformer output too high. In order to have 15VDC after bridge rectifier and filter capacitor we need to have 10VAC input.
Line set to 120VAC. And what i suppose to think? Transformer? This unregulated 21V goes to backplane A2 and there distributed to source A1. I thinking to place voltage regulator between A6 (PSU J15) and A2(Back plane).
What do you think?
BTW i have supplied 15V to A2 from lab supply and it did not fix an error. So i assume A1 is damaged.

TiN:
Isolated voltages on A1 generated by separate switching supply, so higher input voltage does not matter much I think.

Check BP error signal generation circuitry on backplane.
IMG

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