| Electronics > Repair |
| Repair : HP 3245A precision DC/AC source |
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| TiN:
No, it's not empty, there is ribbon cable running to source board. And X2816BP U18 ROM + few RAM and logic on inguard section chips (not battery backed) there as well. It's not socketed, and only DMM needed to do full calibration, so I did not bother socketing RAM. I'll take few more photos with everything in place, to clarify this. |
| TiN:
Few more photos, as promised Top side: Bottom side: Modification on source PCB: Remove R400, R401, LM399 reference. Solder coax wire in place of LM399's diode location. This connected to Kelvin output (direct connection at LTZ's zener pins). Solder coax wire to +15V and GND to power LTZ's opamps and control circuitry Solder coax wire to +18.5V and power GND to provide separate current path for LTZ's heater, so it would not upset reference output. Now, find a best spot for module location. I think it's best on bottom side, between front panel and HV Opt.002 board. It's far from mains transformer, far from pesky fan. To have it isolated from airflow I added big piece of airlocked foam used in packing electronics. It tied to metal chassis via dual-sided 3M tape, for better contact. Now soldered piece of copper foil for sake of it. It's soldered to ground on power coax wire in single point. Idea to have it for even temperature distribution and bit of shielding. It's likely doing nothing at all, like audiophoolery, but hey, it's shiny and I had it without use anyway. Why not? :D Piece of 4mm rubber pad is holding everything in place securely, screwed down to existing two metal stubs on chassis. Coax wires not touching anything and running at least 1cm from output wires/front panel. Now, let's calibrate it. Password is standard, but calibration have to be done by GPIB. Temperature in room around +26°C. After entering calibration mode, it's just showing "Calibrating..." and output have voltage or current, which need to be measured by DMM and written back by command "CAL VALUE x.xxxxxxxx". After running all values from cal manual, it automatically saves CALRAM. Optionally you can leave a string with CALSTR "TEXT" later. 3458A was ACAL'd and initial calibration was just quick sanity check, to make sure I can get output 10.000V. I did not have too much effort on it to do. It worked well, so I calibrated again, keeping temperature within 1°C span and measuring all at NPLC200 Result after calibration Now I'll leave it overnight without AC, to see how good is tempco. I checked 3458A+EDC MV106 earlier today, outputting 10VDC. That setup had +1.23 ppm/°C tempco. I hope 3245A with LTZ + 3458A can be better. |
| Dr. Frank:
Hi TiN, on the main controller PCB, the address space for the original DALLAS 2kx8 nvRAM is used for the steering of the analogue board. That's what I meant, that the CALRAM is not installed.. Therefore the CAL dump program for the 3458A cannot work. On the analogue board, I found the XICOR X2816, as you already described. This is an EEPROM, 2kx8, therefore should not loose its content. Congrats to the final repair and to this new, nice instrument Frank |
| Zucca:
Congrats TiN, one day with my (was yours) LTZ module I will do something similar! --- Quote from: TiN on November 14, 2015, 07:29:44 pm ---Now soldered piece of copper foil for sake of it. It's soldered to ground on power coax wire in single point. Idea to have it for even temperature distribution and bit of shielding. It's likely doing nothing at all, like audiophoolery, but hey, it's shiny and I had it without use anyway. Why not? :D --- End quote --- Mmm why not place there some silica packs? https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg181096/#msg181096 Just because you mentioned audiophoolery.... ::) well sometime if it costs nothing I am a proud audiophool! ;D Take Care! Z |
| alanambrose:
OK I'll just add onto this thread if it's OK with you TiN... Received my 3245A - end '92 vintage, same 2843 firmware, only ever one factory cal. This is the one with 2 x 10V output. Everything seemed OK for an hour and I was doing some basic cal checks when snap, crackle, pop ... thunder and lightning etc ... it smoked, smelt and flashed a bit and then flipped the mains RCD - despite me turning it off pretty sharpish. I assumed it was the transformer but actually it turned out to be the xxs£$%ss:{@~}@xx^&*xx Schaffner mains filter. Since the filter is outboard of the fuse etc, it has no protection and it smokes 'til it goes pop and relies on a trip somewhere else to protect it - so it's a bit criminal to have a fault like this on it. This was even more galling as I already had a new filter and fan sitting on my desk waiting to be installed. A mess like used sticky engine oil - gory pictures for your amusement. Several hours later, IPA clean up / drilling out the damned rivets and it's operational again. Thinking about it, the switch to 220V from its previous many gears of running at 110V was probably the last straw. Now I'm a bit concerned what else of my HP gear has the same dodgy inlet. BTW TiN - did you write some 3245 / 3458 cal software? Alan |
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