HP 3458A repair's (now there are two of them)

• #25 Reply
  Posted by BFX on 30 Dec, 2016 20:06
• My god that's impossible
  You are really lucky man
  What was the cost of second one?
• #26 Reply
  Posted by tggzzz on 30 Dec, 2016 20:41
• Quote from: TiN on 30 Dec, 2016 11:10

  Let's see more guts photos! Afaik your second box is oldest we ever know across EEVblog crazy-nuts.
  

  
  Different box, pretty pictures, 68 years old 
  https://www.eevblog.com/forum/metrology/1000-my-(hi)story-of-the-weston-cell-of-the-volt-and-of-being-a-volt-nuts/msg1100033/#msg1100033
• #27 Reply
  Posted by TheSteve on 30 Dec, 2016 22:31
• Quote from: BFX on 30 Dec, 2016 20:06

  My god that's impossible
  You are really lucky man
  What was the cost of second one?
  

  
  Less then the first one...
• #28 Reply
  Posted by TheSteve on 30 Dec, 2016 22:53
• TiN had asked me about the 40K reference (R207) on the A1 board installed in my early unit.
  It is marked "VISHAY B 8822 40K000" and "0.1% 0699 -1125" - pics attached.
  
  On my original unit which is 1990-1991 time period the resistor is marked "VISHAY 89012 301031" and "40K000 0.1%".
  
  While I had it open installed I performed Service Note 3458A-01C which is to replace capacitors C142 and C143 on the A3 board with 2.2 uF units which improve linearity at very low levels of input signal.
  I replaced the fans in both units with a Papst model # 622L.
  I also came across a resistor (R403) on the A3 board that had never been properly installed. One leg was stuck under another resistor instead of being soldered in its proper place. They both go to the same place however so it is fully functional.
  
  They are both warming up again.
  

  ---

  

  

  
• #29 Reply
  Posted by VK5RC on 31 Dec, 2016 04:20
• TheSteve,  at the price you can find them,  three 3458 seems essential,  otherwise you have the 'two clocks '  problem!    HiHi.
  Your latest one came out before mine 2823A050xx. (mine also NVRAM failure but 15yo Dallas,   I was  able to scavenge cal data using TL866) but no where near the bargain price!
  Robert
• #30 Reply
  Posted by TheSteve on 31 Dec, 2016 05:10
• The price was just luck - the first one I came across, the second a friend found and messaged me about. Both were bought with best offers, it is amazing nobody else clicked buy-it-now at a higher price - especially after seeing the price two broken/damaged ones closed for today.
  The odds of two were slim, a third doesn't seem likely.
  
  The new fans are working much better then the originals, much more air flow - even though both 3458A's are fully warmed up the CAL 72 values have changed. I'll log both of them to see how the drift looks. I need to find a darned GPIB cable - tough to find locally.
• #31 Reply
  Posted by TiN on 31 Dec, 2016 09:14
• Quote

  resistor (R403) on the A3 board that had never been properly installed.

  
  Lucky bodge with resistor I had cap on A6 with same problem in my 3245A :
  
  
  
  Good old days, when you can see assembly problems with naked eye. Those days are gonsky, with modern 01005 SMDs and BGAs 
• #32 Reply
  Posted by quarks on 31 Dec, 2016 10:02
• Congratulations
  Does anyone know if it is possible to get a U180 without buying a A3 Board?
• #33 Reply
  Posted by Kleinstein on 31 Dec, 2016 10:10
• Quote from: TheSteve on 31 Dec, 2016 05:10

  ...
  The new fans are working much better then the originals, much more air flow - even though both 3458A's are fully warmed up the CAL 72 values have changed. I'll log both of them to see how the drift looks. I need to find a darned GPIB cable - tough to find locally.
  

  With a considerably stronger fan one might consider an extra shield/cover over the reference module, to keep the temperature there at a similar slightly warmer level and avoid to much turbulence.
• #34 Reply
  Posted by HighVoltage on 31 Dec, 2016 11:03
• Quote from: TheSteve on 31 Dec, 2016 05:10

  The odds of two were slim, a third doesn't seem likely.
  

  The rule seems to be:
  The first one you have to find and it can be hard.
  Then they start coming to you very easily.
  
  Congratulations on your second one.
  Very impressive, of what is possible.
  
• #35 Reply
  Posted by TheSteve on 31 Dec, 2016 23:29
• Quote from: Kleinstein on 31 Dec, 2016 10:10

  With a considerably stronger fan one might consider an extra shield/cover over the reference module, to keep the temperature there at a similar slightly warmer level and avoid to much turbulence.
  

  
  I don't think the new fan has a higher CFM then the original, they are just ~25 years newer and as such blow a little better. Looking at the Keysight website the fan they currently spec/sell is the exact fan I used, the Papst 622L. With that in mind I don't think it would be a good idea to mess with shields/covers.
• #36 Reply
  Posted by TheSteve on 01 Jan, 2017 03:15
• With the new fans installed in both units I am logging the CAL 72 values daily.
  
  Date/time                      3458A serial 5XXX            3458A serial 4XX
  
  Day 0, Dec 30, 19:00    .989773311 32.1C            .988870057 31.4C
  Day 1, Dec 31, 19:00    .989773289 32.2C            .988870101 31.5C
  Day 2, Jan 1,   19:00    .989773232 32.2C            .988869970 31.6C
  Day 3, Jan 2,   19:00    .989773424 32.2C            .988870044 31.7C
  Day 4, Jan 3,   19:00    .989773419 32.5C            .988869978 32.1C
  Day 5, Jan 4,   19:00    .989773351 32.2C            .988869669 31.8C
  Day 6, Jan 5,   19:00    .989773242 31.5C            .988869148 31.0C
  Day 7, Jan 6,   19:00    .989773382 31.9C            .988869253 31.5C
  
  Total PPM shift              0.010 PPM/day                  0.116 PPM/day