Products > Test Equipment
HP/Agilent 34970A Teardown
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free_electron:
And another bites the dust.
A 34970A switch multiplexer with built in DMM ( 34401 style )

This one had all kinds of problems. The display was all garbled like segments lighting up together , the rotary encoder did not work quite right either and it kept coming up with errors at power up.

The front panel board

The bourns rotary encoder was at the end of its life i gueass. replaced it with a new one. Works fine now. These are mechanical encoders with a cheap plastic axle. i've seen many of these go bad..

The display was another thing... the darn driver logic sits under the glass... luckily it's a single row affair.


I simply bent the display upward. one of the drivers had shorted outputs. these are high voltage 32 bit shift registers made by TI that discontinued them a long time ago . They are now available from a company called SuperTex.  Luckily the local 'surplus parts' dealer had a bin of these so i grabbed a few for a dollar each. PLCC44. since there's only two of these i swapped both. After bending the display back  it works perfectly fine.

Powerup was intermittent. sometimes it would beep and no display , sometimes it would start fine.


THe problem was the semi-rigid flatcable between mainboard and display module. ( left cable above with the blue stripe) these are sincle strand ribbon cables that use a press-fit connector. they are horrible... contacts oxidize over time. so i unplugged it from its connector , pulled the top connector plastic off , put cable back in and soldered each strand to the connector pin. problem solved. works like a champ.

The brains of this thing is a 80196 with the same ASIC found in the 34401 multimeter. Actually this machine is nothing but a 34401 with a scanner front end. The analog section is housed in a plug in module.


Essentially the same guts as a 34401 mulitmeter. LM199 refernce diode and the same multislope asics. the problem with the module was a burned inductor ( left of the relays ) little TDK  choke at the current input. i guess someone must have overloaded it. The module has no fuses in it and relies on the fuses installed in the multiplexer boards... someone had replaced one with a stub of wire... and fried the meters input.


i got 3 multiplexer boards. 20 voltage inputs , 2 current inputs and 2 4 wire ohms inputs. each

the relay counters on some of em read extreme high numbers , like millions of actuations. i ordered these relays from digikey ( they're like 1.25$ each ) i need to swap about 10 in total. the other contact counters are all in the thousands range. these modules have their own CPU and EEPROM that holds the actuation count.

Machine is healthy again and works fine. Another addition to the 'pile'
andyb:
Just wanted to thank you for posting these, love to look inside equipment like this. Man you run across some great stuff, wish I did!
nanofrog:
You keep coming up with some wonderful finds. Any tips/tricks you care to share?
retiredcaps:

--- Quote from: nanofrog on February 12, 2013, 03:07:18 am ---Any tips/tricks you care to share?

--- End quote ---
https://www.eevblog.com/forum/chat/where-do-you-buy-your-equipment/msg141895/#msg141895
free_electron:
Best tip : move to a high tech area.  That, or ebay. But beware. On ebay there are a lot of companies dealing in iued equipment that think they sit on gold ( they are... They buy that stuff by the pallet from govt surplus for 50$ and then flog it at 500$ on ebay ).

You can find better deals at the local surplus stores or equipment dealers.

If you know what you are doing you may want to buy broken stuff. But you need to know what you are doing. Don't go buying willy-nilly because it will become a money sink. Oh look there's a 8112 pulse generator for 100$ ... Yes indeed, but its got error 12. Grab service manual : first timing stage does not generate pulse .. Suspects are u200... U200 happens to be a custom hybrid that was discontinued 20 years ago... Pure unobtainium. So don't even go after that machine.
Oh , here's another on with error 22... Well that the pulse shaper that is fried.... Same story...

Sometimes broken machines are just beyond repair.

The other thing is your local newspaper. Look for businesses that flunked. That's where you get the real steals
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