Need help identifying a glass diode (hi-res picture, part from circa 1987)

• Need help identifying a glass diode (hi-res picture, part from circa 1987)
  Posted by lkundrak on 13 Jun, 2021 19:27
• Hi,
  
  I've got no luck finding out how to read markings on pictured part & what would be a replacement part I could buy today.
  
  
  
  I'm sure someone with more experience can help?
  
  Thank you!
  Lubo

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• #1 Reply
  Posted by bob91343 on 13 Jun, 2021 19:46
• Where is this diode?  If this is a repair job, how do you know it's defective?
• #2 Reply
  Posted by lkundrak on 13 Jun, 2021 20:20
• This is almost certainly not a defective diode.
  The shot was taken from a part (a vintage logic analyzer probe) that's supposedly working.
• #3 Reply
  Posted by bob91343 on 13 Jun, 2021 20:32
• What probe/analyzer?
• #4 Reply
  Posted by Andreas on 13 Jun, 2021 20:38
• Hello,
  
  the logo seems to be from Unitrode (never knew that they manufactured diodes)
  but obviously they sold the diode part to "MicroSemi"
  
  http://www.aufzu.de/semi/unitrode.html
  
  With best regards
  
  Andreas
  
• #5 Reply
  Posted by lkundrak on 13 Jun, 2021 20:53
• > What probe/analyzer?
  
  A Tektronix P6442 probe for 1230 analyzer.
  Sorry for not having been specific enough.
• #6 Reply
  Posted by cortex_m0 on 13 Jun, 2021 23:15
• I found a photograph of the PCB from that probe: https://w140.com/tekwiki/wiki/P6442
  
  I might guess it is a low-voltage zener, being used there to protect the inputs on the MC74HC04 inverter and the MC74HC240 buffer. But without being able to clearly see the tracks, that's a very rough guess.
  
  However, I see what I think are 10 glass diodes on that board, and if they were protection I might expect 16 (one per bit on the logic analyzer).
• #7 Reply
  Posted by Andreas on 14 Jun, 2021 06:42
• Quote from: lkundrak on 13 Jun, 2021 20:53

  > What probe/analyzer?
  
  A Tektronix P6442 probe for 1230 analyzer.
  Sorry for not having been specific enough.
  

  
  Maybe Tektronix (like many test equipment manufacturers) has its own part numbering scheme.
  So without a "repair/maintenance Handbook" identification may be difficult.
  
  with best regards
  
  Andreas
  
• #8 Reply
  Posted by Terry Bites on 14 Jun, 2021 17:00
• Given the vintage and the 74HC and 74AC logic, I doubt they are anything special. Probably a switching diode like a IN4148. Trace out the circuit. Is it a bit of M²L?
• #9 Reply
  Posted by edavid on 14 Jun, 2021 23:56
• Tektronix would order parts marked with their own part numbers.
  
  Tektronix diode part numbers are 152-nnnn-rr where the rr is a revision number.
  
  When the whole thing wouldn't fit, they only printed the important part, the middle 4 digits.
  
  So, the complete part number is 152-0574-00.
  
  Now you can go to TekWiki and look in the transistor and diode catalog: https://w140.com/tekwiki/wiki/Common_Design_Parts_Catalogs
  
  On page 8-7, the spec is given as 120V, 150mA.
  
  One possible replacement would be 1N458A.