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

[lkundrak]

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

[bob91343]

Where is this diode?  If this is a repair job, how do you know it's defective?

[lkundrak]

This is almost certainly not a defective diode.
The shot was taken from a part (a vintage logic analyzer probe) that's supposedly working.

[bob91343]

What probe/analyzer?

[Andreas]

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

[lkundrak]

> What probe/analyzer?

A Tektronix P6442 probe for 1230 analyzer.
Sorry for not having been specific enough.

[cortex_m0]

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).

[Andreas]

> 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

[Terry Bites]

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?

[edavid]

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.