Electronics > Repair
HP 6177B series zener diodes ??
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coppercone2:
I am replacing the diode on this thing because alot of them are like chipped. I got all the replacements but on the PCB there is a deviation from the manual. VR13 has two diodes soldered together in series.

The manual says
6.19V 5% 1N753.

But on the PCB there is two diodes.

one is a "light blue (almost greyish), yellow ----> brown" (brown I believe indicates the diode orientation, on black glass body).

The second diode looks like a much physically smaller diode.
its bands are

"brown, deep sky blue, yellow".

So it looks like this

"light blue, yellow, brown" -> yellow, sky blue, brown


WTF is this?? they twisted the leads together and bend it over with alot of uncut lead left over


But when you probe it, it measures like a clamp. That is, both diodes are facing each other. so positive lead in middle makes both ends beep.


The smaller diode drop is 0.5, the bigger one is 0.7
coppercone2:

--- End quote ---


did they decide to drop the voltage by 0.5 volts? as far as I can tell thats all it does
coppercone2:
Oh Its in change notes but not documented in the diagram. its hp 1901-0461
andrewtaylor:

--- Quote from: coppercone2 on May 16, 2024, 05:23:11 am ---

did they decide to drop the voltage by 0.5 volts? as far as I can tell thats all it does

--- End quote ---

the simple but significant reason: temperature compensation for the voltage in the overall circuit..
coppercone2:
is this still recommended with modern diodes?

the device did not improve by enough to negate this benefit did it?
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