Author Topic: HP 6177B series zener diodes ??  (Read 506 times)

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Online coppercone2Topic starter

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HP 6177B series zener diodes ??
« on: May 16, 2024, 05:15:41 am »
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
« Last Edit: May 16, 2024, 05:19:11 am by coppercone2 »
 

Online coppercone2Topic starter

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Re: HP 6177B series zener diodes ??
« Reply #1 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
 

Online coppercone2Topic starter

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Re: HP 6177B series zener diodes ??
« Reply #2 on: May 16, 2024, 05:29:31 am »
Oh Its in change notes but not documented in the diagram. its hp 1901-0461
 

Offline andrewtaylor

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Re: HP 6177B series zener diodes ??
« Reply #3 on: May 16, 2024, 06:24:29 am »


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

the simple but significant reason: temperature compensation for the voltage in the overall circuit..
 

Online coppercone2Topic starter

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Re: HP 6177B series zener diodes ??
« Reply #4 on: May 16, 2024, 07:29:57 am »
is this still recommended with modern diodes?

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

Online coppercone2Topic starter

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Re: HP 6177B series zener diodes ??
« Reply #5 on: May 16, 2024, 07:50:46 am »
also is it possible this component was matched for drift? maybe I should leave it alone, even if its chipped. it reads fine on the meter
 

Online ArdWar

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Re: HP 6177B series zener diodes ??
« Reply #6 on: May 16, 2024, 08:16:50 am »
That's a signal voltage clipper/limiter zener, no one got time to put temperature compensation for that.

More likely they just don't want it to forward conduct when some user inevitably do a fuck up and force the guard to higher voltage.
« Last Edit: May 16, 2024, 08:19:16 am by ArdWar »
 


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