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Technical Topics => The RF Workbench => Topic started by: radiogaga on October 13, 2017, 2359 UTC

Title: Zener diode testing?
Post by: radiogaga on October 13, 2017, 2359 UTC

Working on GLA 1000 amplifier, has no idle current.
Tested bias Zener with dmm. on ohms scale.
5.6 Meg ohms one way, infinite w/ leads reversed.
Good or bad...?

Thanks
rgg

Title: Re: Zener diode testing?
Post by: redhat on October 14, 2017, 0022 UTC

Sounds normal.  Best way is with an adjustable bench supply and a suitable dropping resistor, maybe 10K.  Ramp up the supply while monitoring the voltage across the diode.  It should keep rising until you reach its breakdown voltage, then stay there as input voltage is increased.

Keep in mind if the diode is backwards, it will function as an ordinary diode with a 0.5~0.7V forward drop.  You can verify this with your DMM on diode check.

+-RH

Title: Re: Zener diode testing?
Post by: radiogaga on October 14, 2017, 0113 UTC

Thanks redhat,
I will reinstall zener and key amp and measure voltage drop, changeover relay is an obvious replacement and probably burned  contacts.

rgg

Title: Re: Zener diode testing?
Post by: skeezix on October 14, 2017, 0119 UTC

Sounds like the classic black-hole diode-

Quote

Another new addition in the small-components market is the 7N-∞ BHD (black-hole diode). This device has two inputs and no output. Care must be taken to shield this component appropriately or it may absorb the unit it is placed in. The 7N-∞ will accept any voltage or current value. It is useful for GI (garbage-in) applications. Due to the light-absorption qualities of the device, we could not provide a photograph. Contact Spatial Regression Ltd, POB 463, Paulborough NH 03458.

http://aprilfool.s3.amazonaws.com/1981blackhole.jpg

Title: Re: Zener diode testing?
Post by: radiogaga on October 20, 2017, 0108 UTC

Well the diode has bias voltage but the meter mult-switch only works on plate voltage.other contacts are toast, is this a suitable eBay replacement for voltage current and relative power out?
https://m.ebay.com/itm/2-Pcs-20mm-Shaft-Length-2P3T-2-Pole-3-Position-Band-Rotary-Switch-/122687082022?epid=1139450437&hash=item1c90b84e26%3Ag%3AinUAAOSwFqVZriZG&_trkparms=pageci%253A5c0234ba-b532-11e7-be9f-74dbd180728c%257Cparentrq%253A374da1af15f0abc3208b47fafffff368%257Ciid%253A9
Here is snip of schematic :
Thank you

Title: Re: Zener diode testing?
Post by: redhat on October 20, 2017, 0114 UTC

It looks like the switch does more than those three metering position.  Front panel shows off-standby-volts-current-relative output.....that's 5 positions and judging from the schematic at least a three deck switch.

More research needed.

+-RH

Title: Re: Zener diode testing?
Post by: radiogaga on October 20, 2017, 0201 UTC

Those two spst contacts were separate mounted on rear of wafer, shot  and abandoned.
On off is now toggle switch and stand-by is not needed.
rgg

Title: Re: Zener diode testing?
Post by: redhat on October 20, 2017, 0457 UTC

In that case, those wafer switches should be fine.  Mouser and digikey should have other options as well.

+-RH