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How to test a tunnel diode?

John Hudak
 

I am troubleshooting an older tek scope that has sweep issues and after doing a bunch of checks, am beginning to think the tunnel diode may be bad. The only way I know to test these is to remove them and put them in a fairly simple test ckt (voltage source, current meter, voltage divider before and load resistor) and watch the current as voltage is varied. Can also use a scope to see if it oscillates when the breakover voltage is exceeded.)

Is there a way to test them in place? (generally speaking). Also, if there is a way to test them out of the board that is different than what I described above, please let me know.

I just hate to stress the PCB with a lot of needless removal-reinsertion. I am well versed in the use of various soldering/unsoldering techniques as well as having the proper tools, I just don't like needlessly hacking on a board. Of course I wouldn't do this without doing a rather thorough ckt check and am fairly certain that the device is bad.

I do know not to test them with the typical diode test on a DMM as it will cause them to fail.
thanks
j
 

Many older TEK scopes (465-475 for example) use a socketed tunnel diode. They may at first appear to be soldered, however, TEK used those miniature solder in sockets in those board locations. Same sockets that they used for their transistors.

--
Michael Lynch
Dardanelle, AR
 

On Sat, Nov 20, 2021 at 05:14 PM, John Hudak wrote:

Is there a way to test them in place? (generally speaking).
Yes, but of course it depends in what and how other components are connected to the TD.
You will get more to the point replies when you mention the type of scope and the TD number in the schematics.
Albert
 

Hi John,
Tunnel Diodes can be checked on a curve tracer. I will send you some resources off list in a separate E-mail. Some others here have reported that you can have a "Good" TD that is NOT GOOD at high frequency switching. Just be aware some might test good but not be good in say a trigger circuit or pulser.

Zen

-----Original Message-----
From: [email protected] <[email protected]> On Behalf Of John Hudak via groups.io
Sent: Saturday, November 20, 2021 11:14 AM
To: [email protected]
Subject: [TekScopes] How to test a tunnel diode?

I am troubleshooting an older tek scope that has sweep issues and after doing a bunch of checks, am beginning to think the tunnel diode may be bad. The only way I know to test these is to remove them and put them in a fairly simple test ckt (voltage source, current meter, voltage divider before and load resistor) and watch the current as voltage is varied. Can also use a scope to see if it oscillates when the breakover voltage is exceeded.)

Is there a way to test them in place? (generally speaking). Also, if there is a way to test them out of the board that is different than what I described above, please let me know.

I just hate to stress the PCB with a lot of needless removal-reinsertion. I am well versed in the use of various soldering/unsoldering techniques as well as having the proper tools, I just don't like needlessly hacking on a board. Of course I wouldn't do this without doing a rather thorough ckt check and am fairly certain that the device is bad.

I do know not to test them with the typical diode test on a DMM as it will cause them to fail.
thanks
j
[email protected]
 

would one of the atmiga 328 based component tester work i wonder,or destroy it,anyone any idea?
 

On Sat, Nov 20, 2021 at 10:14 AM, John Hudak wrote:


Is there a way to test them in place? (generally speaking). Also, if there is
a way to test them out of the board that is different than what I described
above, please let me know.

I just hate to stress the PCB with a lot of needless removal-reinsertion. I am
well versed in the use of various soldering/unsoldering techniques as well as
having the proper tools, I just don't like needlessly hacking on a board. Of
course I wouldn't do this without doing a rather thorough ckt check and am
fairly certain that the device is bad.
If your components are in sockets, and if the scope simply will not trigger; one simple way to test is to swap the "A" and "B" Trigger circuit components one at a time and see if the problem transfers to the other trigger circuit. When or if it does, then you have located a "bad" part. It is rare to find 4 Tunnel Diodes that fail at the same time.

--
Michael Lynch
Dardanelle, AR
 

I use a 50ohms function generator and a simle octopus,

Check shunt resistor for not exced the max TD rated current

/g/TekScopes/photo/249051/2975689?p=Created%2C%2Cs51%2C20%2C2%2C0%2C0
 

Thanks for that explanation Miguel. I knew there was a way to do this. I have a Curve Tracer, so I have not had to use your method. .

--
Michael Lynch
Dardanelle, AR
 

Yes, I have a curve tracer too. I think that is John Hudak who is asking

Now I?m trying to measure the TD capacitande.

/g/TekScopes/album?id=260881

If you set low series resistor in curve tracer you can see all the curve that can?t be seen if serial resistor is high.
 

atmega tester don?t have enought current tor drive a 10mA TD. It will be seen as a low ohms resistor, 10 ohms aprox for a 10mA TD diode
 

IIRC, it's about a 680 ohm resistor driven from 5 volts, the base resistors are 470K when switched in.

Harvey

On 11/20/2021 3:30 PM, Miguel Work wrote:
atmega tester don?t have enought current tor drive a 10mA TD. It will be seen as a low ohms resistor, 10 ohms aprox for a 10mA TD diode
 

On Sat, Nov 20, 2021 at 08:14 AM, John Hudak wrote:


if there is a way to test them out of the board
AFAIK, the TD was used in the pulse generator sub-system of the triggering system... of 'older' Tek scopes. (500? 400?) ... I think, 453,454 used a TD that way.
AFAIR TD is used as a fast (relative to the day) current controlled switch, with a bias current (453,454? et. al?)
Anyway, IMO you'd have to test the TD that way, it that's how it's being used in the trigger system... I'm speculating. (You don't say which Tek scope you're working on.)

IMO (and since you profess proficiency with pcbs) ... I'd be more worried about damaging the tunnel diode 'testing' it.
Since you're probably (most probably) only going to find the right TD, for your scope (whichever Tek it is) in another similar Tek scope with a working trigger... if it the diode is blown

--
Roy Thistle
 

I have been looking for a situation where in situ testing is not that easy.
In the 3T77 trigger pulse TD D42 has anode to GND via a T42 winding, and the cathode via 5.1 ohms R41.
Just a slightly complication is where two TDs are almost in parallel, like in the 465 and the 7T11 trigger circuits.
Albert

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