Hello,

I have a Tektronix 465 which is perfect in every way except that the
horizontal trigger has gone belly up and the trace free-runs no matter
what.

Clue, please?

Thanks,

--
JF

"John Fields" wrote in message
...
Hello,

I have a Tektronix 465 which is perfect in every way except that the
horizontal trigger has gone belly up and the trace free-runs no matter
what.

Clue, please?

Thanks,

--
JF


Bad tunnel diode?

Do you have the service manual?

http://bama.edebris.com/manuals/tek/465(2)/

Can you trigger the B sweep?

On 1/18/2013 12:44 PM, John Fields wrote:
Hello,

I have a Tektronix 465 which is perfect in every way except that the
horizontal trigger has gone belly up and the trace free-runs no matter
what.

Clue, please?

Thanks,

The 465 was one of those products sold to government agencies and large
corporations in great numbers.
If you bring out a new model number, you open yourself up to competitive
bidding.
If you change what's under the hood and keep the model number...not so much.
The 465 underwent many changes over its lifetime.
Can't say how many of those were in the trigger circuit.
Any service manual can help...you can download one...but
one matching the serial number is best.

The trigger is a bunch of switches and amplifiers driving a tunnel diode
or two.
Pretty easy to follow the signal with another scope.
If I had to bet, I'd bet on a TD being bad.

I did have a 453 that had trigger problems on some ranges caused by a
leaky timing cap
in the trigger holdoff circuit.

You should be able to determine something from the relative behavior
of the A and B triggers.
My 465 is in the attic, so I can't try it, but there's a trigger view
function that's picked up after the switching at the first amplifier.

If you find that it is a bad TD, you'll be tempted to sacrifice the
B-trigger to fix the A-trigger. Depending on the TD package,
there's significant risk of busting all the TD's. Mess with the TD's
as a last resort.

I'm sure this hasn't happened to you, but I've chased my tail many times
only to find that some pot switch had been inadvertently switched
off the detent.

I'm also assuming that you have personally seen the working trigger and
it broke later.
That's different from, "I bought this thing on ebay..." where someone
may have already harvested the TD's.

John Fields schrieb:
Hello,

I have a Tektronix 465 which is perfect in every way except that the
horizontal trigger has gone belly up and the trace free-runs no matter
what.

I'm sure you'll find some help

he http://tech.groups.yahoo.com/group/TekScopes/

HTH

Reinhard

On Fri, 18 Jan 2013 13:45:26 -0800, mike wrote:

If you find that it is a bad TD, you'll be tempted to sacrifice the
B-trigger to fix the A-trigger. Depending on the TD package,
there's significant risk of busting all the TD's. Mess with the TD's
as a last resort.

Yep. I found a bad tunnel diode in a 465B that I was fixing, so I
tried to move the B channel diode to the A side and ended up with two
dead diodes. Oops. I think I killed it with too much heat from my
soldering iron.

I eventually had to cannibalize them from another Tek 465 that had too
much damage to be worth repairing. I couldn't find any online at a
reasonable price. I was lucky and got two diodes out of the carcass.
Tucker has the diodes for $25/ea (ouch):
http://www.etestparts.com/Search.aspx?Mfg=TEK&Page=17

Info on tunnel diodes:
http://w140.com/tekwiki/wiki/Tunnel_diodes
http://w140.com/tek_xref_tunnel_diodes.pdf

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Fri, 18 Jan 2013 16:36:30 -0500, "tm"
wrote:


"John Fields" wrote in message
.. .
Hello,

I have a Tektronix 465 which is perfect in every way except that the
horizontal trigger has gone belly up and the trace free-runs no matter
what.

Clue, please?

Thanks,

--
JF


Bad tunnel diode?

Do you have the service manual?

http://bama.edebris.com/manuals/tek/465(2)/

---
Yes
---

Can you trigger the B sweep?

---
Yes.

--
JF

"John Fields" wrote in message
...
On Fri, 18 Jan 2013 16:36:30 -0500, "tm"
wrote:


"John Fields" wrote in message
. ..
Hello,

I have a Tektronix 465 which is perfect in every way except that the
horizontal trigger has gone belly up and the trace free-runs no matter
what.

Clue, please?

Thanks,

--
JF


Bad tunnel diode?

Do you have the service manual?

http://bama.edebris.com/manuals/tek/465(2)/

---
Yes
---

Can you trigger the B sweep?

---
Yes.

--
JF

The TDs are Ge and heat will kill them. Use forceps against the body to
solder them. Do you have access to a curve tracer? If so, check the TDs for
the A sweep. I usually check them in circuit. I think they are 4.5 ma or 10
ma diodes.

Feed in a test waveform to the external trigger input and see if the trigger
view works.

You do have it in norm mode vs auto, right?

Can you line trigger?

Jeff Liebermann wrote:

On Fri, 18 Jan 2013 13:45:26 -0800, mike wrote:


If you find that it is a bad TD, you'll be tempted to sacrifice the
B-trigger to fix the A-trigger. Depending on the TD package,
there's significant risk of busting all the TD's. Mess with the TD's
as a last resort.


Yep. I found a bad tunnel diode in a 465B that I was fixing, so I
tried to move the B channel diode to the A side and ended up with two
dead diodes. Oops. I think I killed it with too much heat from my
soldering iron.

I eventually had to cannibalize them from another Tek 465 that had too
much damage to be worth repairing. I couldn't find any online at a
reasonable price. I was lucky and got two diodes out of the carcass.
Tucker has the diodes for $25/ea (ouch):
http://www.etestparts.com/Search.aspx?Mfg=TEK&Page=17

Info on tunnel diodes:
http://w140.com/tekwiki/wiki/Tunnel_diodes
http://w140.com/tek_xref_tunnel_diodes.pdf

I wonder if a NPN transistor used kind of backwards around a diode to
take advantage of the negative beta to give you that snap effect would
of done the same for you ?

Jamie

On 1/19/2013 6:04 PM, Jamie wrote:
Jeff Liebermann wrote:

On Fri, 18 Jan 2013 13:45:26 -0800, mike wrote:


If you find that it is a bad TD, you'll be tempted to sacrifice the
B-trigger to fix the A-trigger. Depending on the TD package,
there's significant risk of busting all the TD's. Mess with the TD's
as a last resort.


Yep. I found a bad tunnel diode in a 465B that I was fixing, so I
tried to move the B channel diode to the A side and ended up with two
dead diodes. Oops. I think I killed it with too much heat from my
soldering iron.

I eventually had to cannibalize them from another Tek 465 that had too
much damage to be worth repairing. I couldn't find any online at a
reasonable price. I was lucky and got two diodes out of the carcass.
Tucker has the diodes for $25/ea (ouch):
http://www.etestparts.com/Search.aspx?Mfg=TEK&Page=17

Info on tunnel diodes:
http://w140.com/tekwiki/wiki/Tunnel_diodes
http://w140.com/tek_xref_tunnel_diodes.pdf

I wonder if a NPN transistor used kind of backwards around a diode to
take advantage of the negative beta to give you that snap effect would
of done the same for you ?

Jamie

Remember that this was designed 40 years ago.
There are ways to get negative resistance, but the TD is/was simple and
fast.

On Sat, 19 Jan 2013 21:04:50 -0500, Jamie
t wrote:

I wonder if a NPN transistor used kind of backwards around a diode to
take advantage of the negative beta to give you that snap effect would
of done the same for you ?
Jamie

Probably not. Too many other changes would be required.

The problem will be finding a TD with what I guess(tm) has a 5ma
turning point and the correct max capacitance. I would be tempted to
substitute a more modern silicon or GaAs device. The problem is that
they will probably oscillate. Therefore, I would stay with germanium.

My best guess for a substitute are the GE 1N3712 thru 1N3721 series of
germanium TD's. The 1N3712 looks like something close to 5ma
(152-0125-01). The 1N3712 Cmax is 11pf while the Tek part is 18pf.
Close enough.

I haven't gone through all the specs to make sure they're identical
and don't plan to do that until the OP identifies the desired Tek part
number. Too much work.
http://w140.com/tek_xref_tunnel_diodes.pdf

There are various DO-17 packaged germanium diodes in the 1N3712 thru
1N3721 series available on eBay, but no 1N3712.

Clues on TD substitutions:
http://www.reprise.com/host/tektronix/reference/tunnel_diode.asp
Note that this is for a different scope.




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 19 Jan 2013 21:07:00 -0800, Jeff Liebermann
wrote:

There are various DO-17 packaged germanium diodes in the 1N3712 thru
1N3721 series available on eBay, but no 1N3712.

Look what I found in my collection:
http://802.11junk.com/jeffl/crud/Tek-Tunnel-Diodes.jpg
Sealed from the factory and untouched for who knows how long. The
tunnel diodes came from a rather large collection of original Tek
repair parts. There are probably more tunnel diodes in the box, but
it will take some effort as many of the smaller parts are not in
numerical sequence:
http://802.11junk.com/jeffl/crud/Tek-Parts.jpg
Make me an offer (via email please).

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 19 Jan 2013 18:59:59 -0500, "tm"
wrote:


"John Fields" wrote in message
.. .
On Fri, 18 Jan 2013 16:36:30 -0500, "tm"
wrote:


"John Fields" wrote in message
...
Hello,

I have a Tektronix 465 which is perfect in every way except that the
horizontal trigger has gone belly up and the trace free-runs no matter
what.

Clue, please?

Thanks,

--
JF


Bad tunnel diode?

Do you have the service manual?

http://bama.edebris.com/manuals/tek/465(2)/

---
Yes
---

Can you trigger the B sweep?

---
Yes.

--
JF

The TDs are Ge and heat will kill them. Use forceps against the body to
solder them. Do you have access to a curve tracer? If so, check the TDs for
the A sweep. I usually check them in circuit. I think they are 4.5 ma or 10
ma diodes.

---
OK
---

Feed in a test waveform to the external trigger input and see if the trigger
view works.

---
It does.
---

You do have it in norm mode vs auto, right?

---
In AUTO it free runs, no matter what, and in NORM it does nothing, no
matter what.
---

Can you line trigger?

---
No.

--
JF

Jeff Liebermann wrote:

On Sat, 19 Jan 2013 21:07:00 -0800, Jeff Liebermann
wrote:


There are various DO-17 packaged germanium diodes in the 1N3712 thru
1N3721 series available on eBay, but no 1N3712.


Look what I found in my collection:
http://802.11junk.com/jeffl/crud/Tek-Tunnel-Diodes.jpg
Sealed from the factory and untouched for who knows how long. The
tunnel diodes came from a rather large collection of original Tek
repair parts. There are probably more tunnel diodes in the box, but
it will take some effort as many of the smaller parts are not in
numerical sequence:
http://802.11junk.com/jeffl/crud/Tek-Parts.jpg
Make me an offer (via email please).

I too have some TD's, just not sure what numbers they are, however, I
remember not too long ago replacing a TD circuit with a fast dual
comparator from Analog devices. I was able to get the valley effect
to make the following circuit happy.. This was to keep an old piece
of equipment operating (not a scope).

Jamie

"John Fields" wrote in message
...
On Sat, 19 Jan 2013 18:59:59 -0500, "tm"
wrote:


"John Fields" wrote in message
. ..
On Fri, 18 Jan 2013 16:36:30 -0500, "tm"
wrote:


"John Fields" wrote in message
m...
Hello,

I have a Tektronix 465 which is perfect in every way except that the
horizontal trigger has gone belly up and the trace free-runs no matter
what.

Clue, please?

Thanks,

--
JF


Bad tunnel diode?

Do you have the service manual?

http://bama.edebris.com/manuals/tek/465(2)/

---
Yes
---

Can you trigger the B sweep?

---
Yes.

--
JF

The TDs are Ge and heat will kill them. Use forceps against the body to
solder them. Do you have access to a curve tracer? If so, check the TDs
for
the A sweep. I usually check them in circuit. I think they are 4.5 ma or
10
ma diodes.

---
OK
---

Feed in a test waveform to the external trigger input and see if the
trigger
view works.

---
It does.
---

You do have it in norm mode vs auto, right?

---
In AUTO it free runs, no matter what, and in NORM it does nothing, no
matter what.
---

Can you line trigger?

---
No.

--
JF

The transistors and ICs are all in sockets and on the Trigger board that
faces to the right. While it is a good bet that the "Fire" TD has failed, it
may be worth your time to open the scope up and poke around those parts.
U-870, and the transistors around that area. There are many waveforms given
in the manual and with another scope they can save much time. Luckily it's
all out in the open.

While it is open, you might verify all the power supply voltages and ripple
levels per the manual. In fact, do that first.

Good luck, the 465 is a fine instrument.

Regards,
tm

On Sun, 20 Jan 2013 11:17:05 -0500, "tm"
wrote:


"John Fields" wrote in message
.. .
On Sat, 19 Jan 2013 18:59:59 -0500, "tm"
wrote:


"John Fields" wrote in message
...
On Fri, 18 Jan 2013 16:36:30 -0500, "tm"
wrote:


"John Fields" wrote in message
om...
Hello,

I have a Tektronix 465 which is perfect in every way except that the
horizontal trigger has gone belly up and the trace free-runs no matter
what.

Clue, please?

Thanks,

--
JF


Bad tunnel diode?

Do you have the service manual?

http://bama.edebris.com/manuals/tek/465(2)/

---
Yes
---

Can you trigger the B sweep?

---
Yes.

--
JF

The TDs are Ge and heat will kill them. Use forceps against the body to
solder them. Do you have access to a curve tracer? If so, check the TDs
for
the A sweep. I usually check them in circuit. I think they are 4.5 ma or
10
ma diodes.

---
OK
---

Feed in a test waveform to the external trigger input and see if the
trigger
view works.

---
It does.
---

You do have it in norm mode vs auto, right?

---
In AUTO it free runs, no matter what, and in NORM it does nothing, no
matter what.
---

Can you line trigger?

---
No.

--
JF

The transistors and ICs are all in sockets and on the Trigger board that
faces to the right. While it is a good bet that the "Fire" TD has failed, it
may be worth your time to open the scope up and poke around those parts.
U-870, and the transistors around that area. There are many waveforms given
in the manual and with another scope they can save much time. Luckily it's
all out in the open.

While it is open, you might verify all the power supply voltages and ripple
levels per the manual. In fact, do that first.

Good luck, the 465 is a fine instrument.

---
Yup.

I bought this one, (S/N B011240) used, about 20 years ago, and this is
the first trouble it's given me.

I also have a 2215A, a T922, a 2465A, and an HP54602; all working and
all beauties. :-)
---

Regards,
tm

---
Thanks for the help, it's appreciated.

--
JF

"John Fields" wrote in message
...

Hello,

I have a Tektronix 465 which is perfect in every way except that the
horizontal trigger has gone belly up and the trace free-runs no matter
what.

Clue, please?

Thanks,

--
JF

That Oscope is so old! Why don't you point a gun at it and pull that
"TRIGGER"

On Mon, 21 Jan 2013 13:46:57 -0600, "Growl" wrote:

"John Fields" wrote in message
.. .

Hello,

I have a Tektronix 465 which is perfect in every way except that the
horizontal trigger has gone belly up and the trace free-runs no matter
what.

Clue, please?

Thanks,

--
JF

That Oscope is so old! Why don't you point a gun at it and pull that
"TRIGGER"

---
I take my trusty old pets to the vet when they get sick, and try to
save them.

You seem to working behind a rather more destructive agenda.

--
JF

On Mon, 21 Jan 2013 13:46:57 -0600, "Growl" wrote:

That Oscope is so old! Why don't you point a gun at it and pull that
"TRIGGER"

Because repair is better than recycling.
http://www.ifixit.com/Manifesto

Please note that his is a usenet repair newsgroup, not a recycling
newsgroup.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Growl wrote:

That Oscope is so old! Why don't you point a gun at it and pull that
"TRIGGER"


Not everyone is as useless as you are, so why don't you pull _that_
trigger?