Topics

475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?


stan_katz
 

I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.

Stan


 

The 475 trigger pickoff circuit is significantly different than the
468 circuit. From your description, something is wrong with or around
U370 on schematic 3. Take a close look at R403 which if open would
affect triggering of both channels.

X-Y mode and the channel 2 vertical signal out on the rear of the
oscilloscope also depend on biasing from R403 so checking those
functions may provide more information.

On Fri, 25 Jan 2013 20:46:14 -0000, "stan_katz" <stan_katz@...>
wrote:

I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.

Stan


Bert Haskins
 

On 01/25/2013 03:46 PM, stan_katz wrote:
 

I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.

Stan


Probably not.
Going from what I had on 465Bs the triggering problem is often that
the tunnel diodes have changed in value.
There are many! threads about this in the archives.
It may be worth your time to try swapping the TDs from the B sweep section
with the A section to see if things change.
I had this problem come up when I was hunting for a process control network
problem while working in factory in a different country.
I swapped the TDs and the scope has been near perfect ever since.
Go figure.




 

If you do work on the tunnel diodes, be sure to use a heat sink right up against the diode body. Ge tunnel diodes are easily ruined with heat.
 
However, I think David's comments are more likely the issue. That is because of the external trigger working.
 
Do you have the correct service manual for your 475?
 
Regards,
tom
 

----- Original Message -----
Sent: Friday, January 25, 2013 5:09 PM
Subject: Re: [TekScopes] 475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?

 

On 01/25/2013 03:46 PM, stan_katz wrote:
 

I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.

Stan


Probably not.
Going from what I had on 465Bs the triggering problem is often that
the tunnel diodes have changed in value.
There are many! threads about this in the archives.
It may be worth your time to try swapping the TDs from the B sweep section
with the A section to see if things change.
I had this problem come up when I was hunting for a process control network
problem while working in factory in a different country.
I swapped the TDs and the scope has been near perfect ever since.
Go figure.




stan_katz
 

Hello Tom,

I will gladly avoid touching the tunnel diodes, and will start with David's suggestion. The only service manuals I have are from BAMA, which are the Army TM--- model manuals. Will these do, or can you point me in a better direction? BTW, Bert's post is a warning to me that the 475 has potentially unobtanium parts. Right now, Tucker has Tek tunnel diode kits for sale. Can you, or Bert, post the proper kit part number for my scope? I should buy a kit now if it's one of those listed at Tucker. Tom, I noticed my thanks for your input on my 3325 repair effort got cut. Let me thank you here.



Stan

--- In TekScopes@..., "Tom Miller" wrote:

If you do work on the tunnel diodes, be sure to use a heat sink right up against the diode body. Ge tunnel diodes are easily ruined with heat.

However, I think David's comments are more likely the issue. That is because of the external trigger working.

Do you have the correct service manual for your 475?

Regards,
tom

----- Original Message -----
From: Bert Haskins
To: TekScopes@...
Sent: Friday, January 25, 2013 5:09 PM
Subject: Re: [TekScopes] 475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?




On 01/25/2013 03:46 PM, stan_katz wrote:


I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.

Stan



Probably not.
Going from what I had on 465Bs the triggering problem is often that
the tunnel diodes have changed in value.
There are many! threads about this in the archives.
It may be worth your time to try swapping the TDs from the B sweep section
with the A section to see if things change.
I had this problem come up when I was hunting for a process control network
problem while working in factory in a different country.
I swapped the TDs and the scope has been near perfect ever since.
Go figure.


 

I used the same military manual from Bama.

I had two reasons not to suggest that the tunnel diodes are the
problem:

1. The common failure point for the symptoms does not implicate the
tunnel diode part of the trigger circuit. External triggering and I
would assume line triggering both work and neither of them go through
U370 which could cause all of the problems.

2. The tunnel diodes are fragile and difficult to replace so fiddling
with them if they are not definitely the problem is asking for
trouble. :)

On Sat, 26 Jan 2013 23:56:53 -0000, "stan_katz" <stan_katz@...>
wrote:

Hello Tom,

I will gladly avoid touching the tunnel diodes, and will start with David's suggestion. The only service manuals I have are from BAMA, which are the Army TM--- model manuals. Will these do, or can you point me in a better direction? BTW, Bert's post is a warning to me that the 475 has potentially unobtanium parts. Right now, Tucker has Tek tunnel diode kits for sale. Can you, or Bert, post the proper kit part number for my scope? I should buy a kit now if it's one of those listed at Tucker. Tom, I noticed my thanks for your input on my 3325 repair effort got cut. Let me thank you here.

Stan

--- In TekScopes@..., "Tom Miller" wrote:

If you do work on the tunnel diodes, be sure to use a heat sink right up against the diode body. Ge tunnel diodes are easily ruined with heat.

However, I think David's comments are more likely the issue. That is because of the external trigger working.

Do you have the correct service manual for your 475?

Regards,
tom

----- Original Message -----
From: Bert Haskins
To: TekScopes@...
Sent: Friday, January 25, 2013 5:09 PM
Subject: Re: [TekScopes] 475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?

On 01/25/2013 03:46 PM, stan_katz wrote:

I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.

Stan

Probably not.
Going from what I had on 465Bs the triggering problem is often that
the tunnel diodes have changed in value.
There are many! threads about this in the archives.
It may be worth your time to try swapping the TDs from the B sweep section
with the A section to see if things change.
I had this problem come up when I was hunting for a process control network
problem while working in factory in a different country.
I swapped the TDs and the scope has been near perfect ever since.
Go figure.


 

Hi Stan,
 
It's up to you and your wallet as to picking up a spare set of tunnel diodes. For me, it seems that parts 475 scopes are available at good prices. Since there are four TDs in each scope, your chances for getting a good one are reasonable. The main problem is many times you wind up with a parts unit that can be restored.
 
Email manuals@... (Dave) with your serial number and ask for a quote. He will be sure you get the correct manual for your serial number range.
 
Glad you found the problem with the 3325 and that it was a simple fix. Good job.
 
Best regards,
Tom
 
 

----- Original Message -----
From: stan_katz
Sent: Saturday, January 26, 2013 6:56 PM
Subject: [TekScopes] Re: 475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?

 

Hello Tom,

I will gladly avoid touching the tunnel diodes, and will start with David's suggestion. The only service manuals I have are from BAMA, which are the Army TM--- model manuals. Will these do, or can you point me in a better direction? BTW, Bert's post is a warning to me that the 475 has potentially unobtanium parts. Right now, Tucker has Tek tunnel diode kits for sale. Can you, or Bert, post the proper kit part number for my scope? I should buy a kit now if it's one of those listed at Tucker. Tom, I noticed my thanks for your input on my 3325 repair effort got cut. Let me thank you here.

Stan

--- In TekScopes@..., "Tom Miller" wrote:
>
> If you do work on the tunnel diodes, be sure to use a heat sink right up against the diode body. Ge tunnel diodes are easily ruined with heat.
>
> However, I think David's comments are more likely the issue. That is because of the external trigger working.
>
> Do you have the correct service manual for your 475?
>
> Regards,
> tom
>
> ----- Original Message -----
> From: Bert Haskins
> To: TekScopes@...
> Sent: Friday, January 25, 2013 5:09 PM
> Subject: Re: [TekScopes] 475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?
>
>
>
>
> On 01/25/2013 03:46 PM, stan_katz wrote:
>
>
> I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.
>
> Stan
>
>
>
> Probably not.
> Going from what I had on 465Bs the triggering problem is often that
> the tunnel diodes have changed in value.
> There are many! threads about this in the archives.
> It may be worth your time to try swapping the TDs from the B sweep section
> with the A section to see if things change.
> I had this problem come up when I was hunting for a process control network
> problem while working in factory in a different country.
> I swapped the TDs and the scope has been near perfect ever since.
> Go figure.
>


unclebanjoman
 

--- In TekScopes@..., "stan_katz" wrote:

I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.

Stan
I think the TD is the problem. I got a similar problem in my 3B4 plugin.

Try to detach one terminal of the TD CR566 (using adequate protection against heating, like a pliers) and check if the behavior is the same.

If the TD is defective (i.e. open), the trigger still works, but only in presence of sufficiently steep and large signals, like square waves and/or external trigger pulses (which are generally square waves or pulses). With sinewaves it's likely that trigger doesn't work, but with squares do.
The same test may apply to CR556 (the arming TD).

You can also check for the presence of a pulse signal on either bases of Q556 and Q566. If they're present, all the circuitry preceding Q556/566 are well-working.

Max


stan_katz
 

Amazing!?

Tunnel diodes in a 561A!

Tek must have started using tunnel diodes shortly after they came out in 1960. Leave it to Tek to go with bleeding edge esoteric. Since I'm a rather low budget experimenter, the only other scope I have is a Telequiment D51 "student scope" with a 4mhz bandwidth. Is this scope adequate to view the pulses at Q556/Q566?

Thanks,
Stan

--- In TekScopes@..., "Max Mazza" wrote:



--- In TekScopes@..., "stan_katz" wrote:

I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.

Stan
I think the TD is the problem. I got a similar problem in my 3B4 plugin.

Try to detach one terminal of the TD CR566 (using adequate protection against heating, like a pliers) and check if the behavior is the same.

If the TD is defective (i.e. open), the trigger still works, but only in presence of sufficiently steep and large signals, like square waves and/or external trigger pulses (which are generally square waves or pulses). With sinewaves it's likely that trigger doesn't work, but with squares do.
The same test may apply to CR556 (the arming TD).

You can also check for the presence of a pulse signal on either bases of Q556 and Q566. If they're present, all the circuitry preceding Q556/566 are well-working.

Max


 

I am not exactly sure when Tektronix started using tunnel diodes but
the 545 lacks them while the 547 has them which explains the later's
outstanding triggering bandwidth. It may be that they had the only
engineers able to understand how to use them for trigger circuits.

You will not need a very fast oscilloscope to see if the tunnel diode
circuit is operating correctly. Yours should work fine.

On Sun, 27 Jan 2013 03:51:35 -0000, "stan_katz" <stan_katz@...>
wrote:

Amazing!?

Tunnel diodes in a 561A!

Tek must have started using tunnel diodes shortly after they came out in 1960. Leave it to Tek to go with bleeding edge esoteric. Since I'm a rather low budget experimenter, the only other scope I have is a Telequiment D51 "student scope" with a 4mhz bandwidth. Is this scope adequate to view the pulses at Q556/Q566?

Thanks,
Stan

--- In TekScopes@..., "Max Mazza" wrote:



--- In TekScopes@..., "stan_katz" wrote:

I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.

Stan
I think the TD is the problem. I got a similar problem in my 3B4 plugin.

Try to detach one terminal of the TD CR566 (using adequate protection against heating, like a pliers) and check if the behavior is the same.

If the TD is defective (i.e. open), the trigger still works, but only in presence of sufficiently steep and large signals, like square waves and/or external trigger pulses (which are generally square waves or pulses). With sinewaves it's likely that trigger doesn't work, but with squares do.
The same test may apply to CR556 (the arming TD).

You can also check for the presence of a pulse signal on either bases of Q556 and Q566. If they're present, all the circuitry preceding Q556/566 are well-working.

Max


stan_katz
 

Hi David,

I sampled rear panel ch2 vertical signal per your suggestion. It's coming out at only 1/20th the signal true amplitude. So maybe R403 should be examined? However, a confounding symptom, occurs when I try 1v to 20v sine waves at 60hz with line triggering. I couldn't get a lock. no lock at any other freq. for line source. Another bad sign, which has presented itself since I started exercising all controls through full range...neither of the v/div controls will advance past 5v/div...no 10/20/50v positions possible on either channel. Is this op. error, or what? Ch 2 v/div control skirt illuminator is not lit. Just burned out, or is illuminator driven by other circuitry?

Stan

--- In TekScopes@..., David wrote:

I used the same military manual from Bama.

I had two reasons not to suggest that the tunnel diodes are the
problem:

1. The common failure point for the symptoms does not implicate the
tunnel diode part of the trigger circuit. External triggering and I
would assume line triggering both work and neither of them go through
U370 which could cause all of the problems.

2. The tunnel diodes are fragile and difficult to replace so fiddling
with them if they are not definitely the problem is asking for
trouble. :)

On Sat, 26 Jan 2013 23:56:53 -0000, "stan_katz"
wrote:

Hello Tom,

I will gladly avoid touching the tunnel diodes, and will start with David's suggestion. The only service manuals I have are from BAMA, which are the Army TM--- model manuals. Will these do, or can you point me in a better direction? BTW, Bert's post is a warning to me that the 475 has potentially unobtanium parts. Right now, Tucker has Tek tunnel diode kits for sale. Can you, or Bert, post the proper kit part number for my scope? I should buy a kit now if it's one of those listed at Tucker. Tom, I noticed my thanks for your input on my 3325 repair effort got cut. Let me thank you here.

Stan

--- In TekScopes@..., "Tom Miller" wrote:

If you do work on the tunnel diodes, be sure to use a heat sink right up against the diode body. Ge tunnel diodes are easily ruined with heat.

However, I think David's comments are more likely the issue. That is because of the external trigger working.

Do you have the correct service manual for your 475?

Regards,
tom

----- Original Message -----
From: Bert Haskins
To: TekScopes@...
Sent: Friday, January 25, 2013 5:09 PM
Subject: Re: [TekScopes] 475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?

On 01/25/2013 03:46 PM, stan_katz wrote:

I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.

Stan

Probably not.
Going from what I had on 465Bs the triggering problem is often that
the tunnel diodes have changed in value.
There are many! threads about this in the archives.
It may be worth your time to try swapping the TDs from the B sweep section
with the A section to see if things change.
I had this problem come up when I was hunting for a process control network
problem while working in factory in a different country.
I swapped the TDs and the scope has been near perfect ever since.
Go figure.


 

The extra three markings on the Volts/Div knob are there for use with a x10 probe, which enables a different lamp behind the Volts/div skirt, so the 5V/Div setting is mechanically the same as the 50V/div setting. The change of lamp is only made with a probe with the correct BNC with probe range pin which connects a resistor from the outer ring of the BNC socket to ground to indicate the type of probe.

Dave

-----Original Message-----
From: TekScopes@... [mailto:TekScopes@...] On Behalf Of stan_katz
Sent: 27 January 2013 19:58
To: TekScopes@...
Subject: [TekScopes] Re: 475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?

Hi David,

I sampled rear panel ch2 vertical signal per your suggestion. It's coming out at only 1/20th the signal true amplitude. So maybe R403 should be examined? However, a confounding symptom, occurs when I try 1v to 20v sine waves at 60hz with line triggering. I couldn't get a lock. no lock at any other freq. for line source. Another bad sign, which has presented itself since I started exercising all controls through full range...neither of the v/div controls will advance past 5v/div...no 10/20/50v positions possible on either channel. Is this op. error, or what? Ch 2 v/div control skirt illuminator is not lit. Just burned out, or is illuminator driven by other circuitry?

Stan


stan_katz
 

I've uncovered what I think is a significant symptom. If I inject a 1 volt square wave, at 1khz or above, set v/div to 20mv/div, and play with the position control, I can get the trigger source lamp to light. If I try the same stunt with a sine wave, I need at least 500khz to get the scope to trigger. This symptom seems to play into what Max was suggesting by lifting one lead of a tunnel diode, and then determining if I can get trigger with high slew rate sources. Of course, with the scope setup to the above test conditions, it's useless.

Stan

--- In TekScopes@..., "stan_katz" wrote:

Hi David,

I sampled rear panel ch2 vertical signal per your suggestion. It's coming out at only 1/20th the signal true amplitude. So maybe R403 should be examined? However, a confounding symptom, occurs when I try 1v to 20v sine waves at 60hz with line triggering. I couldn't get a lock. no lock at any other freq. for line source. Another bad sign, which has presented itself since I started exercising all controls through full range...neither of the v/div controls will advance past 5v/div...no 10/20/50v positions possible on either channel. Is this op. error, or what? Ch 2 v/div control skirt illuminator is not lit. Just burned out, or is illuminator driven by other circuitry?

Stan

--- In TekScopes@..., David wrote:

I used the same military manual from Bama.

I had two reasons not to suggest that the tunnel diodes are the
problem:

1. The common failure point for the symptoms does not implicate the
tunnel diode part of the trigger circuit. External triggering and I
would assume line triggering both work and neither of them go through
U370 which could cause all of the problems.

2. The tunnel diodes are fragile and difficult to replace so fiddling
with them if they are not definitely the problem is asking for
trouble. :)

On Sat, 26 Jan 2013 23:56:53 -0000, "stan_katz"
wrote:

Hello Tom,

I will gladly avoid touching the tunnel diodes, and will start with David's suggestion. The only service manuals I have are from BAMA, which are the Army TM--- model manuals. Will these do, or can you point me in a better direction? BTW, Bert's post is a warning to me that the 475 has potentially unobtanium parts. Right now, Tucker has Tek tunnel diode kits for sale. Can you, or Bert, post the proper kit part number for my scope? I should buy a kit now if it's one of those listed at Tucker. Tom, I noticed my thanks for your input on my 3325 repair effort got cut. Let me thank you here.

Stan

--- In TekScopes@..., "Tom Miller" wrote:

If you do work on the tunnel diodes, be sure to use a heat sink right up against the diode body. Ge tunnel diodes are easily ruined with heat.

However, I think David's comments are more likely the issue. That is because of the external trigger working.

Do you have the correct service manual for your 475?

Regards,
tom

----- Original Message -----
From: Bert Haskins
To: TekScopes@...
Sent: Friday, January 25, 2013 5:09 PM
Subject: Re: [TekScopes] 475 Triggering Issue -- Will recent 468 Triggering Issue Thread Help Me?

On 01/25/2013 03:46 PM, stan_katz wrote:

I have an ancient 475 scope which works fine with an external trigger, but will not trigger on any of the internal sources. Should I start by reviewing the recent 468 triggering issue thread to get me going? If not, can anyone recommend a thread I should start with? Of course, I'd be delighted to receive help on this thread.

Stan

Probably not.
Going from what I had on 465Bs the triggering problem is often that
the tunnel diodes have changed in value.
There are many! threads about this in the archives.
It may be worth your time to try swapping the TDs from the B sweep section
with the A section to see if things change.
I had this problem come up when I was hunting for a process control network
problem while working in factory in a different country.
I swapped the TDs and the scope has been near perfect ever since.
Go figure.


unclebanjoman
 

--- In TekScopes@..., "stan_katz" wrote:

I've uncovered what I think is a significant symptom. If I inject a 1 volt square wave, at 1khz or above, set v/div to 20mv/div, and play with the position control, I can get the trigger source lamp to light. If I try the same stunt with a sine wave, I need at least 500khz to get the scope to trigger. This symptom seems to play into what Max was suggesting by lifting one lead of a tunnel diode, and then determining if I can get trigger with high slew rate sources. Of course, with the scope setup to the above test conditions, it's useless.

Stan
This was exactly the same behavior I noted when debugging my 3B4 timebase unit. With 1 KHz square wave of adequate amplitude, the triggers works. With a sinewave, it must be 100 KHz or above to trigger, with difficult.
If disconnecting the TD the behavior is exactly the same, assume that 99% the TD is open.

To get a definitive certainty, you should check if some signal is present on the anode of TD (with TD in place). If the amplitude swing during the TD's commutation is around 200-300mV pk-pk, the TD is OK. If a few mV, the TD is shorted. If more than 500mV, the TD is open.
Do that check before you detach one TD's lead and then after.
Compare the results.
Let us know.

Max


unclebanjoman
 

The rear output signal it's not directly correlated to the input signal amplitude, but to the amplitude in major divisions on the screen.
Tek stated that output voltage is approximately 20mV/division into 1 Megaohm load or 10mV/division into 50 ohm load.
So I think that you've observed is absolutely correct.

Max

--- In TekScopes@..., "stan_katz" wrote:

Hi David,

I sampled rear panel ch2 vertical signal per your suggestion. It's coming out at only 1/20th the signal true amplitude. So maybe R403 should be examined?


 

Line triggering triggers the sweep from the AC power line so the sweep
will synchronize with AC power supplies. It will not synchronize with
other low frequency signals unless they are also synchronized with the
AC power line.

The 10/20/50 volts/division attenuator settings depend on using a x10
probe which attenuates the input signal by 10 times. Whether the x1
or x10 attenuator skirt illumination occurs depends on the readout
connection from the probe used. A normal BNC connection or probe
without that feature will always illuminated the x1 indicator on the
skirt.

Tektronix has made a very nice PDF copy of the 475 service manual
available here although you need to register with them:

http://www.tek.com/manual/475

The KO4BB manual is excellent also:

http://www.ko4bb.com/manuals/index.php?dir=Tektronix/Tektronix_-_475_Oscilloscope

On Sun, 27 Jan 2013 19:57:34 -0000, "Stan_katz" <stan_katz@...>
wrote:

Hi David,

I sampled rear panel ch2 vertical signal per your suggestion. It's coming out at only 1/20th the signal true amplitude. So maybe R403 should be examined? However, a confounding symptom, occurs when I try 1v to 20v sine waves at 60hz with line triggering. I couldn't get a lock. no lock at any other freq. for line source. Another bad sign, which has presented itself since I started exercising all controls through full range...neither of the v/div controls will advance past 5v/div...no 10/20/50v positions possible on either channel. Is this op. error, or what? Ch 2 v/div control skirt illuminator is not lit. Just burned out, or is illuminator driven by other circuitry?

Stan


unclebanjoman
 

Yes, Tek engineers started to experiment and using TD as soon as they were introduced. Tek 544, 546 and 547 already they had TD in their circuitry.
I've gained expertise working and studying circuits in my TEK 3B4, 3T77, 3T77A plugins and 465 also.
TDs are very rare and hard to find, but the models used in 465 and 475 scopes (respectively 152-0125-00/01 and 152-0140-01) still can be found with some patience.
I've got two of these, Tek original, from a Greek surplus dealer for a reasonable price, about 40$ plus shipping, two years ago. One of these replaced the broken TD in my 3B4. The other is jealously guarded in my drawer with other Tek original spares, since the TD model 152-0125-00 fits equally well in #b4 and 465....

The only, very UNOBTAINABLE TD is the 1N3129, used in 3T77 and 3T77A sampling sweep units. My 3T77 had one TD dead.
After 3 years of fruitless search, the past year I finally decided to make the jump: I bought some russian TD, GaAs military, from an ukrainian dealer, carefully choosing and comparing their specs against the original Teks ones.

Then I changed the polarization network, to adapt the GaAs diode (Ge diodes has Vp-Vv of about 300-500mV, GaAs can be 800 mV or more, for the same Ip, so the polarization network must be modified accordingly)

After some hours of calculations, graph comparisons, measurements of TD curves on my curve tracer (a curve tracer I made especially for TD measurements), I changed some resistors in the 3T77 unit, put the russian GaAs TD in place of the original dead 1N3129 and voila! My 3T77 returned to live, with the same specs of the original: it triggers with sine wave signals up to 600/700Mhz and a mere 20 mV amplitude. With external trigger signal it works up to 1Ghz with no problems, in conjunction with my 3S1 sampling unit.

For the chronicle, two years ago I found ONE 1N3129 offered to the miserable price of $ 150 (I refused, damn... was gold or platinum? Or maybe, diamond?), while the russian diodes I've paid about $ 10 each

Max

--- In TekScopes@..., "stan_katz" wrote:

Amazing!?

Tunnel diodes in a 561A!

Tek must have started using tunnel diodes shortly after they came out in 1960. Leave it to Tek to go with bleeding edge esoteric. Since I'm a rather low budget experimenter, the only other scope I have is a Telequiment D51 "student scope" with a 4mhz bandwidth. Is this scope adequate to view the pulses at Q556/Q566?

Thanks,
Stan


unclebanjoman
 

For the chronicle, I investigated why the TD on my 3T77 unit, purchased used on ebay two years ago as "not working" was dead.

The 3T77 does not trigger at all, and that because simply for the fact that one TD was dead.
Incidentally, the TD was the one that its signal was sent ALSO to the TRIGGER OUT BNC on the front panel via a simple pulse transformer.
Very useful but... imagine if you, by mistake, send a "full-bodied, fat" trigger signal (5,10 V or so) TO the scope putting it in the WRONG connector (TRIGGER OUT instead on TRIGGER IN)? The TD surely reacts in a very negative manner!
That was the event made by the previous owner, that destroyed the 1N3129 TD, IMO.

Max


stan_katz
 

Max,

Remember, these measurements are made with a student scope that has its own problems and can't measure below 100mv/div. So with 10x probe its hard to read. Amplitude and pulse widths given are very approximate.

I'm still working up the courage to pull out a TD lead. Anyway, with both TDs in circuit:

2v p-p square wave in
.5v/div ... auto ... trigger source lamp extinguished
CR566 -- nothing
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

2v p-p square wave in
20mv/div...auto...trigger source lamp lit
CR566...crummy,noisy elongated commutation pulses approx -300mv approx 400us width.
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

Isn't this experiment sufficient to prove CR566 is shorted?
Should I still pull a lead. If so. On CR566 or CR556? And what/where do I measure? I'm confused about the post pull procedure.


stan

--- In TekScopes@..., "Max Mazza" wrote:



--- In TekScopes@..., "stan_katz" wrote:

I've uncovered what I think is a significant symptom. If I inject a 1 volt square wave, at 1khz or above, set v/div to 20mv/div, and play with the position control, I can get the trigger source lamp to light. If I try the same stunt with a sine wave, I need at least 500khz to get the scope to trigger. This symptom seems to play into what Max was suggesting by lifting one lead of a tunnel diode, and then determining if I can get trigger with high slew rate sources. Of course, with the scope setup to the above test conditions, it's useless.

Stan
This was exactly the same behavior I noted when debugging my 3B4 timebase unit. With 1 KHz square wave of adequate amplitude, the triggers works. With a sinewave, it must be 100 KHz or above to trigger, with difficult.
If disconnecting the TD the behavior is exactly the same, assume that 99% the TD is open.

To get a definitive certainty, you should check if some signal is present on the anode of TD (with TD in place). If the amplitude swing during the TD's commutation is around 200-300mV pk-pk, the TD is OK. If a few mV, the TD is shorted. If more than 500mV, the TD is open.
Do that check before you detach one TD's lead and then after.
Compare the results.
Let us know.

Max


 

I think you would be better off using a triangle or sine wave as a
test signal so you can distinguish the TD changing state and the test
signal.

I noticed that the earlier oscilloscopes which use the same trigger
circuit like the 465 and 464 have more detailed schematics which show
voltage levels and waveforms. They also show the details of U520 and
U720 (they are paraphase amplifiers used to selectively invert the
trigger signal which selects the slope) although that is not really
needed.

On Mon, 28 Jan 2013 04:45:35 -0000, "stan_katz" <stan_katz@...>
wrote:

Max,

Remember, these measurements are made with a student scope that has its own problems and can't measure below 100mv/div. So with 10x probe its hard to read. Amplitude and pulse widths given are very approximate.

I'm still working up the courage to pull out a TD lead. Anyway, with both TDs in circuit:

2v p-p square wave in
.5v/div ... auto ... trigger source lamp extinguished
CR566 -- nothing
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

2v p-p square wave in
20mv/div...auto...trigger source lamp lit
CR566...crummy,noisy elongated commutation pulses approx -300mv approx 400us width.
CR556 -- approx. -500mv nice commutation approx. 300us pulse width

Isn't this experiment sufficient to prove CR566 is shorted?
Should I still pull a lead. If so. On CR566 or CR556? And what/where do I measure? I'm confused about the post pull procedure.


stan


--- In TekScopes@..., "Max Mazza" wrote:



--- In TekScopes@..., "stan_katz" wrote:

I've uncovered what I think is a significant symptom. If I inject a 1 volt square wave, at 1khz or above, set v/div to 20mv/div, and play with the position control, I can get the trigger source lamp to light. If I try the same stunt with a sine wave, I need at least 500khz to get the scope to trigger. This symptom seems to play into what Max was suggesting by lifting one lead of a tunnel diode, and then determining if I can get trigger with high slew rate sources. Of course, with the scope setup to the above test conditions, it's useless.

Stan
This was exactly the same behavior I noted when debugging my 3B4 timebase unit. With 1 KHz square wave of adequate amplitude, the triggers works. With a sinewave, it must be 100 KHz or above to trigger, with difficult.
If disconnecting the TD the behavior is exactly the same, assume that 99% the TD is open.

To get a definitive certainty, you should check if some signal is present on the anode of TD (with TD in place). If the amplitude swing during the TD's commutation is around 200-300mV pk-pk, the TD is OK. If a few mV, the TD is shorted. If more than 500mV, the TD is open.
Do that check before you detach one TD's lead and then after.
Compare the results.
Let us know.

Max