SC502 fixed, partially.
One horizontal and one vertical plate leads were disconnected.

https://groups.io/g/TekScopes/photo/250733/0?p=Created,,,100,2,0,0

Last issue with this one, the “TRACE” variable precision resistor Is gone.
I have to look at the layout, but my guess is it’s probably the trace rotation.
I’ll figure something out, because over here these things are impossible to find in that form factor.

https://groups.io/g/TekScopes/photo/250733/0?p=Created,,,100,2,0,0
https://groups.io/g/TekScopes/photo/250733/1?p=Created,,,100,2,0,0

On Sun, Jul 19, 2020 at 12:46 PM, Harvey White wrote:

Plugin gets Hot:

check for shorted tantalums.  Check power supply voltages first.

Will check for shorted tantalums. Power supply check isn’t gonna be easy without an extension, but I think I can manage by just installing that one plugin, removing the top of the TM506, and the sides of the plugin.

A little update though: I redid some suspect solder joints where the board showed obvious and important signs of overheating. The unit is not fixed yet, but the BNC connectors at the front are now just barely luck warm. Whereas before they were burning hot after only less than a few minutes. And so where the heat-sinked transistors.

The TM5000/500 series does not use regulated supplies (except for some
in the TM5000).  The plugins rely on 1) knocking down existing bulk
voltages with on board regulators.  2) using the PNP and NPN pass
transistors on the frame as regulating elements with the controls on the
plugin.  3) using the uncommitted transformer windings to make a raw DC
voltage that gets regulated down to something.

Separate transistors (PNP/NPN, one pair) per slot.  Separate transformer
windings (isolated) per slot.  Common bulk supplies.

The mantra of fixing stuff is that the power supplies have to be OK
first.  This includes ripple.  Had a 1000 volt calibrator that wouldn't
go above 250 volts.  Finally figured out that the circuit could regulate
ok if the voltage was 250 or less, but couldn't get higher.  Replace one
of the main filter capacitors and things were ok.

Not the same circuit, but possibly something to think about.

Looked at the waveform.  Suspect + supply driving output, shorted
tantalum there, or perhaps bad transistor pulling up the output to the
supply.

Harvey

I will definitely check that tomorrow. Maybe some transistors on that slot disconnected during shipping.

On Sun, Jul 19, 2020 at 01:54 PM, Andy Warner wrote:

WRT extenders, following advice here, I picked up one of these:

https://www.ebay.com/itm/401747463642

Some quality time with a dremel to cut the slot in the PCB, and removing a
few wires on what form the high numbered pins (which I left unconnected.)
Works great, and the price can’t be beat.

Thank you Andy. This item is not available anymore, but I just got this one:
https://www.ebay.fr/itm/202651641649

On Sun, Jul 19, 2020 at 02:52 PM, snapdiode wrote:

that's a good link.

Also if you search through the messages... you'll find a discussion where Dennis is relating how Tektronix, at one past point, was behind HP in triggering technology... that was not a good place for Tek to be... since an oscilloscope that triggers well is the one that gives you the display you need to see.
Another bit of triggering trivia is that while fully digital triggering (that's a digital triggering system gets its data from the ADC) is beginning to show up now... most scopes, analog or digital, had/have an analog trigger system... at least up to last couple of years.
Tek's modern DSOs have a wide variety of very useful triggers available... edge, runt, window... and many other triggers very useful for working with the signals found in modern digital systems.
I don't know of a book that is the modern equivalent of the Circuit Concepts one... that is a book that discusses the analog design, and the software design, of modern DSO triggering systems.

On 2020-07-20, at 03:20, Chuck Harris <cfharris@erols.com> wrote:

Everything is known to cause cancer in the state of
California.... Makes me glad I don't live there.

They say:


Why is this here?
As of August 2018 the State of California has changed the requirements of the "Prop 65" law. We now must list on our website any possible chemicals the can cause cancer, birth defects or reproductive problem.

As an example:
• ABS plastic contains styrene
• PVC wire insulation can contain Di(2-ethylhexyl)phthalate (DEHP)
• electrolytic capacitors can contain Ethylene glycol
• Brass can contain Lead
• flame retardant pc boards can contain Tetrabromobisphenol A (TBBPA)
• Aluminum alloys can contain Chromium

To put it simply we are a small company and do not have the resources to test every single part, so we list every thing as hazardous. Please recycle all electronic parts responsibly and under no circumstance eat, drink or smoke these parts and wash your hands after touching!


Typical cop-out created by non-thinking regulation.
But I generally agree with the advice not to try smoking ferrite beads.

Grüße, Carsten

Everything is known to cause cancer in the state of
California.... Makes me glad I don't live there.

-Chuck Harris

Roy Thistle wrote:

WRT extenders, following advice here, I picked up one of these:

https://www.ebay.com/itm/401747463642

Some quality time with a dremel to cut the slot in the PCB, and removing a
few wires on what form the high numbered pins (which I left unconnected.)
Works great, and the price can’t be beat.

On Sun, Jul 19, 2020 at 19:00 Tom Miller <tmiller11147@comcast.net> wrote:

I might add to Harvey's comments. Do an ohmmeter check of all the
supplies first to rule out shorted supply busses.

Regards

On 7/19/2020 7:46 PM, Harvey White wrote:

Plugin gets Hot:

check for shorted tantalums. Check power supply voltages first.

The TM5000/500 series does not use regulated supplies (except for some
in the TM5000). The plugins rely on 1) knocking down existing bulk
voltages with on board regulators. 2) using the PNP and NPN pass
transistors on the frame as regulating elements with the controls on
the plugin. 3) using the uncommitted transformer windings to make a
raw DC voltage that gets regulated down to something.

Separate transistors (PNP/NPN, one pair) per slot. Separate
transformer windings (isolated) per slot. Common bulk supplies.

The mantra of fixing stuff is that the power supplies have to be OK
first. This includes ripple. Had a 1000 volt calibrator that
wouldn't go above 250 volts. Finally figured out that the circuit
could regulate ok if the voltage was 250 or less, but couldn't get
higher. Replace one of the main filter capacitors and things were ok.

Not the same circuit, but possibly something to think about.

Looked at the waveform. Suspect + supply driving output, shorted
tantalum there, or perhaps bad transistor pulling up the output to the
supply.

Harvey


On 7/19/2020 5:50 PM, Stephen wrote:

Pictures of some wave forms have been posted here in the same folder.
I wrote what you’re looking at underneath each one.

https://groups.io/g/TekScopes/album?id=250733

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus




--

Andy

I might add to Harvey's comments. Do an ohmmeter check of all the supplies first to rule out shorted supply busses.

Regards

--
This email has been checked for viruses by Avast antivirus software.
https://www.avast.com/antivirus

On 7/19/2020 5:36 PM, Stephen wrote:

On Sun, Jul 19, 2020 at 09:40 AM, Harvey White wrote:

Apparently his definition of "work" has been exaggerated...

Indeed!!

The display is scanned.  It's not scanning.  A recommendation would be
to remove all the socketed ICs, clean the pins, and using DeOxit (or the
local equivalent), clean the sockets.

Yep. I’ll have to take the whole thing apart. There are many on the middle board.

Not too hard to do, the sockets can often be a problem.  Some transistors may be socketed too.

- I don’t have a current probe to check the AM503.

Those may be hard to come by.  Some current probes are quite fragile, so
take care not to subject them to undue stress (such as dropping them).

Whenever I get one, if I ever do, I‘lol make sure to be extra careful. Thank you for the heads up.

Sure.  They're fragile, and the hall effect sensor is about impossible to come by.  Read up on the probes and which fits what.

- The PS503A Power Supply is working properly.

Good, it'll have the highest output current potential in the high
current slot.

That’s where I placed it.

You might check the current limit capabilities and measure for ripple at the outputs over all the voltages.  This is just to be paranoid.

- The FG502 is, I think, not working as I expected. Or I just don’t know

how to make it work like a regular function generator... It has some weird
behaviors.
Ok, on the 502, as I remember it, the modes with adjustable duty cycles
reduce the current frequency setting by 10.  Your baseline test would be
a sinewave, squarewave, or triangle.  Select 1.0 on the dial and 1K, and
amplitude at mid dial.  It's very nonlinear below 1, and ditto above 10.

Yes, regarding the 10:1 ratio, I read that in the manual.

But that’s not the issue I have. It has to do with the level and also the DC offset.
I can’t get a decent sine wave above 450mV. And that’s with the DC offset engaged. Otherwise it’s even worse. And it still gets distorted, and finally becomes a triangle at a level higher than 500mV or so.
And the scope has to be AC coupled too. Otherwise I mostly have nothing...
I’ll post pictures soon.

Saw them.  I think power supply voltages are important, and what you get as voltages to pull the output up to the proper voltage.

Many of the outputs have a coil wound on a resistor as a choke, then a tantalum to ground.  Look for signs of toasted resistor and always measure on both sides of the coil.  The coils have been known to burn out with a shorted tantalum.

Also the square waves are really ugly and distorted. The whole thing isn’t acting the way I’m used to.
More pictures to follow.

I'm (just because) suspecting the output stage.

The little scope has a weird trace which is only 3 divisions wide

horizontally, and distorted. And as I increase the intensity, the traces
curve and collide... I’ve never seen that before. See the pictures.

Trace seems bright enough, you could just have a problem with the
horizontal amplifier.  Turn it to XY and see if you can move a *dim*
spot over the screen with the horizontal and vertical positioning
controls, that may give you a hint.

XY is “working”. But the dot doesn’t move horizontally to the left past the center vertical line or so. And it barely moves vertically.

I'd suspect the transistor in the horizontal amp that drives it to the right, or it could be as simple as the CRT deflection plate inadvertently disconnected.

As far as the vertical is concerned, your problem may be earlier in the circuit.

I also noticed some smoke when I plug something in the 1st compartment. So

I don’t anymore. It burned a resistor on the PS503A, which I replaced. And
I also saw smoke when I connected the AM503. But nothing is apparently burned
inside, and it powers up fine.
Smoke is never good.

You don’t say. LOL

Hard to say what the problem is, I think that a shorted pass transistor giving way too much voltage could be a problem.

I’m definitely not skilled enough to troubleshoot all this by myself. So

I’m probably going to need your guys expertise, I you’re so inclined to
help.

One thing at a time.  You may want to look for some inexpensive
extenders which will simplify troubleshooting.  The scope takes two,
everything else should take 1.

Can’t find any. Didn’t see the parts number either on TekWiki. They’re probably 3 or 4 times more expensive than what I paid for the whole thing...

Maybe.  Look on EBAY for Tek 500 series extenders.  They've been available, and people have made them.  If you're good with making PC boards (or sending them off to China), you could do it.

Harvey

Harvey

Thank You

Plugin gets Hot:

check for shorted tantalums.  Check power supply voltages first.

The TM5000/500 series does not use regulated supplies (except for some in the TM5000).  The plugins rely on 1) knocking down existing bulk voltages with on board regulators.  2) using the PNP and NPN pass transistors on the frame as regulating elements with the controls on the plugin.  3) using the uncommitted transformer windings to make a raw DC voltage that gets regulated down to something.

Separate transistors (PNP/NPN, one pair) per slot.  Separate transformer windings (isolated) per slot.  Common bulk supplies.

The mantra of fixing stuff is that the power supplies have to be OK first.  This includes ripple.  Had a 1000 volt calibrator that wouldn't go above 250 volts.  Finally figured out that the circuit could regulate ok if the voltage was 250 or less, but couldn't get higher.  Replace one of the main filter capacitors and things were ok.

Not the same circuit, but possibly something to think about.

Looked at the waveform.  Suspect + supply driving output, shorted tantalum there, or perhaps bad transistor pulling up the output to the supply.

Harvey

Per requests, I added power meters, couplers and loads to the HP and RF sections, and many other interesting RF widgets. might be something useful there for you. Send me any special requests, we are happy to add them if we have it.
https://www.sphere.bc.ca/test/stuffday.html

there's now several good Tek scopes, including a 7934, 2216, 2465 and a TDS. more to come.
anybody interested in a nice looking 2336 portable?
all the best,
walter (walter2 at- sphere.bc.ca)
sphere research corp.

Did I mention that this plugin gets burning hot?? Even the BNC at the front are extremely hot.
And the Level is very sensitive too, even after I cleaned it with IPA.

If it ain't got tubes, it ain't for me!
Just kidding, that's a good link.

Pictures of some wave forms have been posted here in the same folder.
I wrote what you’re looking at underneath each one.

https://groups.io/g/TekScopes/album?id=250733

FYI Might interest some here:

https://hackaday.com/2020/07/19/upgrading-the-ram-in-a-25-year-old-oscilloscope/

On Sun, Jul 19, 2020 at 09:58 AM, Siggi wrote:

I believe this will typically happen when one of the "pass" transistors in
the power module is bad. I remember smoke under similar circumstances with
my first TM500 power module.

Oddly enough, the eBay pictures the guy posted with the unit on, seemed fine. All the modules were on.
Maybe during shipping...? Weird...

On Sun, Jul 19, 2020 at 09:40 AM, Harvey White wrote:

Apparently his definition of "work" has been exaggerated...

Indeed!!

The display is scanned.  It's not scanning.  A recommendation would be
to remove all the socketed ICs, clean the pins, and using DeOxit (or the
local equivalent), clean the sockets.

Yep. I’ll have to take the whole thing apart. There are many on the middle board.

- I don’t have a current probe to check the AM503.

Those may be hard to come by.  Some current probes are quite fragile, so
take care not to subject them to undue stress (such as dropping them).

Whenever I get one, if I ever do, I‘lol make sure to be extra careful. Thank you for the heads up.

- The PS503A Power Supply is working properly.

Good, it'll have the highest output current potential in the high
current slot.

That’s where I placed it.

- The FG502 is, I think, not working as I expected. Or I just don’t know

how to make it work like a regular function generator... It has some weird
behaviors.
Ok, on the 502, as I remember it, the modes with adjustable duty cycles
reduce the current frequency setting by 10.  Your baseline test would be
a sinewave, squarewave, or triangle.  Select 1.0 on the dial and 1K, and
amplitude at mid dial.  It's very nonlinear below 1, and ditto above 10.

Yes, regarding the 10:1 ratio, I read that in the manual.

But that’s not the issue I have. It has to do with the level and also the DC offset.
I can’t get a decent sine wave above 450mV. And that’s with the DC offset engaged. Otherwise it’s even worse. And it still gets distorted, and finally becomes a triangle at a level higher than 500mV or so.
And the scope has to be AC coupled too. Otherwise I mostly have nothing...
I’ll post pictures soon.
Also the square waves are really ugly and distorted. The whole thing isn’t acting the way I’m used to.
More pictures to follow.

The little scope has a weird trace which is only 3 divisions wide

horizontally, and distorted. And as I increase the intensity, the traces
curve and collide... I’ve never seen that before. See the pictures.

Trace seems bright enough, you could just have a problem with the
horizontal amplifier.  Turn it to XY and see if you can move a *dim*
spot over the screen with the horizontal and vertical positioning
controls, that may give you a hint.

XY is “working”. But the dot doesn’t move horizontally to the left past the center vertical line or so. And it barely moves vertically.

I also noticed some smoke when I plug something in the 1st compartment. So

I don’t anymore. It burned a resistor on the PS503A, which I replaced. And
I also saw smoke when I connected the AM503. But nothing is apparently burned
inside, and it powers up fine.
Smoke is never good.

You don’t say. LOL

I’m definitely not skilled enough to troubleshoot all this by myself. So

I’m probably going to need your guys expertise, I you’re so inclined to
help.

One thing at a time.  You may want to look for some inexpensive
extenders which will simplify troubleshooting.  The scope takes two,
everything else should take 1.

Can’t find any. Didn’t see the parts number either on TekWiki. They’re probably 3 or 4 times more expensive than what I paid for the whole thing...

Harvey

Thank You

On Sun, Jul 19, 2020 at 10:54 AM, @0culus wrote:

http://w140.com/tekwiki/images/f/fa/062-1056-00.pdf

That's an older (but very good) "Circuit Concepts" book (they are generally very good; but mostly written... and about... technology that is decades old.)
A newer, but not as well written... in my opinion... "write up" called Triggering Fundamentals is available on the Tektronix Website at
ttps://download.tek.com/document/55W_17291_6_0.pdf
In that they discuss such topics as "triggering on runt pulses"... and yes it is legal to do that in most states.
Also, there are way too cool colour pictures!

On Sun, Jul 19, 2020 at 12:38 PM, Glydeck wrote:

I used these with good results.

WARNING: May cause cancer or reproductive harm?.. at least in the state of California?

On Sun, Jul 19, 2020 at 4:40 PM Harvey White <madyn@dragonworks.info> wrote:

Interleaved comments:

On 7/19/2020 4:09 PM, Stephen wrote:

I also noticed some smoke when I plug something in the 1st compartment.

So I don’t anymore. It burned a resistor on the PS503A, which I replaced.
And I also saw smoke when I connected the AM503. But nothing is apparently
burned inside, and it powers up fine.
Smoke is never good.

I believe this will typically happen when one of the "pass" transistors in
the power module is bad. I remember smoke under similar circumstances with
my first TM500 power module.