Topics

TM506


Stephen
 

I purchased a TM506 (with Option 2) from eBay, and it arrived 2 days ago. This is my very first TM series ever.
Pictures here: https://groups.io/g/TekScopes/album?id=250733

It came with all the modules you see installed. The SG503 You see on top, I already had.

I thought it was a good deal. The guy said that everything was working except for the little scope.
I paid 210€ + 40€ shipping from Germany. However, upon arrival, I realized that many plugins did not work. Or at least not as they should, or expected, I think.

- The DC503 had a display that was pretty weird. Every time I powered on the TM, the “0” was in a different location (as you can see in the pictures), and sometimes nothing at all. And of course it’s not counting anything.

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

- The PS503A Power Supply is working properly.

- 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.

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.

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.

Anyway, I got a 100€ refund from the seller. So I got all this for 150€.
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.

Thank You


Harvey White
 

Interleaved comments:

On 7/19/2020 4:09 PM, Stephen wrote:
I purchased a TM506 (with Option 2) from eBay, and it arrived 2 days ago. This is my very first TM series ever.
Pictures here: https://groups.io/g/TekScopes/album?id=250733

It came with all the modules you see installed. The SG503 You see on top, I already had.

I thought it was a good deal. The guy said that everything was working except for the little scope.
I paid 210€ + 40€ shipping from Germany. However, upon arrival, I realized that many plugins did not work. Or at least not as they should, or expected, I think.
Apparently his definition of "work" has been exaggerated...

- The DC503 had a display that was pretty weird. Every time I powered on the TM, the “0” was in a different location (as you can see in the pictures), and sometimes nothing at all. And of course it’s not counting anything.
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.

- 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).



- The PS503A Power Supply is working properly.
Good, it'll have the highest output current potential in the high current slot.


- 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.

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.



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.
Anyway, I got a 100€ refund from the seller. So I got all this for 150€.
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.

Harvey



Thank You



Siggi
 

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


Stephen
 

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




Stephen
 

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...


Stephen
 

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


Stephen
 

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.


Harvey White
 

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



Harvey White
 

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




 

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 Warner
 

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 <@tmiller> 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


Stephen
 

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


Stephen
 

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.


Stephen
 

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


Roger Evans
 

Stephen,

The DC502 has a lot of switches for counting interval, AB switching, totalling ... They are prone to give intermittent contacts with age and can usually be improved substantially by a lot of exercising back and fore. The scanning/multiplexing of the LED display is controlled by U332, U333, U335. You should see the basic pulse train at U330 pin 10 and divided and decoded signals on U335. Pins 13, 14, 15 should be square waves successively divided by two, the pins at the bottom of U335 on schematic <3> should each pulse low for one in 8 pulses of the basic clock frequency.

You should also for obvious reasons begin by checking the regulated supplies for +15V, +5V (all the logic), and -22V, schematic <2> in the manual.

It can take some patience to track signals through the divider chains and the switches but I managed ok without the extender and working with the cover off a TM503 and the module under test in the middle slot. I daresay the TM506 is more difficult to manouvre for ease of access.

Regards,

Roger


Roger Evans
 

Sorry for the mistype, the module is of course the DC503.

Roger


Stephen
 

On Sun, Jul 19, 2020 at 10:53 PM, Roger Evans wrote:


Stephen,

The DC502 has a lot of switches for counting interval, AB switching, totalling
... They are prone to give intermittent contacts with age and can usually be
improved substantially by a lot of exercising back and fore. The
scanning/multiplexing of the LED display is controlled by U332, U333, U335.
You should see the basic pulse train at U330 pin 10 and divided and decoded
signals on U335. Pins 13, 14, 15 should be square waves successively divided
by two, the pins at the bottom of U335 on schematic <3> should each pulse low
for one in 8 pulses of the basic clock frequency.

You should also for obvious reasons begin by checking the regulated supplies
for +15V, +5V (all the logic), and -22V, schematic <2> in the manual.

It can take some patience to track signals through the divider chains and the
switches but I managed ok without the extender and working with the cover off
a TM503 and the module under test in the middle slot. I daresay the TM506 is
more difficult to manouvre for ease of access.

Regards,

Roger
Thank you Roger, and all the others of course for your valuable input.
Yes the TM506 is not particularly easy to maneuver. That thing is heavy!
I was also think of taking the top off, which I did. Much, much easier!

I’m trying to do one thing at a time. I’ve started to clean some IC sockets. Transistors are soldered on.
I will remove the top board to clean the IC sockets that are underneath and unreachable.
I’ve clean many switches already, to no avail so far. Sometimes the display displays one zero at startup, sometimes nothing. And never in the same location. You probably have seen pictures. On top of that, some one segment is missing on two locations. All of That lead me to think that one or more of the IC that control the display have either gone bad, or are really dirty. I haven’t looked deeply at the schematic yet. And I’m definitely no expert anyway. I’m learning as I go.


Stephen
 

On Sun, Jul 19, 2020 at 10:55 PM, Roger Evans wrote:


Sorry for the mistype, the module is of course the DC503.

Roger
Yes, I figured it was a typo. No problem. ;-)


Stephen
 

When you think all is good, it’s not.
Now the scope shuts off almost immediately after starting. I see a trace for 4-5 seconds, and it’s gone along with the power indicator...

But the weird thing is, there is no trace, but the screen is glowing a bit, as if something was there, and when I turn it manually OFF, the display gets darker.. and although the unit is in the ON position, the power LED indicator is off.

I suspect a rectifier or a diode.

So many issues with 3 different plugins... Arghhhh!!


Roger Evans
 

If the scren is glowing but there is no trace the beam is probably deflected way off screen and you see some reflected electrons from the walls of the CRT.

The power light is driven by the +20V regulated supply, so that probably has died. The +20V powers the first stages of the X and Y amplifiers so with that missing the voltages on the deflection plates will be wrong. The regulator for +20V is one of the power transistors in the TM506, you can check that the unregulated voltage is OK on R507 or R512 in the SC501. If the mainframe power transistor is the culprit then the SC501 should be OK in a different slot. If the fault is in the SC501 see if you can unsolder one leg of C514 and does the power light stay on? You should also look for other capacitors from the +20V line to ground, I only found C156 on a quick look.

Roger