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Re: Mystery Pulse Generator

 

I'd guess that it's an instrument made for internal use at Tektronix. The unfinished rear panel (2 unused holes for GR connectors and the hand lettering support this suspicion) Also, the complete lack of a Model number and a serial number (not even a sub 100 S/N). It might be one-of-a-kind, built by an engineer for a specific project. The 3 prong power connector indicates that it is not ancient.

The 0.2 nS risetime is impressive, when compared with my R293 (1 nS, using an avalanche transistor). The R263 is probably much better in the pulse shape and width control department, however.


Re: 7D20 with unknown options or mods

 

Thanks Clark, Chuck. Very interesting. The leads to the CCDs don't appear to be connected to any of its DIL pins. They look like they are soldered directly on to the substrate. The SL92104 looks a quite complicated MCM affair. I'm not sure I want to go poking around there! I haven't been able to find a datasheet for the SL92104 chip. Any idea whether such a document exists?


Re: Strange Tek2440 issue

 

Your old capacitors are best tan new, sure!


-----Mensaje original-----
De: [email protected] [mailto:[email protected]] En nombre de Vince Vielhaber
Enviado el: mi¨¦rcoles, 9 de septiembre de 2020 5:50
Para: [email protected]
Asunto: Re: [TekScopes] Strange Tek2440 issue

Ok, here's where I'm at.

ALL of the electrolytics, except the two big ones in the back, have been replaced. I tested them and they were all good with very low ESR so I'll toss them in a box for now.

Q870 and Q879 have been replaced. Had to order these.

All resistors in the 5V Regulator have been checked and are all well within spec.

The few small caps (.001uf) were also checked and are right on.

Problem still exists.

Before I was toying around with the idea of hanging an external 5V supply on it. I did try that last week and it did NOT do it and according to the meter on the supply, it wasn't really drawing much current from it - less than 100ma.

Tomorrow I'll go thru the supply again and take more measurements, there were a few points I was looking at and couldn't remember if I checked them and if so what they were. So tomorrow I'll check them and take pictures and better notes.

That's it for tonite.

Vince.

On 09/02/2020 02:50 PM, Siggi wrote:
On Wed, Sep 2, 2020 at 2:07 PM Vince Vielhaber <vev@...> wrote:

I had actually done that last nite, but didn't have the parts layout
handy to see which probe was on which pin (I had them on the diodes>.

Here they are with voltage measurements:


Uh, this makes no sense to me.
The base of Q870 should be pulled toward +15V unreg through R864(?
hard to read on the schematic), and the two op amps shunt it towards
ground when they detect too high voltage or too high current,
respectively. Whichever of pins 1/7 is lower is the op-amp in control of the output.

... time passes ...

Yeah, still doesn't make sense to me. I'm going to guess that either
the op-amps are (pins 1/7 are) reversed on the schematic, or that your
channel designations are.
Even so, it still doesn't make sense, as the voltage-control op-amp
starts dialing more voltage (Channel 2 normal at 5.54V rises to
16.94V), while the current limit op-amp goes on the limit (Channel 1
normal at 16.76V dips to 6.16V). What doesn't make sense here is that
the current control op-amp is dialing a voltage that exceeds the voltage control's usual/normal voltage.
I haven't done the maths, but as there's a bias on the current limit
op-amp's feedback input, it might be that it's simply kicking in
because the output voltage has sagged.

I think you need to look further afield, how's the +8V rail doing, the
+-15V rails, raw and regulated? How is the -5V rail doing? Any other
rails you can find...

If you can't find a bad rail, start looking at the biasing for Q870 &
Q879, have the resistors drifted? If R864(?) or R478 have drifted
significantly upward, that'd explain why the transistors can't meet the current demand.
If the biasing is OK, you need to look at the transistors themselves.
If their gain is down, that'd also explain things. You can measure the
base current to Q879 indirectly by the voltage drop over its base
resistor. Even looking at what's happening on Q870's emitter under
collapse - is that transistor going to saturation, indicating that
Q879 is dozing off on the job?

Good luck!


--
K8ZW


Re: Mystery Pulse Generator

 

Dave,

I'm sure you noticed - the faceplate and rear connector panel are all
hand-lettered. A nice lettering job, but is this actually a Tek item? Maybe
if the original silkscreened labels were worn too much to read easily
someone re-lettered over what was there.

Steve H

On Thu, Sep 10, 2020 at 2:06 AM Dave Seiter <d.seiter@...> wrote:

On ebay, 362868002250; not sure what it really is- what caught my eye was
the two 125ohm GR connectors on the rear. Maybe someone's accessory for
part of a 519 system?
-Dave




Re: Help Troubleshooting 466, No +15VDC

 

Actually my partner used that procedure regularly, I think it¡¯s a bit drastic but he swears by it.

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Sep 9, 2020, at 20:50, Jim Ford <james.ford@...> wrote:

?Maybe it does for shorted tantalum capacitors. Not guaranteed to work on shorts inside the PCB. Oh, it will show you where the short is alright, but that doesn't mean the short will clear or the PCB will be usable afterward. Don't ask....

Jim Ford

------ Original Message ------
From: "Stephen Hanselman" <kc4sw.io@...>
To: [email protected]
Sent: 9/9/2020 3:18:34 PM
Subject: Re: [TekScopes] Help Troubleshooting 466, No +15VDC

Our favorite way was to use a HP 2100 power supply 5VDC at 50Amps. Finds¡¯um every time

Regards,

Stephen Hanselman
Datagate Systems, LLC
On Sep 9, 2020, at 07:00, Martin <musaeum@...> wrote:
?Hello Sparky,

my preferred method for instant finding of shorts in these caps is with my IR-Cam.
You may supply the +15V rail with a current limited supply, or shortly apply mains power - the component will instantly reveal itself.

IR-cams are getting more and more accessible, perhaps you can borrow one?

cheers
Martin






Mystery Pulse Generator

 

On ebay,?362868002250; not sure what it really is- what caught my eye was the two 125ohm GR connectors on the rear. Maybe someone's accessory for part of a 519 system?
-Dave


Re: Help Troubleshooting 466, No +15VDC

 

I'd suspect serious consequences on anything other than 2 layer PC boards, and even then....

I think I'd prefer a, perhaps slower, method.

Harvey

On 9/9/2020 11:50 PM, Jim Ford wrote:
Maybe it does for shorted tantalum capacitors.? Not guaranteed to work on shorts inside the PCB.? Oh, it will show you where the short is alright, but that doesn't mean the short will clear or the PCB will be usable afterward.? Don't ask....

Jim Ford

------ Original Message ------
From: "Stephen Hanselman" <kc4sw.io@...>
To: [email protected]
Sent: 9/9/2020 3:18:34 PM
Subject: Re: [TekScopes] Help Troubleshooting 466, No +15VDC

Our favorite way was to use a HP 2100 power supply 5VDC at 50Amps. Finds¡¯um every time

Regards,

Stephen Hanselman
Datagate Systems, LLC
?On Sep 9, 2020, at 07:00, Martin <musaeum@...> wrote:

??Hello Sparky,

?my preferred method for instant finding of shorts in these caps is with my IR-Cam.
?You may supply the +15V rail with a current limited supply, or shortly apply mains power - the component will instantly reveal itself.

?IR-cams are getting more and more accessible, perhaps you can borrow one?

?cheers
?Martin






Re: Help Troubleshooting 466, No +15VDC

 

Maybe it does for shorted tantalum capacitors. Not guaranteed to work on shorts inside the PCB. Oh, it will show you where the short is alright, but that doesn't mean the short will clear or the PCB will be usable afterward. Don't ask....

Jim Ford

------ Original Message ------
From: "Stephen Hanselman" <kc4sw.io@...>
To: [email protected]
Sent: 9/9/2020 3:18:34 PM
Subject: Re: [TekScopes] Help Troubleshooting 466, No +15VDC

Our favorite way was to use a HP 2100 power supply 5VDC at 50Amps. Finds¡¯um every time

Regards,

Stephen Hanselman
Datagate Systems, LLC
On Sep 9, 2020, at 07:00, Martin <musaeum@...> wrote:

?Hello Sparky,

my preferred method for instant finding of shorts in these caps is with my IR-Cam.
You may supply the +15V rail with a current limited supply, or shortly apply mains power - the component will instantly reveal itself.

IR-cams are getting more and more accessible, perhaps you can borrow one?

cheers
Martin




Re: Help Troubleshooting 466, No +15VDC

 

So what do you do to repair craters in the PC board?

Harvey

On 9/9/2020 6:18 PM, Stephen Hanselman wrote:
Our favorite way was to use a HP 2100 power supply 5VDC at 50Amps. Finds¡¯um every time

Regards,
Stephen Hanselman
Datagate Systems, LLC
On Sep 9, 2020, at 07:00, Martin <musaeum@...> wrote:

?Hello Sparky,

my preferred method for instant finding of shorts in these caps is with my IR-Cam.
You may supply the +15V rail with a current limited supply, or shortly apply mains power - the component will instantly reveal itself.

IR-cams are getting more and more accessible, perhaps you can borrow one?

cheers
Martin



Re: Strange Tek2440 issue - SOLVED!

 

Ok, the problem has been solved!

As Siggi said, "this makes no sense". He was right, it made no sense. On the inverting input of U870A is the 4.99V reference. It measured 5.14V and the non-inverting input measured 5.15V (Fluke DVM). The theory of operation mentions that the 5V regulated supply is the same as the 8V regulated supply. So I made some comparisons and saw that on the 8V there was a 0.10V difference between the inverting and non-inverting, not so with the 5V.

As I mentioned before, I lifted one lead of both resistors (and a couple of others) and they were all within spec. Strangely enough, it took another 6.8K across R875 (a 6.19K) to drop pin 2 (inv) on U870 to 0.10V less than pin 3. Measuring R875 again (with a lead lifted) it was giving a new value.

Both resistors (R875 and R877) are now on order.

Thanks!!
Vince.

On 09/08/2020 11:50 PM, Vince Vielhaber wrote:
Ok, here's where I'm at.

ALL of the electrolytics, except the two big ones in the back, have been
replaced. I tested them and they were all good with very low ESR so
I'll toss them in a box for now.

Q870 and Q879 have been replaced. Had to order these.

All resistors in the 5V Regulator have been checked and are all well
within spec.

The few small caps (.001uf) were also checked and are right on.

Problem still exists.

Before I was toying around with the idea of hanging an external 5V
supply on it. I did try that last week and it did NOT do it and
according to the meter on the supply, it wasn't really drawing much
current from it - less than 100ma.

Tomorrow I'll go thru the supply again and take more measurements, there
were a few points I was looking at and couldn't remember if I checked
them and if so what they were. So tomorrow I'll check them and take
pictures and better notes.

That's it for tonite.

Vince.



On 09/02/2020 02:50 PM, Siggi wrote:
On Wed, Sep 2, 2020 at 2:07 PM Vince Vielhaber <vev@...> wrote:

I had actually done that last nite, but didn't have the parts layout
handy to see which probe was on which pin (I had them on the diodes>.

Here they are with voltage measurements:


Uh, this makes no sense to me.
The base of Q870 should be pulled toward +15V unreg through R864(?
hard to
read on the schematic), and the two op amps shunt it towards ground when
they detect too high voltage or too high current, respectively.
Whichever
of pins 1/7 is lower is the op-amp in control of the output.

... time passes ...

Yeah, still doesn't make sense to me. I'm going to guess that either the
op-amps are (pins 1/7 are) reversed on the schematic, or that your
channel
designations are.
Even so, it still doesn't make sense, as the voltage-control op-amp
starts
dialing more voltage (Channel 2 normal at 5.54V rises to 16.94V),
while the
current limit op-amp goes on the limit (Channel 1 normal at 16.76V
dips to
6.16V). What doesn't make sense here is that the current control
op-amp is
dialing a voltage that exceeds the voltage control's usual/normal
voltage.
I haven't done the maths, but as there's a bias on the current limit
op-amp's feedback input, it might be that it's simply kicking in because
the output voltage has sagged.

I think you need to look further afield, how's the +8V rail doing,
the +-15V rails, raw and regulated? How is the -5V rail doing? Any other
rails you can find...

If you can't find a bad rail, start looking at the biasing for Q870 &
Q879,
have the resistors drifted? If R864(?) or R478 have drifted significantly
upward, that'd explain why the transistors can't meet the current demand.
If the biasing is OK, you need to look at the transistors themselves. If
their gain is down, that'd also explain things. You can measure the base
current to Q879 indirectly by the voltage drop over its base resistor.
Even
looking at what's happening on Q870's emitter under collapse - is that
transistor going to saturation, indicating that Q879 is dozing off on the
job?

Good luck!


--
K8ZW


Re: 7D20 with unknown options or mods

 

Richard,

I found some clues about the little board on the Timebase board. It is named "ERD Shift Adjust." ERD is a digitizing mode called "extended real-time digitizing." The little board allows for additional vertical offset correction to the CCD output depending upon the time/div. Without it, you will see a small but irritatingly noticeable vertical shift to the waveform as the time/div is changed in the ERD range. Apparently the original adjustments were not quite enough to cover the entire ERD range. I recall, from long ago, that some of the CCDs produced more voltage offset than others depending upon the clocking frequency; something to do with variations in transfer efficiency. Usually CCDs were clocked at a fixed rate and the offset is adjusted or cancelled by some external circuitry. ERD mode will operate the CCD at a rate unique determined by each time/div setting; hence, the extra offset adjustment. Anyway, that board is standard equipment on later units and not a custom trick for a special customer.

I don't know what the other mod is that has four wires soldered to the CCD. If you are able to tell me which CCD pins, I might be able to find a clue.

Clark


Re: 7D20 with unknown options or mods

 

Richard,

I can consult my micro fiche file for factory modifications. It's a bit tedious and slow to paw through the film, but I'll have a look.

Clark


Re: Help Troubleshooting 466, No +15VDC

 

Our favorite way was to use a HP 2100 power supply 5VDC at 50Amps. Finds¡¯um every time

Regards,

Stephen Hanselman
Datagate Systems, LLC

On Sep 9, 2020, at 07:00, Martin <musaeum@...> wrote:

?Hello Sparky,

my preferred method for instant finding of shorts in these caps is with my IR-Cam.
You may supply the +15V rail with a current limited supply, or shortly apply mains power - the component will instantly reveal itself.

IR-cams are getting more and more accessible, perhaps you can borrow one?

cheers
Martin



Re: Tek 4654M; No Trace, No +5V, No +95V; Help

 

Harrison,

When my U550 failed, I got one from Sphere. I don't think they were listed on his site but, at least at that time, had some pulls from working scopes. You might check there if you still suspect it is in that module.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Harrison" <buma7@...>
To: [email protected]
Sent: Wednesday, September 9, 2020 3:47:17 PM
Subject: Re: [TekScopes] Tek 4654M; No Trace, No +5V, No +95V; Help

I am afraid that I have been jumping around too much and now, even with good
shop notes, am not sure what elements/modules I think are good and which
might be bad. Looking at the troubleshooting diagrams every thing still
points to the HV power supply. Currently there doesn't seem to be any out
there so it is a case of building a complete unit or repairing what is
there. I am coming close to declaring this unit a parts machine and closing
the book on it but I hate to do so. A repair might be right around the
corner or I am missing the obvious and the fix is staring me in the face.




Cleaning Leads of IC Chips (Tektronix Related)

 

I am preparing to remove the Dallas DS1742W-150 NVRAM chip with dead lithium cell from my scope. My plan is to add a low-profile socket, then to cut-out the dead cell and extend the connections to a separately located replacement. Is there a favorite way of cleaning up IC leads (other than with vacuum devices) so as to improve the connection reliability of the reinstalled chip. I have heard Chinese resellers sometimes use a hot peanut oil bath for this purpose.

Bruce, KG6OJI


Re: Tek 4654M; No Trace, No +5V, No +95V; Help

 

I am afraid that I have been jumping around too much and now, even with good shop notes, am not sure what elements/modules I think are good and which might be bad. Looking at the troubleshooting diagrams every thing still points to the HV power supply. Currently there doesn't seem to be any out there so it is a case of building a complete unit or repairing what is there. I am coming close to declaring this unit a parts machine and closing the book on it but I hate to do so. A repair might be right around the corner or I am missing the obvious and the fix is staring me in the face.


Re: Help Troubleshooting 466, No +15VDC

 

Hello Sparky,

my preferred method for instant finding of shorts in these caps is with my IR-Cam.
You may supply the +15V rail with a current limited supply, or shortly apply mains power - the component will instantly reveal itself.

IR-cams are getting more and more accessible, perhaps you can borrow one?

cheers
Martin


Re: 7D20 with unknown options or mods

Chuck Harris
 

Ok,

But there was an option on the 7D20 that made it work with
the 7854 digital storage scope. Perhaps that is the option
you seek?

-Chuck Harris

Clark Foley wrote:

Chuck,

The 7D20T did not require anything extra from the 7D20. Any production 7D20 will function in the T package without modification. You could add the rear access cable for the GPIB that had a companion mod for the R7603. The mainframe for the 7D20T has the necessary 7k interface, rear GPIB wiring and power in a TM5003 skin (the notorious modular package system (MPS)).

Regards,
Clark Foley




Re: Help troubleshooting a 2710 SA

 

From my experience with these, certain PCB revisions have an issue in the EHT section; on one I've repaired, there had been creepage and flashover in the high resistance potential divider chain which caused a cascade of power supply faults. Have a look at the back left corner of the power supply board to seeif there is any sign of burning (under the perspex cover)


Re: P6249 Oscillation

 

Maybe he's of the KISS lobby :)

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Tim Phillips
Sent: 09 September 2020 07:20
To: [email protected]
Subject: Re: [TekScopes] P6249 Oscillation

'Osculation' ????

(Sorry, couldn't resist it !!!)
Tim