Date   

Re: 7A16A high frequency compensation.

Albert Otten
 

Hi Max,

How much nicer do you want it? :-).
I wonder whether the slight aberration you see after 10 ns is due to reflection in a 5 ns cable.

Albert


Re: How to troubleshoot a faulty 7B92A?

Mark Vincent
 

Thierry,

Q410, Q412, etc are 0367. Check all that have this on them from C to E. Likely leaky.

Dan is right about U820 possibly being defective. I had one of these bad before. It is possible dirty contacts, if this one is in a socket.

If you are not getting any sweep on standard or delayed, I have seen Q812 open B to C. This transistor will make U820 look bad if the transistor is bad. A KSP10BU will replace this and the 0367 types. I have had that happen at least once. The Cherry switch on the right side of the plug-in at the front not physically mounted right. That will be open or grounded to P911. See if it is closed and open by a multimeter when you pull and push the time base selector. This is done with no power applied. The screws that mount to the readout board (A12) are oblong and allow movement of the switch. Make sure you have the pin that activates the microswitch there. You will see it with the right side panel removed. R479 and R939 should be 1W. These are stressed and could be high to open. I have heard of someone saying U856 can go bad. This is a 7474 flip-flop

Pulling the time base knob engages the delayed sweep. I do not know if you did or did not test this. See if you get sweep this way. The small intensity knob to the left of the time/div knob. That could be too low. Turn that CW to see of you get sweep. When working right, it will get very bright at full CW. The contrast to the right of this control may need adjusting. The trace sep. knob my be off.

If your S/N is below 60000, it is possible the tunnel diodes are bad on one or both triggering boards.

It is possible the internal dc bal. and/or trg. sens. pots were turned. They may need a slight adjustment. It may bring the triggering back.

Cleaning the switches might help if you have already done so.

I hope this helps.

Mark


Re: How to troubleshoot a faulty 7B92A?

Thierry Delaitre
 

thank you.

The 7B92A is still in the vertical slot.

Regarding pin 7 and the TRIG'D light, the light is off when the scope gets switched-on (with AUTO, AC, INT). The TRIG'D light switches on if i change the mode to NORM. The light stays on if I revert the mode back to INT.

Pin 10 remains at a constant DC high voltage and Pin 8 remains at a constant DC low voltage. both pin 10 and 8 do not show any visible waveform

I use a scope probe on the same scope to troubleshoot.

Thanks

Thierry


Re: 7A16A high frequency compensation.

unclebanjoman
 

Hi Albert,
thank you for the response.
After a further two hours, and comparing with the more detailed explanations given in the 7A16P manual, I was finally able to calibrate the step response in a decent manner.
I could not appreciate any variations by turning the last trim, C770. When I got the plugin the first time, it was almost completely unscrewed. I screwed in some turns to prevent the screw from falling out!

I posted some screenshots showing the final result.
Photos are in https://groups.io/g/TekScopes/album?id=262075
Album title:"A16A step response (with 7854)

What do you think about? All comments are welcome.

Furthermore, I noticed that my PCB is very recent: it shows a S/N 670-2323-08 (see photo). There's a trimmer that does not appear in the schematic.
I've marked in the photo with a red arrow. Green arrow points to the LF compensation trimmer R436 which is present in the schematic. The other one is marked LF (on the PCB) but is not present in the schematic. I presume was an additional trim point for the same purpose of the green one, so I adjusted it in the same manner as R436.

Max


4 photos uploaded #photo-notice

TekScopes@groups.io Notification <noreply@...>
 

The following photos have been uploaded to the 7A16A step response (with 7854) album of the TekScopes@groups.io group.

By: unclebanjoman <mmazza@...>


Re: OT: MC12080 prescaler chip weirdness

Ed Breya
 

Like Tom said, don't drive the control signals with direct logic. Some prescaler types have control interface that's directly compatible with TTL/CMOS, but I don't think the 12080 is. It appears to be pure ECL, so you never pull any inputs solidly down to Vee - they can go to Vcc for high, or left open for low, presuming they have built-in pulldown Rs. If the modulus is to be fixed, just hard wire according to the instructions. For logic-controlled modulus, you can pull high at low impedance, but only pull low via a high resistance, like tens of k ohms. Built in type pulldowns in ECL are typically 50-100 k. For the 12080, it looks like it would be simple to use PNP Qs to pull high to Vcc, and just put them in cutoff to let the ECL inputs pull low.

Ed


Re: 7L5 dot frequency reset bug - any clues or a fix?

Dan G
 

On Fri, Mar 19, 2021 at 12:52 PM, Richard Steedman wrote:

Dan, did you ever get round to trying your proposed fix of increasing the
C841/R841 time constant?
Hi Richard,

Good timing, and thank you for reminding me! I have not had occasion to
open the 7L5 since my last post on this topic, but, as it happens, I am just
now waiting for replacement parts for my L3 module to arrive from Europe.
I expect them to arrive in the next week or two. I will need to do a partial
re-calibration after the replacement, so it will be a perfect opportunity to
give the C841/R841 modification a try.

I will post my results here.

I can confirm that the 7934 mainframe also has the
issue. See two photos [here](https://groups.io/g/TekScopes/album?id=262040)
of the >1s delay after power-on before TS1 pulses appear. I suspect the issue
affects any mainframe using a readout system newer than the original analog
ROM board (e.g. microprocessor for the 7854 and EPROM-based board for 79xx).
I suppose these days one could also whip up a fix using a PIC to drive TS1
pulses into the serial clock input shortly after power-on and then get out the
way to allow option circuitry to take over.
Thank you for posting those photos. They provide a valuable data point, as I
had always assumed that this problem is specific to the 7854. By the way, it
is nice to see a 7623A in action. I have recently replaced a failed CRT in mine,
and it is now a real pleasure to use.


dan


Re: Changing out GR874 connectors +Printact relays

Stephen
 

On Sat, Mar 20, 2021 at 04:48 AM, Charles wrote:


I do too...
Yes, I think they look pretty cool.

Besides that, I have a working S-1 and S-2 sampling head with 874 connectors.
It looks like a delicate operation to put an N connector on the front of
either...
Indeed. At the end of the day, I decided I don’t want to have to mess around with them and leave them alone. I neither need the hassle, nor do ai want to have to deal with the possibility of ruining something for good.


Re: OT: MC12080 prescaler chip weirdness

Ed Breya
 

Is this a deal where you're just adding the 12080 to an existing board in the counter, or are you building the whole prescaler from scratch? Also, what frequencies and input levels are you using to test it with? The 12080 should work just fine if you apply it according to the datasheet, and have the right RF/HF environment around it. RF prescalers like this one must be AC coupled, and have a minimum cutoff frequency depending on the coupling cap size, and need sufficient amplitude and edge speeds to get proper operation. If the signal input isn't right, you can get strange results, and it can self-oscillate when the signal is not present or too small. Odd things can happen if you overdrive it too. Also, don't overlook the bypass caps - besides good supply bypassing, one is needed on the unused differential input.

Ed


Re: OT: MC12080 prescaler chip weirdness

Tom Lee
 

That is a very fussy chip. The most common error is to drive the control signals with TTL level signals. That won't work reliably. They have to be very close to the rails. I don't remember the specs any longer, but IIRC you have to be within a diode drop of the positive supply, and the signals have to be clean. And, of course, the input signal has to be clean as well.

HTH.

Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 3/20/2021 10:46, Michael Dunn wrote:
A Fluke counter I’ve been fixing up and adding homebuilt options to is missing the prescaler option. The vast majority of current chips seem to be binary, so, short of also dividing the reference clock, I decided to use a decade divider, an NOS MC12080 ÷10/20/40/80 chip.

Funny thing is, instead of dividing by 10, it’s dividing by 2! The chip internals consist of a fixed ÷5, followed by a programmable ÷2/4/8/16 stage. It’s like the ÷5 isn’t there, or is bypassed.

After some searching, I found a few other people bemoaning this exact same behaviour. So…at least I’m not crazy. Anyone here experienced something similar?

Gotta wonder what’s going on. Is there some sort of flaw in the chip design that leads to this failure mode? Was it a custom version? Hmm…

md








Re: 7A16A high frequency compensation.

Albert Otten
 

Hi Max,

My 7A16 (not A) manual shows a picture. The 7A16A performance is the same or better I guess.
I did the same setup with PG506, 7854 and "as is" 7A16A, Nice smooth step with rise time 1.55 ns, followed by just one overshoot 6.5% and one undershoot 3.5%. After this negligible aberrations from flat. With a 7A19 rise time was 1.1 ns.

Albert

On Sat, Mar 20, 2021 at 01:01 AM, unclebanjoman wrote:

Moreover, in the manual there is not even a photograph of some typical
waveform that can be used as a reference. Does anyone know where to find a
screenshot of a typical 7A16A step response?


Re: How to troubleshoot a faulty 7B92A?

Dan G
 

On Sat, Mar 20, 2021 at 07:16 AM, Thierry Delaitre wrote:

U820 - Sweep control IC
- Pin 6 (auto delay) is 0.5V ; strange ?? other side of the R828 resistor
(180K) is 14.7V
- Pin 7 (trig D) is 0.5V
U820 contains comparator and discharge circuits on pins 6 and 8.

U820 allows C828 to start charging when it stops receiving trigger signals.
That is how it eventually reaches free-run in AUTO mode.

Your pin 7 being low suggests that your TRIG'D light is on. Is that correct?
It would explain why pin 6 is low, and why you never reach free-run mode.

If your 7B92A is still in the vertical slot, set for AUTO, AC, INT, then there
should not be any trigger signals, and the fact that U820 is in triggered mode
is suspect.

- Pin 8 (hold off timing) is 0V ; strange? according to the schematic there is
a pull-up resistor to the 15V line
Pin 6 and pin 8 cannot be reliably measured with a DMM, as they both
normally have positive-going ramps, and should never get much higher
than +5V. You will need to look at them with a 10X high-Z probe.
(Remember to use an IC probe tip adapter on your probe, or else
be extremely careful not to let the probe tip slip and short adjacent
IC pins. I find that it is usually safer to probe at some other location:
R828 for pin 6, R871 or R872 for pin 10, R834 for pin 8.)

U820 allows hold-off capacitors to start charging at the end of the
sweep, so if pin 8 is stuck at 0V DC, then U820 may think the sweep is
still in progress, or it may have never received a HOLDOFF START pulse
on pin 16.

- Pin 10 (hold off) shows a 4V DC voltage (no sweep)
- Pin 17 (trig disable) is 0V
- Pin 18 (lockout) is low
- Pin 19 (auto mode) is low as it should for auto triggered
Are pins 10 and 8 both constant DC, or is there a waveform visible with
a 10X probe?


dan


OT: MC12080 prescaler chip weirdness

Michael Dunn
 

A Fluke counter I’ve been fixing up and adding homebuilt options to is missing the prescaler option. The vast majority of current chips seem to be binary, so, short of also dividing the reference clock, I decided to use a decade divider, an NOS MC12080 ÷10/20/40/80 chip.

Funny thing is, instead of dividing by 10, it’s dividing by 2! The chip internals consist of a fixed ÷5, followed by a programmable ÷2/4/8/16 stage. It’s like the ÷5 isn’t there, or is bypassed.

After some searching, I found a few other people bemoaning this exact same behaviour. So…at least I’m not crazy. Anyone here experienced something similar?

Gotta wonder what’s going on. Is there some sort of flaw in the chip design that leads to this failure mode? Was it a custom version? Hmm…

md


Re: TDS544A with strange display #photo-notice

Siggi
 

On Fri, Mar 19, 2021 at 6:41 PM durechenew via groups.io <durechenew=
yahoo.com@groups.io> wrote:

Some news, but not what you may expect.
As there were some doubts (and I agree, for good reasons), I opened the
display area again; soldered two wires to shutter connections - totally
random, I have no idea for which colors and I believe it's not relevant.
Shutter connector in normal place, put everything back and started the
scope. Here is the moment to say, for Siggi, that drivers for the shutter
are indeed powerful, initially designed to drive (servo) motors at 20kHz,
max 0.5A DC.
OK, see pictures 5 to 8 in the album.
Synchro signal on Ch1, frame, as I said before, around 17 ms (by signal I
mean waveform).
Picture 5: on Ch2 (should be green but, at low light, camera doesn't make
much of a difference between colors) is signal from output of driver for
one of the shutter's colors.
Picture 6: same signals, different timing.
Picture 7: same as 6 but signal is displayed on Ch4, not Ch2. Some
vertical vectors are obviously of different color (naked eye sees clear
red). If Ch4 light is OFF (pressing Ch1, for example) signal is all blue
(no red vectors).
Picture 8: Same as Picture 6, different shutter channel ( different driver
output/color).
Conclusions:
1. Shutter works fine; period of signal, roughly 370uS or so (just to
have an idea how often the shutter refreshes the colors - definitely not
line frequency). As I don't have the pair signal for the same color I
cannot say if they are really opposite; it may be that some time they are
not (and that color is not ON), depends how the control signals come from
the memory.
The shutter plot thickens.
For the record, I agree with you that the artifact you see is not coming
from the shutter. Nonetheless, I've always been curious to understand how
it works, and sadly I don't think your data is conclusive.
Grousing through the LCD driver board yet again, I see the following:

- The LCS_CLK input to the shutter board is the horizontal line clock.
It's derived from the ~HSYNC signal from the CPU/Display board.
- The LCS_CLK signal then goes to a 74HC4040, a 12 bit ripple counter.
- The first output of the ripple counter used is Q2, which is then
LCS_CLK/4.
However, both edges of this signal are used to latch the output from the
EPROM, alternately into U505 and U510, so the fastest possible differential
output change from those two would be LCS_CLK/2, or every other line.
- The distribution of these signals to the output drivers is curious.
The top and bottom output drivers take signals from one or the other
octal latches, but the middle one takes alternate signals.
- The counter is reset on an ~FSYNC/VIDEO signal that comes from U2011
on the CPU/Display board (A11<24>, 5C),

... time passes ...

Looks like we're back to color-per-frame, rather than color-per-line.
Presumably the ~FSYNC signal is asserted every 3 or 4 frames, to reset the
LCD shutter counter to start again.
Is the line frequency of the CRT then really that high? It wouldn't serve
any purpose that I can see?

Presumably the complicated shutter driving machinery is about generating 0V
DC for each shutter on average. I don't understand why it needs to be
driving at line frequency/2, as it looks like it's really just switching
color shutters between frames. I also don't understand why it needs 12
lines - maybe each shutter is driven by 2 rows by 2 cols?

2. Some waveform information for Ch4 is incorrectly displayed when a
different color (driver output for red) is ON (and on condition that light
of Ch4 is also ON). This back the same conclusion it was suggested before:
Between the point(s) of split from VGA the signal path toward Video for CRT
is corrupted. Still to be discovered where and how...
Yups, I agree. On my TDS784D, the selected trace is intensified, supporting
the hypothesis that an intensity bit is one of the five bits going to the
TLC34075.
Happy hunting!


Re: How to troubleshoot a faulty 7B92A?

Thierry Delaitre
 

have also checked at the collector of Q412 and there is no sweep

T.


Re: Changing out GR874 connectors +Printact relays

 

I do too... and some years ago I bought a large bagful of GR adapters and cables. So I'll stick with them ;)
Besides that, I have a working S-1 and S-2 sampling head with 874 connectors. It looks like a delicate operation to put an N connector on the front of either...


Re: Question about Jared's TM500 tester

Jared Cabot
 

The front panel has 3 parts.
Rear-most metal plate (1mm aluminium IIRC)
Then the center plastic piece, consisting of one of either the blank panel from a blank plugin module, the repurposed panel from the scrapped module you may be using, or the 3D printed piece.
Then finally the supplied white Front Panel PCB on the very front.

The 0.05mm resolution for positioning is mainly due to the 3/4" spacing between binding posts an the module dimensions being converted to mm. Just get as close as you can and it should be fine.
As for the drill sizes, they are just what the data sheet for the respective parts said to use. :)

For anyone with a CNC machine, I can provide DXF's of the front panel if needed too.

Also, I haven't tried 3D printing the plastic panel yet, but it should work fine as it's a pretty simple shape, just let me know if you do print it so I can modify it if required.


Re: Changing out GR874 connectors +Printact relays

Stephen
 

On Sat, Mar 20, 2021 at 02:33 AM, Dale H. Cook wrote:


Walter Shawlee wrote:

In our lab, virtually all high frequency connections are N connectors
In my shop virtually all of the connectors from VHF up atr GR 874 connectors,
because most of that equipment is GR.
I haven’t received it yet, but I decided to leave the GR874 connectors alone as long as I can. If someday I’m having problems, I’ll change them. I actually like the way they look.


Re: Question about Jared's TM500 tester

Michael W. Lynch
 

David,

Is it intended that the front panel should have three parts (metal back
panel, 3D printed front panel, front panel supplied with kit), or is this an
either/or case?<<
The original and the printed part supplied has provisions for 3 piece construction; the front panel, the plastic frame and the rear aluminum plate (which you must fabricate). I used a shortcut method for my construction, where I printed the plastic frame at "full thickness" and eliminated the need for the separate aluminum plate. This also simplifies the 3D printing as the back side is no longer recessed, the part prints flat. This "experiment" worked out fine. I can provide the STL for this printed part with photos of the results and notes for printing.

PS I see the drill holes for a metal front panel are 0.1mm step sizes - is
this because they are conversions from imperial drill sizes?<<

I am sure that you are correct about this.

Sincerely,
--
Michael Lynch
Dardanelle, AR


Re: Changing out GR874 connectors +Printact relays

Dale H. Cook
 

Walter Shawlee wrote:

In our lab, virtually all high frequency connections are N connectors
In my shop virtually all of the connectors from VHF up atr GR 874 connectors, because most of that equipment is GR.

6741 - 6760 of 187118