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Re: Beware of old AntiStatic foam

David Slipper
 

Nasty!!  I wonder what other time-bombs are awaiting us!?

I'll certainly be checking my stock of bits and spares.

I always assumed that a famous brand of NiMh batteries were supposed to be leak proof - Hah! I nearly lost a pair of nice walky-talkies and a multimeter that way, so now cells get removed from rarely used items and I make a point of checking torches and the like regularly.

Sadly not surprised at anything these days,
Dave

On 21/03/2021 13:07, - wrote:
Well, this thread just showed up on EEVBlog. This is exactly the kind of
damage that I used to see happen to IC and to TE accessories that were
stored in the old antistatic foam.

<https://www.eevblog.com/forum/chat/beware-of-old-antistatic-foam/?topicseen



Re: OT: MC12080 prescaler chip weirdness

tekscopegroup@...
 

Perhaps this item might be of use, or at least a good guide as there is a schematic posted as well. No relation to listing.

https://www.ebay.com/itm/153648250450


Beware of old AntiStatic foam

-
 

Well, this thread just showed up on EEVBlog. This is exactly the kind of
damage that I used to see happen to IC and to TE accessories that were
stored in the old antistatic foam.

<https://www.eevblog.com/forum/chat/beware-of-old-antistatic-foam/?topicseen


Re: PS 5010 troubleshooting (no negative, erratical display)

 

Hi Steve,

interesting... I like this supply and use it quite often. You can even use it to drive and control a transistor's base!

When I first used these PS5004 I thought the display was digitally controlled, but since it was able to show a negative voltage or a bit above 20V I began to doubt. And indeed.

For the alignment I was referring to the fact that alignment of the same 3 pots (zero, fine and coarse) is done several times in different chapters.

FIRST: §2 "Full Scale (R2043) and Fine Span (R2044) Presets"
This comes right after §1 coarse reference adjust (the switch).
A note says this should only be done when the reference IC has been changed. It consists of aligning the pots for a voltage of 6,550 volts.

SECOND: §4 "Zero Output Adjust (R3062)"
There is an instruction of how to connect the PS5004 to the voltmeter that I did not really understand. It says
"Connect the PS 5004 OUTPUT to the digital voltmeter input using a bnc cable and a pair of bnc-to-banana plug adapters. The shield side of the bnc is connected to the PS 5004 OUTPUT terminal, and the voltmeter Low input. The voltmeter guard is driven by the Low input. Connect the patch cable from the PS 5004 OUTPUT terminal to the ground post connector."
Anyone else who finds that substandard in terms of clarity? It looks like a cut&paste mess to me, but did Tektronix already have text processing these days?

THIRD: §§5&6: "Full Scale Adjust (R2043) & Fine Span Adjust (R2044)"
This time you align the same pots as in §2 with reference to the real output (in CAL mode). The pots had to be turned quite a bit (plusminus 2 revolutions) to get the right voltage here. But that means that the preset alginment in §2 was useles... No?

FOURTH: §7 "Full Scale (R2043), Fine Span (R2044), and Zero Output (R3062) Final Adjusts"

This time all three pots are re-aligned with reference to the real output, with the unit in normal RUN mode (not CAL mode). Again, I wonder what the alignments in §§2, 4, 5 & 6 were good for. I could have started the whole alignment right here, skipping the previous steps, couldn't I?
Perhaps not because these alignments interact somewhat, so you would have to repeat the steps in §7 several times if the previous steps haven't been done.

The next steps are for alignment of the DMM and current output. I always end up with a quite precise power supply, the DMM usually shows -0,0001 when at minimum. But thats well within specs...

cheers
Martin


Re: chinese witches hats for old probes help

Stephen
 

While I was looking for hook tips for a pair of P6105, I’d read a few reports on these Chinese probe tips. Some sais they worked fine and are good, while some stated the exact opposite... They said they were very fragile and broke easily.
Please let us know what you think when you get them.

Cheers


Re: 7A16A high frequency compensation.

Albert Otten
 

Yeah, it's that aberration "up" in the 10 ns point I can not eliminate. I
didn't think it was the cable. I generally observe the "dribble up"
phenomenon. Do you think is the cable ?
I also have a 7A16 (not A) but I don't think it has that reflection. Maybe
because of the smaller bandwidth?
The 7A16A input causes reflection anyway. When the cable impedance doesn't match the PG506
output impedance then the reflection from there can be observed at the CRT after twice the cable travel time.
I wouldn't bother too much about not perfectly flat, in my opinion the step response is very nice.
(How did you calibrate the PG506?)

What do you think about the trim pot not shown in the schematics? May it be
the very latest revision? I did not find more recent schematics.
That must by R436 in the LF filter leg between pins 2 and 3 of U450. Has always been there according to parts list.
Is present in my 1973 unit.

Albert


Re: chinese witches hats for old probes help

dave G8SFU
 

They were slip on hook tips I was looking for.

Thanks to all who replied about the Chinese witches hats.
I ordered a pack of six so will report back in a few weeks, if they come, if they fit, and if they actually work.
Dave   g8sfu

⁣Sent from BlueMail ​

On 11 Mar 2021, 15:11, at 15:11, Torch <tekscopes@verhey.org> wrote:
Are these the screw-on tips, or the slip-on tips?



Re: More fun with avalanche pulsers

Chuck Harris <cfharris@...>
 

A rule of thumb:

If a toroid is painted all over, it is powdered iron.
If a toroid is black, but not painted, it is ferrite.
If a toroid is covered with a form fitting plastic case,
it is a ribbon steel.

-Chuck Harris

Charles wrote:
...An unknown green one saturated too soon and required very few turns - must be an
iron powder one with high permeability. Finally a 3/4" yellow core (72 turns to get
to 250 uH, that was tedious) worked at the original frequency and didn't cause
trouble unshielded :)


Photo Avalanche pulser breadboard 2. Output at 5 ns/div, 2 v/div. updated #photo-notice

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

The following photos have been updated in the Sampling with 3S2 album of the TekScopes@groups.io group.

By: Charles <charlesmorris800@...>


More fun with avalanche pulsers

 

I rebuilt the pretrigger and avalanche pulser onto one tightly packed board, and added SMA connectors for the output and the charge line to allow fast change. BNC for the ~65 volts from the power supply.
I'd discovered a GR 874 shorted termination in my bag of adapters, so I spent some time playing with shorted lines and reflections. Then I wanted to make a smaller toroid for the power supply - the junkbox one was (relatively) huge and wouldn't fit in a compact box. The Tek 130 LC meter got a workout figuring out AL for various cores. I was able to make a half-inch core work (think it was a T50-43) but the clock frequency required was high enough that it was getting into the unshielded pulser sitting next to it. An unknown green one saturated too soon and required very few turns - must be an iron powder one with high permeability. Finally a 3/4" yellow core (72 turns to get to 250 uH, that was tedious) worked at the original frequency and didn't cause trouble unshielded :)

A better RG-58 cable (SMA to BNC) worked well as a charge line, whereas a similar RG-174 cable was a droopy disaster. Putting the cheap BNC RG-58 cables on the end (with a barrel adapter) was also unsuitable. The "better" cable is too short by itself to be useful for risetime measurements on slower scopes, since the flat top is only about 3.5-4 ns long. As mentioned in the "3T77A tunnel diodes (again)" thread, I will try RG-402 (.141 semirigid) before calling it good enough. I doubt I have the skill or patience to build a really fast pulser to push the S-2(72 ps) or especially the S-4 (25 ps) to its limits.

Added a couple pics to the Sampling with 3S2 album of the breadboard so far and the pulse output.


Re: How to troubleshoot a faulty 7B92A?

Dan G
 

On Sat, Mar 20, 2021 at 04:19 PM, Thierry Delaitre wrote:

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.
This is definitely abnormal. When switching from AUTO to NORM, the TRIG'D
light should flash briefly, but then go out. This suggests that the sweep timing
capacitors did not charge, or that sweep end detection circuits are not working.
It also explains why the hold-off and auto ramps are stuck low.

As Mark suggested, if you have not already done so, make sure all mechanical
switches, especially S490, operate correctly.

I would also look at pins AV (Aux Gate signal) and AR (Main Gate signal)
to see whether the plug-in thinks it has started a sweep or not. These
are normally square pulses, but yours are probably stuck. Whether they
are stuck high or low may provide a clue as to what is wrong.

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
This now makes sense given your TRIG'D explanation above.
While this is not what these signals should look like, I think it is the result
of problems earlier in the sequence of events. They may be ok once
the plug-in is able to complete the sweep ramp.

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


dan


Re: 1S1 on ebay

Sean Turner
 

I received it...seller did a great job packing it. It appears to be functional, certainly moreso than my prototype one. I think it will need some caps done as well, but having a mostly working one will be a massive help troubleshooting!

Sean

On Sun, Mar 14, 2021 at 06:35 PM, Sean Turner wrote:


Guilty as charged. LOL! I need another one so I can hopefully have a reference
to compare things I find in my prototype 1S1 to.

Sean
Hide quoted text ( #quoted-182801618 )

On Sun, Mar 14, 2021 at 04:17 PM, Charles wrote:



So who got the 1S1... there were 8 bids and it went for $104!


Re: PS 5010 troubleshooting (no negative, erratical display)

ditter2
 

Hello Martin,

On the PS5010, my reference to the voltage and current ramping is the programming that takes place in the current and voltage limit DACs on a user request through front panel ON/OFF switch, or through remote control. This action takes place in both ON > OFF and OFF > ON operations. If you are monitoring the DAC outputs with a scope when the Output is toggled, you will see this programming action. It is to protect the output relay. Because the supply will normally go into CC mode during this transition, the software does not monitor the loop status during this time, to prevent reporting of the mode change.

If you need to draw a small amount of current to get regulation, then the minimum load is not sufficient to keep the output regulated. This could be either in the supply itself, or possibly (??) C-E leakage around the pass transistor in the mainframe. That would explain different amounts of the effect in different mainframe slots.

For the PS5004 – I designed all of it. For some fun, get a schematic and quickly try to find the precision 16 bit DAC needed to support the output resolution. If you are looking for a large “brick”, you won’t find it. 16 bit DACs were available at the time, but cost about 2.5 times the proposed manufacturing cost target for the entire built and tested instrument. The DAC I designed is a gated charge pump, using simple digital counter logic to set the duty factor of the current gate clock. BTW, Sony independently came up with the same idea for the 16 bit DACs needed in CD players about the same time.

I believe the part of the cal procedure you are referring to asks you to set output V to max, then back down one count (If my memory is correct – that was designed 40 years ago.) What you are doing is setting the full scale of the fine span of the DAC. Rather than take the full 16 bit resolution in one span, there are two charge pumps, scaled – I believe 200 counts (Each is 8 bits, the fine is 1/200th the coarse. They don’t map 1:1 with the digital pot coarse-fine range). Since calibration requires use of the digital knobs to set ranges, and the display is a volt meter measuring the measured output (not the programmed value as in the PS5010), the only way to set known values with the knob is at the extremes. So “0” is easy to set – turn both knobs to the left several turns and you can calibrate out the offsets in the system. Turn either or both knobs to the right several turns and you are at full scale – it is now possible to set the full span gain of the coarse current pump. Turning only the fine control down one “click” reduces the coarse stage DAC count by 1, and sets the fine DAC to is max scale. Now the user can calibrate the full scale of the fine . The order might not be the same as what I wrote in the cal procedure 40 years ago, but the process is the same.
Steve


Re: 7A16A high frequency compensation.

unclebanjoman
 

Hi Albert,
thanks!
Yeah, it's that aberration "up" in the 10 ns point I can not eliminate. I didn't think it was the cable. I generally observe the "dribble up" phenomenon. Do you think is the cable ?
I also have a 7A16 (not A) but I don't think it has that reflection. Maybe because of the smaller bandwidth?

Anyway, now the response of my 7A16A is much better than before. Initially was horrible. I think the previous owner tried to calibrate it but then gave up.
Really a tour de force: more than 4 hours fiddling the pots!

What do you think about the trim pot not shown in the schematics? May it be the very latest revision? I did not find more recent schematics.

Max


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

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