Date   

Re: Tek 492AP: problems with 2072MHz and 829MHz inputs

Ed Breya
 

Just noticed there's a whole 492 "not working" on ebay for $799 BIN. It does light up but the display is all messed up. From the pictures it appears to say options 1 2 3 on a tag. This may be a good possibility to make one SA out of two, and have plenty of spare parts and extra stuff to fool around with. May be worth a look, and contact seller for more info.

Ed


Re: Small Parts for 2400 Series?

 

I measured the one on my parts scope.  Its 0.25 inch with about 1/8 inch head.  I believe the specification is 6-32, 0.25 inch, pan head torx. 

From: "Barry n4buq@... [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Monday, April 11, 2016 9:39 AM
Subject: Re: [TekScopes] Small Parts for 2400 Series?

  I see that seller has the TORX screws. Does anyone know the proper length for that particular screw (right rear A1 board as viewed with the scope upside-down from the front)? I think its a 3/8" but not sure. I hate too have to buy 25 of them to start with but would really hate it to get the wrong length...

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "machine guy @Mac [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Friday, April 8, 2016 3:33:50 PM
Subject: Re: [TekScopes] Small Parts for 2400 Series?

I bought my 6 foot, right angle  power cord from Monoprice,  held in place
with a P-clamp cable clamp from my local hardware store.  I bought the torx
head screws on eBay from Albany County Fasteners.  The washers are captive
washers from my local hardware store.  They are  like OEM without the
problem of finding decent used ones.

From: "Barry n4buq@... [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Friday, April 8, 2016 1:34 PM
Subject: Re: [TekScopes] Small Parts for 2400 Series?

  I had searched for a Tektronix cable and wasn't finding much. Was hoping
  for an OEM but that's not terribly important. I'd like one with the
  little clip on the plug end so it will stay put when wrapped. I notice
  the one from Farnell does indeed have that.

I may get lucky and find one at the second-hand stores around here as well. I
need to make a pass through them as well. Power cords are pretty plentiful
and very inexpensive at those places.

Thanks Malcom,
Barry - N4BUQ

----- Original Message -----
From: "Malcolm Hunter malcolm.r.hunter@... [TekScopes]"
<TekScopes@...>
To: TekScopes@...
Sent: Friday, April 8, 2016 1:24:32 PM
Subject: Re: [TekScopes] Small Parts for 2400 Series?

On 8 April 2016 at 19:14, Barry n4buq@... [TekScopes] <
TekScopes@...> wrote:

Also, would like to get a right-angle power cable and its associated
clamp/screw. Mine came with a standard cable which makes it inconvenient
to
store upright.

​You can get the power cable from Farnell or Ebay (e.g. #​331823750116).

Malcolm


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Re: Tek 492AP: problems with 2072MHz and 829MHz inputs

Ed Breya
 

Yes, you want a true multi-section coaxial LPF there for best performance. There should be some available at the usual places. The common ones are about 4-6" long by 1/2" diameter, with SMA connectors. The most common brands I recall from that era are K&L and RLC. Whatever you get will have to fit the limited space on the RF deck, so choose wisely, and consider the connectors etc. You may be able to find an actual one from a Tek SA, since they're fairly common too.

Another thing to consider is to maybe look for a junker one of the 49X series that happens to have the stuff you need - it may be cheaper than buying all of it separately.

Ed


Re: Tek 492AP: problems with 2072MHz and 829MHz inputs

Tom Gardner
 

On 11/04/16 18:50, edbreya@... [TekScopes] wrote:

I think you will need a few more pieces if you want to go back to a "normal" 492-ish SA. You should study the manual and circuits for that model and the 494 for comparison - the RF block diagram should tell most of the story. If this one is like the 494, there should be a couple of coaxial relays to route the input to the mixer through the LPF, or the preselector, and maybe an extra 3 dB attenuator, as I recall. And the associated coaxial cables, driver circuitry and wiring, etc. The low band of course is then only up to 1.8 GHz, but the IF feedthrough problem will be gone.

If you mostly need to use the low end of the low band, you can put an external LPF up front. I think the original one for that architecture cuts at 1.8 GHz, and is pretty far down (80-100 dB?) by 2072 MHz, for IF rejection. Even a 2 GHz one may be pretty good for this. The 1.8 and 2 GHz LPFs are probably quite common on the used market - likely since they were used in so many SAs for exactly this purpose.

If you really only need that low end, it would be best to put the LPF inside behind the step attenuator, where it normally would go, for better isolation. Then if you ever do need the higher bands, you can rehook it or add the optional parts.
Understood and accepted. I'd included most of those components in my $500 guesstimate, different hardline coax excepted.

I had a quick look at the Minicircuits LPFs but they aren't as good as you indicate the Tek part is. I suspect the Tek is a rod-and-bead filter, unlike the Minicircuits filter.


Re: Tek 492AP: problems with 2072MHz and 829MHz inputs

Ed Breya
 

I think you will need a few more pieces if you want to go back to a "normal" 492-ish SA. You should study the manual and circuits for that model and the 494 for comparison - the RF block diagram should tell most of the story. If this one is like the 494, there should be a couple of coaxial relays to route the input to the mixer through the LPF, or the preselector, and maybe an extra 3 dB attenuator, as I recall. And the associated coaxial cables, driver circuitry and wiring, etc. The low band of course is then only up to 1.8 GHz, but the IF feedthrough problem will be gone.

If you mostly need to use the low end of the low band, you can put an external LPF up front. I think the original one for that architecture cuts at 1.8 GHz, and is pretty far down (80-100 dB?) by 2072 MHz, for IF rejection. Even a 2 GHz one may be pretty good for this. The 1.8 and 2 GHz LPFs are probably quite common on the used market - likely since they were used in so many SAs for exactly this purpose.

If you really only need that low end, it would be best to put the LPF inside behind the step attenuator, where it normally would go, for better isolation. Then if you ever do need the higher bands, you can rehook it or add the optional parts.


Re: Tek 492AP: problems with 2072MHz and 829MHz inputs

Tom Gardner
 

On 11/04/16 16:59, 'Thomas S. Knutsen' @la3pna [TekScopes] wrote:


2) add the essential components, probably $500, problems with calibration
and/or
getting everything working with the firmware
I think you can find the things you need to add option 1 to the analyzer on
ebay.
Yes; I would have to check if there is any significant difference between driver board 670-5552-03 and -05.

Adding option 1 is just getting the YIG filter and driver, then is just
flipping the correct DIP switches to get it to recognize it.
I haven't found any indication of the relevant switches in any of the documents I've seen. From that I have inferred, correctly or not, that the driver's presence is auto detected. Without that I would be reduced to randomly flipping switches, and there are too many combinations for me to feel comfortable with that.

My firmware is v6.0/1.1 (not 4.6, doh).

3) ensure the first mixer isn't subtly damaged, and replace if necessary

Given that the first mixer is mixing, is it working as well as can be
expected
or has it been subtly borked?
What level of spurious responses would be expected in a working/damaged
first mixer?
Page 15: http://www.ke5fx.com/49x_notes.pdf
That should cover most anything about the 1. mixer.
Unfortunately it doesn't indicate the acceptable/unacceptable level of spurs, and I don't have sufficient experience to understand them. If mixers are either OK or dead, then I don't have a problem.


Re: Tek TDS694C advice pls

mosaicmerc
 

Seems that heat sinking the TDS694 trigger IC's is a good idea. Kinda like the U800 in the 24xx series.

Ancel


Re: Tek 492AP: problems with 2072MHz and 829MHz inputs

Thomas S. Knutsen
 


2) add the essential components, probably $500, problems with calibration
and/or
getting everything working with the firmware
I think you can find the things you need to add option 1 to the analyzer on
ebay.
Adding option 1 is just getting the YIG filter and driver, then is just
flipping the correct DIP switches to get it to recognize it.


3) ensure the first mixer isn't subtly damaged, and replace if necessary

Given that the first mixer is mixing, is it working as well as can be
expected
or has it been subtly borked?
What level of spurious responses would be expected in a working/damaged
first mixer?
Page 15: http://www.ke5fx.com/49x_notes.pdf
That should cover most anything about the 1. mixer.

Br.
Thomas.












__


Re: Tek 492AP: problems with 2072MHz and 829MHz inputs

Tom Gardner
 

I now understand what's happening much better, although still imperfectly. Thanks to all those that have contributed their thoughts, and now I'd be grateful for any insight into the question the last paragraph.

The key issue is that all textbooks describing SAs show a block diagram including a preselector or low pass filter depending on whether a high IF or low IF is used. My 492 has neither, since those essential components are an "optional extra" (option 01).

Given what I paid for the SA, I'm not complaining. But quite frankly I expected more from "old school Tek", and I can only assume that the sales department had to advertise something (anything) under an arbitrary price limit ("from only $4999"). All other options are, reasonably, to add non-essentials or delete essentials.

It seems I have three ways forward:

1) use it "as is", which is less useful than I was expecting, albeit still useful

2) add the essential components, probably $500, problems with calibration and/or getting everything working with the firmware

3) ensure the first mixer isn't subtly damaged, and replace if necessary

Given that the first mixer is mixing, is it working as well as can be expected or has it been subtly borked?
What level of spurious responses would be expected in a working/damaged first mixer?


Re: 465 oscilloscope problem

Siggi
 

Hey Kevin,

I have the manual - the 55V power supply isolation procedure is on page
8-57.

The troubleshooting tree for the 55V supply is on page the very next page,
8-58.
This is a great procedure, as it discriminates between a short on the
regulated 55V rail versus trouble in the rectifier or other trouble in the
unregulated supply - without disconnecting or isolating anything. Sadly I
think we're beyond that point, as you've jumped the gun a little and
removed some caps from your scope....

So, please confirm that your 0.9Ohm reading is from TP1536 to ground?

Siggi

On Sun, 10 Apr 2016 at 18:01 Sigurður Ásgeirsson <siggi@...> wrote:

On Sun, 10 Apr 2016 at 17:35 'Tewell, Kevin' tewell.ka@... [TekScopes]
<TekScopes@...> wrote:

The serial number is above 250000
Excellent I see you've noted this before and I missed it - such are the
perils of the centithread :).
I've gone ahead and bought the relevant manual from Artek so that we can
be on the same page - so to speak.

[Non-text portions of this message have been removed]


Parting out: two Tektronix 528 NTSC waveform monitors

Brad Thompson <brad.thompson@...>
 

Hello--

I'm parting out two Tek 528 NTSC waveform monitors which have sustained front-panel damage (the CRTs are intact).
Given that parts-only units are offered for $20.00, and working units are offered for around $50.00 (or best offer), and
ignoring the $200.00 (what are the sellers smoking?) units available on the auction site, it's unlikely that any
demand exists for harvested parts from these two 528s.

But I thought I'd ask, just in case someone needs something specific.

73--

Brad AA1IP


Re: Small Parts for 2400 Series?

n4buq
 

I see that seller has the TORX screws. Does anyone know the proper length for that particular screw (right rear A1 board as viewed with the scope upside-down from the front)? I think its a 3/8" but not sure. I hate too have to buy 25 of them to start with but would really hate it to get the wrong length...

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "machine guy @Mac [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Friday, April 8, 2016 3:33:50 PM
Subject: Re: [TekScopes] Small Parts for 2400 Series?

I bought my 6 foot, right angle  power cord from Monoprice,  held in place
with a P-clamp cable clamp from my local hardware store.  I bought the torx
head screws on eBay from Albany County Fasteners.  The washers are captive
washers from my local hardware store.  They are  like OEM without the
problem of finding decent used ones.

From: "Barry n4buq@... [TekScopes]" <TekScopes@...>
To: TekScopes@...
Sent: Friday, April 8, 2016 1:34 PM
Subject: Re: [TekScopes] Small Parts for 2400 Series?

  I had searched for a Tektronix cable and wasn't finding much. Was hoping
  for an OEM but that's not terribly important. I'd like one with the
  little clip on the plug end so it will stay put when wrapped. I notice
  the one from Farnell does indeed have that.

I may get lucky and find one at the second-hand stores around here as well. I
need to make a pass through them as well. Power cords are pretty plentiful
and very inexpensive at those places.

Thanks Malcom,
Barry - N4BUQ

----- Original Message -----
From: "Malcolm Hunter malcolm.r.hunter@... [TekScopes]"
<TekScopes@...>
To: TekScopes@...
Sent: Friday, April 8, 2016 1:24:32 PM
Subject: Re: [TekScopes] Small Parts for 2400 Series?

On 8 April 2016 at 19:14, Barry n4buq@... [TekScopes] <
TekScopes@...> wrote:

Also, would like to get a right-angle power cable and its associated
clamp/screw. Mine came with a standard cable which makes it inconvenient
to
store upright.

​You can get the power cable from Farnell or Ebay (e.g. #​331823750116).

Malcolm




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[Non-text portions of this message have been removed]


Re: 2465B U400 Availability?

n4buq
 

My replacement U400 arrived and I replaced the one in my 2465B. That took care of vertical issues. Also was able to properly get the scope into CAL mode and used CAL 07 to adjust vertical centering and height. Scope is getting better and better.

Still seeing "sparkle"/"jitter"/"whatever" in the display that I don't see in my 2445 so still wondering if I have other problems I've not found/fixed yet but at least some of the issues are resolved now.

Thanks,
Barry - N4BUQ

----- Original Message -----
From: "Barry" <n4buq@...>
To: TekScopes@...
Sent: Sunday, April 3, 2016 1:10:20 PM
Subject: Re: [TekScopes] Re: 2465B U400 Availability?

I finally got a chance to get back into the 2465B. Voltages are as close as
my Fluke 25 (old style 25) will measure. 10.00 shows 9.99 so not sure if
that's the meter (it isn't calibrated) but assume it's close enough - at
least not to do damage to anything. Other voltages showed in range. Ripple
- not so sure about (more about that below).

Swapped U400 with the one from my 2445 and the vertical compression seen
before does not present itself so I assume U400 is bad. Will be looking
into a replacement.

Regarding ripple measurement: When measuring (using the 2445), I don't
exactly see what appears to be PS ripple, but lots of low-level noise (when
viewed with LINE triggering). I assume that's CPU and/or other digital
noise. It presents itself as a band of about 5mV. Is this normal? I have
a 10x probe inserted into J119 and the ground clip attached to one of the
heat-sink fins on one of the Uxxx modules. I'd think this "noise" shouldn't
be getting back into the rails but perhaps it's normal (or, perhaps,
something wrong with the way I'm measuring it)?

One of the rails (I don't remember exactly which one and will have to check
again to find that out) exhibited a small "double blip" that appeared to me
like it's coming from a typical unfiltered full-wave bridge but it was only
a few mV. Not sure if that's normal but I think it was within tolerance.

A few more questions:

1. Is there a vertical centering adjustment for just the text? The top line
of text is very close to the top of the CRT and is equally displaced "up"
from the bottom. I looked in the manual for an adjustment for that but
didn't find one. There's a rather involved procedure for setting the
vertical centering but I think that's for the trace and perhaps not for the
text display and was hoping there was a simple way to get the text moved
down a few millimeters.

2. Text appears to "sparkle" or "jitter" slightly. When I say "jitter", the
text doesn't move around, but appears to be the result of a slow or noisy
refresh. Is this possibly normal due to the CPU being busier in this scope
than, say, the 2445, or do I have some other problem(s) I need to
investigate?

Thanks again,
Barry - N4BUQ

----- Original Message -----
From: "machine guy @Mac [TekScopes]"
<TekScopes@...>
To: TekScopes@...
Sent: Wednesday, March 30, 2016 3:44:21 PM
Subject: Re: [TekScopes] Re: 2465B U400 Availability?

You are right, it could be U400.  But I would try the other things first,
lol.  In Barry's case, he has a source for an alternate U400.  I would try
that AFTER verifying all voltages are in spec.  No need to damage the
alternative U400 with bad supply voltages.
I am waiting to hear that your "new" U400 corrects your problem.

From: "very_fuzzy_logic@... [TekScopes]"
<TekScopes@...>
To: TekScopes@...
Sent: Wednesday, March 30, 2016 3:21 PM
Subject: Re: [TekScopes] Re: 2465B U400 Availability?

  Two points:

Barry's 2465B and mine have very similar issues with non-linearity on ch1
and
ch2 but ch3 and ch4 OK. At least on my scope the power rails are ok for
voltage and ripple. I also checked the power supplies where they have
common
decoupling to U100 and U200 and so far have not found anything amiss. There
are threads here and elsewhere suggesting U400 as a possible cause and it's
price is consistent with it failing frequently! I haven't yet checked U400
bias current or the voltages on the channel select inputs.

Secondly, Barry has several noisy analogue controls, DAC stability could be
a
common cause. Do the y and t cursors move smoothly? If they don't then it
would be well worth checking the DAC output, there is setup procedure near
the beginning of the calibration section of the manual that puts the DAC
output on one of the DIP header pins and it responds to cursor movement -
should be a good test.

Meanwhile my replacement U400 has been stuck in transit for over a week en
route to the UK!

Roger #yiv2028227971 #yiv2028227971 -- #yiv2028227971ygrp-mkp {border:1px
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Re: Tek TDS694C advice pls

 

The truth is .... you only need one, namely the one for the channel that you use to trigger the 'scope. You may e.g. display CH4 and trigger on CH1.
IOW, moving the chips isn't necessary, just choose your channel.

Raymond


Re: Tek 492AP: problems with 2072MHz and 829MHz inputs

Tom Gardner
 

On 08/04/16 21:08, 'Thomas S. Knutsen' @la3pna [TekScopes] wrote:

With a lack of option 1 (preselector) you just use the identify (ident)
function to determine if its a real or false product you are seeing on the
screen for bands above 1.8GHz.
I now understand what that is and how it works.

Unfortunately it can only be invoked at <=50kHz/div, i.e. 500kHz across the
display. That makes some sense for narrowband signals, but I was hoping to use
the SA for wideband and/or ultra-wideband signals.


Re: Tek TDS694C advice pls

 

My S-4s have an annoying amount of blow-by so I prefer the S-1 and S-2
which are also repairable.

The 7T11 is one of the rare exceptions of a sampling oscilloscope
which can display a pulse edge without a pretrigger signal or delay
line.

On 11 Apr 2016 03:00:54 -0700, you wrote:

...

Classic sampling 'scopes are well suited to judging repetitive signals, including pulse edge shape. A 7000 mainframe with an S-6 or better yet, an S-4 vertical input head, provides 11 or 14 GHz BW. I prefer the S-4 mostly because it has an internal trigger pickoff, which is easier to work with and avoids distortion caused by extra (splitting) cabling if there's no separate trigger signal. Generally, because there's no delay line, for pulse work you need a pretrigger signal (or an accurate separate delay).

Using such a setup in a 7854 is a real treat.

Raymond


Re: Tek TDS694C advice pls

John Miles
 

I can't believe it, either, but... if the two chips aren't superfluous, why
does the scope work well (on all four channels) without them?



Lots of retired Tek engineers around this neck of the woods. Maybe I'll be
lucky enough to run into somebody from the group responsible for the TDS694C
at one of the local hamfests...



-- john, KE5FX



From: TekScopes@... [mailto:TekScopes@...]
Sent: Monday, April 11, 2016 4:25 AM
To: TekScopes@...
Subject: [TekScopes] Re: Tek TDS694C advice pls





Thanks for the link, John, I'll have a look over there.
I "strongly doubt" that what i said in the EEVBLOG thread about the 2
"superfluous" trigger chips is correct.

Apart from this problem, I find the TDS694C a very nice 'scope. Wish I could
repair the missing trigger channels OR trust the remaining two to go on
living...

Raymond


Re: Tek TDS694C advice pls

 

Thanks for the link, John, I'll have a look over there.
I "strongly doubt" that what i said in the EEVBLOG thread about the 2 "superfluous" trigger chips is correct.

Apart from this problem, I find the TDS694C a very nice 'scope. Wish I could repair the missing trigger channels OR trust the remaining two to go on living...

Raymond


Re: Tek TDS694C advice pls

 

They don't seem to run excessively hot.
Thanks for the link, John, I'll have a look over there.

There's no heat spreader or anything on top of these chips but they seem to have a solid metal tab underneath.
In my TDS694C, two of them were too hot to touch for even 5 seconds after operating for less than a minute,
hence my theory that the tab has come loose (bad/non-existent solder flow) or the chip has come loose inside, as per one of the theories on the infamous U800 in the 24X5 series.

In my TDS694C, trigger chips for CH1 and 2 don't get very hot. CH3 and especially CH4 do. CH3 has become intermittent, CH4 is dead now. I only got this 'scope very recently and I opened it up because of the trigger problems. Putting a heat sink on top helped a little for a while.
I don't think that a non-cooling-related problem caused these chips to heat up in the first place.

None of the other chips on the acquisition board get very hot. A small fan while open suffices, but for the trigger chips.

Looking at a <= 200 ps edge with either a TDS694C or a 10 GHz+ sampling 'scope makes quite a difference.
With practice, a classic sampling 'scope is not too difficult to use, especially if you know what to expect...

Raymond


Re: Tek TDS694C advice pls

Phil Hobbs
 

My 694C is my favourite scope. (I have 8 in use at the moment, including two 1180x sampling scopes and about 20 plugins.) If I could have only one, it would be the 694C.

With the matching P6249 FET probes, the 694C becomes more or less a general purpose scope. You do have to watch out that you don't blow the probes up with overvoltage, and they're only 20k // 1 pF, but the combo is very powerful.

Cheers

Phil Hobbs