Date   

Re: If you had $1, 000 to buy a 100 MHz scope...

Siggi
 

On Fri, 29 Jun 2018 at 12:45 Pete Lancashire <xyzzypdx@gmail.com> wrote:

I'm trying to break the habit of buying old scopes. I'm looking for
suggestions 100 megahertz or better, 4 channels, supports a mode where
multiple pulses are shown over and over again and shows Distortion errors.
I would say that's the one unique thing.

So what would members of this is esteamed group suggest.

And older tek scope that is higher, TDS784D for example or a new Tek /
keysight / Regal
My TDS784D is only turned on when I need the bandwidth or one of its
features, I'll usually reach for the 2467 or the HP54622D - in that order
of preference.

If Rigol is under consideration, you may want to also look at the Siglents.
For $1k you can get the 4 channel SDS1104X-E <
http://www.saelig.com/siglent-sdsx-series/sds1104x-e.htm> model with the 16
channel logic probe & analyzer. Alternatively you could go for the 200MHz
model inside $1k. I believe Siglent throws in all manner of serial
decoders, which is a nice bonus.
Disclaimer: I've never used a Siglent scope, and I've not read the one
thorough looking review I found <
https://www.eevblog.com/forum/testgear/siglent-sds1104x-e-in-depth-review/>.


Re: Tek 465 no display

johnlegros
 

i have the papier version for en After 25000   ,but it conversation before modèles ,to repair power rails you need to switch through all the Book ,but à good start is how PS operates ,then go to schematics, if you want i will make photos , John

Envoyé depuis mon Redmi 4X

Le Albert Otten <aodiversen@concepts.nl>, 29 juin 2018 8:04 PM a écrit :








On Fri, Jun 29, 2018 at 07:35 am, musicamex wrote:


Does anyone have a clearer copy of the access board layout?  Maybe an
actual
photo of that page?  The only ones that I have downloaded so far are all
but
impossible to read.  Thanks!  Russ
Hi Russ, you mean board A9? I can send you 2 jpg's at 1200 dpi of about
6.5 MB each. Enlargeable until you have the screen almost filled with one
component number. When you reply via Private I have your e-mail address
and can send it as attachment.
BTW the original is rather vague also. There are several "partial" board
layouts in the manual at which components involved in the next
schematic(s) are shown in bold while other components are vague. Bad luck
that Tek didn't do so for the Power schematic.

Albert






Re: Tek 465 no display

Albert Otten
 

On Fri, Jun 29, 2018 at 07:35 am, musicamex wrote:


Does anyone have a clearer copy of the access board layout? Maybe an actual
photo of that page? The only ones that I have downloaded so far are all but
impossible to read. Thanks! Russ
Hi Russ, you mean board A9? I can send you 2 jpg's at 1200 dpi of about 6.5 MB each. Enlargeable until you have the screen almost filled with one component number. When you reply via Private I have your e-mail address and can send it as attachment.
BTW the original is rather vague also. There are several "partial" board layouts in the manual at which components involved in the next schematic(s) are shown in bold while other components are vague. Bad luck that Tek didn't do so for the Power schematic.

Albert


Re: Tek 465 no display

musicamex
 

One step closer! C1549 looked like it might have been replaced with a mylar cap. As soon as I unsoldered one side and turned on the scope, the fan came on! So i replaced it with a 47mf 25 v electrolytic and now had a bit of a trace but way off vertical axis. Good call Albert!

The voltages now are112.5, 55.66, 15.1, 4.9 and -6.4

I see that the vertical axis is associated with the -8 rail and read the troubleshooting for vertical axis anomalies but before I go further I thought I check for advice here first.

Thanks in advance, Russ


Re: 575 restoration

Sebastian Garcia
 

Hi John,

Lack of shielding, maybe (RFI from HV circuit)? I think the '575 doesn't have a shield lid in the HV area, but you can try again with the bottom lid in its place.

Regards,
Sebastian.

PS: Pete, please note that John provided pictures in the Photo files area.


Pete Lancashire 10:38am #149306
How about some pictures
. . .

On Fri, Jun 29, 2018, 10:35 AM John <John@...> wrote:
My 575 mod 122C arrived at the weekend. It did basically work when
brought up gently on a variac. I've been through most of the valves and
replaced a few which were well down on emmision, including the 6AQ5 /V810.
Similarly, most of the paper caps have been replaced with polyester 600V.
I've just been through the cal. procedure and everything seems fine, but
there is now a slight dot-pattern on the trace which I don't recall
noticing when it had the "old" caps and "old" valves in place. As there
doesn't appear to be any Z-mod capability, I'm wondering what might cause
this? Or is it normal? I've checked the -1700V with a P6015 probe, and it
looks clean. There's small amount of ripple on the +2300V anode, but only
c 20V p-p.
Photo album uploaded under "575 dot-pattern trace"
John


Re: 575 restoration

Pete Lancashire
 

How about some pictures

On Fri, Jun 29, 2018, 10:35 AM John <John@sykesj.co.uk> wrote:

My 575 mod 122C arrived at the weekend. It did basically work when
brought up gently on a variac. I've been through most of the valves and
replaced a few which were well down on emmision, including the 6AQ5 /V810.
Similarly, most of the paper caps have been replaced with polyester 600V.
I've just been through the cal. procedure and everything seems fine, but
there is now a slight dot-pattern on the trace which I don't recall
noticing when it had the "old" caps and "old" valves in place. As there
doesn't appear to be any Z-mod capability, I'm wondering what might cause
this? Or is it normal? I've checked the -1700V with a P6015 probe, and it
looks clean. There's small amount of ripple on the +2300V anode, but only
c 20V p-p.
Photo album uploaded under "575 dot-pattern trace"
John




Re: If you had $1, 000 to buy a 100 MHz scope...

stefan_trethan
 

I have a TDS544 at home, which is somewhat similar to the newer
TDS784D, and I really dislike the display, menu structure, and general
lack of responsiveness.
To me this is the point where Tek went wrong, and I have not liked any
Tek scope from this point on.
Often I prefer to fire up the 7d20 digitizer in a 7k mainframe, when I
know it's only slow signals and I don't need 4 channels.

The later TDS3000 series was extremely popular, but I just straight
out hate the darn things.
From that vintage on I really much prefer Lecroy, even a LC series,
with LCD screen if you can get it instead od the CRT, yes, I would
much prefer that over the Tek ones.
I used to have a Lecroy DDA125 as my main work scope until a year or
two ago, and it is _A LOT_ of scope which you may now get in the $1000
range (The DDA is the same as a LC684 only with special HDD options
added). Not as repairable as old Tek (but so is new Tek).

Now I have a HRO64Zi at work which I got a really good deal on when
they discontinued the series, but still well outside your $1k budget.
That is a fine scope, but _even less_ responsive than the TDS544 or
DDA125. It needs to think and calibrate itself _all the f-ing time_.
But you can so so much with it, it somewhat compensates for the lack
of responsiveness. And the 12 Bit, I wouldn't want to miss that.
It is not the best scope for random debug or fault finding, but for
analysis when you need to get numbers out, document or compare stuff,
it's great.

Anyway, that's well out of price range, all I'm saying is I do miss
using the old DDA125 some days.
So for me the decision for a used scope in the 1k range would be easy,
the DDA125 or something very similar any day.

But is it really better than a modern low end scope, like a Rigol?
Hard to tell. There is something those old "lab grade" scopes have
that you just don't get in a low end scope.
We have a Keysight 3000x at work that I use some times, and it always
infuriates me when you are limited by stupid things such as not enough
reference channels, or not enough math, or...
Also, on that Keysight you can't switch off analog persistence (just
like a Tek TDS3000) and I dislike that.

Of course a new scope will have convenient modern features you just
won't find on one made around the year 2000.
And it will be lightweight, easy to carry around, likely work reliably
without needing repair.

It is the same as with a car, do you prefer a used quality car, or a
cheap and cheerful new car?
I don't mind old, but I do like quality.

What I can say is that the new very lowest end Tek/Keysight/Lecroy are
_not_ worth the money in my mind.
You still pay extra for the brand, but you get nothing above and
beyond say a Rigol, less actually.
They try to capture that market by either re-labeling imported crappy
scopes, or building their own crappy scopes to the cheapest price, but
they can never beat a lesser brand with their high overheads.


So the choice for me would be between a Rigol 1000Z, or something, and
a DDS125, or something like it.

If you can still do that thing where you buy the low end Rigol and
they let you upgrade it to a higher end model, I'd be hard pressed to
make a choice.
Luckily, I don't have to.


ST

On Fri, Jun 29, 2018 at 6:45 PM, Pete Lancashire <xyzzypdx@gmail.com> wrote:
I'm trying to break the habit of buying old scopes. I'm looking for
suggestions 100 megahertz or better, 4 channels, supports a mode where
multiple pulses are shown over and over again and shows Distortion errors.
I would say that's the one unique thing.

So what would members of this is esteamed group suggest.

And older tek scope that is higher, TDS784D for example or a new Tek /
keysight / Regal



575 restoration

John
 

My 575 mod 122C arrived at the weekend. It did basically work when brought up gently on a variac. I've been through most of the valves and replaced a few which were well down on emmision, including the 6AQ5 /V810.
Similarly, most of the paper caps have been replaced with polyester 600V. I've just been through the cal. procedure and everything seems fine, but there is now a slight dot-pattern on the trace which I don't recall noticing when it had the "old" caps and "old" valves in place. As there doesn't appear to be any Z-mod capability, I'm wondering what might cause this? Or is it normal? I've checked the -1700V with a P6015 probe, and it looks clean. There's small amount of ripple on the +2300V anode, but only c 20V p-p.
Photo album uploaded under "575 dot-pattern trace"
John


If you had $1, 000 to buy a 100 MHz scope...

Pete Lancashire
 

I'm trying to break the habit of buying old scopes. I'm looking for
suggestions 100 megahertz or better, 4 channels, supports a mode where
multiple pulses are shown over and over again and shows Distortion errors.
I would say that's the one unique thing.

So what would members of this is esteamed group suggest.

And older tek scope that is higher, TDS784D for example or a new Tek /
keysight / Regal


Re: Kludging together a TDR or similar?

Pete Lancashire
 

It's one of those things you may only use once every two years but damn
does it make it easy.

I have a 1503 as well as a 1502 and I had to find where in my attic the
Romex was tapped into. I was able to locate the junction box which was
hidden two within less then one foot. That paid for it many times over.

The other one were at paid for itself was a broken wire restoring a r390a
HF receiver I was able to locate the brake in a wire in the middle of a
wiring harness to within an inch.

On Fri, Jun 29, 2018, 9:13 AM Richard Solomon <dickw1ksz@gmail.com> wrote:

I picked up a working 1502 a few years
ago on that auction site.

The batteries were shot, but I found a
paper on using a resistor and a big cap
to fool it into thinking it had batteries.

I think I have used if less than 5 times
over the years, but for the price it was
a nice addition to the test equipment
pile.

It didn't hurt that I had an original manual
for it.

73, Dick, W1KSZ

On Fri, Jun 29, 2018 at 4:11 AM, Tom Gardner <tggzzz@gmail.com> wrote:

I really like 1502 (not a, b, 1503 etc), and have some I ought to sell.

There are two principal weaknesses other than the usual PSU caps:

* the tunnel diode is relatively fragile, and can be destroyed by a DC
voltage
on the cable or even a static charge in the cable - hence the special
shorting BNC connector. Having aid that, all 5 that I have seen are
intact
* the battery pack must be present before it will switch on: the PSU
detects
missing and uncharged batteries. All 5 that I have seen have had
faulty
batteries. There are ways of faking a battery, or they can be replaced
by
new sub-C NiCds or NiMH. With NiMH be very careful with "Chinese
capacity
specifications" and the trickle charging current.



On 29/06/18 04:09, Pete Lancashire wrote:

Yeah if you need the short distance performance the 1502 is the only way
to
go. The newer models which have LCD redoubt if the LCD has not gone bad
now
it will. And the unfortunate part is the LCD was custom.

keep your eyes open a lot of sellers don't know what they have but like
another member said make sure the tunnel diode is good.

A few people have looked at the ex Soviet tunnel diodes but as far as I
know no one has found a substitute.

To me sounds like a perfect project to use a modern pulsar there are an
awful lot of 1502s out there.

On Thu, Jun 28, 2018, 1:00 PM Harvey White <madyn@dragonworks.info>
wrote:

On Thu, 28 Jun 2018 11:02:57 -0700, you wrote:

As Stefan said, how fast a step pulse you need and how much scope
bandwidth you need both depend on how much resolution you need. Do you
happen to have sampling plug-in set for your 7000 series mainframes?
If
not, how much scope bandwidth do you have available? Also, how fast a
risetime can you generate in a pulse?

Also as Stefan mentioned, if you can get down to a nS, you should be
able
to get pretty close!

I'd recommend (for the long term) that you keep an eye on ebay for a
good
deal on a Tektronix 1502 TDR. One of the handiest units I have. A
person
can't have too many TDRs though! Check out a 7S12 when you have time.
Absolutely delightful! :-)

The 1502 (not a/b/c) certainly has a tunnel diode in it for the main
generator. It is difficult to impossible to get ahold of when damaged
(and it damages easily since it's right across the input). If you do
get a 1502, make sure that the TD is working.

I don't know anything about the 1502 A/B/C, so I cannot speak of the
tunnel diode (if any) in it.

A 1503 does not have a TD to generate the pulse, has 10 times the
distance at effectively 1/10 the resolution, that is, if the 1502
would be good to 1 cm, the 1503 is good to 10 cm.

Harder to damage, though.

Harvey


Best of luck with the cable!

Tom










Re: Kludging together a TDR or similar?

Richard Solomon <dickw1ksz@...>
 

I picked up a working 1502 a few years
ago on that auction site.

The batteries were shot, but I found a
paper on using a resistor and a big cap
to fool it into thinking it had batteries.

I think I have used if less than 5 times
over the years, but for the price it was
a nice addition to the test equipment
pile.

It didn't hurt that I had an original manual
for it.

73, Dick, W1KSZ

On Fri, Jun 29, 2018 at 4:11 AM, Tom Gardner <tggzzz@gmail.com> wrote:

I really like 1502 (not a, b, 1503 etc), and have some I ought to sell.

There are two principal weaknesses other than the usual PSU caps:

* the tunnel diode is relatively fragile, and can be destroyed by a DC
voltage
on the cable or even a static charge in the cable - hence the special
shorting BNC connector. Having aid that, all 5 that I have seen are
intact
* the battery pack must be present before it will switch on: the PSU
detects
missing and uncharged batteries. All 5 that I have seen have had faulty
batteries. There are ways of faking a battery, or they can be replaced
by
new sub-C NiCds or NiMH. With NiMH be very careful with "Chinese
capacity
specifications" and the trickle charging current.



On 29/06/18 04:09, Pete Lancashire wrote:

Yeah if you need the short distance performance the 1502 is the only way
to
go. The newer models which have LCD redoubt if the LCD has not gone bad
now
it will. And the unfortunate part is the LCD was custom.

keep your eyes open a lot of sellers don't know what they have but like
another member said make sure the tunnel diode is good.

A few people have looked at the ex Soviet tunnel diodes but as far as I
know no one has found a substitute.

To me sounds like a perfect project to use a modern pulsar there are an
awful lot of 1502s out there.

On Thu, Jun 28, 2018, 1:00 PM Harvey White <madyn@dragonworks.info>
wrote:

On Thu, 28 Jun 2018 11:02:57 -0700, you wrote:

As Stefan said, how fast a step pulse you need and how much scope
bandwidth you need both depend on how much resolution you need. Do you
happen to have sampling plug-in set for your 7000 series mainframes? If
not, how much scope bandwidth do you have available? Also, how fast a
risetime can you generate in a pulse?

Also as Stefan mentioned, if you can get down to a nS, you should be
able
to get pretty close!

I'd recommend (for the long term) that you keep an eye on ebay for a
good
deal on a Tektronix 1502 TDR. One of the handiest units I have. A
person
can't have too many TDRs though! Check out a 7S12 when you have time.
Absolutely delightful! :-)

The 1502 (not a/b/c) certainly has a tunnel diode in it for the main
generator. It is difficult to impossible to get ahold of when damaged
(and it damages easily since it's right across the input). If you do
get a 1502, make sure that the TD is working.

I don't know anything about the 1502 A/B/C, so I cannot speak of the
tunnel diode (if any) in it.

A 1503 does not have a TD to generate the pulse, has 10 times the
distance at effectively 1/10 the resolution, that is, if the 1502
would be good to 1 cm, the 1503 is good to 10 cm.

Harder to damage, though.

Harvey


Best of luck with the cable!

Tom








Re: Tek 465 no display

Harvey White
 

On Thu, 28 Jun 2018 19:57:26 -0700, you wrote:

I'm so sorry that I havent kept up with all of the help here, Albert. I wasn't expecting such a willingly helpful group when i joined the group. This has been an exceptionally busy June for me. I'm recovering from recent heart surgery and seem to be falling behind on my lab repair work among other things. But i did get a bit of time [about 30 min] to follow up on some of the suggestions here. The access board layout diagram is pretty hard to read and not all that much is labeled on the actual board so it is going slower for someone used to point to point and turret board electronics. I have almost zip experience with transistors or pcb layout. But I'm determined to get this figured out.
You might, for the sake of general learning, get some breadboard kits,
general purpose transistors, and start breadboarding some transistor
amplifiers and switches. It would give you a feel for the parts.

For PCB layout, consider that you are doing the same as wiring a
breadboard (the type with millions of holes). The rules, though, is
that the traces cannot cross each other on the same side (otherwise
they're the same trace). They must go from layer to layer through a
plated through hole called a via. On dual layer boards, you have
simply a top and bottom, and the vias go all the way through. On 4
layer boards, there's a top, bottom, and two inner layers. Frequently,
some of the layers are reserved for power and ground.

So PC boards are not all that bad.




One question: did you mean c1549 and cr1549? You were mentioning the 15v rail and c1559 and cr 1559 are on the 5v rail.

Re the video, it was the model and post sn 250000 that caught my eye an invoked my comment. Misery likes company and to see someome trying to fix a no screen problem gave me a bit of hope. There is not much other video tutorial that I could find, good or bad, re what i have a problem with. I am completely self taught in electronics and despite recognizing the less than stellar technique, I actually learned a little about layout even if nothing else was up to par judging from the comments.

I knew almost nothing about this 465 before I started this thread and I'm gaining ground. Poco a poco andamos lejos.
You might want to look at linear supplies and how they work. The
principles between a linear regulator for tubes and transistors are
identical, but the different parts will give you different voltages on
the transistors (vs the tubes). Depletion mode N channel FETS are
most like tubes, once you get to that point. (triodes, thank you).

As in any such project, suspect the power first, then look at
functional blocks. I've had 468's with high voltage resistor network
problems, which will throw off the high voltage. There's a high
voltage divider network that's part of the feedback from the high
voltage output back to the regulator.

Harvey





Thanks again to all for the patience and wealth of info. I have a birthday on Saturday. Maybe i will have time to spend a few more hours figuring this out. Seeing a trace on the screen would be way better than candles. ?



Re: Tek 465 no display

musicamex
 

Does anyone have a clearer copy of the access board layout? Maybe an actual photo of that page? The only ones that I have downloaded so far are all but impossible to read. Thanks! Russ


Re: TDS 380 won't trigger

Siggi
 

On Fri, 29 Jun 2018 at 00:19 Gary Appel <garyappel@twc.com> wrote:

It's alive!

The parts arrived today.

I replaced the acquisition RAM with a MB8464 - not the original part, but
it
appears that the original part was unobtainium. The 'scope now displays
traces correctly at all sweep rates, and the offset and calibration are
again correct.
Excellent - congrats on the fix.


Re: Dead 7603

Mark Wendt
 

On 06/28/2018 09:07 PM, garp66 wrote:
hi all,

The above written description is quite good, and clear.

Due to diversity in human nature, sometimes a picture or video supplementing information for a procedure can be helpful to some, including the uninitiated.

I wonder if some Tektronix YouTube 'expert' videos might be linked to some discussions ?
We all gain with additional clarity, helps prevent accidents, and it seems that added image/video teaching tools have proved themselves over text-only technology.

Tekscopes List evolution ?
Which "above written description" are you talking about?  Unless you quote from the email you are replying to, we have no idea what you are talking about.  Notice how I quoted your email reply?  Now folks know who and what I'm replying to, and have the context of the conversation.

Top or bottom replying is a religious discussion for another day.

Mark


Re: Kludging together a TDR or similar?

Tom Gardner
 

I really like 1502 (not a, b, 1503 etc), and have some I ought to sell.

There are two principal weaknesses other than the usual PSU caps:

* the tunnel diode is relatively fragile, and can be destroyed by a DC voltage
on the cable or even a static charge in the cable - hence the special
shorting BNC connector. Having aid that, all 5 that I have seen are intact
* the battery pack must be present before it will switch on: the PSU detects
missing and uncharged batteries. All 5 that I have seen have had faulty
batteries. There are ways of faking a battery, or they can be replaced by
new sub-C NiCds or NiMH. With NiMH be very careful with "Chinese capacity
specifications" and the trickle charging current.

On 29/06/18 04:09, Pete Lancashire wrote:
Yeah if you need the short distance performance the 1502 is the only way to
go. The newer models which have LCD redoubt if the LCD has not gone bad now
it will. And the unfortunate part is the LCD was custom.

keep your eyes open a lot of sellers don't know what they have but like
another member said make sure the tunnel diode is good.

A few people have looked at the ex Soviet tunnel diodes but as far as I
know no one has found a substitute.

To me sounds like a perfect project to use a modern pulsar there are an
awful lot of 1502s out there.

On Thu, Jun 28, 2018, 1:00 PM Harvey White <madyn@dragonworks.info> wrote:

On Thu, 28 Jun 2018 11:02:57 -0700, you wrote:

As Stefan said, how fast a step pulse you need and how much scope
bandwidth you need both depend on how much resolution you need. Do you
happen to have sampling plug-in set for your 7000 series mainframes? If
not, how much scope bandwidth do you have available? Also, how fast a
risetime can you generate in a pulse?
Also as Stefan mentioned, if you can get down to a nS, you should be able
to get pretty close!
I'd recommend (for the long term) that you keep an eye on ebay for a good
deal on a Tektronix 1502 TDR. One of the handiest units I have. A person
can't have too many TDRs though! Check out a 7S12 when you have time.
Absolutely delightful! :-)

The 1502 (not a/b/c) certainly has a tunnel diode in it for the main
generator. It is difficult to impossible to get ahold of when damaged
(and it damages easily since it's right across the input). If you do
get a 1502, make sure that the TD is working.

I don't know anything about the 1502 A/B/C, so I cannot speak of the
tunnel diode (if any) in it.

A 1503 does not have a TD to generate the pulse, has 10 times the
distance at effectively 1/10 the resolution, that is, if the 1502
would be good to 1 cm, the 1503 is good to 10 cm.

Harder to damage, though.

Harvey


Best of luck with the cable!

Tom





Re: Tek 465 no display

Albert Otten
 

Sorry to hear about your health problems Russ. First things first of course.

One question: did you mean c1549 and cr1549? You were mentioning the 15v rail and c1559 and cr 1559 are on the 5v rail.
There you got me! I remember I was typing with the laptop on my knees. I had to look skew at the manual and though I even checked twice I made this mistake.

Success,
Albert


Re: Tek 422 ac/dc power supply issues

Renée
 

just checked to see that pictures aligned with the text...NOT!  it is a mess, not sure how to fix that, nor am I sure how/what happened. ended up with some of my pwr sply too! hmmmm all out of order.
I will deal with it later.
sorry for the mess
Renée

On 2018-06-28 03:28 PM, Renée wrote:
Hi Jeff-
I have the little bugger up and running using 2n5881 xstrs, runs 2.5A draw at 11.5V and ~900ma at 26V scope runs all the way down to 10.5V!!!!


Re: Kludging together a TDR or similar?

Michael A. Terrell
 

If lightning hit that drop, there is likely more than one damaged area, or even long stretches of the shield is gone. I worked in CATV repairing the electronics and I have seen damaged coax where the entire outer conductor had vaporized. The worst damage is usually at sharp turns, like the corner of a building. We often had to run temporary drops to replace buried lines, until or Ditchwitch was available to bury it. This was in the Cincinnati area, so lightning was a big problem. It wiped out thousands of power transformers in the set top boxes, as well.


There should be a tap to reduce the signal level to the modem which may also be damaged. It is usually at the house end of the drop, and it is easily damaged by lightning. Mine is 17dB.

Michael A. Terrell
--

-----Original Message-----
From: Kevin Oconnor <kjo@cryden.com>
Sent: Jun 28, 2018 11:04 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Kludging together a TDR or similar?

TV coax problem....
As noted, u don’t indicate the run length u have. If it goes from ur house terminal to the typical green post in the yard and it is 100ft or less, it would be more efficient to just run a new coax over the ground to verify operation.
If you have buried coax with a fault, I wouldn’t trust any of it.

Kjo


Re: TDS 380 won't trigger

Gary Appel
 

It's alive!

The parts arrived today.

I replaced the acquisition RAM with a MB8464 - not the original part, but it appears that the original part was unobtainium. The 'scope now displays traces correctly at all sweep rates, and the offset and calibration are again correct.

Thanks again for pointing me to the information on EEblog, and the technical manual.

Gary Appel

-----Original Message-----
From: Siggi
Sent: Sunday, June 24, 2018 6:32 AM
To: TekScopes@groups.io
Subject: Re: [TekScopes] TDS 380 won't trigger

On Sat, 23 Jun 2018 at 20:45 Gary Appel <garyappel@twc.com> wrote:

Thank you Siggi.

The gentleman on EEVBlog has a 'scope that reported exactly the same
errors
as I have, so it sounds like it may very well be the same problem. I tried
squirting a little freeze mist on the acquisition memory. It didn't "fix"
the problem, but the trace certainly responded. With a little freeze mist
it
tried to come back to the same value as when the trace was rolling.

After spending some more time looking at the 'scope today, it does appear
to
be triggering. I'm not sure if that has changed since last night, or if I
was not setting the trigger correctly last night. As you suggested, I set
the trigger to AC and with the level at the center line it triggered on
Ch1,
Ch2, Ext, and line.

Cool - it all sounds consistent with RAM failure then.

At low sweep speed, where the trace rolls across the screen, the 'scope is
displaying a waveform, and it makes sense that they wouldn't be using the
acquisition memory for that, although there is an substantial offset and
calibration error in that mode. With a 0 offset and 0 position ground lies
about two divisions above the center line. Using the measure menu to
measure
the level, it does not agree with the volts / division. So there is likely
a
second problem.
If you've tried to run signal path compensation after the acquisition
system wonked out, this could be working as intended. The acquisition
system will have been used to measure the DC offset to compensate, and it
could have measured a large "ghost" offset.

Most of the IC's have a '95 date code. The Dallas chip has a '96 date code.
It is certainly on borrowed time. I have seen a number of references to
replacing the Dallas chip, after first copying the contents. It's probably
time for that as well.
I'm not sure it's worth the effort to preserve the memory contents of the
NVRAM, as the calibration procedure for this scope looks like a piece of
cake.
All you need is some DC and a "fast rise" (<10ns) pulse generator. This is
pretty typical for the CCD-based scopes, it was easy as pie to calibrate my
2430 using what I already had around the lab, plus some spit and bubblegum.


I do have an analog 'scope as well - a 2465A, that is also likely on
borrowed time. I suspect the Dallas chip in that 'scope is probably just
about as old.
Piffle - my 2467 has a keeper with an '85 date code in it, and it's still
going strong :). Of course I'm set to calibrate it, should the keeper give
up the ghost, so I'm not too bothered - I'm quite curious to see how long
the battery will last.


It sounds like my first task should be to replace that acquisition memory.
Yups, sounds like.


Meanwhile, in my impatience, I just ordered a replacement 'scope. It's
only
100 MHz, but now that I'm not earning a living with my equipment, I'm not
sure I need a 400 MHz digital 'scope any more.

Thanks for your assistance, I will post if I make some progress.
Good luck!

37841 - 37860 of 187136