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Hi Dave,
What does a 7704A with a P7001 have to do with curve tracers???
The reason I changed the topic was to separate the discussion about
500 series scopes from the discussion going on about transistor curve
tracers with the same subject.
Dennis Tillman W7PF

Hi Dave,
Tek sometimes uses this modularity in very interesting ways. I think the 7704 was the first scope they designed to be modular from the start.
The top section is completely removable and held to the bottom section
with only a few screws. This was done so Tek could insert the
interface section of the DPO (Digital Processing Oscilloscope) in between the top and bottom of the 7704. The DPO used a DEC PDP-8 minicomputer to capture data from the 7704 lower section plugins and display the results on the 7704 upper display section.
Tek listed the DPO in its catalogs from 1974 to 1981. In 1981 Tek
introduced the 7854 which does all of this in a normal size 4-wide mainframe using a microcomputer instead of the PDP-8 minicomputer.

Dennis Tillman W7PF

On Aug 20, 2019, at 11:01 AM, Steve Lindberg <steve_tech@...> wrote:


These puppies were OEMed by Tek. The one I got had banana plugs broken loose from PCB.

Steve Lindberg


Sent from Mail<> for Windows 10

On Aug 15, 2019, at 19:31, Mark Schoonover <mark@...> wrote:

Hello,

I'm interested in purchasing my first scope and looking for opinions on the
TDS744A. I'm not interested in purchasing a Rigol/Siglent, etc - not that
they are bad scopes, I've used Teks before at different employers. It's
just that I'm not familiar with this particular model. It'll be used for
working on amateur radio related radios, experimentation and general
messing around :) I know it can be modified to a 1GHz scope and might do
that in the future.

Thanks for reading.

73! Mark KA6WKE

Website:
Author: 4NEC2 The Definitive Guide EMail List:: [email protected]

On Aug 20, 2019, at 08:00, Chuck Harris <cfharris@...> wrote:

I am duly chastened.

You all have argued, to the internet's satisfaction, no doubt,
that every opto coupler in every circuit should be replaced on
sight... ;-)

...And yet, in the hundreds of switchers I have repaired over the
years, I have never needed to replace even one optocoupler.

How can that be??? The internet clearly knows them to be highly
unreliable, and recommends that they be shot on sight.

I suppose it is possible that some supplies that I didn't fix had
bad optocouplers, but I would think they would have shown open loop
regulation failures, since most of the optocouplers (in switchers)
are used to isolate the PWM voltage regulator's feedback loop.

Which, I am pretty sure isn't happening here with supplies that won't
turn on.

The overwhelming majority of the failures I have seen have been
capacitor related. The overwhelming majority of the completely
dead switchers I have seen have had bootstrap problems.

I guess we will never know if I have been not fixing optocoupler
failures in switching supplies all this time....

Still, I stand by my less than 1% statement.

[If I were an IEEE member, I might check out the papers referenced...
But, like most of my colleagues, I gave up my IEEE membership many
years ago as it just had no tangible value to practicing USA EE's.

Where IEEE could have earned our membership dollars is if they did
anything at all to help prevent USA engineering jobs from being
exported to the third world over the internet. Or, did anything to
prevent H1B Visa holders from taking our jobs, and depressing our
wages. But IEEE, being an international organization, considered
those to be highly desirable things.]

I didn't, but, if I did check out the papers, I bet I would find that
the authors are panicking over a failure rate that is 4 or 5 sigma,
rather than the 6 sigma usually considered human perfection by the
semiconductor industry.

(Note:
1 sigma= 31% good,
2 sigma= 69% good,
3 sigma= 99.3% good,
4 sigma= 99.4% good,
5 sigma= 99.97% good,
6 sigma= 99.999997% good
)

At 4 or 5 sigma, with two optocouplers per switching supply, I would
have to fix a lot more than a few hundred switchers to see any
significant failure problem in optocouplers.

So might you... How many supplies are we fixing again?

-Chuck Harris

Glenn Little wrote:

Where I used to work, we used optocouplers to Isolate TELCO ring from our circuit and
detect ring.
We found that as the opto aged the ability of the photo device to see the emitter
decreased.
We replaced a lot of these because of this.
It got to the point that when a board came in for repair and was shown to be faulty
in the test set, the first thing replaced was the opto.
This fixed about 90% of the field returns.
It may be that we used optos close to their low limits?

Glenn

On Aug 20, 2019, at 11:21, Stephen Hanselman <kc4sw.io@...> wrote:

I’m kind of surprised they handed out “seconds” to JA folks. In ‘79 I was a JA advisor at Opto div, at that time if JA needed it JA got it. We did an electronics project and our division PCB designer laid it out, the manufacturing div made the PCB and our div controller certified the books, HP really went all out for JA.

At the time I was there were several amazing things I found, the 7 segment displays for Cadillac were color/intensity matched an order of magnitude better than the eye could resolve. We started building transistors for one of the instrument divisions because our Fab Dept had better quality control.

This is why I never understood the problem, the Opto-couplers worked fine they just seemed to break more often additionally the push to use in-house parts that were waaay cheaper than brand “X” was high.



Regards,

Stephen Hanselman
Datagate Systems, LLC
3107 North Deer Run Road #24
Carson City, Nevada, 89701
(775) 882-5117 office
(775) 720-6020 mobile
s.hanselman@...
www.datagatesystems.com
a Service Disabled, Veteran Owned Small Business
DISCLAIMER:
This e-mail and any attachments are intended only for use by the addressee(s) named herein and may contain legally privileged and/or proprietary information. If you are not the intended recipient, any dissemination, distribution or copying of this e-mail and any attachments is strictly prohibited. If you have received this e-mail in error, please immediately notify me and permanently delete the original and all copies and printouts of this e-mail and any attachments.

On Aug 20, 2019, at 02:16, Dave Seiter <d.seiter@...> wrote:

In the late 70's I was in a Junior Achievement program sponsored by a couple of guys from HP optical (Page Mill); they took us on tours, told us lots of stories (some rather racy), and gave some of us who were interested lots of "samples" that were mostly seconds (wrong tints, poorly filled molds, loose specs, etc) from single LEDs to laser modules, but never any optocouplers. When I asked for some, I was eventually given "real" samples because the "failure rate was so low". At least on the types I was interested in.
-Dave
On Monday, August 19, 2019, 02:33:24 PM PDT, Chuck Harris <cfharris@...> wrote:

Steve,

As a life long EE, I would not have put up with that for
a minute. Either the circuit would get redesigned, or the
vendor of defective parts get banned.

But, I have always been a bit of a hard-ass about stuff like
that.

-Chuck Harris

Stephen Hanselman wrote:

Chuck,

He would change them 3 or 4 at a time. Now we see two or three over 5 or 6 units. The 6130C uses 22 (or so) and the OEM HP ones were unstable. HP got better, but at the time (1979) they broke at the drop of a hat.

Other folks, Monsanto, LiteOn, etc, all seemed more stable and reliable.

steve

On Aug 20, 2019, at 02:16, Dave Seiter <d.seiter@...> wrote:

In the late 70's I was in a Junior Achievement program sponsored by a couple of guys from HP optical (Page Mill); they took us on tours, told us lots of stories (some rather racy), and gave some of us who were interested lots of "samples" that were mostly seconds (wrong tints, poorly filled molds, loose specs, etc) from single LEDs to laser modules, but never any optocouplers. When I asked for some, I was eventually given "real" samples because the "failure rate was so low". At least on the types I was interested in.
-Dave
On Monday, August 19, 2019, 02:33:24 PM PDT, Chuck Harris <cfharris@...> wrote:

Steve,

As a life long EE, I would not have put up with that for
a minute. Either the circuit would get redesigned, or the
vendor of defective parts get banned.

But, I have always been a bit of a hard-ass about stuff like
that.

-Chuck Harris

Stephen Hanselman wrote:

Chuck,

He would change them 3 or 4 at a time. Now we see two or three over 5 or 6 units. The 6130C uses 22 (or so) and the OEM HP ones were unstable. HP got better, but at the time (1979) they broke at the drop of a hat.

Other folks, Monsanto, LiteOn, etc, all seemed more stable and reliable.

steve

Maybe the cap IS leaking, and heated some of the resistors on the right hand side of the schematic up?

After disconnecting the cap, the resistors cooled back down and found their normal DC working area, hence the focus stayed ok?

Still interested,

Leo

On Aug 20, 2019, at 07:37, Siggi <siggi@...> wrote:

Hey Dana,

IIRC the standby power supply that allows soft-power on is also responsible
for powering the main switcher. Maybe the standby supply needs recapping.

The TDS5/6/7As are also well documented to suffer from capacitor plaque.
There are SMD electrolytic capacitors all over the acquisition, CPU and
front panel boards. If yours hasn't been re-capped, then that's also a
possible explanation for what you're seeing.

Siggi

On Tue, Aug 20, 2019 at 10:25 AM danadak <danaaknight@...> wrote:

This scope has been excellent to date. Now when turned on it
power cycles. It will start up, most of the time complete the POST,
then power itself off after a minute or two.

Before I spend the next century trying to find the problem anyone
have a similar experience ?


Regards, Dana.

Where I used to work, we used optocouplers to Isolate TELCO ring from our circuit and
detect ring.
We found that as the opto aged the ability of the photo device to see the emitter
decreased.
We replaced a lot of these because of this.
It got to the point that when a board came in for repair and was shown to be faulty
in the test set, the first thing replaced was the opto.
This fixed about 90% of the field returns.
It may be that we used optos close to their low limits?

Glenn

This scope has been excellent to date. Now when turned on it
power cycles. It will start up, most of the time complete the POST,
then power itself off after a minute or two.

Before I spend the next century trying to find the problem anyone
have a similar experience ?


Regards, Dana.