Hi Chuck,

Thank You for your reply

I always learn something for your expert replies to Tekscopes

The electros have been changed in the power supply for high temperature versions

Below is my original posting on Tekscopes 1 (received no reply),became confused running the diagnostics
but eventually suspected the eproms

My TEK 494 has lost its display except for a couple of graphics characters and the marker spot.

Originally the power supply would not start due to a shorted Tant. cap in the circuit around the 1^st oscillator? YIG

Power supply has been recapped and is working correctly (made a dummy load to confirm its O/K)

494 worked for? a little while ,then became intermittent? (would sometimes come good by gently tapping the tops of the boards)

Now does not show the software version on start up? only the above display

Sometimes after start up the front panel buttons (that are on ) respond but other times? are frozen

Have checked CRT voltages which all appear spot on for the display i am getting

3 of the led light? on the memory board are sometimes on.

Do not know how to properly approach this problem (is this a problem with the instrument bus ?) ....any help? greatly appreciated

Regards

George Livanes (in Australia)

?

494's that suddenly start acting erratically, are likely to
have power supply problems.

Tektronix stuffed an awful lot of power supply (amd heat) into
a very small area. They used single filter caps, where low
ESR/high temperature prudence would have recommended using 2 or
3 in parallel.

I would go there first. I have found supplies where it got so
hot that the heatshrink tubing that covers the cans shrunk so
much that it looked like trowsers on teen that just went through
a groth spurt. Use the best, lowest ESR, highest temperature
long life electrolytic capacitors you can afford.

150C for certain.

If you find that a new capacitor is going to be smaller than the
original, up the voltage rating and capacitance until you get to
the original can size.

Be careful when your SA is out of its case. It is heavy, and it
is not ok to let the SA hang over the edge of your bench, while
resting its weight on the covers of the internal modules! You
may break some internal connections that are very hard to fix.

-Chuck Harris


On Mon, 07 Aug 2023 21:26:40 -0700 "George Livanes"
<gmt1@...> wrote:

Hi Everyone,
My TEK 494 is displaying signs of faulty Eproms (I think)
This is an early 494 (No A or AP) just plain 494
All the files on the net are for later models I suspect
The eproms include 1600-2366-04, 1600-2367-04? (on the labels) etc
Any feedback greatly appreciated (probably my favorite piece of Tek
gear) Very hard to get help down here in Sydney, Australia for this
kind of instrument) Regards
George Livanes

开云体育

Hi Everyone,
My TEK 494 is displaying signs of faulty Eproms (I think)
This is an early 494 (No A or AP) just plain 494
All the files on the net are for later models I suspect
The eproms include 1600-2366-04, 1600-2367-04? (on the labels) etc
Any feedback greatly appreciated (probably my favorite piece of Tek gear)
Very hard to get help down here in Sydney, Australia for this kind of instrument)
Regards
George Livanes

This is indeed a sad day. Being located in the UK I've not been able to avail myself of too many goodies from Sphere due to general unfavourable costs of buying stuff from across the pond. I've combed through the website on numerous occasions! I would just love to be able to rock up and buy stuff from the store but that's not going to happen!

But anyway, as soon as I read this I was immediately reminded of one of my favourite songs from George Harrison...... "All Things Must Pass" .......very appropriate lyrics!

I wish you both the best of luck for whatever the future holds for you both.?

Nigel Pritchard

开云体育

Due to a bad combination? of serious illness and old age,
we will be closing our Sphere business at year end.

We will do our best to provide good service up to the end,
but responses and page updates will be slower.

All our curated parts collections (Tek, HP, Fluke plus fans, semiconductors
and passive parts) are for sale, all offers are welcome. Please contact Susan
at Susan Shawlee <susan@...>

we have many items not on line, and coming by to see for yourself is really the best plan.
tons of parts are free, plus two out buildings full of free gear. help your self. PLUS a huge shelf full of Tek and HP manuals, take all you want. sorry, we just don't have the resources to ship you this free stuff, it has to be picked up.

Our thanks to the dozens of customers that have already come by in person to help us
clear out parts and equipment, we really appreciate the effort you made on our behalf
with this difficult problem.

We have really enjoyed operating Sphere, and I hope it has been a useful tool for you
to keep your test gear up and running.

best regards,

walter & susan

-- 
Walter Shawlee 2
Sphere Research Corp. 3394 Sunnyside Rd. 
West Kelowna, BC, V1Z 2V4 CANADA
Phone: +1 (250-769-1834 -:- 
+We're all in one boat, no matter how it looks to you. (WS2)
+All you need is love. (John Lennon)
+But, that doesn't mean other things don't come in handy. (WS2)
+Nature is trying very hard to make us succeed, but nature does not depend on us. 
We are not the only experiment. (R. Buckminster Fuller)

I don't see value in commenting on Youtube. The information is not searchable at all, the chances of someone actually benefiting from it are slim to none. Maybe the maker of the video would see it, but I'm not convinced most are reading their comment sections in depth, that could be a full time job in and of itself.

Agree with comments about video length, it didn't need to be 50 minutes long. The scratching was horrible; I don't like that it was presented as a tutorial for others to follow.

The input BNC might've had an intermittent connection, I don't know if it's common or not but it was worth checking for completeness sake.

It would be good to add some cooling while running the scope out of its cabinet. Yes, it's optional for the analog 2400s but why take chances?

I love watching test equipment repair videos! The guts of these things are works of art. The fact that a 20+ year old precision analog device is still in spec is amazing. I see it all the time when I find broken / dirty equipment.
I've owned a couple of these scope that he is working on, and I have a couple of them now that I am re-homing, but I don't think I ever had to crack one open. Love seeing that!

Well, he likes the sound of his own voice for sure.? But nowhere did I hear him mention or advise to use ESD safety precautions when working on those.? Gloves (if worn) should be conductive too, for ESD reasons.

Frankly, I got bored about half way through.? Mainly due to the poor fuzzy video, a lot of detail you just could not see.

Dave G8KBV.

--
Created on and sent from a Unix like PC running and using free and open source software:

Hi,

Due to other interests I came across this video today. I was initially very sceptical that it would end well. However, to my very amateur eyes, it didn't end too badly. There has been some commenting on the video suggesting the 'scratching' was not an optimum procedure.

I would be interested to hear what others here have to say. And perhaps we could even add some suggestions to the comments on the video to improve the outcome for the 2445.

Brian.

开云体育

I've seen similar behavior when one of the vertical deflection plates
is disconnected.

And, of course, it could be one of the two deflection amps.

-Chuck Harris


On Thu, 2 Mar 2023 09:45:23 -0600 "John Griessen" <john@...>
wrote:

I am testing several 556's that will be for sale and one has a lower
beam that behaves badly with different plugins installed, so the gain
in the mainframe is the problem. I can vary the position of a
square wave from the cal out up and down with either the lower or
upper CRT zone and time base, but on the lower beam the height of the
square wave decreases as I position it toward the bottom of the CRT
face. I'm going to start reading the manual soon today, but wonder
if this is a common thing with an explanation like, "has to be in the
last amp before driving the CRT pins", or "Can be the CRT internally
damaged...".

When driving the upper beam on the upper CRT zone, height of the
square wave stays constant all the way until part of it is off screen.

if i was you i would check all power rails using a digital multi meter set to ac volts,that will show the ripple voltage indicating a bad cap.

On Sun, Jul 16, 2023 at 08:57 AM, Alex wrote:

Thanks for that, all components located now. You must have a much better copy of the A10 layout than mine.

This is what I used:


Ozan

Selecting time base B is correct. However, it looks like the scope is in delayed B-sweep mode. In that mode "A" trigger is used, we want to use "B" trigger.

After selecting B time base as before, in the trigger area push A/B button (light should turn off), then move trigger to "NORM". You should see a full waveform. At least that is what I expect based on a 2467B with similar controls.

Ozan



===

Yes I do have several copies of the same SM.

Thanks for that, all components located now. You must have a much better copy of the A10 layout than mine.

On Sun, Jul 16, 2023 at 02:47 AM, Ozan wrote:

Looking at the screen scope could be in delayed B sweep, we need B-trigger (not delayed). I don't have the exact scope but looking at the picture of the front panel:
1) Mode needs to be "B". You may need to rotate time/div knob one click in clockwise direction after selecting "B" to be in B-sweep
2) Trigger needs to be "B" trigger by pushing A/B select in trigger area and selecting "NORM" in B side.?
If you take another video seeing the setting is useful.

B trigger has almost the same exact blocks like A trigger but it is a different path. If they both behave the same, the issue is in the common path between them, or supplies/reference voltages.

Ozan

The only timebase options are A, ALT, B, and XY. I had selected B.
Trigger was in Auto, I moved the selection to Normal.
The delay reading at the top of the screen can be varied with the Time Position/Delay knob, this knob has no turning limit, and no click. If I turn the knob fully clockwise the indication will go all the way up to 2.00000mS, and turning that knob makes the wave form progressively move towards the left side of the screen until at some point it disappears completely from view. If instead I start turning the knob counterclockwise the reading goes all the way down to "? 0.00000mS" and the wave form stays at the same position as shown in the latest video.

With B selected, and now trigger set to Normal, the tail of the waveform is still doing exactly the same as shown in the previous video. Nothing changed. Not sure I am missing something.

Perhaps it might help to take a look at the 2247A front panel here:

(I just pulled this image from the web).