开云体育

On Thu, 5 Jul 2018 at 02:53 Roger Evans via Groups.Io <very_fuzzy_logic=
[email protected]> wrote:

I tried my very early PG506 with a 7904 / 7A29 or 7A16p / 7B92A. I can't
measure any jitter between the trigger output and the fast rise outputs at
the 50-100psec level. The rise time of the high amplitude output into
50ohm is about 10nsec and due to the time delay between the trigger and
high amplitude pulse I have to use the delayed sweep on the 7B92A to get to
1nsec/div so more uncertainty but the jitter is at the 100ps or less
level. 1.5nsec sounds like something badly wrong.

Thanks, I'm looking at the output of the pulser which is after the hi-ampl
output. I should look at the output of the PG506 directly.

On Thu, 5 Jul 2018 at 05:35 Albert Otten <aodiversen@...> wrote:

The PG506 specs mention delay time 18 ns between trigger out and Hi Ampl
pulse out. I don' know of course how much delay time is added by your home
made pulse generator. But if you didn't deliberately build in a delay there
then the total delay time likely as much less than required to see the
same-as-triggered-on leading edge at the sampling combination. Hence you
might be looking at the leading edge of the next pulse and jitter will
include the between-pulses jitter of the PG506.

On the 2467 I'm looking at the edge right after the trigger, and I'm pretty
sure the 7S12/S-53 is also looking at the first edge.

Small Tek TD pulse generators were driven by the scopes calibrator output
or unterminated PG506 Hi Ampl output, with relatively slow rise times.
Roger looked at the terminated Hi Ampl output. What is your design?

Yeah - I aped the Tek design that uses the Hi Ampl output, I guess the slow
rise leads to jitter.

Hi to All,

Still looking for this Module User Manual. The only item I could find isn't available for those outside the US. Anybody?

Greetings,

Egge Siert

Hi Siggi,

The PG506 specs mention delay time 18 ns between trigger out and Hi Ampl pulse out. I don' know of course how much delay time is added by your home made pulse generator. But if you didn't deliberately build in a delay there then the total delay time likely as much less than required to see the same-as-triggered-on leading edge at the sampling combination. Hence you might be looking at the leading edge of the next pulse and jitter will include the between-pulses jitter of the PG506.
Small Tek TD pulse generators were driven by the scopes calibrator output or unterminated PG506 Hi Ampl output, with relatively slow rise times. Roger looked at the terminated Hi Ampl output. What is your design?

Albert

Hi Siggi,

I tried my very early PG506 with a 7904 / 7A29 or 7A16p / 7B92A. I can't
measure any jitter between the trigger output and the fast rise outputs at the
50-100psec level. The rise time of the high amplitude output into 50ohm is
about 10nsec and due to the time delay between the trigger and high amplitude
pulse I have to use the delayed sweep on the 7B92A to get to 1nsec/div so more
uncertainty but the jitter is at the 100ps or less level. 1.5nsec sounds like
something badly wrong.

Roger

as reply to

I have a little shop-made TD pulser I drive off my PG506 high ampl output.
I also now have a 7S12 with an S-4 and an S-53, so I figured I'd be able to
look at the rise of my pulser, as the PG506 has a TRIG OUT. When I pulled in close, however, it was all fuzz on the sampling gitup. Initially I figured my newly ePrayed S-53 might be wonked out, but I'm seeing the same thing on the venerable 2467.
Looks like ~1.5ns of jitter - is this typical?

Siggi

Hi Siggi,

I tried my very early PG506 with a 7904 / 7A29 or 7A16p / 7B92A. I can't measure any jitter between the trigger output and the fast rise outputs at the 50-100psec level. The rise time of the high amplitude output into 50ohm is about 10nsec and due to the time delay between the trigger and high amplitude pulse I have to use the delayed sweep on the 7B92A to get to 1nsec/div so more uncertainty but the jitter is at the 100ps or less level. 1.5nsec sounds like something badly wrong.

Roger

Hey y'all,

I have a little shop-made TD pulser I drive off my PG506 high ampl output.
I also now have a 7S12 with an S-4 and an S-53, so I figured I'd be able to
look at the rise of my pulser, as the PG506 has a TRIG OUT. When I pulled
in close, however, it was all fuzz on the sampling gitup.
Initially I figured my newly ePrayed S-53 might be wonked out, but I'm
seeing the same thing on the venerable 2467.
Looks like ~1.5ns of jitter - is this typical?

Siggi

Hello Russ,

My comments just after yours, below...
Rgrds,
Fabio

On Mon, Jul 2, 2018 at 09:16 pm, musicamex wrote:

Hi Fabio, Thanks for your comments. The film cap seemed like it was zdded
as a repair attempt and wasn't particularly large. Maybe 7 mm square and
clearly marked 47 mf. Like a small blue chicle. I have lots of similar
sized caps for use as tone caps but of less capacitance. They are usually
of higher voltage ratings. I believe this one was 63v. Ill check to see if
i tossed it.

Hmmm, "Small blue chicle", to me, this shape resembles very well a dipped tantalum capacitor...but I agree with you that someone must have changed it, because the usual dipped tantalum capacitor Tek employed on this period would be color coded (striped) and wouldn't have the value marked numerically... (the page 4-4 of your manual have a graphic description of how the color coding of the dipped tantalum capacitors were).
But definitely, your description fits how the regular commercial dipped tantalum capacitors are usually marketed, a single color blob, usually mustard or blue, with value marked in numbers.
Sometimes, the voltage is also marked, sometimes it's omitted or it's coded on the color of the body.
A 7 square mm mylar (or 7 x 7) cap could never be 47uF... I have 8.2uF mylar caps that are 30mm x 20mm x 8mm, and they're just 100V. OK that it would surely be smaller, for a smaller voltage but it would never be that small (and my example is just 8.2uF)

The - 8v is the only rail that is still low. Ill do some further testing
tomorrow hopefully. We can get some pretty close lightning strikes during
our monsoon season and that can cut into my bench time.

Yep, keep away from opened electrical equipment those times... It surely can be a shocking experience!
We also have a lot of thunderstorms in Brazil.

My wife is in the
states for a month also and it takes allot for me to also keep up with what
she does for us too.

Seen that! Been there too! We miss them!

I did take time to watch Brazil ice Mexico today.

We're used to it by now. At least now I know someone from Brazil to
congratulate on a good game. Good luck on the next games.

Thanks! Belgium won't be easy!

I'll report my findings and will certainly have questions, but it seems the
logical next step is to clean out the trash in the -8v rail.

I agree... The -8V is surely the next enemy to fight.
To ease up the chase, try to see what can be possibly disconnected (e.g. unpluggable connectors).
Right out of my mind, I think of the power connector to the Vertical amplifier board...There's -8 going in there, and you can rule that board out by simply pulling out the power supply connector (from the Vertical Output Amplifier board).
Another one, is the power supply cable that goes to the Vertical Preamplifier board...
The power cable (a flat colored one, IIRC of 4 or 5 wires), is soldered directly(without a connector) to the solder side of the preamplifier board and, at its other end, it goes in between the preamplifier board and the bottom, large main board (the so called interface board), and ends in a 4 or 5 pin "harmonica" connector, that you can disconnect, ruling out another possible cause for the -8V being brought down.
BTW, you will see the "harmonica" term on the group discussions quite often... They're inline connectors, with 0.1 inch pitch, and they look like a small harmonica flute.
They're infamous because Tek used a lot of them on the scopes of this period and, although they could have keyed them to avoid inverted and/or shifted insertion, Tek almost never did it so, you guess it, a lot of people already zapped a lot of boards and Tek made unobtanium ICs, by just carelessly inserting those harmonica connectors inverted or shifted by one or two pins.
And before you ask, Yes, they ARE visually keyed. There's always a clear visual indication, both at the board and at the connector itself for which one is the #1 pin... but they're only visual... You need to assertively look for the visual keys and make sure they're aligned!

Rgrds,

Fabio

Thx, Russ

On Monday, July 2, 2018, Fabio Trevisan <fabio.tr3visan@...> wrote:

Hello Russ,

Glad to hear that the +15V PS woke up, and by consequence, the +5V and
also, somewhat, the -8V (although this one is clearly on the lack).

I have two comments...
1. I got confused by some post of another member, after yours #149308,
still providing suggestions for the low +55V condition... as if it would
still be on the low side.
This takes me to conclude that it's not very clear to everybody there's
nothing wrong anymore, either with the +55V, or with the +15V.
Maybe you can elucidate a little on that to avoid further misunderstanding.
I`m also somewhat puzzled by the description of the capacitor you found
guilty at the C1549 position.
There couldn't be a mylar capacitor there... first because a 47uF mylar
capacitor would be humongous and wouldn't even fit in that space... second
because it would be very unlikely to fail under such low voltage... The
least voltage I've ever seen a film capacitor was something like 63V.
Well, me puzzled or not... it seems you grabbed the bulls by the horn.
Cheers for that.

2. Regarding the -8V power supply... I'm afraid that, while you were so
lucky on the +15V side, to find the shorted culprit in the very first
attempt, you may not be so lucky this time... First because it's not a
"dead short"... it can be just something drawing too much current (such as
another decoupling capacitor), or maybe the -8V power supply is at fault.
Anyway, when you find a wrong power supply rail, there's not much
troubleshooting advice than to hunt down the power sucker... it can be
anything connected to that particular rail.
Sometimes you're lucky and that supply is distributed through connectors
and cables... and in such case, you can rule-out possible culprits by just
lifting the pin on the connector, narrowing down the number of places to
look for possible culprits.
The -8V power supply looks rather unintuitive, because they chose to make
it a "positive supply", and hook the "regulated" positive output to ground,
while taking the negative output from the "unregulated" output of the
rectifier and bulk capacitor.
But other than that, it is and it works exactly the same as the +15V
supply, and the troubleshooting is also the same, just transposing the
measurements to the corresponding components.

Kindest Rgrds,

Fabio
P.S. Sorry for your fellow folks there in MEX. Today was our lucky day
(I`m Brazilian).

On Fri, Jun 29, 2018 at 10:57 am, musicamex wrote:

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

--
Good judgement comes from experience; experience comes from bad judgement.

99 times out of 10 a blown fuse is not due to a bad fuse.....

I remember seeing 7912ADs and HBs in final test and Cal. They would use
them lead that had holes drilled in it for all the adjustments and test
points. today at wouldn't be hard to use a piece of luck Sanders just a
sheet of scrap aluminum. But what the 7912 you do want to make sure there's
air moving across everything

Hi Craig,

That's not an odd question at all, it's one that I should have asked myself before thinking about blown racks!

The fan pulls air in (quite a lot of it), through the PSU module which then exhausts through a wide horizontal slot low down on the module front face. From there it effectively blows between a gap under the 'widthways' cardframe carrying the PSU interface and MPU cards and thence into the 'open' end of the 'longways' cardframe carrying the other seven cards among which, perhaps significantly, is the video processor and scan control card. The chassis vents at the top, front half of each side panel so the airflow is along the cardframe backplanes, up between the cards and across the top front then out the sides.

So by running with no top panel I may well have short circuited the flow by allowing most of the flow to escape to atmosphere from the top of the first frame and prevented any effective cooling of the second?

I will replace the panel, test and report - I was contemplating doing a temperature test under controlled conditions but turns out this beast is too long for my environmental chamber!

Adrian

On Wed, Jul 4, 2018 at 1:20 PM, zenith5106 <hahi@...> wrote:

The same article (as 7L5) was also in the 7854 archive. There were no

other specifically for this problem

There was another about readout issues which may, or more likely, may not

fix your problem.

You can find it here:

/H?kan

I just checked and my 7854 already has this mod, so I'm out of luck. Thanks
for sharing the mod anyway.
I suppose this problem is in the firmware (ROM), since it's the CPU that
decodes the readout and sets the scale factor. Unless there's documentation
or anybody familiar with 7854 ROM content, I doubt there's anything that
can be done about it.

Best Regards,
Nenad Filipovic

Here's what may seem an odd question - does the rear fan pull air in, or push it out?

Craig

Adrian,

My 7912AD runs happily with no extra cooling, I think the interior layout is designed to pull air past the major boards. I have had it running for a couple of hours with no problems. The graticule and main intensities change markedly in the first 10 minutes or so but this is mentioned in the manual.

Most of your images that look 'wrong' have multiple spots rather than continuous traces and I notice you still have the graticule turned on even though the brightness is fairly minimal. One image shows a graticule with rotated and misplaced spots. Try turning the graticule intensity down to minimum, that should turn the graticule generator off and remove one of the possible culprits.

When it is working it looks really good!

Roger

On Tue, 03 Jul 2018 22:46:01 -0700, you wrote:

Hi Keith,
If you have the extension shaft to pot couplers available, I'd be very interested. They are the cast aluminum with plastic insert ones with 2 #4 set screws, like on the "var" knobs on the voltage combo controls. I have 2 that are broken that i cobbled together some Mexico style repairs on. One with shrink tube because the plastic was broken, the other with a brass standoff that i drilled and tapped. I could probably use a few other small parts too. Like the cord wrap plastic tabs. I'll look up the proper names if you want me to.

If they are the same as the ones in a 7A18, 7A26 and so on, I may have
some. What's the shaft diameter?

Harvey

Thanks, Russ

Hmm, I think we are getting there! See 'Getting there'* in album:

/g/TekScopes/album?id=62098&p=Name,,,20,1,0,0

So what did I do? Well not a lot except move the stuff to a different bench and, more importantly I suspect, switched things on early today before the sun moved round - well, ok it stayed still(ish) but the planet rotated - and started warming up the barn.

It ran happily for about 15 minutes then collapsed in a heap again, let it cool off for 5 minutes and it ran for a couple more then failed again. So something is getting hotter than it likes.

There is no cooling in this thing other than in the PSU, I wonder if it was assumed it would be mounted in a blown rack? I've put it up on blocks with a desk fan blowing across it and we'll see if that helps but I'm going to swap out all the tant caps I can see on A38 and A28 for a start!

* Sorry about the Non-Tek scopery lurking in the background - hope I don't get struck off!

Thanks again for all the help and advice,
Adrian

I'm sure this problem is fully on the 7854 side. Do by any chance these WW
articles have any info on 7854 readout mods? Any hint where I could
find/download them?

Best Regards,
Nenad Filipovic

The same article (as 7L5) was also in the 7854 archive. There were no other specifically for this problem
There was another about readout issues which may, or more likely, may not fix your problem.
You can find it here:

/H?kan

Hi Keith,
If you have the extension shaft to pot couplers available, I'd be very interested. They are the cast aluminum with plastic insert ones with 2 #4 set screws, like on the "var" knobs on the voltage combo controls. I have 2 that are broken that i cobbled together some Mexico style repairs on. One with shrink tube because the plastic was broken, the other with a brass standoff that i drilled and tapped. I could probably use a few other small parts too. Like the cord wrap plastic tabs. I'll look up the proper names if you want me to.

Thanks, Russ

I didn't realize I had that exact same scopemobile, here are some pictures of the drawer that may or may not help :

/g/TekScopes/album?id=62217

As you can see there are no runners or anything, and the thing at the top of the back obviously keeps it from falling out. In the last picture you can see that the drawer is lockable by that hole, which I checked and it does have corresponding hole on the main thing. (I don't want to call it a mainframe of course)

As far as I can see, you probably need brute strength to get it to come out. If it is not locked then, what else is there ? No rails no nothing. It just fits in the space.

In the back it seems to have a recess but it ends with a piece of sheet metal that blocks any attempt to push from the rear. The handle is attached by 2 screws and that's it. Your work is not cut out for you.

My best recommendation at this time is to pry between the lo locking surface you see in the last of the photos where it mates with the main thing. Ideally if you have the right prying tool (fat chance) you should attempt to attack it from the side as high as possible, as close to the drawer and the frame as you can get to avoid bending it all up.

Sorry I didn't catch this earlier, there is a handle from a 422 that's been giving me the blues obscuring the model number. Nit bottom line, there are no complex runners or rollers or any of that shit. Looks like they wanted to hold to the KISS theory on that.

If you have other people around you might be better off prying on all the points at once, that should minimize any damage. Two on the handle, two on the bottom. One guy each side. Or your olady if you have one, this is not like pulling a car out of a ditch.

(one time when I was young the cops gave us until the tow truck got there to get my car out of the ditch, we did ! I was driving sideways on slicks through the park with ice and snow. If that wasn't stooopid enough, I had bald tires in the front, three guys pushing and me on the clutch to get us out)

Anyway, a bit of "friendly" persuasion should do it.

On Mon, Jul 2, 2018 at 04:21 pm, David C. Partridge wrote:

H?kan,

Do you have scans of the Wizards Workshop articles. They sound like an
incredibly useful reference.

Wizards Workshop was an internal Service magazine distributed to all Field Offices.
It contained service tips and mod info on pretty much any supported Tek product.
I don't recall how often it came, possibly on a monthly basis. Articles for each instrument
were then saved together on microfiche and added to the collection of the instrument.

So the answer to your question is no but I have pretty much all on microfiche.

Nedad, I'l check on 7854 tomorrow.
/H?kan

Adrian,

I don't know what the rep rate of your pulser is but if you aim for one or two cycles of a square wave or just two edges if the mark space ratio is very large, that should be an unambiguous trace. It looks like you have at present 1usec/div and many pulses per usec so a very detailed trace.

Regards,

Rpger

Thanks, Really enjoyed the story.