Date   

Re: Is my Tek 468 beyond repair?

John
 

On Sat, Oct 17, 2020 at 05:46 AM, <robeughaas@gmail.com> wrote:


I see the IPROM's are still on the way to you. I've started a survey of the 13
468's in the Museum's boneyard and of the first seven, found two with shorted
+5 Storage Supplies, as evidenced by blown F4007 and F4009, 5-amp picofuses at
the back of the trigger board. I've dismantled one and found a shorted CR169,
the catch diode in the supply. I'll go through the remainder tomorrow, and I
suspect I'll find more with shorted supplies. Of the six I've been able to
test ROM's on, I have found all the ROM's were good. I suspect that the power
supply problem is causing the failure that is thought to be ROM rot.
That's an interesting observation. Some time ago I came across a 465 that had an intermittent shorting -8V supply due to a faulty smoothing can but so far in the 468 all supplies are good and as it turns out, the ROMs are good as well. The problem turned out to be a non-running CPU. I don't know much about the history MOSTEK EEPROMs but can't help wondering how long these are likely to last although I am glad to have backup spares "just in case" courtesy of a helpful contributor on here. Still it is a testament to Teks' engineering that they can be brought back to life and still work 40 years later.... For sure the 468 is an interesting example of a vintage scope with early storage computing.


Re: Is my Tek 468 beyond repair?

John
 

On Sun, Oct 18, 2020 at 10:31 PM, John wrote:



In analogue XY mode the X input comes via Q582/Q583 and the manual shows
the
DC switching signals (+5V and -8V) to turn on this input (and disable the
sweep). So you need to check that the +5V, -8V switching signals are
present
and that Q582, Q583 are OK.
Will check these out as well although I can confirm the presence of -8V at the
input to R689, but also at the junction of CR679 and R679. There is also +15V
at R380. I will do some more investigation and confirm the +5V input tomorrow.
I finally found it! :-)

After checking that -8V and +15V were present around the trigger offset inputs and voltages around the diodes were as indicated, and so ruling out this part of the circuit, I turned my attention to Q582/Q583. The problem turned out to be here.

Both +5V and -8V supplies were present but the voltages at Q582_b and Q583_b were considerably adrift from those indicated (-800mV/-100mV instead of -1.8 [-1.5V?] and -2.8V). This means that Q583 would fail to turn on affecting the output from between R480/R481 which is directly connected to U564_p2.

The transistors were fine and tracking back led me to J683, the connector providing the input from the X axis. On pulling this out I discovered that the centre pin was bent and evidently not making contact with the socket on the PCB. Since I had not touched this at any time, I plead not guilty! Once the pin was straightened and the connector plugged back in, the spot moved onto the screen. The X-gain was low and required a tweak of (V)R681 but otherwise X_Y mode now worked fine. When switching between X_Y and triggered modes an adjustment of the POSITION control of about half the width of the CRT display is still required but at least this is now within comfortable adjustment range.

Thanks Harvey for pointing me in this direction and both Harvery and Roger for their circuit descriptions, bit of which were immensely helpful as once that fell into place, it allowed me to better understand and rule out the sweep generator part of the circuit, which I had got side-tracked into, and allowed me to concentrate on other possible causes.

Everything on the scope now works fine although I have not yet tested B-delay yet as I need to research this. Once everything is properly re-assembled I should hopefully be able to move on to running through the calibration steps although from what I have seen so far, everything looks just about spot on.


Re: 519 -- broken rate generator; stuck at a very high frequency?

Tom Lee
 

So, the multivibrator is producing the correct waveforms with controllable frequencies, and the only problem is that the final output is running at 250kHz, independently of what the multivibrator is doing? Have you verified that the swing out of the multivibrator is correct? And is your rate generator an early or late one?

As you said, there isn't much left to check, so by definition you're close!

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 10/18/2020 16:10, sdturne@q.com wrote:
Well, no dice there either. The transistor seems fine. I'm officially stumped. The contacts for the multiplier switch are working fine, establishes by the fact that the multivibrator is both running nominally (which also implies the two 6DJ8s are fine) and controllable by the multiplier switch and the cycles/sec pot. There's really not much else to this circuit...nothing could really go wrong with the charge line right? It's just a coil of coax.

Sean

On Sun, Oct 18, 2020 at 03:34 PM, @0culus wrote:

Couldn't find anything amiss...all the passives appear to be fine. I scoped
the multivibrator as shown in the schematic, and it is works fine. It responds
to the controls as it should. I reckon the problem is most likely the
avalanche transistor. Luckily, I also have a 577D1 now...

Sean


Re: Air filters for big 500 series scopes

snapdiode
 

My range hood has two metal filters that I clean weekly by spraying both sides with Scrubbing Bubbles, I let it soak for five minutes, then rinse off with hot tap water.
I do it in the bathtub where the shower thingy is removable.
This cleans em up real good.


Re: OT Hameg HM103 blanking

Jean-Paul
 

Pete: Many thanks, Indeed a small ceramic cap, perhaps 6 mm diameter and 2 mm thick.

Three are used for peaking the optocoupler response, across the -1.8 kV HV to the CRT grid and cathode.
They look fine your point of cleaning is great, as they are connected to transistor bases and the PCB is somewhat exposed under cooling grille holes in the cabinet.

Other Hameg repairs have mentioned failed caps

I will try some isopropyl alchol later on.

Best Regards,

Jon


Re: Air filters for big 500 series scopes

Chuck Harris <cfharris@...>
 

What we have here is a failure to communicate.

After you use your stove to cook a pan full of bacon,
your filter will be coated with cooking grease... specifically,
bacon grease.

Then you make hamburgers, and they will then have a coating
of bacon grease and hamburger grease... Fry some eggs, and
they will have a coating of bacon grease, hamburger grease,
and butter....

New, they are coated with nothing but the mill oil from
when they were machined. After you use them for the first
time, they are coated with cooking grease until you do the
hideous task of cleaning them.

-Chuck Harris

Roy Thistle wrote:

On Thu, Oct 15, 2020 at 08:46 PM, Chuck Harris wrote:


Of course range filters are coated... coated with
cooking grease.
Well... I was out here in the colonies... masked and by the local home despot... and I decided to hike over to the kitchen section.
I asked the probrotradesman kitchen guy if those aluminum range filters come coated with cooking grease. He said... not as he knows for... and thinks they aren't sprayed with anything... but, might be a good idea if there was something to spray them with.
Anyway... ya, I think the manufacturers don't coat them.






Scope, cooling ICs - refresh or not?

Staffan
 

Hello,

I have an TDS744A oscilloscope, which is working really well. Just adjusted screen brightness and it is almost as new!
I believe I've seen some discussions that the heat transfer paste (silicon grease?) between components and the coolers may dry out over time. This unit has quite a few coolers and they got reasonably warm just during the time it took to adjust the display. They seem actually to be glued on top of the ICs - unclear how.
Question is: can - or should - the cooler interface be refreshed by adding some paste or similar? What would be the proper way in that case?
I imagine a unit of this age with a 2 GSPS acquisition can get fairly hot. Does anyone have suggestion for which ICs should be paid attention to (there seems to be six bigger and two smaller coolers on the acquisition board)?
I have seen general comments, but can't say I've seen specific suggestion for what devices on the 744 that should be taken care of. Are there more coolers than the ones visible when just pulling the cover?

Regards,
Staffan


Re: FS: S-100 stuff, electronic stuff, model railroad stuff, books and magazines!

momemeca
 

Hello Richard,
So sorry to hear of your health issues. All I can send you are best wishes and courage.

I am also a teacher and physicist and I teach youngsters about computer architecture ...etc and often hark back to the "good old days" as examples.
I would greatly appreciate it if you would consider my request :-)

Cheers,

Rick.

Rick

On 19 Oct 2020, at 13:46, Richard R. Pope <mechanic_2@charter.net> wrote:

Hello all,
It looks like the S-100 stuff is available again. Sorry for the confusion!
GOD Bless and Thanks,
rich!

On 10/18/2020 12:36 AM, Richard Pope via cctalk wrote:
Hello all,
The S-100 stuff is sold pending payment. I appreciate the interest and help!
GOD Bless and Thanks,
rich!

On 10/17/2020 10:44 PM, Bruce wrote:
I believe there is an S-100 meuseum - think they specialize in Altare
- but they woul probably be a good home for the stuff

Cheers!

Bruce

Quoting Jeff George <driftwoodturning@gmail.com>:

Hi there, I’m sorry to hear about your expected diagnosis, that’s a tough
one. My neighbor Had cancer of the liver last year, he tried the “Rick
Simpson oil” treatment along with standard chemo and is cancer free today.
Maybe look into it?

On a selfish note, Im a high school physics teacher in Tn and would love to
find good price on some equipment so that my students could get their feet
wet with some actual good equipment. Scopes, frequency generators, vtvm’s,
dmm’s, etc.. I am a ham radio operator and tinkerer, some skills at
repairing equipment but not a whole lot.

Please let me know if you have anything appropriate for my students at a
high school budget. Happy to give you my info so that you can verify my
employment.

Jeff

On Sat, Oct 17, 2020 at 10:14 PM Richard R. Pope <mechanic_2@charter.net>
wrote:

Hello all.
I have 22 S-100 boards for sale. There are two backplanes. One is a
9 slot bare board and the other is a 19 slot fully populated board. Both
boards have active termination. There are 8080, Z80, FDC, HDC, Serial,
68030, a Display board, a Front Panel board. There are also 3 Mean Well
power supplies supplying the +9VDC and the +_16VDC. There are also
voltmeters and amp meters . I want $500 plus shipping for all of it. I
can provide a full inventory and pictures for anyone who is truly
interested.
I probably have cancer and if I do I am dying. I want all of this
to go to a good home and not to the landfill. If anyone is interested I
have some test equipment, electronic components, and model railroad
equipment Please only serious inquires for I tire very easily.
GOD Bless and Thanks,
rich!





--
Paying Attention, Not a Tutor!





FS: S-100 stuff, electronic stuff, model railroad stuff, books and magazines!

Richard R. Pope
 

Hello all,
It looks like the S-100 stuff is available again. Sorry for the confusion!
GOD Bless and Thanks,
rich!

On 10/18/2020 12:36 AM, Richard Pope via cctalk wrote:
Hello all,
The S-100 stuff is sold pending payment. I appreciate the interest and help!
GOD Bless and Thanks,
rich!

On 10/17/2020 10:44 PM, Bruce wrote:
I believe there is an S-100 meuseum - think they specialize in Altare
- but they woul probably be a good home for the stuff

Cheers!

Bruce

Quoting Jeff George <driftwoodturning@gmail.com>:

Hi there, I’m sorry to hear about your expected diagnosis, that’s a tough
one. My neighbor Had cancer of the liver last year, he tried the “Rick
Simpson oil” treatment along with standard chemo and is cancer free today.
Maybe look into it?

On a selfish note, Im a high school physics teacher in Tn and would love to
find good price on some equipment so that my students could get their feet
wet with some actual good equipment. Scopes, frequency generators, vtvm’s,
dmm’s, etc.. I am a ham radio operator and tinkerer, some skills at
repairing equipment but not a whole lot.

Please let me know if you have anything appropriate for my students at a
high school budget. Happy to give you my info so that you can verify my
employment.

Jeff

On Sat, Oct 17, 2020 at 10:14 PM Richard R. Pope <mechanic_2@charter.net>
wrote:

Hello all.
I have 22 S-100 boards for sale. There are two backplanes. One is a
9 slot bare board and the other is a 19 slot fully populated board. Both
boards have active termination. There are 8080, Z80, FDC, HDC, Serial,
68030, a Display board, a Front Panel board. There are also 3 Mean Well
power supplies supplying the +9VDC and the +_16VDC. There are also
voltmeters and amp meters . I want $500 plus shipping for all of it. I
can provide a full inventory and pictures for anyone who is truly
interested.
I probably have cancer and if I do I am dying. I want all of this
to go to a good home and not to the landfill. If anyone is interested I
have some test equipment, electronic components, and model railroad
equipment Please only serious inquires for I tire very easily.
GOD Bless and Thanks,
rich!





--
Paying Attention, Not a Tutor!









Re: Air filters for big 500 series scopes

Roy Thistle
 

On Sat, Oct 17, 2020 at 01:54 AM, Dave Daniel wrote:


soak them in a solution of Professional Brewer's Was
Those tend to be alkaline peroxide based cleaners. (Alkaline peroxides are good at dissolving microbes, and grease; but can/do attack some metals. Sometimes, passivators are used, to help protect the metal.)
I used a trisodium phosphate solution, which is an alkaline phosphate based cleaner. Trisodium phosphate is a very good degreaser; but, it can/will attack some unpassivated metals.
After some time, aluminum forms a very strong, but thin thin layer, of Aluminum oxide, that acts as passivation. On these very old filters (decades old?), the surface of the aluminum is bound to have oxidized.
I've cleaned up aluminum 500 series filters several times using trisodium phosphate. And, very dirty filters cleaned up so as they looked like new. However, milage may vary... and thus, caveat emptor.


Re: 519 -- broken rate generator; stuck at a very high frequency?

Sean Turner
 

Hi Chuck,

I haven't seen anything like that inside or outside the case. I will keep my eyes peeled though.

Sean

On Sun, Oct 18, 2020 at 05:04 PM, Chuck Harris wrote:


Hi Sean,

I know nothing about the 519, but I do know that tektronix
had a habit of making all sorts of configurations available
on similar scopes. The folks that would buy a 519 often
had divergent interests.

Look carefully for binding posts that should have a strap
connecting them. They could be on the front panel, or the
back.

There also could be other forms of strapping inside of the
scope. It should show up in the schematics.

-Chuck Harris


Re: Air filters for big 500 series scopes

Roy Thistle
 

On Thu, Oct 15, 2020 at 08:46 PM, Chuck Harris wrote:


Of course range filters are coated... coated with
cooking grease.
Well... I was out here in the colonies... masked and by the local home despot... and I decided to hike over to the kitchen section.
I asked the probrotradesman kitchen guy if those aluminum range filters come coated with cooking grease. He said... not as he knows for... and thinks they aren't sprayed with anything... but, might be a good idea if there was something to spray them with.
Anyway... ya, I think the manufacturers don't coat them.


Re: 519 -- broken rate generator; stuck at a very high frequency?

Chuck Harris <cfharris@...>
 

Hi Sean,

I know nothing about the 519, but I do know that tektronix
had a habit of making all sorts of configurations available
on similar scopes. The folks that would buy a 519 often
had divergent interests.

Look carefully for binding posts that should have a strap
connecting them. They could be on the front panel, or the
back.

There also could be other forms of strapping inside of the
scope. It should show up in the schematics.

-Chuck Harris

sdturne@q.com wrote:

Well, no dice there either. The transistor seems fine. I'm officially stumped. The contacts for the multiplier switch are working fine, establishes by the fact that the multivibrator is both running nominally (which also implies the two 6DJ8s are fine) and controllable by the multiplier switch and the cycles/sec pot. There's really not much else to this circuit...nothing could really go wrong with the charge line right? It's just a coil of coax.

Sean

On Sun, Oct 18, 2020 at 03:34 PM, @0culus wrote:


Couldn't find anything amiss...all the passives appear to be fine. I scoped
the multivibrator as shown in the schematic, and it is works fine. It responds
to the controls as it should. I reckon the problem is most likely the
avalanche transistor. Luckily, I also have a 577D1 now...

Sean





qex@groups.io

Reginald Beardsley
 

Generally I do not cross post, but it seems to me appropriate in this case. These are the lists where the people I admire hang out.

Some time ago I created the group, but only informed a single person that I had done so.  However, enough people found it and joined that I decided I should take it live.

This is intended to be a forum primarily for discussing QEX articles as that should save authors from repeating the same answers to multiple correspondents. 

However, I should also like it to serve as a forum for serious work on a variety of topics from modulation systems similar to FT8 to teaching how to design an HF amplifier or oscillator from scratch as opposed to simply copying older designs.  Experts conversing with experts and also taking the time to instruct novices. I am hoping for a substantial educational content.

The group is unmoderated.  Unless someone gets seriously outside the bounds of polite social behavior I have no intent of exercising any control unless compelled to do so.

It is also my hope that in conjunction with QEX becoming a print option for ARRL members it will help stimulate readership and advertising revenue to support QEX. I have requested that option and my ARRL membership hangs in the balance. I will continue to subscribe to QEX in print independent of whether I continue as an ARRL member.

It is my hope that this will help QEX develop the technical stature that QST once enjoyed. I have no interest in contests and trophies. I'd like to believe I am not alone in my passion for the technology of radio.

Have Fun!
Reg


Re: 519 -- broken rate generator; stuck at a very high frequency?

Sean Turner
 

Well, no dice there either. The transistor seems fine. I'm officially stumped. The contacts for the multiplier switch are working fine, establishes by the fact that the multivibrator is both running nominally (which also implies the two 6DJ8s are fine) and controllable by the multiplier switch and the cycles/sec pot. There's really not much else to this circuit...nothing could really go wrong with the charge line right? It's just a coil of coax.

Sean

On Sun, Oct 18, 2020 at 03:34 PM, @0culus wrote:


Couldn't find anything amiss...all the passives appear to be fine. I scoped
the multivibrator as shown in the schematic, and it is works fine. It responds
to the controls as it should. I reckon the problem is most likely the
avalanche transistor. Luckily, I also have a 577D1 now...

Sean


Re: 519 -- broken rate generator; stuck at a very high frequency?

Sean Turner
 

Couldn't find anything amiss...all the passives appear to be fine. I scoped the multivibrator as shown in the schematic, and it is works fine. It responds to the controls as it should. I reckon the problem is most likely the avalanche transistor. Luckily, I also have a 577D1 now...

Sean


Re: 'Tektronix Short Destroyer'

ditter2
 

I suspect this belonged to R. Michael Johnson, who managed TM5000 engineering when I started at Tek. My cube was directly across from his. He may have worked in portables engineering previously, as a label indicates.
There were many versions of “short destroyer” throughout the engineering and production areas at Tek. In the early days of multi-layer circuit boards, registration of the individual layers was not always perfect. Occasionally you would see a board where a ground plane layer is slightly mis-registered to where one or two pads are shorted to ground. The short destroyer could be used to attempt to burn out the short. Most employed a capacitor bank to store a charge to quickly vaporize the short. Applying low voltage at high current continuously tended to burn the board, whereas a quick zap with higher voltage would quickly vaporize the short without burning the board.

Steve


Re: 519 -- broken rate generator; stuck at a very high frequency?

Sean Turner
 

OK, I got the scope on it's side. That wasn't as hard as I feared, because the 519 is very much bottom heavy. Looking at the part of the rate generator circuit that is on the bottom side, I can see nothing obvious, so I'm going to do some measurements of the passives and see if anything sticks out.

Sean


Re: OT Hameg HM103 blanking

petertech99h
 

Jean-Paul,
Is the 68pf 2Kv cap a ceramic disk cap? Sounds like it is.  I can't remember the last I had a leaky disk cap!
If there is evidence of dirt, oil, old flux right around the cap, I would clean it instead.
If it is cracked or chipped then replace for sure!

Pete

On Sunday, October 18, 2020, 11:53:45 a.m. EDT, Jean-Paul <jonpaul@ix.netcom.com> wrote:

Hello again all!

Ray thanks for the PM,


I Have just posted schematic markup and trace image in album "HM103 Hameg"

I now suspect the 68 pF coupling cap C705 is leaky and has damaged the NPN transistor.

But am traveling and Limited in tools and parts to disassemble main board and replace the 68 pF 2kV caps.

Open to your kind advise!

Jon


Re: Is my Tek 468 beyond repair?

John
 

On Sun, Oct 18, 2020 at 05:10 PM, Roger Evans wrote:

Q760 and Q772 are PNP common emitter amplifiers, they have very close to unity
current gain and they conduct because their base is positive with respect to
the emitter so the BE junction is forward biassed. In XY mode (see page 3-26
of the manual) the sweeps are disabled, the BE junction should be reverse
biassed, there is almost no collector current and they just look like a high
impedance from the output side.
Thank you for that explanation. Much appreciated.

In analogue XY mode the X input comes via Q582/Q583 and the manual shows the
DC switching signals (+5V and -8V) to turn on this input (and disable the
sweep). So you need to check that the +5V, -8V switching signals are present
and that Q582, Q583 are OK.
Will check these out as well although I can confirm the presence of -8V at the input to R689, but also at the junction of CR679 and R679. There is also +15V at R380. I will do some more investigation and confirm the +5V input tomorrow.

You're looking at a configuration called common base (can be common base, common emitter, common collector). Common collector is an emitter follower, common emitter is what most people think of as a transistor amplifier.
Harvey, thank you also for such a detailed explanation.

I had read through the Detailed Circuit Description section in the Theory of Operation chapter of the manual. Details of X_Y operation are throughout the chapter and I picked up bits and pieces but your description fills in the blanks which is very helpful.

Note that the horizontal amplifier is playing with a current input, not really voltage.
Noted. I grasped the fact that there must be a variance in current between the two halves of the circuit when I found different voltage readings at the emitters of Q760 and Q772 but I wasn't quite sure what that meant.

Had you looked at Q781 and Q782? the trigger view offset voltage goes through a diode or so (as does the trigger view offset enable) and that contributes to the offset of the horizontal amplifier.
Yes I did swap them around to see whether the problem would shift to the opposite side. It did not. I also substituted the two ICs (U690 and U789) and checked that signals at the gates were as indicated. All looked good. However, I completely omitted to investigate the right hand side of Q781/Q782 including the inputs and diodes you mention. I will check that out and re-read your comments tomorrow morning when when my mind is fresh when hopefully this will all fall into place.

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