Date   

Re: 7B15, 7B10 questions

Chuck Harris
 

Not an assertion I would make!

I had one 7104 that had a permanently etched reverse image
of a square wave and a triangle wave... obviously from a
function generator.

I know that there is a large contingent of folks that own
these scopes, that have no real work for them, but seriously,
how long could you stand to view a square wave and a triangle
wave on your 7104's screen?

It boggles the imagination.... well mine anyway...

A more likely explanation is that the ebay seller had the
function generator traces on the screen, really really bright
because that is what 7104's are known for, and burned an image
in the screen while preparing for, and taking a photograph...
All staying within the protective timers very limited protection.

The amber limited viewing LED comes on whenever the image is
about what one would consider normal brightness for a 7904.
You have to have a pretty dim environment to be able to run
a 7104 comfortably, never activating that warning.

The 2467B does a much better job of protecting the MCP. It never
allows the readout to be on the screen continuously without a
trace being on the screen, without putting the readout into flicker
mode. It moves the readout around periodically to wear level the
readout area of the MCP. It limits the trace intensity to a
perceived value of screen brightness by strobing the intensity of
the beam hitting the MCP. It leaves the MCP at its lowest
amplification setting when the Intensity control is set to view
low performance images, only raising it when the Intensity control
is turned up near full... stuff like that.... In addition to the timers.

-Chuck Harris

Roy Thistle wrote:

On Sun, Nov 19, 2017 at 10:12 AM, Dennis Tillman W7PF wrote:


Damaging the CRT is one thing you don't have to worry about
Hi Dennis:
We have 2 7104s... and occasionally I see one for sale, and the picture of it usually shows it operating with the amber "limited viewing time" indicator illuminated.
I'd only pay the prices most are asking for a 7104, if I thought I could get a good spare MCP CRT, with some good life left in it. A cheap 7104 might be worth it, just for the parts though.
I take it by your post... that even though the janitor tripped over a 7104 in the hallway, outside the research lab, and is now selling it... the CRT should be good, even though it may have operated in "limited viewing time" mode frequently?
Best regards and wishes.
Roy


Re: TDS 644A Power Supply problem

Siggi
 

Hey Peter,

I repaired one of those from a TDS684A which had failed in an interesting
mode. The TVSes had become uni-directional, and so current was flowing
through the TVSes, T3 and Q9 continuously. Out of circuit they measured as
a diode in one direction, but as an open in the other (I didn't have any
way to measure their threshold voltage). It seems only RT4/5 were limiting
the current/damage at that point. I couldn't figure out why the TVSes had
failed, but apparently it's not uncommon for them to do so.
I suspect you'll find a very close schematic on Håkan's download page:
http://www.hakanh.com/dl/kits.htm. Looking at the schematic, it occurs to
me that CR7 & C15 make a snubber, whereas the TVSen are clamps. If the
snubber fails, I'd expect the TVSes and the switching transistor to suffer
higher transients, so maybe that's one place to look. R21 is also perhaps
suspect, as it will presumably discharge C15 between cycles.

Good luck,
Siggi

On Tue, Aug 20, 2019 at 3:33 AM peter bunge <bunge.pjp@gmail.com> wrote:

A year ago I repaired a TDS 644A power supply.with overheated VR4 and VR5
snubbers and blown Q9 switch transistor. Q9 was replaced with an MJE8501
which was pencilled in on the schematic. The transistor that I removed was
a BU508A but replacements I ordered from China tested about 500v on a curve
tracer so the MJE8501 was left in.
I also found that C17 was defective and replaced it.
A year later the new VR4 and VR5 show signs of overheating and Q9 is blown
again.
VR4 and VR5 should never handle any current, only clip transients. Q9
should not experience excessive voltages because the regulator and all lock
out circuits were tested and are working. I had adjusted R18 (A19 power
factor control) slightly to set the bulk voltage at 408v as it was a bit
high.
Does anyone have any experience with suggestions to repair this power
supply.




Re: Tek 576 chatters

Bob Koller <testtech@...>
 

It may have a PSU problem as Chuck described.
However, if the 100V supply is being loaded, this sounds like the CRT HV transformer problem typical of the older brown encapsulated transformer design. Coupled with your comment of "However turning it off and on it ran for a few minutes then did the same thing"
If your CRT HV transformer is the black silicone encapsulated type, you can disregard, but if not, that would be my very strong suspicion.


Re: Thoughts on TDS744A

Mark Schoonover
 

I got 0.07 USD for a class action lawsuit on bad motherboard capacitors
back in the day. Probably related to many different products.

73! Mark KA6WKE

Website: https://www.ka6wke.net
Live Stream: https://www.ka6wke.net/live-stream
YouTube Live!: https://bit.ly/bench-therapy-live
Author: 4NEC2 The Definitive Guide EMail List:: 4nec2defguide@groups.io


On Wed, Aug 21, 2019 at 4:27 AM greenboxmaven via Groups.Io <ka2ivy=
verizon.net@groups.io> wrote:

The condensers you mention were a worldwide scourge. Many millions of
them were made when an angry employee stole the electrolyte formula from
one company and took it to another. The problem was the formula was not
complete. In many cases the electrolyte gasses off slowly and escapes
without leaving a residue, but the condenser has no capacitance. Having
restored many items using these bad condensers, I strongly recommend
that you mark the locations, value, and polarity of all the condensers,
remove them all, and then gently scrub the board with hot soapy water.
Rinse it thouroughly and dry it in flowing warm air before soldering the
new condensers on.

Bruce Gentry, KA2IVY


On 8/21/19 5:22 AM, Jay Walling via Groups.Io wrote:
Hi Siggi,

While the models I mention do have aluminum SMT electrolytics on the
front panel, I have not seen any that were leaking. I suspect that the
leaking caps on the older models were a quality problem with the cap vendor
they were using at the time.
Jay







Re: 7B15, 7B10 questions

@0culus
 

Roy,

I got very lucky a couple weeks ago and scored a basically pristine 7104 and it's intended plugin complement at a .gov surplus auction for a very good price (all of the above for $125). It is obviously well cared for, as the crt is crisp, bright, with the only signs of any problems being around the readouts, which are a bit dim compared to the traces (which isn't unexpected I suppose). I've found it is very easy to get a perfectly usable trace for all but the fastest signals at very low brightness levels...low enough that the limited view circuit either isn't kicking in or it's in the 20 minute timeout region (beam current above 0.2 microamps, but less 2 microamps) than rather than 2 minutes (2 microamps or above).

It's truly a tour de force for Tektronix analog scope engineering; beautifully crafted inside and out, with incredible performance.

Sean

On Wed, Aug 21, 2019 at 06:55 AM, Roy Thistle wrote:


Hi Dennis:
We have 2 7104s... and occasionally I see one for sale, and the picture of it
usually shows it operating with the amber "limited viewing time" indicator
illuminated.
I'd only pay the prices most are asking for a 7104, if I thought I could get a
good spare MCP CRT, with some good life left in it. A cheap 7104 might be
worth it, just for the parts though.
I take it by your post... that even though the janitor tripped over a 7104 in
the hallway, outside the research lab, and is now selling it... the CRT should
be good, even though it may have operated in "limited viewing time" mode
frequently?
Best regards and wishes.
Roy


Re: Tek 576 chatters

Chuck Harris
 

I don't know what shape your 576 is in, but I have found
many with bad 5V filter capacitors. They suddenly go open
circuit. They are the Mallory FP style, and the internal
aluminum strip that connects to the solder lugs etches
open circuit.

The usual symptom is the 576 goes completely goofy. The
relays chatter, the screen goes away, bat bleep crazy.

You can safely parallel a modern capacitor to the terminals
on the FP can and put the capacitors somewhere convenient
while you wait for a better solution.

Worth a look see.

-Chuck Harris

peter bunge wrote:

I have not had any replies on the TDS644A power supply problem. I have my repair log for the last repair if anyone is interested. It is not a simple power supply.
While troubleshooting I needed my Tek 576 curve tracer to check the TVS and HV transistors, especially the replacement BU508A (the last batch from China were only good to 400v). I had used MJE8501 (pencilled in on a TDS544A schematic) but have not been able to find a parts list to show the correct transistor. HELP!
My curve tracer now does not show any curves. While troubleshooting it suddenly made a sound like a relay chattering and the display went blurry and jumped around. The +100v supply was at 60v. However turning it off and on it ran for a few minutes then did the same thing. I left it off for dinner and when I returned it ran for over an hour while I continued troubleshooting the step generator which does not seem to be getting to the test transistor.
The manual says to check the DAC but does not say where it is.
I am about to start again. Any suggestions?
PeterB




Tek 576 chatters

peter bunge
 

I have not had any replies on the TDS644A power supply problem. I have my repair log for the last repair if anyone is interested. It is not a simple power supply.
While troubleshooting I needed my Tek 576 curve tracer to check the TVS and HV transistors, especially the replacement BU508A (the last batch from China were only good to 400v). I had used MJE8501 (pencilled in on a TDS544A schematic) but have not been able to find a parts list to show the correct transistor. HELP!
My curve tracer now does not show any curves. While troubleshooting it suddenly made a sound like a relay chattering and the display went blurry and jumped around. The +100v supply was at 60v. However turning it off and on it ran for a few minutes then did the same thing. I left it off for dinner and when I returned it ran for over an hour while I continued troubleshooting the step generator which does not seem to be getting to the test transistor.
The manual says to check the DAC but does not say where it is.
I am about to start again. Any suggestions?
PeterB


Re: Why U800 is such a big problem in Tek Scopes

 

We don't offer the re-bake process on U800's any longer at Sphere (because Toru in Japan does not do it any longer). The actual root cause of the primary problem with U800 is as follows:

The modified DIP package has a very large heatsink pad, *bonding the chip to the pad is very difficult*, and it was a process that sometimes left the chip attached with essentially a cold solder joint, with high thermal resistance. This made the chip exhibit a range of problems as it warmed up. The re-bake process essentially re-seated the chip to the pad by re-flowing the attachment. *IF* the faults were related to this issue, the success rate was quite high.

The chip also had other stress failures not related to this specific issue, they cannot be cured by re-flowing the die attachment. Heatsinking the chip seems to help improve life, and I did it to any 24xx scope that I worked on. Even a 2" square of plate aluminum attached to the package makes a very big difference in package and die temperature.

This is not the only 24xx series ship to exhibit die attachment thermal problems, it also occurs in the 155-0236, and they have also been recovered by this process.

While I like the 24xx series operationally, the product did not age as well as earlier designs, and repairs and calibration often prove quite difficult after 30 years, especially if U800 is involved.

best regards,
walter

--
Walter Shawlee 2
Sphere Research Corp. 3394 Sunnyside Rd.
West Kelowna, BC, V1Z 2V4 CANADA
Phone: +1 (250-769-1834 -:- http://www.sphere.bc.ca
+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)


Re: Will this capacitor fail?

Mlynch001
 

George and DW

Definitely a 170uF Cap. I would check the ESR on that old cap very carefully, if it checks "good" for capacity, ESR and ripple, leave it alone. I just finished with a 577 and the filter caps all checked good for ESR and Ripple current. In my experience, the 577 was much more plagued with bad tantalum caps. I found 7 bad ones on mine, which completely disabled the thing. Just my opinion and experience, of course. Best of luck in your project.

--
Michael Lynch
Dardanelle, AR


Re: 2235A Vertical Trace Issue

Chuck Harris
 

Think of a CRT's electron gun as being like a machine gun. Just like
a machine gun fires bullets at a fixed continuous rate, so does an
electron gun with electrons.

Let's imagine our electron gun fires off electrons at 10 electrons per
second.

If you sweep our electron gun across the width of the screen in 10 seconds,
there will be about 100 electrons striking the screen, evenly spaced along
a line.

Similarly, the same thing will happen if the electron gun's beam of
electrons travels from the top to the bottom of the screen in 10 seconds.

Further suppose the beam goes from top to bottom in only 1 second, while it
is also traveling from left to right in 10 seconds.

Since the trace is only 10 seconds long, it will still contain a total of
100 electrons, but during the time it is traveling from top to bottom, there
will only be 1 second's worth of electrons, or about 10 electrons.

Suppose still further that the beam travels top to bottom in 1/10th of a
second while it is taking 10 seconds to travel from left to right. The
total trace will still contain only 100 electrons, but the section that
goes from top to bottom will now contain only 1 or maybe 2 electrons!

If we keep reducing the time it takes for our beam to go from top to bottom,
while it is taking its 10 seconds to travel from left to right, eventually
it will traverse from top to bottom of the screen without recording even a
single electron striking the screen.

The record of our electron beam's travels will look as though the beam
instantly traveled from the top to the bottom of the screen.

This is exactly what is happening on your scope. The number of electrons
the electron gun shoots at the screen is at a rate that is a million times
faster, but parts of the trace where the bean travels great distances in
very little time will not have as many electrons hitting the screen as will
parts where the beam is puttering along slowly... The beam will appear to
have no brightness in those sections where it is traveling really fast..

-Chuck Harris

Ed Pavlovic wrote:

I'm slowly going through my 2235A scope, replacing the Schaffner line filter and the RIFA capacitors on the Pre Regulator board. The RIFA caps were visibly crazed, so I'm glad I'm replacing them before they failed like the ones in an old computer PSU I have.

Issue I'm having is the vertical traces are very dim compared to horizontal traces. Most noticeable on a square wave, but if you introduce a horizontal element, a sinewave or sawtooth pattern, the trace looks normal.

I'm waiting on parts from Mouser to replace the failure prone inlet caps with new ones, so I'm unable to check voltages and ripple at the moment.

Is it just an issue with the width of a vertical trace affecting the brightness on the screen, or is there maybe a deeper issue going on here?

Thanks

Ed Pavlovic
KC9MMM




Re: 7B15, 7B10 questions

Roy Thistle
 

On Sun, Nov 19, 2017 at 10:12 AM, Dennis Tillman W7PF wrote:


Damaging the CRT is one thing you don't have to worry about
Hi Dennis:
We have 2 7104s... and occasionally I see one for sale, and the picture of it usually shows it operating with the amber "limited viewing time" indicator illuminated.
I'd only pay the prices most are asking for a 7104, if I thought I could get a good spare MCP CRT, with some good life left in it. A cheap 7104 might be worth it, just for the parts though.
I take it by your post... that even though the janitor tripped over a 7104 in the hallway, outside the research lab, and is now selling it... the CRT should be good, even though it may have operated in "limited viewing time" mode frequently?
Best regards and wishes.
Roy


Re: Will this capacitor fail?

Glydeck
 

You should be fine. 20% above 200 volts would be 240 volts. BTW, the schematic shows the value C744 as 170 micro farad.

George KD6NEW

On Aug 20, 2019, at 9:16 PM, DW <wilson2115@outlook.com> wrote:

I have a Tektronix 577 curve tracer and I am recapping the power supply board that is located at the rear of the instrument. I am looking at replacing C744 which is a 250V 1700uF capacitor. I found a 250V 1800uF capacitor but the capacitor installed is a 275V capacitor though the manual states 250V. I am curious how much voltage typically runs across C744 so I don't destroy a capacitor, thanks



Re: Need Help Troubleshooting Tektronix PS280

daven9ooq <daven9ooq@...>
 

I would stick with what you have, maybe it's time to do a little service on it, sometimes you need a dual supply or even 3voltages it's rare though.
I should have done more resurch on this before I bought it. But it's the same  era as my TM500 equipment so it should fit right in. Around 1981.Many thanks !Daven9ooq


Re: Thoughts on TDS744A

greenboxmaven
 

The condensers you mention were a worldwide scourge. Many millions of them were made when an angry employee stole the electrolyte formula from one company and took it to another. The problem was the formula was not complete. In many cases the electrolyte gasses off slowly and escapes without leaving a residue, but the condenser has no capacitance. Having restored many items using these bad condensers, I strongly recommend that you mark the locations, value, and polarity of all the condensers, remove them all, and then gently scrub the board with hot soapy water. Rinse it thouroughly and dry it in flowing warm air before soldering the new condensers on.

Bruce Gentry, KA2IVY

On 8/21/19 5:22 AM, Jay Walling via Groups.Io wrote:
Hi Siggi,

While the models I mention do have aluminum SMT electrolytics on the front panel, I have not seen any that were leaking. I suspect that the leaking caps on the older models were a quality problem with the cap vendor they were using at the time.
Jay



Re: 2235A Vertical Trace Issue

Glenn Little
 

The dim traces on the vertical part of a square wave is normal.
This is due to the speed which they are "drawn" on the CRT face.
The faster the rise time of the trace, the dimmer the trace will be.
The faster the trace speed, the dimmer the trace.

It is like painting with a spray can.
If you hold the nozzle down and paint a horizontal line then quickly paint a vertical line, the vertical line will have less paint on it per unit of length than the horizontal line.

Glenn

On 8/21/2019 1:43 AM, Ed Pavlovic wrote:
I'm slowly going through my 2235A scope, replacing the Schaffner line filter and the RIFA capacitors on the Pre Regulator board. The RIFA caps were visibly crazed, so I'm glad I'm replacing them before they failed like the ones in an old computer PSU I have.

Issue I'm having is the vertical traces are very dim compared to horizontal traces. Most noticeable on a square wave, but if you introduce a horizontal element, a sinewave or sawtooth pattern, the trace looks normal.

I'm waiting on parts from Mouser to replace the failure prone inlet caps with new ones, so I'm unable to check voltages and ripple at the moment.

Is it just an issue with the width of a vertical trace affecting the brightness on the screen, or is there maybe a deeper issue going on here?

Thanks

Ed Pavlovic
KC9MMM


--
-----------------------------------------------------------------------
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Amateur Callsign: WB4UIV wb4uiv@arrl.net AMSAT LM 2178
QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE ARRL TAPR
"It is not the class of license that the Amateur holds but the class
of the Amateur that holds the license"


Re: Thoughts on TDS744A

 

Hi Siggi,

While the models I mention do have aluminum SMT electrolytics on the front panel, I have not seen any that were leaking. I suspect that the leaking caps on the older models were a quality problem with the cap vendor they were using at the time.
Jay


Re: General Radio 874 Connector, inner conductor "bendies"

Richard Knoppow
 

The General Radio part of the IEC site has many old GR catalogs. They will help identify the connectors used and those available as parts. GR used a couple of variations of binding posts, mostly combined with banana plugs or jacks. I have not checked but think the 274 type dual banana plugs and jacks had the same spacing for decades making them compatible. On many GR instruments with 874 connectors there is a combination binding post mounted under the coaxial connector. These are ground connections but a 274 dual banana plug with fit between the center part of the 874 and the binding post. This is sometimes handy where one is dealing with audio or low frequency RF although it does not have the effective shielding of the 874 connector.
GR made adapters going to nearly anything from the 874 and both GR and others, like Pomona, made adapters of all sorts for the 274.

On 8/20/2019 11:16 PM, Roy Thistle wrote:
On Sat, Aug 17, 2019 at 08:56 AM, Dale H. Cook wrote:


probably because they are AF, or RF units?
I found a 1001A that I though had a BNC output connector; but, it was an 874 to BNC adapter, inserted into the front panel 874.
I have some GR units, mostly older than 1950, mostly audio, 600 ohm stuff, I guess... mostly in wooden cabinets, so old I guess too... like a 546-C, with binding posts. (sometimes seen referred to 546-0, because of the front panel stenciling?).
Anyway, even though I have, and have run across GR stuff... my introduction to the 874 was on Tek stuff (like pulse gens, sample heads, and 7000 plugins)… which I was not interested in, at the time... so just made a note of that odd looking connector, on the front panel.
I guess that was just the peculiarity of my situation... which led me to think it was an old Tek connector, when it was really GR!
Best regards and wishes all.
Roy
--
Richard Knoppow
dickburk@ix.netcom.com
WB6KBL


Re: 7000 series carrying handles - how strong are they?

Roy Thistle
 

On Sun, Aug 18, 2019 at 05:54 PM, evan foss wrote:


I once carried a 7704A a little over a mile.
I've carried the 500s and 7000s, for long distances occasionally 1Km plus, and frequently carried them a couple of hundred meters.. and lots of times carried them 10 to 20 meters, from lab to lab, through the halls... or across the lab. (I know... there is a new invention called wheels; but, the scope carts are always jammed up with junk!) The only times a metal strap broke... and that was before I lifted the scope... the steel strap broke (just by pulling on it)... it was very obviously rotted and rusted through, . A couple of times, on the 500s, I braided a rope (1.5 mm rope/string) handle on, just so I could carry it... when I thought the rusty steel handle present might suddenly fail, under inconvenient circumstances.
That said... the steel strap is only as "strong", as the fittings it engages, and the bolts (screws really) that hold the whole assembly to the body of the scope. Checking those are sound, and will continue to be sound, seems prudent.
I get the willies too, wondering whether the handle is going to break, on these heavy scopes... but under the weight and strain, I quickly start to trust the steel, and I worry more about banging the front panel into something, and bending those little knobs!
I have a 1200 series Tek logic analyzer, that has a bail type handle... but it has one corner of the bottom compressed, upwards... like it was dropped, straight down, from letting go of the handle... and then the thing landing on just one corner... so how does that happen?... the handle is fine.
Roy


Re: 7000 series carrying handles - how strong are they?

Roy Thistle
 

On Sun, Aug 18, 2019 at 03:38 PM, Bruce Griffiths wrote:


austenitic stainless (300 series) is non magnetic
unless it is cold worked (like stamping it?)... and then it develops a magnetic response. The strength of which [compared to stainless numbers that are magnetic]… I guess... depends on the amount of cold working.
Roy


Re: General Radio 874 Connector, inner conductor "bendies"

Roy Thistle
 

On Sat, Aug 17, 2019 at 08:56 AM, Dale H. Cook wrote:


probably because they are AF, or RF units?
I found a 1001A that I though had a BNC output connector; but, it was an 874 to BNC adapter, inserted into the front panel 874.
I have some GR units, mostly older than 1950, mostly audio, 600 ohm stuff, I guess... mostly in wooden cabinets, so old I guess too... like a 546-C, with binding posts. (sometimes seen referred to 546-0, because of the front panel stenciling?).
Anyway, even though I have, and have run across GR stuff... my introduction to the 874 was on Tek stuff (like pulse gens, sample heads, and 7000 plugins)… which I was not interested in, at the time... so just made a note of that odd looking connector, on the front panel.
I guess that was just the peculiarity of my situation... which led me to think it was an old Tek connector, when it was really GR!
Best regards and wishes all.
Roy

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