Date   

Re: Automatic Brightness Control : was it ever implemented ??

Vincent Trouilliez
 

Thanks for your perseverance ;-) I get it now.

That's bad news then.. means they will never ever release any schematics.

I wonder though, why they were not "scared" or releasing their schematics up to the '80s, and decided it was suddenly too "risky" when they entered the "digital" age in the early '90's with the first TDS scopes and such.

Only hope would be (not a lawyer again) : if law states for example, that any patent on such devices, can only be valid up to 30 years no matter what... then it means Tek could release all the schematics with a 30 year (or whatever) delay, knowing that even if they did unwillingly infringe some patent, no matter what it was... they would be safe. Unless such a scenario exist, then yeah I guess there is nothing to hope for, even in 50 years time... :-(


Vincent Trouilliez


Re: vintageTEK Museum Microfiche FINANCIAL help

David Berlind
 

I would like to donate $25. How do I do that?

On Fri, May 18, 2018 at 1:56 PM, Dennis Tillman W7PF <dennis@...>
wrote:

Hi Vincent,
As an original member of the museum I thank you for your donation and for
raising the importance of the museum and the work it will be capable of
doing when they start scanning all those fiche.

The museum needs just $785 to reach their goal. With 7,264 members surely
we can push the museum over the top.

IF JUST 1% OF OUR MEMBERS DONATE $10 I WILL BE HAPPY TO MAKE UP THE REST
TO REACH $6,000.

If you ever have a reason to come to Seattle you have a place to stay here
with us. You can take a train down to Portland (3 hours away) and see the
museum while you are here. You can also take the Boeing Factory Tour and
see them assembling the 747, 767, 777, and 787 planes. You can also take a
ferry ride through the beautiful San Juan Islands in Puget Sound.

Dennis Tillman W7PF

-----Original Message-----
From: Vincent Trouilliez, Sent: Friday, May 18, 2018 9:15 AM

Just made a little donation (35, not a US citizen so not tax
deductible...), every little helps.

Been a month and a half and I see only 90 people donated ? Despite the
important number of members on this forum ?

Must say I am little surprised/disappointed... :-/

Good news is that despite that, they have almost reached their 6,000 USD
goal... still missing 840 bucks.

Hopefully this message will bump the topic and people who may have
missed/not heard of this donation campaign, now will be aware ! :-)

I am so very excited at the prospect of unlocking this mountain of
documents and see what's in it ! :-D

Wish I lived nearby the museum so I could give some of my time to help
them
scan all these microfiche... gonna take while for sure... gonna be an on-
going effort. In the meantime, hopefully we can start by pulling the
"most
wanted" instruments...

Vincent Trouilliez



--
Dennis Tillman W7PF
TekScopes Moderator




about group

Akhila Adepu
 

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about groupe

Akhila Adepu
 

akhilaadepu143@...


about me

Akhila Adepu
 

hi friend i am joining in your this is first time, so i don't know how to give reply so please understand me my email ID is rajuadepu009@...


about me

Akhila Adepu
 

hi friend i want join in your groupe


Re: vintageTEK Museum Microfiche FINANCIAL help

 

Hi Vincent,
As an original member of the museum I thank you for your donation and for raising the importance of the museum and the work it will be capable of doing when they start scanning all those fiche.

The museum needs just $785 to reach their goal. With 7,264 members surely we can push the museum over the top.

IF JUST 1% OF OUR MEMBERS DONATE $10 I WILL BE HAPPY TO MAKE UP THE REST TO REACH $6,000.

If you ever have a reason to come to Seattle you have a place to stay here with us. You can take a train down to Portland (3 hours away) and see the museum while you are here. You can also take the Boeing Factory Tour and see them assembling the 747, 767, 777, and 787 planes. You can also take a ferry ride through the beautiful San Juan Islands in Puget Sound.

Dennis Tillman W7PF

-----Original Message-----
From: Vincent Trouilliez, Sent: Friday, May 18, 2018 9:15 AM

Just made a little donation (35, not a US citizen so not tax
deductible...), every little helps.

Been a month and a half and I see only 90 people donated ? Despite the
important number of members on this forum ?

Must say I am little surprised/disappointed... :-/

Good news is that despite that, they have almost reached their 6,000 USD
goal... still missing 840 bucks.

Hopefully this message will bump the topic and people who may have
missed/not heard of this donation campaign, now will be aware ! :-)

I am so very excited at the prospect of unlocking this mountain of
documents and see what's in it ! :-D

Wish I lived nearby the museum so I could give some of my time to help them
scan all these microfiche... gonna take while for sure... gonna be an on-
going effort. In the meantime, hopefully we can start by pulling the "most
wanted" instruments...

Vincent Trouilliez



--
Dennis Tillman W7PF
TekScopes Moderator


Re: Automatic Brightness Control : was it ever implemented ??

Chuck Harris <cfharris@...>
 

I think you have it backwards.

It is very hard to look at circuitry that one of
your engineers creates, and know for certain that
it is free of patent infringements. Most engineers
are likely to independently "invent" most inventions
given the right set of needs and circumstances.

So, tektronix (purely as an example) has a cabal
of engineers develop a product, and they create
tons of circuitry and code; the odds are very good
that it infringes someone's patent somewhere.

If you put the circuits and the source code out
there for public viewing, then those that are
trolling for infringements only have to get a manual
and look it over for stuff that looks like it might
be in their portfolio of patents, and you are screwed.

If, however, you keep all of that literature secret,
then the trolls have to decompile all of your code,
and figure out what it does, and how. And they
have to trace your circuit boards, and brute force
the code in your ASICS. All before they can see if
you have infringed any of their property.

One act costs you the loan of a manual. The other
is a long term research project taking thousands of
hours.

-Chuck Harris

Vincent Trouilliez wrote:

Hi Chuck,

Thanks for that... didn't occur to me :-(

So in short, the patents that Tek filed originally with the intent of PROTECTING themselves... is 20 years down the line playing AGAINST them ? Their own patent keeps the from releasing component level info on their '90's stuff.. shame.

I thought a patent was own by the company, that they could do whatever they wanted with it (they paid to file it, after all), sell it to another company, give it out to whoever as a gift... I guess I am no lawyer, that's for sure ;-)

There is good news though, in what you say (if I do understand correctly that is ! Frog here, not native...) --> it implies/suggests that maybe, maybe... Tek does have a will to release schematics for their newer stuff, progressively, as the patents progressively expire and their hands get untied...
Or maybe someone at Tek will be brave enough to copy all these manuals on a USB drive and post them on the net ! Just like you can find pirate copies of all the schematics for all Apple laptops, as soon as they hit the market... and despite Apple going to great length to keep third party repair shops from repairing anything. So if their schematics escaped,in real time, from a XXXXX billion dollar company that does have an impressive will for anything not to leak.... then maybe schematics will some day manage to escape Tektronix's servers... Just kidding...
Maybe when I am old and grey, I will be able to download the full schematics for my little TDS 320, and the 784D or 694C I am hoping to buy one day.

For now I am happy to at least have the manuals for my beloved 317, 2232 and 5111, and partial schematics for my TDS 544A :-)

Vincent Trouilliez


Re: Automatic Brightness Control : was it ever implemented ??

Vincent Trouilliez
 

Hi Chuck,

Thanks for that... didn't occur to me :-(

So in short, the patents that Tek filed originally with the intent of PROTECTING themselves... is 20 years down the line playing AGAINST them ? Their own patent keeps the from releasing component level info on their '90's stuff.. shame.

I thought a patent was own by the company, that they could do whatever they wanted with it (they paid to file it, after all), sell it to another company, give it out to whoever as a gift... I guess I am no lawyer, that's for sure ;-)

There is good news though, in what you say (if I do understand correctly that is ! Frog here, not native...) --> it implies/suggests that maybe, maybe... Tek does have a will to release schematics for their newer stuff, progressively, as the patents progressively expire and their hands get untied...
Or maybe someone at Tek will be brave enough to copy all these manuals on a USB drive and post them on the net ! Just like you can find pirate copies of all the schematics for all Apple laptops, as soon as they hit the market... and despite Apple going to great length to keep third party repair shops from repairing anything. So if their schematics escaped,in real time, from a XXXXX billion dollar company that does have an impressive will for anything not to leak.... then maybe schematics will some day manage to escape Tektronix's servers... Just kidding...
Maybe when I am old and grey, I will be able to download the full schematics for my little TDS 320, and the 784D or 694C I am hoping to buy one day.

For now I am happy to at least have the manuals for my beloved 317, 2232 and 5111, and partial schematics for my TDS 544A :-)

Vincent Trouilliez


Re: Automatic Brightness Control : was it ever implemented ??

Chuck Harris <cfharris@...>
 

Hi Vincent,

It is all much easier to understand if you are a money grubbing,
scoundrel thief.

In a word, the reason they won't make the information available: lawyers.

If they show you the source code for their computer parts, they will get
sued for patent infringement, and will have handed the proof of the
infringement to the opposition for use in court.

If they show you the circuitry they used for their scopes, again they
will get sued for patent infringement.

This is one case where there is a pretty good level of security through
obscurity. It takes real work to figure out if an algorithm used in
a scope, that has been compiled and linked is something that belongs to
you, but is being infringed. Especially if the scope compresses the
code in the flash devices, and uncompresses it before it is put into
memory.


-Chuck Harris

Vincent Trouilliez wrote:


But where I don't get it, is why Tektronix can't make available all their newer stuff, the "modern" instruments that were designed in the early '90's, all the CRT TDS series for example, which are so popular.


Re: 7a26 rise time

Brendan
 

Fabio. There is no way a simple 33 ohm resistor could cause that... pshhh... HAHA. Nice job!!

https://groups.io/g/TekScopes/photo/49370/7?p=Name,,,20,1,0,0

https://groups.io/g/TekScopes/photo/49370/6?p=Name,,,20,1,0,0

Now I can put the old blocks back in and.... Wait until the next problem rolls around.

Thanks for everyones help again!!!

On Fri, May 18, 2018 at 08:55 am, Fabio Trevisan wrote:


Hello Lop Pol,

Well... Attenuator blocks are not really swapable "Plug-andPlay" as they are
usually adjusted to match each 7A26's input capacitance...
But, since the behavior is consistent and the performance is good on the other
attentuator settings, I think you successfully ruled-out the attenuator block
as a possible cause.

With all that in perspective, I can only see 3 possible causes for this
problem (if logic is sound and if Mr. Murphy is not fooling around your 7A26).
1. A poor leaf switch contact(s) of the X2 attenuation section (the B
contacts, as they're named on the schematics), either the one before the X2
attenuator block, or the one after the X2 attenuator block.
2. Or the R106 / LR106, whichever is the case on your particular 7A26.
3. Bad contact (or dry solder joint) at the X2 attenuator block contact pins,
but that seems rather unlikely as those are gold plated "collet-type" socket
pins and seems very reliable to me.

From all 3, the most likely seems to be number 1, the leaf switch contacts...
The problem is that those contacts are the ones on the back side of the
attenuator block PCB (the same side of the attenuator rotary cam which is a
lot of work to disassemble).
If the bad contact doesn't clear with contact cleaner (and be sure you use
only the ones that are safe to plastics), I`m afraid you have some tough work
ahead because, to clean them as per the manual, with IPA and paper, you'll
have to dismantle the whole thing.

Rgrds,

Fabio



On Fri, May 18, 2018 at 06:51 am, lop pol wrote:

I changed the attenuators with a set of known good ones. Still the same 20mV
issue.
20mV https://groups.io/g/TekScopes/photo/49370/4?p=Name,,,20,1,0,0
10mV https://groups.io/g/TekScopes/photo/49370/3?p=Name,,,20,1,0,0
50mV is the same as the 10mV so you get the picture.
Pretty crazy bad.


Re: Automatic Brightness Control : was it ever implemented ??

Vincent Trouilliez
 

Yeah, I am not a librarian so if you say it costs so much to stock all their paper/printed manuals.. well you certainly know what you are talking about, it's your area of expertise after all, dealing with tons of manuals. ;-)

But that goes only for the old manuals that were born as printed documents. For these, I gather that Tektronix had them all stored on microfiche, which the VintageTek museum got hold of from a generous service center. Just need to scan/unlock that resource ! They need 6K to get a suitable scanner, and the fund raising campaign so far gleaned nearly 5,200 of those 6K, almost there ! :-D
I just made a little donation.. 35 USD, not much, but every little helps, hopefully ! Can't afford to give 100 bucks at the moment, and it's not tax deductible as I don't live in the US.

So, at some point, VintageTek Museum will sort us out for all the old stuff.

But where I don't get it, is why Tektronix can't make available all their newer stuff, the "modern" instruments that were designed in the early '90's, all the CRT TDS series for example, which are so popular. Their manuals were designed from the get go in digital form it appears, and hard disk space is cheap enough these days (compared to the size of a PDF manual, even millions of them would fit a single cheap hard drive...), and they already have this existing IT platform to let people download some of the manuals... what would it cost to just add all their existing, digital manuals to this platform ?! Does not need large rooms to store paper manuals, does not need time to scan/process them... just move them from one folder to another...
OK, maybe in the early '90s there was no PDF, can't remember, or not as widespread/accepted as it is now. So maybe they need to convert from their original file format, whatever it was, into PDF that people can read... but you only have to write the converter once...

Last thing, as you said : "They don't care because people who want these old manuals, are not the ones who have money to spend on new instruments"... yes, I understand. Most companies reason like this... but it's still a bit short sighted I think : If they had a policy to release manuals for 100% of their instrument, INCLUDING component level manuals as soon as an instrument is out of warranty, or not supported anymore by the service centers, and "advertised" this policy to their customers... this would make these instruments more valuable on the second hand market.. so when you are to shell out 50K for a NEW instrument, and you have the choice between say Tek or HP/Keysight, same price, same specs... the resale value, included in the Total Cost of Ownership, would be higher for an instrument that the SECOND hand market will value more, because it knows it can fix it and maintain it ?!

Hell... AT LEAST they could offer a service : "give us some money and we will process/revive the manual you want. We charge 50 bucks + 25 cents per page, take it or leave it ". And the they can add this particular manual to their existing on-line database. I am not even asking to get it for free, it's not the point...the point is to be able to get the manuals... at all....
I would happily pay to get manuals for future Tek products I might purchase in the future, just like I was more than happy to buy from you a CD manual a year back, for my '70s rack mount Tek 5111 scope...

Anyway, OK, just day dreaming, Tek is just yet another company that doesn't give a damn for its own history....

At least we have VintageTek that's motivated... can't wait for them to shout out : "we finally got the scanner, fasten your seat belt it's gonna rock and roll from now on ! " ^^




Vincent Trouilliez


Re: vintageTEK Museum Microfiche FINANCIAL help

Vincent Trouilliez
 

Just made a little donation (35, not a US citizen so not tax deductible...), every little helps.

Been a month and a half and I see only 90 people donated ? Despite the important number of members on this forum ?

Must say I am little surprised/disappointed... :-/

Good news is that despite that, they have almost reached their 6,000 USD goal... still missing 840 bucks.

Hopefully this message will bump the topic and people who may have missed/not heard of this donation campaign, now will be aware ! :-)

I am so very excited at the prospect of unlocking this mountain of documents and see what's in it ! :-D

Wish I lived nearby the museum so I could give some of my time to help them scan all these microfiche... gonna take while for sure... gonna be an on-going effort. In the meantime, hopefully we can start by pulling the "most wanted" instruments...


Vincent Trouilliez


Re: 7a26 rise time

Fabio Trevisan
 

Hello Lop Pol,

Well... Attenuator blocks are not really swapable "Plug-andPlay" as they are usually adjusted to match each 7A26's input capacitance...
But, since the behavior is consistent and the performance is good on the other attentuator settings, I think you successfully ruled-out the attenuator block as a possible cause.

With all that in perspective, I can only see 3 possible causes for this problem (if logic is sound and if Mr. Murphy is not fooling around your 7A26).
1. A poor leaf switch contact(s) of the X2 attenuation section (the B contacts, as they're named on the schematics), either the one before the X2 attenuator block, or the one after the X2 attenuator block.
2. Or the R106 / LR106, whichever is the case on your particular 7A26.
3. Bad contact (or dry solder joint) at the X2 attenuator block contact pins, but that seems rather unlikely as those are gold plated "collet-type" socket pins and seems very reliable to me.

From all 3, the most likely seems to be number 1, the leaf switch contacts...
The problem is that those contacts are the ones on the back side of the attenuator block PCB (the same side of the attenuator rotary cam which is a lot of work to disassemble).
If the bad contact doesn't clear with contact cleaner (and be sure you use only the ones that are safe to plastics), I`m afraid you have some tough work ahead because, to clean them as per the manual, with IPA and paper, you'll have to dismantle the whole thing.

Rgrds,

Fabio

On Fri, May 18, 2018 at 06:51 am, lop pol wrote:

I changed the attenuators with a set of known good ones. Still the same 20mV issue.
20mV https://groups.io/g/TekScopes/photo/49370/4?p=Name,,,20,1,0,0
10mV https://groups.io/g/TekScopes/photo/49370/3?p=Name,,,20,1,0,0
50mV is the same as the 10mV so you get the picture.
Pretty crazy bad.


Re: TCP202 current probe

Christopher Jones
 

When I replaced the bottom half of the probe body, the replacement part did not have an opening to allow adjustment of the DC offset Trimmer. I disassembled the probe and drilled 1/8" hole in the bottom half of body to allow access to trimmer with a small screwdriver.


Re: 180A Time Mark Generator

tom jobe <tomjobe@...>
 

Hello,
I didn't see that you got a reply to your fan mount question yet so let me 'take a swing' at it.
The manual for the 180A does not show us a picture of the fan mounts, but they might be the ordinary ones that were used on many of the 500 series tube style scopes and curve tracers of similar vintage.
If the mounts are rubber with a simple threaded metal stud sticking out of each end, you can buy them from McMaster-Carr and other suppliers.
Maybe have a look at this page of the Mcmaster-Carr catalog, they have quite a selection of that style mount.
https://www.mcmaster.com/#rubber-mounts/=1cw8nub
tom jobe...

On 5/16/2018 12:34 PM, Jerome D Leach wrote:
Recently picked one of these up in good, original condition. Seems to be an earlier one, with the serial being 5005. Pretty filthy, but literally has no dents, and does not exhibit any evidence of being tampered with.

The one issue that is obvious at this point, is that it possesses those rubber fan mounts, and they have rotted away.

Seems I have read here in the past that some folks have developed a repair for this situation. If so, I would appreciate knowing what others have done. Being a toolmaker by trade, I am sure I can come up with some sort of mounts. Still, I would like to see how other owners have addressed the problem.



.


Re: 7a26 rise time

Brendan
 

On Fri, May 18, 2018 at 02:24 am, cmjones01 wrote:


On Thu, May 17, 2018 at 10:16 pm, lop pol wrote:
Messing around today after i THOUGHT i had things straighted out, I was
looking at the rise time again and 50mV is good 10mV is fine but now 20 mV
only has horrible rise time. Do you guys think that means another cap is
open
somewhere?
If it's only happening on the 20mV/div setting, it's probably something to do
with the attenuator compensation capacitors. These are also prone to problems,
though I've found that it's not so much the capacitors that cause trouble as
the solder joints to the pins of the attenuator module. They need a careful
hand and a fine iron to tidy up.

You won't be able to set the attenuator compensation correctly without an RC
normalizer on the input. I made my own with a little box containing a 1Mohm
resistor and a trimmer cap (set the trimmer cap like you would a scope probe
on a known-good input). Without the normalizer, the attenuator will appear to
set up correctly though some adjustments have very little effect, but in fact
the result is badly wrong. The adjustments on the attenuator modules interact
because they're cascaded, so it's important to follow the procedure in the
manual. I found that the 100mV/div setting (the first 10x attenuator) was hard
to get right so that the square wave looked right both with and without the
normalizer, so I had to make gentle tweaks adding and removing the normalizer
to get the best setting.

The point of all this is to get the frequency compensation and input
capacitance the same at all attenuator settings.

The procedure I use if I can't be bothered to find the manual is this:
- set attenuator to 10mV/div (straight-through, no attenuation)
- connect fast rise square wave generator to input with in-line 50R terminator
(to make sure there are no aberrations due to the cable), *no* RC normalizer
- set up LF/MF/HF trimmers on amplifer board for optimum settings
- insert RC normalizer between square wave gen and input. You can remove the
terminator if it makes it easier for your generator to produce the right
output, because we no longer need such fast edges for the rest of the
adjustments
- adjust normalizer trimmer for optimum square wave
- set attenuator to 20mV/div. Adjust 2x attenuator trimmers for optimum corner
and flat top.
- set attenuator to 50mV/div. Adjust 5x attenuator trimmers for optimum corner
and flat top.
- set attenuator to 100mV/div. Adjust first 10x attenuator trimmers for
optimum corner and flat top.
- check 200mV/div and 500mV/div settings on the way past
- set attenuator to 1V/div. Adjust second 10x attenuator trimmers for optimum
corner and flat top.
- check 2V/div and 5V/div settings
- go back and check all attenuator settings again
- remove normalizer
- check all attenuator settings again
- repeat until it's good enough

Don't do this without the screening cover over the attenuators because it
makes a significant difference to the adjustments. I wasted enough time with
that!

Chris
I changed the attenuators with a set of known good ones. Still the same 20mV issue.

20mV https://groups.io/g/TekScopes/photo/49370/4?p=Name,,,20,1,0,0

10mV https://groups.io/g/TekScopes/photo/49370/3?p=Name,,,20,1,0,0

50mV is the same as the 10mV so you get the picture.

Pretty crazy bad.


Re: 7a26 rise time

cmjones01
 

On Thu, May 17, 2018 at 10:16 pm, lop pol wrote:
Messing around today after i THOUGHT i had things straighted out, I was
looking at the rise time again and 50mV is good 10mV is fine but now 20 mV
only has horrible rise time. Do you guys think that means another cap is open
somewhere?
If it's only happening on the 20mV/div setting, it's probably something to do with the attenuator compensation capacitors. These are also prone to problems, though I've found that it's not so much the capacitors that cause trouble as the solder joints to the pins of the attenuator module. They need a careful hand and a fine iron to tidy up.

You won't be able to set the attenuator compensation correctly without an RC normalizer on the input. I made my own with a little box containing a 1Mohm resistor and a trimmer cap (set the trimmer cap like you would a scope probe on a known-good input). Without the normalizer, the attenuator will appear to set up correctly though some adjustments have very little effect, but in fact the result is badly wrong. The adjustments on the attenuator modules interact because they're cascaded, so it's important to follow the procedure in the manual. I found that the 100mV/div setting (the first 10x attenuator) was hard to get right so that the square wave looked right both with and without the normalizer, so I had to make gentle tweaks adding and removing the normalizer to get the best setting.

The point of all this is to get the frequency compensation and input capacitance the same at all attenuator settings.

The procedure I use if I can't be bothered to find the manual is this:
- set attenuator to 10mV/div (straight-through, no attenuation)
- connect fast rise square wave generator to input with in-line 50R terminator (to make sure there are no aberrations due to the cable), *no* RC normalizer
- set up LF/MF/HF trimmers on amplifer board for optimum settings
- insert RC normalizer between square wave gen and input. You can remove the terminator if it makes it easier for your generator to produce the right output, because we no longer need such fast edges for the rest of the adjustments
- adjust normalizer trimmer for optimum square wave
- set attenuator to 20mV/div. Adjust 2x attenuator trimmers for optimum corner and flat top.
- set attenuator to 50mV/div. Adjust 5x attenuator trimmers for optimum corner and flat top.
- set attenuator to 100mV/div. Adjust first 10x attenuator trimmers for optimum corner and flat top.
- check 200mV/div and 500mV/div settings on the way past
- set attenuator to 1V/div. Adjust second 10x attenuator trimmers for optimum corner and flat top.
- check 2V/div and 5V/div settings
- go back and check all attenuator settings again
- remove normalizer
- check all attenuator settings again
- repeat until it's good enough

Don't do this without the screening cover over the attenuators because it makes a significant difference to the adjustments. I wasted enough time with that!

Chris


Re: Help using this Group

Merchison Burke
 

But you must pay close attention to your return address or you will end up sending mail from the wrong address. Ask me how I know. I have 3 e-mail addresses with Yahoo and I use Thunderbird as my e-mail client.

Merchison


On 2018-May-18 12:06 AM, Michael A. Terrell wrote:
You can use more than one Email program at a time.


Michael A. Terrell


-----Original Message-----
From: Jeff Urban <JURB6006@...>
Sent: May 17, 2018 11:26 PM
To: TekScopes@groups.io
Subject: Re: [TekScopes] Help using this Group

There is more than one way to skin a cat. Actually one could just open a new email account just for this group and possibly a very few other things. Problem there is logging out of one and on to the other all the time, I just stay signed in to mine and eliminate the hassle. Having physical control of my PCs simplifies security quite a bit.

---
This email has been checked for viruses by AVG.
https://www.avg.com


Re: 7a26 rise time

Brendan
 
Edited

Messing around today after i THOUGHT i had things straighted out, I was looking at the rise time again and 50mV is good 10mV is fine but now 20 mV only has horrible rise time. Do you guys think that means another cap is open somewhere?

On Wed, May 16, 2018 at 08:29 am, Fabio Trevisan wrote:


Hi Lop Pol (again),
As others answered, it seems those tiny 5mm trimmer caps are prone to fail.
I had one of such failed on the pre-amplifier of my 464, and had also one
failed on the vertical output amp of the 7623A.
I noticed, in both cases (so it doesn't seem to be only coincidence) that
they're were too stiff to move when first attempted to calibrate them and
then, on applying more force - snap - the tiny screw driver head would turn,
but I noticed that in both cases, the ceramic discs were not turning.
And in both cases (the 464 and the 7623A), I managed to use a tiny pliers
covered with rubber to force turn the ceramic disk which was stuck (maybe due
to dried out lubricant) and was also able to make the screw head "bond" again
to the ceramic disc by applying a little bit of flux to the head and
re-heating it with a soldering iron.
On the 464, the repair ended-up flaky. It didn't survive and I had to replace
the trimmer cap.
On the 7623A, it worked well and it's still there.
Rgrds,
Fabio

On Tue, May 15, 2018 at 09:20 pm, lop pol wrote:


I was going to calibrate my 7a26 plugins and immediately i found the rise

time

on channel one is horrible
https://groups.io/g/TekScopes/photo/49370/1?p=Name,,,20,1,0,0

Channel 2 seems fine
https://groups.io/g/TekScopes/photo/49370/0?p=Name,,,20,1,0,0

Any thoughts as what to look at would be appreciated. Thanks guys

cmjones01
That's the symptom of one of the trimmer capacitors going open-circuit on that channel. I think it's the one labelled 'LF' or 'MF' but I can't remember exactly. It's easy to identify because adjusting it will have no effect.

I've seen exactly that symptom on more than one of my 7A26s. I haven't yet replaced the offending trimmers so can't advise on a suitable part, I'm afraid.

Chris

zenith5106
4:54 am #147977

On Tue, May 15, 2018 at 09:20 pm, lop pol wrote:


Any thoughts as what to look at would be appreciated. Thanks guys

See messages #140760 and #140775


I replaced the caps https://groups.io/g/TekScopes/photo/49370/2?p=Name,,,20,1,0,0
Now I can calibrate the darn thing. Many thanks guys!!

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