Topics

TDS 684A needs recapping?


Rogerio O
 

Hi,
I have bought a tds 684A at Ebay some years ago and it was working ok.
As soon as I received it I opened it up to check if there was some indication of leaking capacitors.
It seems it was assembled in 1994.
Since I could not find any, I closed the instrument.
Everything went well for some years but the instrument started to show some "flicker" on the display from time to time.
Also the data shown is wrong, so it seems I will have to change the NVRAM.
I have already posted a question about possible causes of this flicker and it was suggested that I checked the power supply (and/or all the caps in the unit).
Since I am afraid of damaging the boards replacing the SMD capacitors I have uploaded some pictures of the boards to get an advice about the need to replace them since all solder joint (in my opinion) show no indication of corrosion.
The album is "TDS 684A needs recapping?"
Would you please check the photos and give some advice about the need of replacement?
Concerning the NVRAM, I have read conflicting information about loosing the calibration if I replace it.
What is the current NVRAM model that I can buy?
There is a person selling a FRAM replacent for these scopes but the price is a little high for me ($100).
Any advice on this issue?
Thank you all.
Roger


Ray
 

I got a tds694A, it had some ripple, super imposed on the waveforms so I recapped the power supply.The 684 and 694 are very similar, the powersupply is the same as far as I knowAnyways the ps electrolytic caps are all through hole.There is about 30 +- a few. 2 where bad. The rest I changed out to get better esr and have peace of mind.Get good quality, 105 deg rated and 5000 hr or better rating.Things got better but I wound up changing all tantalums on the aquisition board as well. Then I changed the tantalums on the output of the 3.3 v dc dc converter.The converter creates a lot of ripple on 3.3 and i am actually looking to replace it with a better, modern eqivalent.Your mileage will differ since the aquisition board is different.Another area will be the display unit.There are lot of caps in there as wellBtw I used a 45 years old weller wtcp solder iron to do all the work. Small tip for the smd tanatalums.Just use a needle nose to lightly pull on the smd caps body then heat one side and switch back and forth a few times and it comes right off. The through hole caps where actually the hardest to get out. Had to use solder sucker and or just steady heat and pull on thr cap and wiggle them out.RaySent from my T-Mobile 4G LTE device------ Original message------From: Rogerio ODate: Sat, Sep 12, 2020 09:07To: TekScopes@groups.io;Cc: Subject:[TekScopes] TDS 684A needs recapping?Hi,
I have bought a tds 684A at Ebay some years ago and it was working ok.
As soon as I received it I opened it up to check if there was some indication of leaking capacitors.
It seems it was assembled in 1994.
Since I could not find any, I closed the instrument.
Everything went well for some years but the instrument started to show some "flicker" on the display from time to time.
Also the data shown is wrong, so it seems I will have to change the NVRAM.
I have already posted a question about possible causes of this flicker and it was suggested that I checked the power supply (and/or all the caps in the unit).
Since I am afraid of damaging the boards replacing the SMD capacitors I have uploaded some pictures of the boards to get an advice about the need to replace them since all solder joint (in my opinion) show no indication of corrosion.
The album is "TDS 684A needs recapping?"
Would you please check the photos and give some advice about the need of replacement?
Concerning the NVRAM, I have read conflicting information about loosing the calibration if I replace it.
What is the current NVRAM model that I can buy?
There is a person selling a FRAM replacent for these scopes but the price is a little high for me ($100).
Any advice on this issue?
Thank you all.
Roger


Siggi
 

On Sat, Sep 12, 2020 at 10:06 AM Rogerio O <@rodd414> wrote:

Everything went well for some years but the instrument started to show
some "flicker" on the display from time to time.
My TDS784D had an annoying intermittent horizontal wiggle on the CRT.
Eventually I tracked this down to the connector for the horizontal
deflection coil, which was oxidized and presumably high-resistance or
intermittent. Cleaning the connector with some DeOxit and reseating it
took care of that.


Concerning the NVRAM, I have read conflicting information about loosing
the calibration if I replace it.

The calibration data is stored in the acquisition board in EEPROM per the
service manuals, which makes sense for board-level serviceability.


Simon
 

You might look at this YouTube for a brutal but effective way of recapping boards.
https://www.youtube.com/watch?v=X8N9O3a9jiM
Smon


Ray
 

Niffty!I wish the previous owner of my 2797 had know that.Instead it was butcherd up by replacing smd caps with ordinary ones. A few pads bit the dust as well. Took me hours to fix the damage.RayPs: If you get a 2797 or better a 279x since they are very similar, then find and change the smd electrolytics. They where all starting to leak on mine plus the ones that had been replaced in the past obviously had the same issue.I counted 13 of them.Sent from my T-Mobile 4G LTE device------ Original message------From: tenareze32@...: Tue, Sep 15, 2020 00:25To: TekScopes@groups.io;Cc: Subject:Re: [TekScopes] TDS 684A needs recapping?You might look at this YouTube for a brutal but effective way of recapping boards.
https://www.youtube.com/watch?v=X8N9O3a9jiM
Smon


 

Ray wrote:
Nothing. Is it just me, or everytime that "Ray @Ray3B5F5E" posts something there's zero content?


Roger Evans
 

If, like me, you are using the web interface you have to click on 'show quoted text' to see what Ray has written. Like so many other web things, I don't know why, but it works.

Roger


Colin Herbert
 

It must be you. I have some four posts from him which are ok. I get my messages as emails and use Outlook 2010.
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Jay Walling via groups.io
Sent: 16 September 2020 14:36
To: TekScopes@groups.io
Subject: Re: [TekScopes] TDS 684A needs recapping?

Ray wrote:
Nothing. Is it just me, or everytime that "Ray @Ray3B5F5E" posts something there's zero content?


Ray
 

Roger,Thanks for clarifying that.I was getting worried there for a moment.RaySent from my T-Mobile 4G LTE device------ Original message------From: Roger Evans via groups.ioDate: Wed, Sep 16, 2020 11:18To: TekScopes@groups.io;Cc: Subject:Re: [TekScopes] TDS 684A needs recapping?If, like me, you are using the web interface you have to click on 'show quoted text' to see what Ray has written. Like so many other web things, I don't know why, but it works.

Roger


 

On Wed, Sep 16, 2020 at 02:02 PM, Ray wrote:


Roger,Thanks for clarifying that.I was getting worried there for a moment
Weird. Yeah, if I go online I have to click on "view quoted text" to see what you wrote...
For some reason, your emails to the list appear as quoted text.


Ray
 

Roger,


So I'm sending this letter from my PC rather than the phone.
Wondering if this looks any better.

I have seen my own letters from the phone since I send to all and thus getting a "Copy"
Well they're all word wrapped with missing linefeeds.

There is some strange stuff happening.....


Thanks


-Ray

On 09/17/2020 7:52 AM Jay Walling via groups.io <jayw_comark=yahoo.com@groups.io> wrote:


On Wed, Sep 16, 2020 at 02:02 PM, Ray wrote:


Roger,Thanks for clarifying that.I was getting worried there for a moment
Weird. Yeah, if I go online I have to click on "view quoted text" to see what you wrote...
For some reason, your emails to the list appear as quoted text.



 

So I'm sending this letter from my PC rather than the phone.
Wondering if this looks any better.
Looks good to me, and I don't have to go online to see your posts now...
Jay


Siggi
 

On Mon, Sep 14, 2020 at 8:52 AM Sigurður Ásgeirsson <siggi@...> wrote:

On Sat, Sep 12, 2020 at 10:06 AM Rogerio O <@rodd414> wrote:

Concerning the NVRAM, I have read conflicting information about loosing
the calibration if I replace it.

The calibration data is stored in the acquisition board in EEPROM per the
service manuals, which makes sense for board-level serviceability.
Hey Roger,

I'd like to amend my statement here, as I'm likely wrong about this as far
as concerns your scope. I've just downloaded the TDS NVRAM saver
application from this EEVBlog thread:
https://www.eevblog.com/forum/testgear/tektronix-tds500600700-nvram-floppy-dump-tool/.
According to the information in there, the B/C/D-series scopes have an
EEPROM for calibration data on the acquisition board, whereas the earlier
scopes stored the calibration data in NVRAM.
I'm guessing this is the source of confusion - not all the TDS5/6/7XX
scopes are the same in this respect, whereas people (like me) assume they
are.

There's an info.txt file in the archive with a description of the various
tools, where it says:

"tdsAcqEEPROMFloppyDumper and tdsAcqEEPROMMinimalFloppyDumper:

Dumps the contents of the calibration constants 24C02 EEPROMs located
on the acquisition boards of the -B, -C and -D series scopes, to a file.


*-A series scopes have no such EEPROMs on the acquisition board andstore
these constants in regular NVRAM, albeit in a hardware-protectedregion*.
Both 24C02 EEPROMs are read as 0x200 bytes in a single file,
where the first EEPROM is the top 0x100 half of the file, and the second
one the bottom half."

Siggi


 

never seen tds6xx with recap required. test is easy: with heat fan at 380 *C desolder one of 5V caps (say SRAM area) from acqisition board. if it desolders without erruprion (not serious, but wear glasses anyway) - just place it again there and forget about recapping. it was relatively small 5xx party with leaky caps, many people suffered from it, but it was before 6xx.

--
best regards,
kora.


Jokken Feldhaar
 

Hi,

I've had this exactly with a 684, about half an inch radius around the
SMT Lytics showed oxidization, it took me 2 days to safely unsolder the
72 capacitors in this unit without harming the pads. Installing the new
ones was a lot faster ;-)

I also had to change some of the ICs of the ACQ Board due to oxidated
pins on them, mostly TL084 (or was it 074?), and some 4051 multiplexers.

That was really a heap of work, but in order to save a 684 I considered
it time well spent!

Cheers, Jochen DH6FAZ

Am 30.09.2020 um 11:55 schrieb kora:

never seen tds6xx with recap required. test is easy: with heat fan at 380 *C desolder one of 5V caps (say SRAM area) from acqisition board. if it desolders without erruprion (not serious, but wear glasses anyway) - just place it again there and forget about recapping. it was relatively small 5xx party with leaky caps, many people suffered from it, but it was before 6xx.