Author Topic: Tektronix TDS 540A repair  (Read 9678 times)

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Offline feedback.loop

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Tektronix TDS 540A repair
« on: December 30, 2015, 05:13:14 am »
Check out this repair video. Classic problem with leaky capacitors. Huge thanks to another topic (https://www.eevblog.com/forum/repair/tds644a-not-working/) and personally to Jwalling for the schematics.

https://youtu.be/7V0LCL4mL-8
« Last Edit: January 06, 2016, 07:21:56 am by feedback.loop »
 
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Offline feedback.loop

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Re: Tektronix TDS 540A repair
« Reply #1 on: January 26, 2016, 08:17:53 pm »
By the way, does anyone have an experience hacking these scopes to enable some options?
My older TDS 540A doesn't have option 2F (FFT), but the hardware seems to be identical to this scope, which does.
Would it be a good idea to try NVRAM from one scope in the other? Are there some calibration parameters, which won't match?
Or even better, does anybody know a particular location in the NVRAM to be modified to enable option 2F?
I have DS1650Y NVRAM chips socketed in both scopes, and backed up (as DS1250Y, which is hopefully correct). So I think I can risk modifying a few bytes.
« Last Edit: January 28, 2016, 08:03:21 am by feedback.loop »
 

Offline skennedy

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Re: Tektronix TDS 540A repair
« Reply #2 on: January 27, 2016, 01:21:43 am »
I have done it on a TDS544a which is very similar to your TDS540A. Enabling the options is really very easy if you have GPIB connection. Unlock the scope with the password string then enable the options one by one.

Tektronix forums has all of the details here


 

Online Andy Watson

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Re: Tektronix TDS 540A repair
« Reply #3 on: January 27, 2016, 01:37:57 am »
I've done it on a TDS510A. From what I have read on various forums, this series of TDS5xx/6xx use the same memory address and constants. The Tek forum listed above is a good place to start, also, see this thread:

https://www.eevblog.com/forum/testgear/hackingupgrading-old-scope-(tds754d)/
 

Online Jwalling

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Re: Tektronix TDS 540A repair
« Reply #4 on: January 27, 2016, 11:21:49 am »
Check out this repair video. Classic problem with leaky capacitors. Huge thanks to another topic (https://www.eevblog.com/forum/repair/tds644a-not-working/) and personally to Jwalling for the schematics.


No need to thank me, I just supplied the link.  :) Not sure who managed to get them and post them to the internet.
Congrats on the repair!

Jay
Jay

System error. Strike any user to continue.
 

Online Jwalling

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Re: Tektronix TDS 540A repair
« Reply #5 on: January 27, 2016, 11:58:09 am »
Check out this repair video. Classic problem with leaky capacitors. Huge thanks to another topic (https://www.eevblog.com/forum/repair/tds644a-not-working/) and personally to Jwalling for the schematics.


No need to thank me, I just supplied the link.  :) Not sure who managed to get them and post them to the internet.
Congrats on the repair!

Jay

Ah, it was Hakan, who posts occasionally in the Yahoo Tekscopes group.
http://hakanh.com/dl/kits.htm

Near the bottom of the page, there are a number of schematics for some of the TDS scopes.




Jay

System error. Strike any user to continue.
 

Offline feedback.loop

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Re: Tektronix TDS 540A repair
« Reply #6 on: January 28, 2016, 07:31:44 am »
I have done it on a TDS544a which is very similar to your TDS540A. Enabling the options is really very easy if you have GPIB connection. Unlock the scope with the password string then enable the options one by one.

Tektronix forums has all of the details here

Unfortunately, I don't have a GPIB adapter.
I looked at the topic you linked, and now I am confused. They are talking about 1245Y chip, and also about 1486, which they propose to read as 1245. Is it the same chip?

In my two 540A scopes there are two chips: 1650Y and 1286.
Which one has the options?
I backed up 1650Y as 1250Y - is this the right way?
How can I read the 1286 (TL866 programmer doesn't support 1286)? Do I need to?

I also discovered that the backup file I made a few years ago of 1650Y from my older 540A looks quite different from the backup I made from the scope in the repair video. I used some other programmer, which I borrowed from a friend.
So I opened up my older scope and read the 1650Y again using the TL866 programmer. The result is very different from the old backup, and looks similar to the dump from the scope in the video.
Now I wonder if any of the dumps are correct at all.
« Last Edit: January 28, 2016, 08:14:57 am by feedback.loop »
 

Offline evb149

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Re: Tektronix TDS 540A repair
« Reply #7 on: January 28, 2016, 07:57:00 am »
Which model's schematics did you get?
I've got one I'm working on fixing.  I've ordered most of the logic bypass capacitors for it but I need to also order some more parts to handle the PSU/monitor electrolytic capacitors and get some supplies to clean the PCBAs of the corrosive dried on leakage from years past.

Seems like I found some schematics and service manual for a "related model" in the general family but not exactly the right model and I noticed people complaining that they never found the service / parts manual for the exact model.  I don't know if you did or not.

Apparently there were also different revisions of them from the early 90s and on for several years after that and so of course there will be schematic / parts differences according to those changes.
If I recall correctly I saw that in some of the later model revisions they eliminated many of the logic bypass electrolytic capacitors and fixed the voltage derating problem on the couple that weren't even rated to operate at the normal DC voltage across them.  Something like 10V caps. on a 15V rail or something like that (from a foggy memory without my notes in front of me at the moment).

Mine is an early model from around mid 91.  Don't recall offhand whether it is even the "A" or whether there was a non revision designated "TDS540" before that which I have.
Seems like it has been subject to a lot of unsuccessful tinkering / repair attempts including some minor missing wiring / broken mechanical parts before I got it so it'll be an ongoing project to fully recondition all the boards.

Anyway there are some threads on tek's forums that seemed relevant, and a few here and some in other places.

If you have the one with lots of electrolytics they will pretty much all need replacing and inspecting/cleaning of the areas as step 1 since they're well past their "expiration" life.  The underrated ones in the front panel circuit assembly are particularly critical ones though the majority (statistics by sheer numbers anyway) of the failures I've heard about have been on one of the main boards of course since they have dozens each, and often with corrosion of tracks at and also underneath SMD ICs / passives in the vicinity of the caps.

Losing the cal. memory / "NV" memory is another problem.  Battery backed calibration / option data / configuration data memories in those DALLAS modules with batteries that'll be dying/dead most likely by now.

 

Online andy2000

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Re: Tektronix TDS 540A repair
« Reply #8 on: January 28, 2016, 10:24:50 pm »
I have done it on a TDS544a which is very similar to your TDS540A. Enabling the options is really very easy if you have GPIB connection. Unlock the scope with the password string then enable the options one by one.

Tektronix forums has all of the details here

Unfortunately, I don't have a GPIB adapter.
I looked at the topic you linked, and now I am confused. They are talking about 1245Y chip, and also about 1486, which they propose to read as 1245. Is it the same chip?

In my two 540A scopes there are two chips: 1650Y and 1286.
Which one has the options?
I backed up 1650Y as 1250Y - is this the right way?
How can I read the 1286 (TL866 programmer doesn't support 1286)? Do I need to?

I also discovered that the backup file I made a few years ago of 1650Y from my older 540A looks quite different from the backup I made from the scope in the repair video. I used some other programmer, which I borrowed from a friend.
So I opened up my older scope and read the 1650Y again using the TL866 programmer. The result is very different from the old backup, and looks similar to the dump from the scope in the video.
Now I wonder if any of the dumps are correct at all.

The DS1286 only has 50 bytes of storage, which I don't think is used for anything important (if at all).  The DS1650/1250 is the important one because it contains the options and cal constants. 

For later models (like the TDS7XX series), there is a DS1486 clock which has 128 kB of storage.  You can treat that as a DS1245 when reading it.  I believe that's where the options are stored.  The cal constants are stored in a pair of EEPROMs on the acquisition board.  The DS1250 is used for various user data like the event log, probe cal, SPC, and stored settings. 
 

Offline feedback.loop

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Re: Tektronix TDS 540A repair
« Reply #9 on: January 29, 2016, 05:32:08 am »
I've done it on a TDS510A. From what I have read on various forums, this series of TDS5xx/6xx use the same memory address and constants. The Tek forum listed above is a good place to start, also, see this thread:

https://www.eevblog.com/forum/testgear/hackingupgrading-old-scope-(tds754d)/

In that thread I see commands for a console adapter or GPIB. Addresses in NVRAM are mentioned with respect to TDS784D it seems. I don't quite understand if it is known which is the right address for option 2F in TDS540A, and how to adjust the check sum.
 

Offline feedback.loop

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Re: Tektronix TDS 540A repair
« Reply #10 on: January 29, 2016, 05:36:41 am »
Which model's schematics did you get?

I got these schematics, and they matched my TDS540A exactly everywhere I looked:
http://hakanh.com/dl/docs/hardtofind/TDS544A_A10(Acq).pdf
http://hakanh.com/dl/docs/hardtofind/TDS544A_A11(CPU).pdf
 

Offline feedback.loop

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Re: Tektronix TDS 540A repair
« Reply #11 on: February 07, 2016, 06:52:42 am »
I managed to enable the 2F option by copying the NVRAM from the scope with the option. After running the signal path compensation everything looks great.

Also, it seems I was wrong in the repair video saying that probably the DS1650Y NVRAM can be treated as DS1250Y. I had no success copying the chip as 1250 using the TL866CS programmer.
I managed to copy the chip using GQ-4X programmer, which I borrowed from a friend. This programmer supports DS1650Y.

A copy of DS1650Y with options 1M and 2F is attached.

Check out the follow up video:
https://youtu.be/iJt2O5zaLRE
« Last Edit: February 07, 2016, 07:12:54 am by feedback.loop »
 

Offline Fennec

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Re: Tektronix TDS 540A repair
« Reply #12 on: February 08, 2016, 12:39:59 am »
Hi,

I've found the Tek calibration Software for the TDS500 series on an old floppy Disk. Seems still working after several years.. Short check with Win 98SE without MS-Dos. So NO WARRANTY. Maybe it helps.

All you need is an old PC with a Pentium 133MHz with ISA slot and MS-Dos 6.22a . A GPIB Card you can find on ebay for under $US 20. It must be a PCII or PCIIA. PCI slot does NOT work, maybe timing problems i don't know.

http://www.ebay.com/itm/National-Instruments-GPIB-PCII-IIA-IEEE-488-2-ISA-Card-181065-01-Rev-E-/121889113061?hash=item1c612843e5:g:m9kAAOSw~OVWuLKr
« Last Edit: February 08, 2016, 10:38:10 pm by Fennec »
 


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