Tektronix TDS 544A issue : Acquisition RAM POST Errors

[andy2000]

I did some more work on my TDS544A.  I found one open trace, but repairing it made no difference.

Next, I probed around to verify basics like clocks and power.  I found that U501 (acquisition clock buffer for channels 1 and 2, part number 234-0718-40) had no output.  It's twin for channels 3 and 4 (U502) did have an output.  After verifying the inputs to U501, I removed both U501 and U502, then installed U502 in place of U501.  U501 now has a good output, so I know the IC was bad.  With a good U501 (and no U502) it cleared the DAC system failure error, but it still has no trace, no trigger, and those two memory errors.

The other problems could be related to the missing clocks, or may be a different problem.  Either way, more troubleshooting is wasted time without a replacement 234-0718-40.

[Vince]

Alm, thanks for shedding some light.

I do have this "VISA" thing installed, that's the 50MB package I downloaded from NI's website. It also installed with it, this "MAX" software you see in my screen captures. MAX stands for "Measurement and Automation Explorer".  "Automation"... kinda implies it can do a little bit more than just scanning the bus, so I will dig into it a little, though not holding much hope obviously...

Labview, well maybe NI was kind enough to let go on their old Win95 variant, maybe they offer it for download nowadays, will check.  If not, will see if it can be found it "elsewhere".... if nowhere to be found, I think I heard there are similar products, cheaper, and even maybe a free and open-source alternative. So will look into all that.

I did play a bit with Labview nearly 20 years ago I remember. In 1999 I was doing my industrial placement as a student in some small company in the UK, "Webtec Instruments", specialized in the hydraulic industry, designing and manufacturing valves and manifolds, as well as some field/portable test equipment for maintenance/trouble-shooting to go with it . Boss wanted me to start the initial prototyping work on what would later become this thing :

https://www.webtec.com/products/ITT4LB16

Basically measures flow, pressure and temperature, computes power from that, and displays it on a 4x20 LCD screen. The finished product they sell now is less ambitious than what I was working on at the time, though. This one is a stand alone unit and records data locally, but what I was working on was to daisy chain several of these guys using a serial bus, and retrieve data over the bus to some hypothetical terminal/master unit that was yet to be drafted...
So I had to write ("draw"...) a little driver/virtual instrument for this on Labview. Driver would allow for up to 6 instruments. I think I have a picture of this somewhere ! Yeah, digital cameras were not quite widespread and cheap back then...

Anyway, getting my hands back on to Labview 20 years later, brings a little tear to the eye, trip down memory lane ! 

As for language I will stick with C, the only thing I know. Plus it's old enough to be used also under MS-DOS, NI provided bindings for C for his DOS driver,  should I wish/need to, and C will probably still be around in 20 years time... I bet.

I do have a book on GPIB which I bought 20 years ago while at school... could make a lot sense of it; not having any GPIB stuff to practice with... 20 years later I do it appears ! LOL  So reading it a second time, but this time with a much more hands-on/real world perspective ! 
Have only read the first few pages of it, covering low level stuff to start with, what every individual line of the bus is for and how it all works together... not quite necessary for practical, but I want a solid ground on which to build ;-)

Anyway, I am all excited about this GPIB thing, and all the things you can do with it, and the fact that this bus was implemented on even very old instruments, so even ancient '70's instruments can be connected to it, along with your '80's instruments, '90's gear as well, and I see that even brand new mega expensive STILL come (at least as an option) with GPIB, somehow !!! Obviously I understand it's for backward compatibility, but still, the point is that GPIB is worth investing your time  in it, as it's really useful to connect a extremely wide variety of instruments, both very old and brand new, all on the same bus ! I find this fascinating, in a world where all things come and go so quickly now.

[Vince]

Either way, more troubleshooting is wasted time without a replacement 234-0718-40.

Ah, getting there ! 

Is this ECL chip custom ??  Worst case, I guess you could always salvage that chip from a cheap (pun intended) Acq donor board from Ebay ??

Your Avatar doesn't not state what country you live in, but if you are in the US like most on this forum, then buying from Ebay is very cheap since you don't have to pay for silly shipping fees and import related taxes like other people have.

[andy2000]

Either way, more troubleshooting is wasted time without a replacement 234-0718-40.

Ah, getting there ! 

Is this ECL chip custom ??  Worst case, I guess you could always salvage that chip from a cheap (pun intended) Acq donor board from Ebay ??

Your Avatar doesn't not state what country you live in, but if you are in the US like most on this forum, then buying from Ebay is very cheap since you don't have to pay for silly shipping fees and import related taxes like other people have.

The chip is branded Tektronix and only has their part number on it, but I haven't done any research yet to see if it might be an off the shelf part. 

I am in the US, so I'm sure I'll be able to find a donor sooner or later.    It's a low priority "fun" project, so I'm in no rush.  I already have several better scopes. 

There's nothing cheap on ebay at the moment.  If anyone has a scrap acquisition board, please contact me.  I think the TDS540 and 520 should have the same part.

[Vince]

It's a low priority "fun" project, so I'm in no rush.  I already have several better scopes. 

Better scopes ?! Lucky you, I envy you !   
This TDS 544A is my beast, spent 500 Euros for it (that's roughly at least as many US dollars), which was a real bargain considering it was recapped and the seller was willing to prove that it actually worked. That's extremely rare.

My dream scope would still be a TDS, but the later 'D' series, so as not to suffer from leaky caps, and have better analog BW and sampling rate. Would love a TDS 784D or 794D, with a memory option, but 700D models are mega rare over here, and when they show up it's usually anywhere between 1500 to 4000 bucks, with just a pic of the unit powered off, laying outside on a wet ground, text saying just "very good condition", take it or leave it ! LOL
Yeah right.... 


I think once I will be in a market for one of those, I will buy from Ebay US... shipping will be silly expensive but it will still end up vastly cheaper than buying one locally, and I would not have to wait 10 years to find one, and I would be able probably to find a cheap one for repair,, instead of paying 1500/4000 for a unit that's described as "in great condition !", like it were some piece of furniture or something, but which in reality is most likely faulty !!!


Anyway, played some more with GPIB, my dodgy GPIB cable was kind enough to behave for a couple hours, so could exploit all the good stuff I found in the "Programmer Manual" I just downloaded. several hundred pages thick, and all pertaining to my 544A at that (all commands are common to all the 'A' series it appears, great), but none the less an easy/quick read : just a dozen pages at the start to explain how the syntax works, then just a long list/catalog detailing every available command, nicely sorted by type. So I could quickly find the commands of particular interest, and played with them all.

Of particular interest : the scope has an "Application" menu, a dedicated button on the front panel. On my scope this menu is completely empty. Kinda annoyed me at first, I thought the Firmware and/or NVRAM might be screwed in some way, and I might be missing some cool features, how frustrating !
But it turns out that no, I am not missing missing anything, it's normal for this menu to be empty. This menu is meant to work with GPIB only. It's only purpose in life is to offer a way for the operator/user to interact with the GPIB setup : you can create custom labels/menu entries in this menu, then the operator presses the soft buttons to select them, the scope then tells the GPIB controller/computer which button was pressed, and the computer can then run a GPIB program/ to make the scope perform such or such test procedure.  So I played with that, see below 

You can also display a message window with you own text in it, and you can customize the width/height/position of the window as you desire, can even be full screen if you like.

Now the bad news : this Programmer  Manual as thick/comprehensive as it is, does NOT tell you what's the command to clear that bloody err log !  Grrr....  quite disappointed, I am.  You can run diag procedures, and retrieve the results, just like you can do from the front panel, but you can not clear the error log, nor even simply read it actually.

So, I am kinda annoyed that I can't get working this little dedicated DOS utility you gave me Andy ! Still, it's only 10KB so I ha d a go at it. Looked at tit in a hex file editor, thinking all it does is probably sending a single command over GPIB, and since they are all plain/legible ASCII text, I should logically be able to see it in the executable file !  Well... yes and no ! As you can see below, one can see an interesting " sendcmd{ " string ! So the GPIB command must folliow the opening "curly bracket", mustn't it ! Sadly no ! As you can see, all that follow the opening bracket is just a long string ofr random characters, most of which are not even printable ones !  And we can't even see the matching closing bracket !  So... could it be that the text string containing the command name and arguments if any, has been scrambled/encrypted in some way, for security purposes, to avoid simple hacks like what I was trying to do ? Could Tek have been THIS paranoid ?!     Can'"t believe it, there must be some other explanation.... just don't know what it is, yet.

So Andy, you said you might have another software that might be able to clear this bloody error log ? I am all ears !   

Anyway, making progress on GPIB then, this first approach was a success I think ! And I am glad because it might be put to good use real soon : might help me repair my TDS 310 !!!  I mean, it's front panel is become totally unresponsive but the scope is otherwise working. So GPIB would be ideal to let me take full control of the scope despite the lack of front panel ! But.... that's assuming this scope does have GPIB ! That was hardly a given, considering it was a TDS 300 series hence bottom of the TDS range, and to top it all, the TDS 310 I have is, I think, possibly, the lowest spec 300 one can possibly think of !!!  I mean, has only 2 channels, only 50MHz of analog BW and a mere 200MS/s, almost a toy in other words ! LOL  But well, I looked at its butt just in case, and what do you know, it DOES have a GPIB port, YEAH !!!! Even has serial and centronics ports as well.  I am over the moon. Can't wait to resume work on this repair.

[Vince]

Looking at the hex dump of the error log clear S/W..  trying to make sense of this scrambled ASCII string.

I thought maybe it's not encrypted, maybe it's just compressed... maybe somehow this S/W doesn't load straight into RAM "as is", maybe it uncompresses some block of data... but how ridiculous that would be, the executable is only 10KB so it could run on a pocket calculator, no need to compress anything.

Then, I searched for the strings that the program prints on the screen when you load it, like "Tektronix (c) 1993 Error Log Clear program for the TDS Family", something like that.... surely this is hardly sensitive information, so no reason whatsoever to scramble/disguise it... yet.. it IS scrambled ! ARRRRRRGH ! I am lost.

Thought maybe my Hex editor is playing up, though I don't see how it could have gotten this wrong, but what do I know. So I searched for another Hex editor in my package management software. Saw a program by teh name of "Bless", but whatever. Point is... there were some reviews attached to this software, and some people complained that "it lacks EBCDIC support, not all text is ASCII encoded ! "   Ah ? Might be on something there ! Maybe the strings in that executable are stored in some weird format other than ASCII ! So searched for that EBCDIC format. It's an old format that was used in the early days of computing, when main frames were still using punch cards :

https://en.wikipedia.org/wiki/EBCDIC

Found a site that gives conversion tables :

http://www.simotime.com/asc2ebc1.htm

Unfortunately, unless I am using these tables incorrectly, I would say that these strings are not in EBCDIC format either... hmmm... some other encoding then, but what might it be....


TDS310 : plugged it to GPIB, no response whatsoever, the GPIB controller fails to find it when it scans the bus, front panel still unresponsive to user input, but appears to react appropriately to stimuli from the main scope/main board. Also, I notice that the front end is trouble some too : fails to display any signal, all the screen show is a tiny 1mV signal, and on top of that it progressively shift up and up. Starts at teh bottom of the screen and over the course of a few minutes, it ends up off screen at the top. I say that's one very sick puppy ! I think I will open a new thread for him, looking like an interesting repair...

[Vince]

Not sure if the link has been posted yet, but there may also be some helpful software on Hakan H.'s site.

Thanks (again) for this link alm !  SUCCESS !!!

On this page :

http://hakanh.com/dl/

8th link from the top, is listed an error log VIEWER for the TDS scopes, clicked on it anyway, then saw a screen cpature of its user interface and noticed that... oh... what do I see there, am I dreaming or what.... there is also a CLEAR error log button in there ?!
And the software runs, for a change, on Window 95 not MS-DOS, and requires NI' back-end ? Just what I needed !

ANdy, was that the other software you had in mind ?

Installed that software, ran like a dream, pulled the full error log from the scope in an eye blink, 71 errors no less, and it cleared them all in a split second, good boy ! That's some good S/W, and it's home made as well !  Must send the guy an e-mail to thank him for bothering writing such a useful piece of code, and sharing it on his site. That's one good man !   

The error log in the scope is now a beautifully... empty window, success ! Quite strange actually, never seen it empty before ! LOL

So, the scope is fixed, and the error log is clean, the scope starts from a clean sheet... I call this repair done, what do you say ?! 

Thank you to all who helped in one way or another ! 

Now on to my TDS 310 repair... a new thread soon to be created I feel ! 

[andy2000]

I've never tried that Windows error log viewer, but now that you mention it, I have heard of it. 

I'm sure it was a DOS program I used.  I'll have to pull out my old portable DOS computer which I set up for GPIB.  I only used it once for my TDS784D.

Keep an eye out on ebay.  My 784D came from Israel, and was a bit of a project to say the least (bad CRT, missing front panel, broken BNC connectors,...).  Fortunately, the processor and acquisition boards were good, and it even had the hard drive option.  The replacement parts I needed are common to all of the 700 series scopes, so weren't hard to find.  I paid about $500 for it, including shipping (5 years ago).

I like the "digital phosphor" mode of the D series.  It's excellent for viewing chaotic signals such as a TV video signal.

[Vince]

Israel ?! Now you mention it, I do remember coming across  many adds on ebay for cheap "as is" instruments, that all came from a specialized company precisely in Israel. Isreal is a lot closer to me than to you in the US, so the better (for shipping fees...).  Nice to hear from someone who has actually experience of this company, I will be less hesitant to use them then, if they were good to you. I mean the scope was in a sorry state but advertised as such, so they didn't lie on its condition, and they actually shipped the product to you, rather than just taking your money and giving you the middle finger.

That's quite encouraging... I will dream of my future 784D every night now, until I can afford to get one 

[Jwalling]

I did some more work on my TDS544A.  I found one open trace, but repairing it made no difference.

Next, I probed around to verify basics like clocks and power.  I found that U501 (acquisition clock buffer for channels 1 and 2, part number 234-0718-40) had no output.  It's twin for channels 3 and 4 (U502) did have an output.  After verifying the inputs to U501, I removed both U501 and U502, then installed U502 in place of U501.  U501 now has a good output, so I know the IC was bad.  With a good U501 (and no U502) it cleared the DAC system failure error, but it still has no trace, no trigger, and those two memory errors.

The other problems could be related to the missing clocks, or may be a different problem.  Either way, more troubleshooting is wasted time without a replacement 234-0718-40.

I have three TDS540 or A scrap boards that succumbed to leaky caps. These are the ones you need?
Send me a PM. You can have 'em both for the cost of postage if you email me a shipping label from USPS
for a "small flat rate priority mail" box.

[Jwalling]

A close up. looks like the right part.

[Vince]

Yep they are the ones indeed. Andy lucky you... can't wait for you to solder these chips in place and report back on your repair 

[andy2000]

I decided to try connecting the outputs of the good IC to the pads of the missing one.  Much to my surprise, it now has a trace, triggers, and even passes SPC.  As expected, there are some timing errors, but it's encouraging.  It still has the two memory errors, but I now know those are unrelated to the other problems.

[Vince]

Hey clever, why not, it paid it appears !   

Making good progress then, great ! Go change this chip and keep working at it, looking good so far !

[andy2000]

I replaced the bad U501, and now it seems to be working properly!  I'm not sure if it was a coincidence, but it didn't give me the two memory errors when I booted it, or when I manually ran the self test. 

Thanks to all those who helped, and I hope this will help someone in the future. 

[Vince]

SUCCESS then !!!   Great Andy, that's TWO 544A fixed in one thread ! 

Glad to hear that !   

[andy2000]

The CRT is good, but there are some bad spots on the LCD color shutter.  The early CRTs like this one have an optical gel between the CRT and shutter.  Later ones just have an air gap.  I think the gel puts slight pressure on the LCD panels which can cause damage over time. 

If anyone has a weak CRT with a good LCD shutter, I'd be interested in it as a parts donor. 

[Vince]

The CRT is good, but there are some bad spots on the LCD color shutter.

Yeah noticed that on your pics... yours seems quite bad indeed, sadly   
Mine does it as well but it's very slight, not really noticeable unless you know about it and look for it... so I will just leave it like that I think...

The early CRTs like this one have an optical gel between the CRT and shutter.  Later ones just have an air gap.

Good to know ! One more reason for me to favor a later model when I can a TDS 700...

[andy2000]

So, I decided to try removing the optical gel to take the pressure off the color shutter.  It was a messy process, and at first there was only a slight improvement.  After a few weeks of sitting, the bad spot has almost completely disappeared.  First it went from about 12mm in diameter to just a few mm.  After 5 more days, it's now less than 1mm.  I think it will be gone in another week.

The gel is a very sticky viscous substance.  To break the bond with the front of the CRT, I injected some air with a hypodermic needle.  Just be careful to put the needle between the shutter and the CRT, not between the two layers of the shutter.

[Jwalling]

So, I decided to try removing the optical gel to take the pressure off the color shutter.  It was a messy process, and at first there was only a slight improvement.  After a few weeks of sitting, the bad spot has almost completely disappeared.  First it went from about 12mm in diameter to just a few mm.  After 5 more days, it's now less than 1mm.  I think it will be gone in another week.

The gel is a very sticky viscous substance.  To break the bond with the front of the CRT, I injected some air with a hypodermic needle.  Just be careful to put the needle between the shutter and the CRT, not between the two layers of the shutter.

Ugh! Yeah, that's one of the worst things you might have to deal with on these scopes other than the leaking caps. Oddly enough, Goo Gone works well to remove the stuff after getting most of the snot off with a plastic scraper. The hypodermic needle is something I never tried - Excellent and thanks for that!

Only the older TDS scopes had that stuff, newer ones did not. Makes me wonder why they thought they needed it to begin with.

Edit: Oh yeah, you just said that (is there an echo in here?)

[andy2000]

Just one final update.  It took a while, but the purple spot is completely gone.  I reattached it to the CRT with some black silicone, and it now looks perfect.  It was definitely pressure form the gel that caused the purple spot. 

[Vince]

Thanks for the update Andy !  Very nice to hear that this horrible problem can be fixed efficiently.. as well as very cheaply  ! These two things usually don't get along very well do they...

I will leave mine alone for now, as the problem is there but only very slightly, so I am worried I am might do more damage than anything if I attempt the repair... but will not hesitate should the symptoms become really visible and annoying...

Too bad you didn't take a few pics of the process, so I can better understand what is involved exactly. I guess it becomes obvious once you start the job, but I would have like to know before hand what I would be in for...

[andy2000]

I probably should have taken some pictures, but there's a good description of the process here.  Overall it was the same, except that I injected air to break the vacuum bond of the gel.  The gel is very sticky!  I managed to keep more of the original silicone intact which made reattachment easier. 

http://jvgavila.com/tds524a.htm

[Vince]

Ahhhh.... I see now !  Thanks for the great link, very helpful indeed ! 

Looks doable no doubt ! 

[charlyd]

dont forget the leaky caps away....or better ALWAYS.. recap the complete 500 series..