Hello! Getting ready to repair a Tek 2467B

[properharmony]

Hello!
Looks like quite the knowledge and community in the forums. Anyway, I'm the newly gifted (unexpectedly) owner of a 2467B with a few issues (some stuff just missing such as the HV shield and rear plastic cover, plus a couple face buttons), however everything else in the unit has been untouched electrically near as I can see. My guess being the previous owner (who died unexpectedly) probably got in over his head upon opening it up, lost the parts and now here it is in my hands now. Anyways...

Upon, plugging in and attempting to power up, the furthest I've gotten is hearing a ticking from the SMPS, and a flashing Trig'd LED. Nothing else so far (no screen display, no further boot sequence that I read these things are supposed to do in terms of the self-test and diagnostic routines that it would normally do and as they explain in the service manual). I did discover that the illumination for the display will pulse as well after messing with that control a little, but that's the only other lighted thing I'm seeing. Voltage readings from the J119 socket are all consistently low by around 2-3 volts, and appear to be cycling up/down slightly on my DMM- point being they are not staying stable. Upon digging out the power supply (not awesome to remove it I will say haha) I see all the electrolytic caps are original to it, none look physically damaged or bloated. The "across the line" caps are all cracked looking on the clear plastic but that's about it there. No scorch marks, burnt up traces/diodes/resistors, etc. Fearing damage could be done to the SMPS (I'm kinda new to this, and this is BY FAR the most complex thing I've tried to fix on my own), I briefly powered the SMPS on the bench no load for maybe 3 seconds. No high-freq whine or ticking noise whatsoever came from it. I turned it off after that; I'd read one could fry the FETs doing that (dunno if that's true but it sketched me out so I did that quickly and turned it off). Anyhow, re-attaching it to the rest of the scope gave same initial power up result. I took up most other suggestions I've read that the caps in there are long past their life and were prone to trouble and ordered as low of ESR replacement caps as I could find via Mouser and thus far I'm in it 25 bucks now which...I can live with that just seeing what's up (they should arrive this coming Wednesday). Depending on what happens after this, I know I'll need help either way if it works or not. Any thoughts, tips, suggestions are most welcome. As I say, I'm fairly new to stuff quite this complicated. My prior success was with fixing an HP 6236B power supply as far as test gear goes. Most of my knowlege is in audio (guitar amps, some hifi, modular sythesizers, etc.) so this one I know is going to be quite a steep mountain to tackle. Again, thanks to all who are willing to give me some guidance on this one.

[tautech]

Welcome to the forum.

Most of what you need to know about these great family of Tek scopes is somewhere in this thread:
https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/

[properharmony]

Ok so I did what I could to follow what and where things were heading in the big 2465 thread; if I need to move this over to the other discussion, then I'm certainly down to help there.  Quick update thus far:
 
-After gutting and removing the old caps, 3 were definitely bad and had leaked a black crusty substance and were replaced along with most of the other electrolytic ones, and the RIFA ones are out too.

-After finding the power switch linkage was broken/missing screws, and discovering at some point the front face had been dis-assembled and mostly re-assembled, that had to be sorted out and repaired with some hardware from my drawers.  Done and done.

-Finally I maneuvered the power supply back in, hooked everything up again, and low and behold...IT TURNED ON AGAIN!  YAY!  However...

-Something is still holding it up from running.  Moving the horizontal definitely moves the trace side-to-side.  Moving up the timebase makes the beam move faster/slower, Putting in a ~1k tone and the Trig'd starts going, remove it and it stops so it seems to be detecting that I'm putting a source into it. 

However, now matter what I put in, or moving the vertical adjust knobs up/down it just stays as a flat line, and stays at the center division. 

The readout that I've seen these scopes display is there (I think?) just all flattened and stuck at the center axis line along with the trace.  Moving thru the coupling selections/buttons seem to do what they should but absolutely no vertical deflection near as I can tell.  I did notice that if I select all 4 channels one by one, then steadily the beam gets brighter and brighter as each one just gets stacked on top of the other.  Also changing the intensity lasts for like...3 seconds, and then it goes back to being quite dim again.  Sure could use just a teeny bit of help here.  Thank you all who read/are interested in helping!

[properharmony]

Ah some luck and success!
At last after some more pondering and curiosity, now I'm getting vertical deflection and a display of sorts which I can read and see !
U600, upon careful removal/inspection was very oxidized where the contacts meet the socket along with probably the rest of those.  One of the nuts on U600 was ever so slightly loose which, was not my doing either.  Either way, tightened down.
Anyhow I carefully and gently swirled the soft non-pointy edge of a dental pick around each of the spots on the asic.  Not scratching per se but enough to remove the dark stains on the pads and plugged it back in and bam it's back up and running.  Further testing awaits to see how close it seems to be to measurements.  I have no way to truly calibrate this thing so...uh...yeah.  Also, I realize I'm essentially on borrowed time with the EEPROM business/battery in that IC.

[0culus]

Be careful tightening those nuts. Overtight can damage the unobtainium chip.

[tautech]

I have no way to truly calibrate this thing so...uh...yeah. 

Generally speaking if the PSU rails are exactly to spec there's no need to make any further adjustments although for equipment of any age component values do drift however Cal usually remains close enough for most needs.

[properharmony]

Noted on the nut tightening.  I went cross-wise not unlike a car tire and stopped once things felt snug but not insane.  No aping was involved lol.  It seems remarkably close as far as accuracy is concerned.  My Rigol was estimating the frequency coming out of my little benchtop generator right on with what this guy was saying (817hz, 830hz on the Rigol).  That improved when I went to a sine to within 3 hz.  Not the greatest signal generator to be honest but eh.  Peak to peak was deadly accurate between the 2 scopes (192mV, 199mV).  Moving back over to J119, the supply lines were also dead on when I checked them again with my Fluke (no more bouncing around) and, out of curiosity, looked at them with the other scope to look at ripple.  All within tolerance there.

My next question is, how does one proceed about the sram as far as retrieving the data, programming a new one, etc?  I guess more specifically, getting a programmer that will suit the needs here that isn't above and beyond what is needed.  It doesn't seem scary to get to, and compared to the power supply, fairly benign as far as extracting a DIP out and socketing it.  I've done a little bit of stuff with Atmels at work (AVRStudio) and very briefly some Arduino, but nothing like this.  Again, mostly just analog types of circuitry under my belt and very few embedded type things.  Does the scope stop from booting if said SRAM has expired?  I didn't see it say something specifically as far as a display warning or some sort of diagnostic code so far when turning it on; however I'm guessing this may need to be accessed beyond what I've been doing when just hitting the power button.  Though I imagine this is now getting into calibration stuff which I know I haven't really explored for it either.  Feel just lucky to say it's alive to some degree.

I found an article that seems to be mentioned here as well (an article by Dr. Holden from 2013) that is most useful.  I'm astonished at my luck thus far.  Just keeping with the tenacity has paid off.  Sorry lot of stuff and quite new to stuff of this nature.  I must say the display on this guy looks really cool and works really nicely after just playing around with it and figuring out how to get it to do some math and display info.

[MarkL]

Don't remove the SRAM.  The SRAM is powered by an external battery, at least in the version of the schematics I have for the 2467B.  If you remove it, you lose your calibration constants.  Even if you have an SRAM with a built-in battery, I still wouldn't remove it.  Many people have lost the SRAM contents this way trying to do a backup.

One safe backup method is to cycle through the calibration constants on the screen while taking a video.  Or if you have the GPIB option for the 2467B and a GPIB card you can retrieve them and store them on your computer.  Both of these methods are described in the thread tautech mentioned above.  Getting the calibration constants back into the SRAM after loss is not trivial, but at least you have a backup.

The other view that some people take is that calibration constants be damned, and it probably needs a recalibration anyway.  But those most vocal about it seem to be those with the equipment to do it.

The scope will still boot if you lose the calibration constants, but it will display an error.  You can acknowledge the error and the scope will operate, but uncalibrated.

[martinr33]

On fixing the SRAM... if you have the version with the socketed Dallas device (earlier units are battery + memory).

Your best bet for the programmer is the TL866. These units are somewhere around $50, and work well.

Removing the IC is a little tricky, as they can be corrupted in the process. I've taken to this order of desoldering the pins:

 - +5V
 - All address and data lines
 - All enable lines
 This should leave just the ground pin. At this point, make sure that all pins are free, then melt the ground and pull the chip. You want to immediately read the device.

Then, install a nice socket, program the new part, and install it. If the data is corrupted, try reloading the memory. If the data was corrupted at read, I find it is usually a single byte. I think there is a dump here on the forum somewhere.

[syau]

When you read the Dallas RAM in your eprom programmer, DO NOT use auto detect as likely it will corrupt the content.

By selecting specific device, the read out will be fine and I have successfully read out many Dallas Ram since the day with parallel port programmer.

[properharmony]

Wow.  My goodness this is a sensitive operation in terms of digging that thing out; DIP type package removal seems to be the theme lately both with this and now at work with a bunch of 7 segment displays for a project that were installed backwards.  So it goes.  Anyway, back to the Tek:

So thus far after it boots, it does in fact load up and seems behave and seems ready to rock n roll after that.  It seems to display/track with the division markers correctly (using the delta V and timebase measurement markers).  I did see the vertical markers are just ever so slightly slanted to the right by maybe half a line's width which... pretty minuscule thing all things considered.  Not having 2 pushbuttons for the coupling selection (it was given "as is") is a bit of a bummer, however I found someone on ebay who had them and got em.  A plastic straw has been my temporary workaround for this.  Small price to pay overall.  I also had a small heatsink on hand and attached it to U800 via piece of soda can strip across the top and over to the 2 posts--I read those have a tendency to give up the ghost.

I did learn yesterday how to get it to run thru the self-tests pushing the delta button, its neighbor and...the third one escapes me at this time, but that "sequence" of buttons and it came back clean when I watched it do it's thing.  Finding the cal constants in the machine and just shooting video of it on my phone sounds like a brilliant insurance method (and I'll investigate that thread once more to find that procedure to get to display that information- thank you for telling me about that, MarkL).

I've got a little future VU meter project to build (which I will need a few parts from Mouser to get working) so I'll snag a replacement sram with that once I place an order for that stuff this week.  And I'll snag said programmer (thank you, martinr33).

[tautech]

I also had a small heatsink on hand and attached it to U800 via piece of soda can strip across the top and over to the 2 posts--I read those have a tendency to give up the ghost.

A common mis belief.
Yes they run hot however if the covers are installed, vents clean, sufficient air gap clearance around the case and the fan is properly operative they apparently give no issues.

Dig through the great 2465B thread for comments on U800 cooling and also those from rf-loop whom has serviced many of these over the years.
Best advice is to leave U800 well alone as even tightening the nuts on them risk doing damage.

[med6753]

I also had a small heatsink on hand and attached it to U800 via piece of soda can strip across the top and over to the 2 posts--I read those have a tendency to give up the ghost.

A common mis belief.
Yes they run hot however if the covers are installed, vents clean, sufficient air gap clearance around the case and the fan is properly operative they apparently give no issues.

Dig through the great 2465B thread for comments on U800 cooling and also those from rf-loop whom has serviced many of these over the years.
Best advice is to leave U800 well alone as even tightening the nuts on them risk doing damage.

Heed this advice. While the Maxim die U800 is more failure prone, which your "B" version will most likely have, monkeying around with the device can create more issues than it will resolve.

[MarkL]

Here is a post of a post from Chuck Harris, copied from the TekScopes mailing list regarding U800:

  https://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg2234124/#msg2234124

Chuck has repaired and calibrated countless 24xx and other Tek scopes over the years, and is still doing so if you find yourself needing a calibration.  I'd take his advice any day.

(I guess that makes this a post of a post of a post.)