Well the other day my beloved trusty Tektronix 2430A greeted me with a self test fail. 
Of course this always happens in at the most inopportune moment, as usual.
I am sure others have seen this issue before me. I am trying to describe what I did try to get the scope back to working order, perhaps this may help someone who is facing the same issue. As it turns out the very special NVRAM chips have finally lost battery charge and corrupted the cal data checksum. The offending chips are U664 (Cal Data) and U350 (Waveform Data). Both chips in my scope were Dallas DS1235ABW-120 vintage 1990. I would not want to complain as these chips kept data much longer than what they were spec'ed at. I found some old new stock on ebay with a fairly 'recent' mfg date and bought some. Despite the corrupted data in these chips, I decided that I may have nothing to loose if I tried to read these chips in a programmer and perhaps pre-load the replacement chips with whatever I can read out of the old ones and perhaps reduce any calibration efforts. As I did not have a programmer, I turned to ebay and bought a cheap one Model TL866CS. I removed the main-board for convenient access as the offending chips were not on sockets and needed to be unsoldered, I installed sockets for the new chips and would recommend that. The old chips still contained some data got loaded into the new chips without problems. Then the pre-loaded chips were installed on the sockets and the main-board was installed and reconnected.
Then as part of the calibration procedure, jumper J156 must be removed to enable extended calibration feature. After successful calibration this jumper should be put back.
I believe I read that it is advisable to operate the scope only with installed case as the air flow is as ist should be, otherwise if the scope is operated without the case in place it may not have sufficient airflow and some chips could die due to overheating.
The calibration is very easy, one needs a decent variable lab power supply that can provide up to 20.0V, A few BNC cables and adapters may come in handy also.
With the enabled calibration features and warmed up scope
Initiate EXT CAL
Run ATTN cal, and follow on scope screen instructions.
Run SELF CAL and turn off scope and turn back on.
Run TRIG cal, and follow on scope screen instructions.
and turn off scope and turn back on.
Run REPET cal.
Run SELF DIAG to confirm the errors were cleared and the scope now passes self test.
If needed repeat calibration as per above.
This should clear the following self test errors
3000 SYS RAM
4000 FPP
6000 CHECKSUM-NVRAM
7000 CCD
8000 PA
9000 TRIGS
Now, I am a happy camper again
I like my Tek Scope and hope it will remain in service for a very long time.
Of course this always happens in at the most inopportune moment, as usual.I am sure others have seen this issue before me. I am trying to describe what I did try to get the scope back to working order, perhaps this may help someone who is facing the same issue. As it turns out the very special NVRAM chips have finally lost battery charge and corrupted the cal data checksum. The offending chips are U664 (Cal Data) and U350 (Waveform Data). Both chips in my scope were Dallas DS1235ABW-120 vintage 1990. I would not want to complain as these chips kept data much longer than what they were spec'ed at.
I found some old new stock on ebay with a fairly 'recent' mfg date and bought some. Despite the corrupted data in these chips, I decided that I may have nothing to loose if I tried to read these chips in a programmer and perhaps pre-load the replacement chips with whatever I can read out of the old ones and perhaps reduce any calibration efforts. As I did not have a programmer, I turned to ebay and bought a cheap one Model TL866CS. I removed the main-board for convenient access as the offending chips were not on sockets and needed to be unsoldered, I installed sockets for the new chips and would recommend that. The old chips still contained some data got loaded into the new chips without problems. Then the pre-loaded chips were installed on the sockets and the main-board was installed and reconnected. Then as part of the calibration procedure, jumper J156 must be removed to enable extended calibration feature. After successful calibration this jumper should be put back.
I believe I read that it is advisable to operate the scope only with installed case as the air flow is as ist should be, otherwise if the scope is operated without the case in place it may not have sufficient airflow and some chips could die due to overheating.
The calibration is very easy, one needs a decent variable lab power supply that can provide up to 20.0V, A few BNC cables and adapters may come in handy also.
With the enabled calibration features and warmed up scope
Initiate EXT CAL
Run ATTN cal, and follow on scope screen instructions.
Run SELF CAL and turn off scope and turn back on.
Run TRIG cal, and follow on scope screen instructions.
and turn off scope and turn back on.
Run REPET cal.
Run SELF DIAG to confirm the errors were cleared and the scope now passes self test.
If needed repeat calibration as per above.
This should clear the following self test errors
3000 SYS RAM
4000 FPP
6000 CHECKSUM-NVRAM
7000 CCD
8000 PA
9000 TRIGS
Now, I am a happy camper again
I like my Tek Scope and hope it will remain in service for a very long time.
Attachments
After replacing the NVRAM in my 2430a I repeated the self and extended calibration a number of times to get things to pass incrementally, but could never get the REPT calibration to pass. After reading the manual a bit I tried doing a COLD START, which clears all calibration, which is especially important for REPT, and then did the self and extended calibration. All calibration and diagnostics passed the first time.
It is likely the battery that maintains the RAM backup in the Dallas Clocks that has died. Plus if there is any older ROM on board, they also do not hold memory indefinately. They can last a long time, but not for ever. I had this happen to a Hewlett Packard 54111D a number of years back. I am not equipped to re-write on these chips but a nice gentleman from one of the HP forums offered to, and he even had the code. I had him write the code back on to the original chips and reinstalled them and the scope worked perfectly. I am personally not a big fan of gear with Dallas Clocks as they seem to be ticking time bombs. Many are obsolete and NLA except by luck. You may have to get a parts scope and hope those are good.
Mark
Mark
Hi ZZzz,
I'm glad things worked out for you. Yes, terminating the input may help, altho for the 20V calibration I would not use 50 Ohm but perhaps 10k or so.
Hi Mark,
well I understand your point on the Dallas chips. When I acquired my Tek scopes, I was not aware that these particular chips were used. I just wanted a decent well performing scope and did not care much about what chips exactly they used inside. Mind you Tektronix likes to use custom chips as well, if there is a problem with one of these, one needs to find a board.
Considering my Tek scope is vintage 1990 I think the Dallas chips did do quite well, far exceeding the data retention spec. So from my side there are no complains about that.
I'm glad things worked out for you. Yes, terminating the input may help, altho for the 20V calibration I would not use 50 Ohm but perhaps 10k or so.
Hi Mark,
well I understand your point on the Dallas chips. When I acquired my Tek scopes, I was not aware that these particular chips were used. I just wanted a decent well performing scope and did not care much about what chips exactly they used inside. Mind you Tektronix likes to use custom chips as well, if there is a problem with one of these, one needs to find a board.
Considering my Tek scope is vintage 1990 I think the Dallas chips did do quite well, far exceeding the data retention spec. So from my side there are no complains about that.
Superb and thanks very much KCT for uploading those very appreciated bin files!
My old TEKTRONIX repaired 2440 oscilloscope works again thanks to you. I today had replaced both U664 and U350 SRAMs thinking calibration would still be possible, but it wasn't without the diagnostics or the scopescreen working. Because someone had posted a text that it was always possible to calibrate the 2440 after the battery voltage was drained completely, as he said had fixed several of them, without any worries. But that turned out to be just a hoax!
After programming both FM1808 chips with my TL866II my scope now worked again splendidly!
And also thanks for the very good calibration step explanation. You are a lifesaver!
My old TEKTRONIX repaired 2440 oscilloscope works again thanks to you. I today had replaced both U664 and U350 SRAMs thinking calibration would still be possible, but it wasn't without the diagnostics or the scopescreen working. Because someone had posted a text that it was always possible to calibrate the 2440 after the battery voltage was drained completely, as he said had fixed several of them, without any worries. But that turned out to be just a hoax!
After programming both FM1808 chips with my TL866II my scope now worked again splendidly!
And also thanks for the very good calibration step explanation. You are a lifesaver!
You will get a lot more help here: Tek2440 Mini teardown, NVRAM replacement and calibration - Page 1 Much more experiece getting those running.
More help here: TekScopes@groups.io | Home
More help here: TekScopes@groups.io | Home
Not to worry Bob!
I almost thought I bricked my 2440 too but thanks to KCT in his post " Tektronix 2430A lost cal data / repair" who uploaded both his 32k bin files for U664 and U350 from his Tek 2430 (that apparently uses the same FW) I could restore my 2440 from a dead scope to a calibratable one. because without those programmed nothing works!
So just use a TL866II to reprogram new FM18(w)08 RAMs for those board positions. And after that just Calibrate your scope back to almost as new. I now also fully calibrated my Tektronix 2440 scope externally!
So I first upgraded my oscilloscope by replacing both old battery backupped 32k SRAMs U664 and U350 by FerroMagnetic FM1808 DIP 28pin chips. Because without the calibration data in these chips the scope won't work, no working screen, no nothing, so I also used the uploaded firmware bin files from this great guy - see following link - to keep my 2440 alive after replacing both SRAMs. And pre-programmed my FM1808 with them so my scope would still work to be able to calibrated it again afterwards! Those bin files (from an almost identical 2430 oscilloscope) can be found here: Tektronix 2430A lost cal data / repair . And if you have a dead 2440 most likely these SRAMs lost there original firmware and need to be restored first! PS: I used my even almost as old SYSTRON 100A Pulse Generator to finish the last external CTE calibration check. And I now have a fully Internally (Selftest) and externally calibrated Tektronix 2440 oscilloscope. Also the above given link provides the easy Calibration steps you can follow. And in Part7 of this Youtube video you can see how to setup the signal for the final CTE calibration step: Tektronix 2440 Pt7 Final Calibration Incudes problematic CTE Cal - YouTube
And be sure to place those new FerroMagnetic RAMs on good quality 28 pins sockets! So you afterwards also will be able to read them to make a bin copy of your calibrated scope!
I afterwards also posted this after my repair on Tektronix 2440 Oscilloscope Repaired- Part 4 | Electronics Repair And Technology News
Success Bob! If I can do it you sure can too!
I almost thought I bricked my 2440 too but thanks to KCT in his post " Tektronix 2430A lost cal data / repair" who uploaded both his 32k bin files for U664 and U350 from his Tek 2430 (that apparently uses the same FW) I could restore my 2440 from a dead scope to a calibratable one. because without those programmed nothing works!
So just use a TL866II to reprogram new FM18(w)08 RAMs for those board positions. And after that just Calibrate your scope back to almost as new. I now also fully calibrated my Tektronix 2440 scope externally!
So I first upgraded my oscilloscope by replacing both old battery backupped 32k SRAMs U664 and U350 by FerroMagnetic FM1808 DIP 28pin chips. Because without the calibration data in these chips the scope won't work, no working screen, no nothing, so I also used the uploaded firmware bin files from this great guy - see following link - to keep my 2440 alive after replacing both SRAMs. And pre-programmed my FM1808 with them so my scope would still work to be able to calibrated it again afterwards! Those bin files (from an almost identical 2430 oscilloscope) can be found here: Tektronix 2430A lost cal data / repair . And if you have a dead 2440 most likely these SRAMs lost there original firmware and need to be restored first! PS: I used my even almost as old SYSTRON 100A Pulse Generator to finish the last external CTE calibration check. And I now have a fully Internally (Selftest) and externally calibrated Tektronix 2440 oscilloscope. Also the above given link provides the easy Calibration steps you can follow. And in Part7 of this Youtube video you can see how to setup the signal for the final CTE calibration step: Tektronix 2440 Pt7 Final Calibration Incudes problematic CTE Cal - YouTube
And be sure to place those new FerroMagnetic RAMs on good quality 28 pins sockets! So you afterwards also will be able to read them to make a bin copy of your calibrated scope!
I afterwards also posted this after my repair on Tektronix 2440 Oscilloscope Repaired- Part 4 | Electronics Repair And Technology News
Success Bob! If I can do it you sure can too!
I'm afraid that your scope, if it is the Tektronix 2440 that gives that screen picture, has a defect DAC or other chip out of control.
Maybe reading my repair articles about the 2440 Part 1 to 4 will help you fix your scope because my scope when I got it was a complete short circuiting disaster only blowing up the power line fuse at first? Part 1 starts here:
Tektronix 2440 Oscilloscope Repaired | Electronics Repair And Technology News
And I was lucky I still could buy a new DAC chip on eBay that had caused the power supply primary short circuiting problem in my 2440 scope.
Maybe reading my repair articles about the 2440 Part 1 to 4 will help you fix your scope because my scope when I got it was a complete short circuiting disaster only blowing up the power line fuse at first? Part 1 starts here:
Tektronix 2440 Oscilloscope Repaired | Electronics Repair And Technology News
And I was lucky I still could buy a new DAC chip on eBay that had caused the power supply primary short circuiting problem in my 2440 scope.