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Tektronix 2440 bad power supply?

 

I recently purchased a 2440 with a 4000 code, battery weak. Everything else appeared to be working. That was the only fault code. I replaced the two ram modules with new. The original were obsolete (DS1235BWL-120) so I purchased DS1230-100+. When I first turned on the scope everything powered up and there were plenty of fault codes so I started a self calibration. It never completed the self calibration. The scope went blank. I was able to power it up only occasionally until it stopped completely. It no longer tries to test when it is powered on the only lights on are the three GPIB lights. The screen will start with some erroneous dots and then go blank. I have tested the low power board and have some readings that do not match the schematics The voltage reading according to the power supply overcurrent check page 478 of the manual do not match. The voltages on the side board are correct so I am not sure where to proceed. I have attached a - of the readings I got from the power supply. Any help is greatly appreciated. Thank you, Rich
/g/TekScopes/files/015-0282-00/TEK%202440%20Power%20supply%20test/TEK2440%20Curret%20test20180627_12351992.pdf
 

Hi Rich:

I don¡¯t have the manual here in front of me, but I did a lot of troubleshooting and calibration of the 2440 series. What you describe, reminds me of the current sense resistors going out of tolerance. If I recall these are very low value resistors, with tight tolerances. If they drift the PSU will start acting very similar to what you describe.

Hopefully, someone can tell you which resistors these are.

Rich Miller

On Jun 27, 2018, at 1:03 PM, RichR via Groups.Io <choicetrans1@...> wrote:

I recently purchased a 2440 with a 4000 code, battery weak. Everything else appeared to be working. That was the only fault code. I replaced the two ram modules with new. The original were obsolete (DS1235BWL-120) so I purchased DS1230-100+. When I first turned on the scope everything powered up and there were plenty of fault codes so I started a self calibration. It never completed the self calibration. The scope went blank. I was able to power it up only occasionally until it stopped completely. It no longer tries to test when it is powered on the only lights on are the three GPIB lights. The screen will start with some erroneous dots and then go blank. I have tested the low power board and have some readings that do not match the schematics The voltage reading according to the power supply overcurrent check page 478 of the manual do not match. The voltages on the side board are correct so I am not sure where to proceed. I have attached a - of the readings I got from the power supply. Any help is greatly appreciated. Thank you, Rich
/g/TekScopes/files/015-0282-00/TEK%202440%20Power%20supply%20test/TEK2440%20Curret%20test20180627_12351992.pdf
 

U664 is where the calibration constants are stored did you copy them to the new ram? If not you will need to do a complete recalibration. I went through a 2430a recently and bought a chip reader and writer to be able to save and copy the constants from one to the other. U360 holds stored waveforms and isn¡¯t as important as the u664. Hope this helps. Mine wouldn¡¯t boot either without writing the calibration constants to the new dallas chip. Even with auto setup it wouldn¡¯t boot after I copied the chips data all went well.

Sent from Mail for Windows 10

From: RichR via Groups.Io
Sent: Wednesday, June 27, 2018 5:53 PM
To: [email protected]
Subject: [TekScopes] Tektronix 2440 bad power supply?

I recently purchased a 2440 with a 4000 code, battery weak. Everything else appeared to be working. That was the only fault code. I replaced the two ram modules with new. The original were obsolete (DS1235BWL-120) so I purchased DS1230-100+. When I first turned on the scope everything powered up and there were plenty of fault codes so I started a self calibration. It never completed the self calibration. The scope went blank. I was able to power it up only occasionally until it stopped completely. It no longer tries to test when it is powered on the only lights on are the three GPIB lights. The screen will start with some erroneous dots and then go blank. I have tested the low power board and have some readings that do not match the schematics The voltage reading according to the power supply overcurrent check page 478 of the manual do not match. The voltages on the side board are correct so I am not sure where to proceed. I have attached a - of the readings I got from the power supply. Any help is greatly appreciated. Thank you, Rich
/g/TekScopes/files/015-0282-00/TEK%202440%20Power%20supply%20test/TEK2440%20Curret%20test20180627_12351992.pdf






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I have no screen at all. The scope does not do a self test so I cannot get to an initial calibration. I did not copy the calibration constants and when I first powered the scope it ran a self test as normal and came up with the expected fail codes. When I tried to do an auto set, it started and then the screen went blank. I have no screen now when I power up. The fan works so I have some power. I will try to find the current sense resistors. Thank you for the replies, Rich

On Wednesday, June 27, 2018, 6:20:09 PM EDT, Dewey Wyatt <kn4wddewey@...> wrote:

U664 is where the calibration constants are stored did you copy them to the new ram? If not you will need to do a complete recalibration. I went through a 2430a recently and bought a chip reader and writer to be able to save and copy the constants from one to the other. U360 holds stored waveforms and isn¡¯t as important as the u664. Hope this helps. Mine wouldn¡¯t boot either without writing the calibration constants to the new dallas chip. Even with auto setup it wouldn¡¯t boot after I copied the chips data all went well.

Sent from Mail for Windows 10

From: RichR via Groups.Io
Sent: Wednesday, June 27, 2018 5:53 PM
To: [email protected]
Subject: [TekScopes] Tektronix 2440 bad power supply?

I recently purchased a 2440 with a 4000 code, battery weak. Everything else appeared to be working. That was the only fault code. I replaced the two ram modules with new. The original were obsolete (DS1235BWL-120) so I purchased DS1230-100+. When I first turned on the scope everything powered up and there were plenty of fault codes so I started a self calibration. It never completed the self calibration. The scope went blank. I was able to power it up only occasionally until it stopped completely. It no longer tries to test when it is powered on the only lights on are the three GPIB lights. The screen will start with some erroneous dots and then go blank. I have tested the low power board and have some readings that do not match the schematics The voltage reading according to the power supply overcurrent check page 478 of the manual do not match. The voltages on the side board are correct so I am not sure where to proceed. I have attached a - of the readings I got from the power supply. Any help is greatly appreciated. Thank you, Rich
/g/TekScopes/files/015-0282-00/TEK%202440%20Power%20supply%20test/TEK2440%20Curret%20test20180627_12351992.pdf






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This email has been checked for viruses by AVG.
 

Same as mine, when I said boot I should have said screen dead. I had the three leds above the screen flashing a code. The code is in the service manual but I cant tell you exactly where. I did have a lighted screen just nothing but a lit screen.

Sent from Mail for Windows 10

From: RichR via Groups.Io
Sent: Wednesday, June 27, 2018 8:22 PM
To: [email protected]
Subject: Re: [TekScopes] Tektronix 2440 bad power supply?

I have no screen at all. The scope does not do a self test so I cannot get to an initial calibration. I did not copy the calibration constants and when I first powered the scope it ran a self test as normal and came up with the expected fail codes. When I tried to do an auto set, it started and then the screen went blank. I have no screen now when I power up. The fan works so I have some power. I will try to find the current sense resistors. Thank you for the replies, Rich

On Wednesday, June 27, 2018, 6:20:09 PM EDT, Dewey Wyatt <kn4wddewey@...> wrote:

U664 is where the calibration constants are stored did you copy them to the new ram? If not you will need to do a complete recalibration. I went through a 2430a recently and bought a chip reader and writer to be able to save and copy the constants from one to the other. U360 holds stored waveforms and isn¡¯t as important as the u664. Hope this helps. Mine wouldn¡¯t boot either without writing the calibration constants to the new dallas chip. Even with auto setup it wouldn¡¯t boot after I copied the chips data all went well.

Sent from Mail for Windows 10

From: RichR via Groups.Io
Sent: Wednesday, June 27, 2018 5:53 PM
To: [email protected]
Subject: [TekScopes] Tektronix 2440 bad power supply?

I recently purchased a 2440 with a 4000 code, battery weak. Everything else appeared to be working. That was the only fault code. I replaced the two ram modules with new. The original were obsolete (DS1235BWL-120) so I purchased DS1230-100+. When I first turned on the scope everything powered up and there were plenty of fault codes so I started a self calibration. It never completed the self calibration. The scope went blank. I was able to power it up only occasionally until it stopped completely. It no longer tries to test when it is powered on the only lights on are the three GPIB lights. The screen will start with some erroneous dots and then go blank. I have tested the low power board and have some readings that do not match the schematics The voltage reading according to the power supply overcurrent check page 478 of the manual do not match. The voltages on the side board are correct so I am not sure where to proceed. I have attached a - of the readings I got from the power supply. Any help is greatly appreciated. Thank you, Rich
/g/TekScopes/files/015-0282-00/TEK%202440%20Power%20supply%20test/TEK2440%20Curret%20test20180627_12351992.pdf






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This email has been checked for viruses by AVG.
 

Hi,

May be trivial, but this has happened to me. Check all the ribbon
cable connections between the boards. I had one that got pulled out
partially when I folded out the board, and was causing all kinds of
weird symptoms. Check that all all firmly seated in their connectors.

If it never completed self cal, there may be garbage in the nvram, so
once you get the scope running, I recommend to do a Cold Start to
clear it, otherwise it may get very much confused.

Also, check the ripple on the power lines, that may be out of spec.
While I'm no fan of the common Internet wisdom of 'recapping cures
everything', I had 3 24xx DSO, and all of them had bad/marginal caps
in the PSU, so I guess one can safely assume that those caps need
replacing. Don't forget about C244 in the control power supply.

Szabolcs


RichR via Groups.Io <choicetrans1@...> ezt ¨ªrta
(id?pont: 2018. j¨²n. 27., Sze, 23:53):


I recently purchased a 2440 with a 4000 code, battery weak. Everything else appeared to be working. That was the only fault code. I replaced the two ram modules with new. The original were obsolete (DS1235BWL-120) so I purchased DS1230-100+. When I first turned on the scope everything powered up and there were plenty of fault codes so I started a self calibration. It never completed the self calibration. The scope went blank. I was able to power it up only occasionally until it stopped completely. It no longer tries to test when it is powered on the only lights on are the three GPIB lights. The screen will start with some erroneous dots and then go blank. I have tested the low power board and have some readings that do not match the schematics The voltage reading according to the power supply overcurrent check page 478 of the manual do not match. The voltages on the side board are correct so I am not sure where to proceed. I have attached a - of the readings I got from the power supply. Any help is greatly appreciated. Thank you, Rich
/g/TekScopes/files/015-0282-00/TEK%202440%20Power%20supply%20test/TEK2440%20Curret%20test20180627_12351992.pdf
 

I don't know if this will help, but I used to have a lot of problems with new 16 bit MC68340 based embedded controller boards that used a pair of battery backed RAM modules. (It was used in multiple product lines at Microdyne.)

The OEM's testing left random data in them, and often the board wouldn't boot. Since they were socketed, I would swap them and that would usually allow the board to initialize them properly. Pairs where that didn't work had to have all the data wiped on a programmer. At one point, I would draw all the new inventory and wipe them before they were issued to the assemblers.

The problem was caused by data that was out of the normal range expected by the EPROM based operating system. The problem didn't start showing up until the board had been in production about four years, and there were too many different OS EPROMs to be modified, so we just noted the problem in the documentation.

Michael A. Terrell

-----Original Message-----
From: Szabolcs Szigeti <szigiszabolcs@...>
Sent: Jun 28, 2018 2:06 AM
To: [email protected]
Subject: Re: [TekScopes] Tektronix 2440 bad power supply?

Hi,

May be trivial, but this has happened to me. Check all the ribbon
cable connections between the boards. I had one that got pulled out
partially when I folded out the board, and was causing all kinds of
weird symptoms. Check that all all firmly seated in their connectors.

If it never completed self cal, there may be garbage in the nvram, so
once you get the scope running, I recommend to do a Cold Start to
clear it, otherwise it may get very much confused.

Also, check the ripple on the power lines, that may be out of spec.
While I'm no fan of the common Internet wisdom of 'recapping cures
everything', I had 3 24xx DSO, and all of them had bad/marginal caps
in the PSU, so I guess one can safely assume that those caps need
replacing. Don't forget about C244 in the control power supply.

Szabolcs


RichR via Groups.Io <choicetrans1@...> ezt ¨ªrta
(id?pont: 2018. j¨²n. 27., Sze, 23:53):

I recently purchased a 2440 with a 4000 code, battery weak. Everything else appeared to be working. That was the only fault code. I replaced the two ram modules with new. The original were obsolete (DS1235BWL-120) so I purchased DS1230-100+. When I first turned on the scope everything powered up and there were plenty of fault codes so I started a self calibration. It never completed the self calibration. The scope went blank. I was able to power it up only occasionally until it stopped completely. It no longer tries to test when it is powered on the only lights on are the three GPIB lights. The screen will start with some erroneous dots and then go blank. I have tested the low power board and have some readings that do not match the schematics The voltage reading according to the power supply overcurrent check page 478 of the manual do not match. The voltages on the side board are correct so I am not sure where to proceed. I have attached a - of the readings I got from the power supply. Any help is greatly appreciated. Thank you, Rich

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