Tektronix TDS 520 - Page 1
Forum section: electronics / repair

author: 97paul
author_rank: Contributor
timestamp: February 01, 2025, 04:20:20 pm
content: Hello everyone, I would like to tell you about the error.The oscilloscope can be switched on, the fan is running and the Key lighting stays on permanently. On the A11 DRAM Processor/Display Board number 8 lights up on the segment display.The device had a problem with all SMD capacitors. Then I replaced all the capacitors and cleaned all Circuit boards.Unfortunately, this action did not fix the error.I then started troubleshooting using the service instructions.Here are the links to it:Volume 1:https://w140.com/tekwiki/images/6/62/070-8312-01.pdfVolume 2:https://w140.com/tekwiki/images/4/48/070-8313-00.pdfI carried out the diagnosis on Volume 1, page 187. The fan is running and after 30 seconds the key lights doesnt turn off. Thereupon According to the instructions, I troubleshooted the processor/front panel procedure (Volume 1 page 195).I checked all the required voltages on connector J2. all OK. The clock signal (3.125Mhz) is also present.According to the instructions, the communication link between the A11 Display/processor board and the A12 front module is faulty. The A12 Front module is most likely defective and should be replaced.Today I took a look at the DALLAS DS1245Y-120 NVRAM. As far as I can tell, the battery is empty and all data is gone.I tried reading it out with Xgpro. Only AA AA AA are displayed throughout.I have already bought a new NVRAM. Unfortunately, I'm just missing the data that belongs on it.Does anyone have an idea where I can get the data for the NVRAM?

author: 97paul
author_rank: Contributor
timestamp: February 01, 2025, 04:29:45 pm
content: TYPE

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 02, 2025, 05:21:38 pm
content: This is the only file I have for the TDS520, maybe it will help?I'll have to see if I have a TDS520 in my collection, if so I can copy out the NVRAM's etc.

author: 97paul
author_rank: Contributor
timestamp: February 02, 2025, 05:30:55 pm
content: Thank you! 😉

author: 97paul
author_rank: Contributor
timestamp: February 21, 2025, 11:26:41 am
content: Quote from: TERRA Operative on February 02, 2025, 05:21:38 pmI've tried this out now. Unfortunately it doesn't work either. The 8 is still displayed. Do you remember which Tektronix TDS 520 you copied from? There are several types, for example the TDS520-C. I only have the TDS520 without an ending.

author: wn1fju
author_rank: Frequent Contributor
timestamp: February 21, 2025, 01:19:48 pm
content: You could try the attached file. I think this was the modified NVRAM contents I used to hack my TDS520 into giving me Option 2F (FFT, math) years ago. No guarantees, but I don't think you can damage anything by trying it.This is for a TDS520, not ones with suffix like "A" or "B".I assume you have changed all the electrolytics on each and every board. You also have to look very carefully around them to see if any traces were damaged or any electrolyte got under adjacent parts. Use a strong light and a magnifying glass.

author: 97paul
author_rank: Contributor
timestamp: February 21, 2025, 01:52:00 pm
content: Thank you! I'll try that out. I replaced all the capacitors. So far I haven't been able to detect any interruptions in the conductor track other than oxidation on some components.

author: CaptDon
author_rank: Super Contributor
timestamp: February 21, 2025, 02:04:47 pm
content: The NVRAM is the least of your problems. What kind of activity do you see on the screen if any? If you had the little round silver electrolytics and any of them leaked you probably have some trace damage!! If when unsoldering them you got any hint of an acrid acid smell or burned rubber smell you probably have trace damage. Those traces in some places are barely wider that about three human hairs. If I recall correctly, even with a missing NVRAM or one with corrupted data the numeric display will still show activity, more than just the stationary '8'. It seems the processor is hung up well before it even tests the front panel.

author: 97paul
author_rank: Contributor
timestamp: February 21, 2025, 02:12:09 pm
content: It definitely smelled while soldering. I also unsoldered some components that looked oxidized and looked underneath. I didn't find a single interruption. Nothing is shown on the screen except a short flash of light when starting. An 8 appears on the segment display.

author: 97paul
author_rank: Contributor
timestamp: February 21, 2025, 02:15:01 pm
content: When I follow the service instructions, I can't find anything. Most steps require the device to boot.

author: TERRA Operative
author_rank: Super Contributor
timestamp: February 21, 2025, 04:39:13 pm
content: IIRC, often I had a scope hang on 8 (usually with a decimal point too, which means error or something), it was the Timekeeper/watchdog NVRAM that holds the firmware that was bad.I can't remember if the TDS520 uses an NVRAM for firmware, but that's where I would take a look.I'll check this weekend re. my TDS520 NVRAM file, but it may have been obtained from somewhere online.

author: bert-bert
author_rank: Contributor
timestamp: June 04, 2025, 01:46:22 pm
content: Hello,I currently have 97paul's scope, a TDS520, and am trying to fix it.I already found out that U1167 on page A11-5 in the service manual, a 74HCT164, next to the fan on the baord was defective. With a new chip the scope boots, but fails to acquire a signal. It constantly shows "filling pretrigger".I also have a defective TDS540 and I already swapped the mainboards, but kept the Flash card at the respective scope and finally cleared the NVRAM (I have backups, but they were cleared anyway).With most configurations I cannot enter the self test menu on the scope, as I get an error when I try to select CAL and it shows "Invalid Selection". Only the TDS540 mainboard with TDS540 scope succeeds to show the error log. All other configurations fail in this respect. I am waiting for a console debug port, but can read the contents of the NVRAM to show the errors.I get the following results:TDS520FAIL Processor, FAIL ACQ/Proc Interface, FAIL Acquisition, FAIL Attn/Acq InterfaceNVRAM: extended cal librarian resetTDS520 with TDS540 mainboardsame result as TDS520 with TDS520 mainboardTDS540FAIL Cal Initialization, FAIL Acq/Proc Interface, FAIL AcquisitionNVRAM: calLibrarianDefaultCk.Libs set to factory defaults: ExtConst acqdataconf addr=0x7300000 exp data=0x7fff actual=0xffff WAS TESTING DIG ATDS540 with TDS520 mainboardat fist boot the same message as with TDS540 mainboard (but I am not sure any more and shot no photo), but after the second boot the Processor fail message arose and the CAL Initialization went to passafter clearing the NVRAM:FAIL Processor, FAIL Cal Initialization, FAIL Acq/Proc Interface, FAIL AcquisitionNVRAM: dsyDiagRegSelect addr=0x7560000 exp data=0x7 actual=0xf calLibrarianDefaultCk.Libs set to factory defaults: ExtConst acqdataconf addr=0x7300000 exp data=0x7fff actual=0xffff WAS TESTING DIG Adoes someone have a clue what to do further?can the firmware be faulty? I attach the read out firmwares.TDS520 FV:v1.10eTDS520.zip(728.32 kB - downloaded 45 times.)TDS540 FV:v2.13eTDS540.zip(726.55 kB - downloaded 44 times.)Thank you in advance!

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 05, 2025, 05:21:57 am
content: Are all the SMD electrolytic capacitors replaced and any damage repaired? These scopes had bad problems with leaky capacitors. I've had to replace them in a few scopes now.

author: bert-bert
author_rank: Contributor
timestamp: June 05, 2025, 11:13:32 am
content: Hello!Thank you for your reply!Paul did a good job replacing all the electrolytic capacitors in the TDS520. They are soldered well and neither he nor I could find a broken trace up to now.The TDS540 is different. Whoever replaced the capacitors there, broke pads. There are some capacitor pads, that clearly are not in the position where they belong. So there may be no contact to the trace. When I took it apart, a capacitor was hanging 90° tilted from the board. I glued the pads to the board with superglue, but did not connect the trace up to now. I thought one missing capacitor will not make a huge difference. And this TDS540 mainboard is the mainboard that shows less error messages than the TDS520 mainboard.There is AFP or VFP written on all the capacitors in the TDS540. Am I correct, that these are replaced capacitors and not the original factory default capacitors as this will be the voltage rating? In some scope that I repaired the factory original capacitors had a voltage rating written on the capacitor not a code like AFP or VFP.But repairing broken traces is difficult when one has no clue where to look. I am looking forward to finding a hint, where to look for broken traces or defective chips. A few months ago I repaired a TDS420 with a broken feedback resistor where I diagnosed that the DAC has no sensible reference voltage. I did not look for broken traces but diagnosed the circuit. Here I have no clue where to look for a broken trace. I cannot look under every chip. Can anyone give me a hint what these messages in the NVRAM mean?In the TDS540 there was something looking like liquid around each capacitor and also at some chips near capacitors. It could have been residue of flux. Or it could have been capacitor puke. I have no clue. I removed it with PCB cleaner liquid. How can one distinguish flux residue from capacitor puke acid?Thank you!

author: bert-bert
author_rank: Contributor
timestamp: June 08, 2025, 11:04:24 pm
content: Hello,as already mentioned, I suspect a failed firmware in the TDS520.I found a "Tektronix_TDS520_2_channel_digital_oscilloscope_500Mhz_EPROM_v2.16e.zip" somewhere on the internet that contains 12 BIN files each 128kB large.Would someone mind supplying a firmware file for the TDS520 that I can flash with unified tektool or explaining how I can flash those 12 BIN files without unsoldering the 12 flash chips?thank you in advance!On the TDS540 I plan to fix the broken capacitor pads on the acquisition board as this may solve the issue, I hope.

author: bert-bert
author_rank: Contributor
timestamp: June 09, 2025, 12:00:00 am
content: in the meantime I combined the 12 files into one file.  tds520_v2.16e.zip deleted as it is defective  Please tell me, is this a correct file? It looks similar to the TDS540 v2.16e that I found somewhere on the internet. Can I flash this with unified tektools?Thank you!

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 09, 2025, 04:26:55 am
content: Can you compare the files to see any differences? There are online file comparison websites that can do it.I wouldn't be surprised if the TDS520 and TDS540 actually use the same firmware, there is a lot of firmware sharing between related models in this range of scopes.

author: bert-bert
author_rank: Contributor
timestamp: June 09, 2025, 04:37:07 am
content: I did compare this combined TDS520 v2.16e with a TDS540 v2.16e that I found somewhere on the net using the paid but great tool Beyond Compare and they look similar. There are differences, but I guess the file is ok.I am just wondering, is there something I have to take care when flashing with the unified tektool? I fear destroying the flash. Will I have to first identify the flash, then erase and finally program?

author: bert-bert
author_rank: Contributor
timestamp: June 09, 2025, 01:15:14 pm
content: Hello,well, things didn't work out as expected.I read out the firmware and NVRAM of the TDS520 again, zero-filled, erased, programmed the flash, then the verify with protected protection switch failed, but succeeded with unprotected switch. So I re-erased and programmed the scope. Now the flash is finally programmed. Compare succeeds always now. But the scope refuses to boot. It always enters program mode where I can maintain the scope via GPIB independent of the position of the switch. I had this behavior some time before flashing but it disappeared again, when trying to disable checks and enabling them again and flipping the protection switch in powered-off state, so I didn't bother much.And the worst, with swapping CPU boards the behaviors stay. So now I always have Processor error on the TDS540 scope, but the TDS540 boots and acquires a distorted signal as before.The TDS520 does not boot any more.My suggestions for the new occurrences in the TDS520:* the firmware flashrom is defective, maybe I constructed it wrongly, or the file where I got the parts was defectiveor* the bootrom is not compatible with the firmwareor* FW 2.16e makes more checks on the hardware before it boots and refuses to boot when there are flawsor* the scope broke down in the meantimeI think all of them are unrealistic, but I see no fifth option.I have no clear idea how the TDS540 can fail Processor now, but succeeded before.I ask you to upload your bootrom for a v2.16e firmware TDS520 or similar model with this firmware version if you have one (this TDS520 and my TDS540 share the same bootrom).Or I ask you to upload your known to be working firmware for a TDS520.thank you in advance!

author: madao
author_rank: Frequent Contributor
timestamp: June 09, 2025, 04:03:19 pm
content: I can told: Not !TDS540 and TDS520 Firmware is difference ! (also TDS520A/524A vs TDS540A/544A)Since TDS500B/700A is Firmware universial, but older 500/500A isn't universial.

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 09, 2025, 04:09:42 pm
content: Do you happen to have the NVSRAM dumps for these scopes too?

author: madao
author_rank: Frequent Contributor
timestamp: June 09, 2025, 06:27:06 pm
content: Of coruse, here of couple TDS500/500A o'ScopeTDS500_500A_NVSRAM.zip(1017.78 kB - downloaded 17 times.)Here, a example, what TDS524A Firmware about TDS540 (= 544A) acqusistion board saidYou can seen some message about "Expect 2, actual 4" or similar..

author: bert-bert
author_rank: Contributor
timestamp: June 09, 2025, 07:50:08 pm
content: Hello matt,thank you for providing the firmware files!My replacement firmware that I created by combining the 12 files was faulty. Now the scope boots again and shows the same status as before flashing the firmware for the first time.There were only very minor differences between the files, between the faulty and this correct, and the differences cover four of those 12 files, strange.But now I am back at trying to fix this scope ... and you won't be able to see what is faulty. I will just have to follow the diagnosis procedures.Matt, would you mind me asking, why you recommend to zero-fill the flash before erasing? I only zero-filled on the first try, but did not zero fill in succeeding programming iterations, and now the flash is correct. So, may I ask what this is good for?Thank you!

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 09, 2025, 10:50:42 pm
content: Quote from: madao on June 09, 2025, 06:27:06 pmI'm not sure what is firmware and what is NVRAM there, the file sizes are all different to what the tektool usually spits out and the filenames are no clue as to what matches what for the firmware/NVRAM.For now I think I'll just stick to getting my own firmware and NVSRAM dumps instead.Thanks anyway.

author: bert-bert
author_rank: Contributor
timestamp: June 09, 2025, 10:54:43 pm
content: according to what I understand this one zip file contains just NVRAM dumps. Flash is larger. And the bootrom is in my zip files.

author: Tantratron
author_rank: Frequent Contributor
timestamp: June 10, 2025, 06:15:25 am
content: Quote from: madao on June 09, 2025, 04:03:19 pmThen we have the enigmatic TDS510A

author: bert-bert
author_rank: Contributor
timestamp: June 15, 2025, 09:44:35 pm
content: Hello,I found out some more about the TDS520. It seems to me that the VCO board A21 is defective. I still have to measure the output of the board with my TDS744A, but a 100MHz scope shows no sensible output from the VCO board.The VCO board has +/-5V, and gets a control voltage of 10,8V, but does not oscillate - unless my scope does not get it. All the components around the VCO are ok. It can only be a defective VCO or that I just miss the signal as my other scope is too bad.Does someone of you have a clue how to fix a VCO, or does someone have a working VCO from a defective compatible scope lying around and can sell it, ideally from within the EU in order not to pay customs?thank you in advance!

author: bert-bert
author_rank: Contributor
timestamp: June 16, 2025, 02:38:23 am
content: the output of the VCO measured with a 400MHz scope and 500MHz probesCH1 pin 2 of A21CH2 pin 3 of A21GND leads connected to pin 7 of A21this is the TDS520I don't mind the 100MHz noise, thats the radio broadcast signal that is so strong here. But the 500MHz signal is too weak and both signals are in phase.and that's what it should look like, positive and negative signal nicely counter-phase:CH1 pin 2 of A21CH2 pin 3 of A21GND leads connected to pin 7 of A21this is the TDS540looks like a defective VCO in the TDS520

author: TERRA Operative
author_rank: Super Contributor
timestamp: June 16, 2025, 04:31:14 am
content: I have this design, maybe it is the same VCO board in your scope? It works perfectly in my scope. It passes performance test perfectly, no recalibration required.https://www.pcbway.com/project/shareproject/Tektronix_TDS500_Oscilloscope_A21_VCO_Board_f268351a.htmlI might even have some spare PCB's, I can stick one in an envelope for the cost of posting a letter.There is only one part that is obsolete though (CR101, MMBV105G), so hopefully that's not the dead bit on yours unless you can find one (or a substitute) locally..Mine just had leaky capacitors, so CR101 was able to be reused from my original VCO board.

author: bert-bert
author_rank: Contributor
timestamp: June 16, 2025, 05:21:38 am
content: thank you for your reply and thank you for your offer!The best of your reply is the parts list as now I know what exact transistors to use to fix the board in case the transistors are faulty.But one ceramic capacitor looks like it has a tiny hole in the middle. It's not shorted, but maybe it lost capacity. I'll investigate further.As I now have the exact list of parts I rather feel like fixing this VCO than building a new one as the PCB looks good.Thank you a ton!I did investigate further, and at the base of Q102 we have the signal:CH1 is the base of Q102here we have the signal.And diode test of Q101 and Q103 measure 100 between base and emitter, and measures 900 between base and emitter of Q102. I conclude that Q102 will be defective.Q102 will be a BFU530WX from NXP.Ordering such a transistor from mouser or digikey is so, so expensive. Does someone know a easier to source alternative or does someone in the EU offer to sell one?Thank you!

author: madao
author_rank: Frequent Contributor
timestamp: June 16, 2025, 07:11:48 pm
content: I can say TDS520 and TDS540 use same VCO board.I have fixing over 10 TDS500-Series with capacitor plague.VCO board semicoductor is never bad, in two case with nonworking VCO: broken trace.If VCO works -> 7V +-1V control voltage on mini pcbs.regardsmatt

author: bert-bert
author_rank: Contributor
timestamp: June 17, 2025, 10:27:11 am
content: Hello matt,thank you for your reply!I am very sure, it will be a bad Q102 in the TDS520.On the input of Q102 - the base - we have a nice 600MHz signal, but on the output we have only a very tiny signal, as you see on the scope pictures.I plan to replace Q102 and am looking forward to fixing the issue thereby.What do you suggest? Do you recommend taking the PCB from Terra Operative and exchanging the whole VCO board? I fear destroying the valuable an not available part CR101 when I swap it and would like to keep that part on the original VCO without tinkering with that part.Furthermore I know some more for the TDS540 in the meantime.I now have a console adapter and the bootlog is:Code:Bootrom Header Checksum passed.Bootrom Total Checksum passed.BootRom Check Sum passed.Bus Error Timeout test passed.Kernel Diagnostics Complete.Calling SDM (monitor) Routine.Enabling Bus Control register. Value = 0x67IMR 1 Register test passed.Misc. Register test passed.Timer Interrupt test (Auto-Vector) passed.NVRam DSACK test passed.NVRam Write protected.Flashrom DSACK and JumpCode test passed.Flashrom Checksums passed.Bootrom Diagnostics Complete.Transferring control to the Flashrom.-> Console Loopback O.K. <-.^^^^ ^^^^^^ ^^^^ ^^ VxWorks Development System^^ ^^^^ ~~~~~~~~ ~~^^ ^^ ~~~ ~^^ ^^ ~~~^^^^ ~ ~~~^^ ~~ ~~~VxWorks version 4.0.2.Stripped Stand Alone Rom Version.Columbia Proc. Brd. Rev GG065801System Ram Size = 1048576, Proc ID = 0x18Clock Interval = 13108 usecs,Bootline Storage Size = 296 stored @0x4000068Flash ID = 0x0, Flash Wait states = 2 (Misc. reg = 0x14),KERNEL: WIND version 1.0. GCC COMPILEDCopyright 1991-2001, Tektronix, Inc.made on: Wed Feb 12 15:28:50 PST 1992.copyright Wind River Systems, Inc., 1986, 1987, 1988, 1989Executing DiagnosticsStart Power-On Diag SequencehwAccountant probe routinesProbe for unexpected pending intsDsp Instr mem sizeDsp D2 mem sizeDsp D1 mem sizeDsy Vect0 mem sizeDsy Vect1 mem sizeDsy Wfm0 mem sizeDsy Wfm1 mem sizeDsy Text0 mem sizeDsy Text1 mem sizeAcq number of digitizersAcq mem sizeCpu timer interval uSecCpu Dram sizeNvRam mem sizeOpt RS232/ Cent presencedspForcedBus ................... passcpuDiagD2MiscReg ............... passcpuDiagDSPIntMaskReg ........... passcpuDiagDsyAccess ............... passdsp68kMemTest .................. passcpuDiagFIFOMem ................. passdspRunVerify ................... passdspBusRequestTest .............. passdspImplicitBusAccess ........... passdspTristarMemTest .............. passdsyDiagResetReg ................ passdsyDiagVscReg .................. passdsyDiagPPRegMem ................ passdsyDiagRasRegMem ............... passdsyDiagRegSelect ............... passdsyDiagRamdacRegMem ............ passdsyDiagAllMem .................. passdsySeqYTModeV0Intens ........... passdsyDiagSeqXYModeV1 ............. passdsyRastModeV0Walk .............. passdsyRastModeV1Attrib ............ passdsyWaitClock ................... passcpuDiagAllInts ................. passoptRS232DuartIO ................ UNTESTEDnvLibrariansDiag ............... ***FAIL***..error details:ERRORID: 149 diagnostic test failure nvLibrariansDiagLibs with crcc failures:ExtConstcalLibrarianDefaultCk .......... ***FAIL***..error details:ERRORID: 149 diagnostic test failure calLibrarianDefaultCkLibs set to factory defaults:IntConstdspForcedBus ................... passacqProcThermistor .............. passdigDiagD1Conf .................. ***FAIL***..error details:ERRORID: 149 diagnostic test failure acqdataconf** addr = 0x7300000 exp data = 0x7fff actual = 0xffff*** WAS TESTING DIG A ***digDiagConf .................... ***FAIL***..error details:ERRORID: 149 diagnostic test failure acqdataconf** addr = 0x7300000 exp data = 0x7fff actual = 0xffff*** WAS TESTING DIG A ***vertAttenStrobeDiag ............ passvertAttenShiftReg .............. passdacRangeDiag ................... passfpDiagConf ..................... passExecuting SmalltalkhwAccountant probe routinesProbe for unexpected pending intsDsp Instr mem sizeDsp D2 mem sizeDsp D1 mem sizeDsy Vect0 mem sizeDsy Vect1 mem sizeDsy Wfm0 mem sizeDsy Wfm1 mem sizeDsy Text0 mem sizeDsy Text1 mem sizeAcq number of digitizersAcq mem sizeCpu timer interval uSecCpu Dram sizeNvRam mem sizeOpt RS232/ Cent presence[Stripped vxWorks]:Smalltalk/V Sun Version 1.12Copyright (C) 1990 Object Technology International Inc.ERRORID: 149 diagnostic test failure extended cal librarian resetWe have a Acquisition board SRAM memory error, but I don't think that the memory will be bad, I think it will be a power issue. The SMD capacitors were all replaced by the previous owner of the scope, but maybe they turned bad again. Is this possible that these are low quality capacitors and that they failed again after a few years?The scope shows this signal when the scope is turned to the fastest possible realtime acquire speed and no input signals connected. It varies a little, but mostly similar signals are shown.About every eighth sample we have a spike.I plan to exchange Q102 on the TDS520 VCO when I get the replacement transistor and plan to exchange the SMD capacitors on the acquisition board of the TDS540 again, unless I change my mind. What do you think?Thank you!

author: madao
author_rank: Frequent Contributor
timestamp: June 17, 2025, 03:45:17 pm
content: How look DC-voltage on Q103 and Q102, it must be similar.I have put two schematic (older and newer revision, choke-version is normally older )Did get both transistor -5.1V via Resistor ?Is capatitor between connected. If there is some trace cutted, then no bis weak signal output.

author: bert-bert
author_rank: Contributor
timestamp: June 17, 2025, 05:41:18 pm
content: matt, you're the best!the connection between R106 and C106 was open. A short wire, and we now have 7,3V on TP502. YEAH!!! VCO repaired!By the way, both, the TDS520 and the TDS540 have the more moderrn version with R110 and R111 without a choke, but there is written T101 on the board and it took me really some time to figure out that there is no T101 long before you wrote this.But the scope does not work either ...still just 'filling pretrigger'all the following scope pictures have Pin 2 of A21 on CH1 and Pin 3 of A21 on CH2before I repaired it:and after I repaired it:

author: madao
author_rank: Frequent Contributor
timestamp: June 17, 2025, 06:27:55 pm
content: next step is repair jitter/interpolator ramp.if there LM311 output stucks low (?) -> trigger stops and "pretrigger filling" message come ..I am not at 100% sure.

author: bert-bert
author_rank: Contributor
timestamp: June 17, 2025, 09:16:48 pm
content: RAMP1 U1603 input Pin 3 (a LM311) is 'stuck' at -1,4V. The output is at +5V.The output Pin 1 of U1601A is way below GND, even below -5V most of the time, this will not short Pin 3 to -1,4VRAMPSW1, ~RAMPSW1, RAMPST1, ~RAMPST1 are all about at 2,5V. I do not like that, but am not sure. They are not exactly the same, maybe they are correct.RAMP2 U1653 input Pin 3 (the next LM311) is at 0V.But the DAC fails according to the error log, I guess I shall first try to fix the DAC, don't you think so?And to me it seems there is at least one either defective or not-responding RAM chip on the acq board.the Debug output:Code:Bootrom Header Checksum passed.Bootrom Total Checksum passed.BootRom Check Sum passed.Bus Error Timeout test passed.Kernel Diagnostics Complete.Calling SDM (monitor) Routine.Enabling Bus Control register. Value = 0x67IMR 1 Register test passed.Misc. Register test passed.Timer Interrupt test (Auto-Vector) passed.NVRam DSACK test passed.NVRam Write protected.Flashrom DSACK and JumpCode test passed.Flashrom Checksums passed.Bootrom Diagnostics Complete.Transferring control to the Flashrom.-> Console Loopback O.K. <-.^^^^ ^^^^^^ ^^^^ ^^ VxWorks Development System^^ ^^^^ ~~~~~~~~ ~~^^ ^^ ~~~ ~^^ ^^ ~~~^^^^ ~ ~~~^^ ~~ ~~~VxWorks version 4.0.2.Stripped Stand Alone Rom Version.Columbia Proc. Brd. Rev GG065801System Ram Size = 1048576, Proc ID = 0x18Clock Interval = 13108 usecs,Bootline Storage Size = 296 stored @0x4000068Flash ID = 0x0, Flash Wait states = 2 (Misc. reg = 0x14),KERNEL: WIND version 1.0. GCC COMPILEDCopyright 1991-2001, Tektronix, Inc.made on: Wed Feb 12 15:28:50 PST 1992.copyright Wind River Systems, Inc., 1986, 1987, 1988, 1989Executing DiagnosticsStart Power-On Diag SequencehwAccountant probe routinesProbe for unexpected pending intsDsp Instr mem sizeDsp D2 mem sizeDsp D1 mem sizeDsy Vect0 mem sizeDsy Vect1 mem sizeDsy Wfm0 mem sizeDsy Wfm1 mem sizeDsy Text0 mem sizeDsy Text1 mem sizeAcq number of digitizersAcq mem sizeCpu timer interval uSecCpu Dram sizeNvRam mem sizeOpt RS232/ Cent presencedspForcedBus ................... passcpuDiagD2MiscReg ............... passcpuDiagDSPIntMaskReg ........... passcpuDiagDsyAccess ............... passdsp68kMemTest .................. passcpuDiagFIFOMem ................. passdspRunVerify ................... passdspBusRequestTest .............. passdspImplicitBusAccess ........... passdspTristarMemTest .............. passdsyDiagResetReg ................ passdsyDiagVscReg .................. passdsyDiagPPRegMem ................ passdsyDiagRasRegMem ............... passdsyDiagRegSelect ............... ***FAIL***..error details:ERRORID: 149 diagnostic test failure dsyDiagRegSelect** addr = 0x7560000 exp data = 0x7 actual = 0xffcalLibrarianDefaultCk .......... ***FAIL***..error details:ERRORID: 149 diagnostic test failure calLibrarianDefaultCkLibs set to factory defaults:IntConstdspForcedBus ................... passacqProcThermistor .............. passdigDiagD1Conf .................. ***FAIL***..error details:ERRORID: 149 diagnostic test failure acqdataconf** addr = 0x7300000 exp data = 0x7fff actual = 0x80ff*** WAS TESTING DIG A ***digDiagConf .................... ***FAIL***..error details:ERRORID: 149 diagnostic test failure acqdataconf** addr = 0x7300000 exp data = 0x7fff actual = 0x80ff*** WAS TESTING DIG A ***vertAttenStrobeDiag ............ passvertAttenShiftReg .............. passdacRangeDiag ................... ***FAIL***..error details:ERRORID: 149 diagnostic test failure Dac Range Test** DAC system failurefpDiagConf ..................... passExecuting SmalltalkhwAccountant probe routinesProbe for unexpected pending intsDsp Instr mem sizeDsp D2 mem sizeDsp D1 mem sizeDsy Vect0 mem sizeDsy Vect1 mem sizeDsy Wfm0 mem sizeDsy Wfm1 mem sizeDsy Text0 mem sizeDsy Text1 mem sizeAcq number of digitizersAcq mem sizeCpu timer interval uSecCpu Dram sizeNvRam mem sizeOpt RS232/ Cent presence[Stripped vxWorks]:Smalltalk/V Sun Version 1.12Copyright (C) 1990 Object Technology International Inc.ERRORID: 149 diagnostic test failure extended cal librarian resetI have no clue about dsyDiagRegSelect, but the NVRAM was deleted, and I did not program it with something sensible up to now.update:I cannot find any malfunction in the DAC system. the DAC is programmed, turns to the desired voltage, then the output is switched to some logic, some sample-and-hold stage, thereby the DAC output voltage jumps to the voltage of the sample-and-hold-stage, and it takes up to 50µs or more until the output gets stable before the next analog voltage is programmed. I believe everything is fine here, except I was worried about this behavior in the first place. I have not checked with the TDS540 whether this is the same there. I am just wondering how the scope checks the DAC. I have no clue up to now.well, well, time for some sleep ...next update:this strange DAC behavior is defitively not normal, as it does not occur on the TDS540. In the TDS540 the DAC output reaches a voltage and stays there.I guess there is too much load on the output on the DAC. Or the DAC is defective. Or my next guess at the next picture.CH1 DAC Pin 3 SUMJCTCH2 DAC Pin 9 VOUTcan this capacitor in the middle be a defective capacitor? I mean the brown part left to the QFDP9203 and right to the resistor with marking 2740. This is C900, the slow down capacitor so that the output op-amp of the DAC does not oscillate as far as I understand this schematics.I cannot find any open trace around the DAC. Every input pin of the DAC I looked at measures sensible, except maybe SUMJCT.C900 has the value '10' in the schematics. Is this 10nF? I am absolutely not sure here.C900 is not shorted. I measure 6kOhm on it in the board with the other components connected on the TDS520 and the TDS540.One guess is a defective U909, a DG444 switch, as this happens with multiple outputs of the U909. At the moment the U909 closes a switch, the voltage drops.In order to find out whether the DAC or the switch works wrongly, I intend to connect a 0.1 capacitor like C1535 to the output of the DAC U900 and look how the DAC behaves. But first I'd need to know whether the 0.1 are nF.And furthermore, would you mind me asking whether these are 1206 resistors and ceramic capacitors?Thank you in advance for any hint!

author: bert-bert
author_rank: Contributor
timestamp: June 18, 2025, 06:03:35 pm
content: now I connected a 10pF and a 10nF capacitor in parallel to C900 and for the 10pF capacitor there is no visible change, and for the 10nF capacitor the system completely misbehaves, we only see rounded curves of voltages. I do not know if this makes any sense, but it was an experiment as I hoped this would solve everything.What is more interesting, is the following:CH2 DAC Pin 9 VOUT connected via a 10nF ceramic capacitor to DAC Pin 16 GNDwe see that the slope that is unavoidable is about 10 times as fast as the slope introduced by the switchingCH2 DAC Pin 9 VOUT connected via a 100nF ceramic capacitor to DAC Pin 16 GNDthis is it. There is some 100nF load somewhere in the scope that the DAC cannot drive. But 100nF is a really large load for a DAC, isn't it?Where can this 100nF load be? Can it be a defective U909 DG444 switch?And I am still wondering what these numbers (e.g. 10 in the schematic for a capacitor) mean and whether these are 1206 resistors.

author: madao
author_rank: Frequent Contributor
timestamp: June 18, 2025, 06:09:08 pm
content: I must recommend you: replaced all corrored op-amp and analog-switch by new parts.

author: bert-bert
author_rank: Contributor
timestamp: June 20, 2025, 10:14:55 pm
content: matt, thank you for that hint!I verified that the DAC in the TDS540 shows a similar behavior when I load it with a 100nF load. I conclude, I will not have to replace the DAC.I already ordered quite a few DG444DY and op-amps. Now I have to wait until they arrive.-- ^ TDS520 ^ -- v TDS540 v --In the meantime I measured a little on the TDS540.both measurements are on the acquisition board of the TDS540:CH2 Pin 28 VCC of SRAM U115 7164Sthe GND cable is connected to Pin 14 GND of the SRAM U115 7164SCH2 Pin 6 of J101 +5.1Vthe GND cable is connected to Pin 8 of J101 GNDthis is both times the same power rail. Once at one SRAM and once at the input from the power supply.900mV pk-pk are way too much, but I believe also 350mV pk-pk are too much. This means, I will have to replace the capacitors on the acq board, that already someone has replaced, yet another time. Do you think, will I have to replace also the capacitors in the power supply, when I want to do it well?Swapping power supplies from TDS520 to the TDS540 did not change much. Both show the same result.

author: bert-bert
author_rank: Contributor
timestamp: July 06, 2025, 08:36:43 pm
content: Hello,well, the TDS540 is driving me nuts. In the meantime I exchanged the 16 pieces of 33µF 10V capacitors around the SRAM that were already replace beforehand by someone else. And nothing changed. Not a tiny bit. Does someone have a clue what this means? We have a very wrong signal at each 8th sample as visible some posts ago on the photo of the scope. This may indicate something, maybe just 1 RAM chip per channel is defective. We have the very fluctuating voltage at the SRAM chips. The voltage at the demultiplexer is smoother and at the ADC perrfect. Shall I exchange the capacitors in the power supply? I just connected a 2000µF capacitor to pin 4 and 6 of J101 (the 5.1V power rail that supplies power to the SRAM) and nothing changed. Is 2000µF to little? Shall I solder a large capacitor to that pin, is it too loose to just clamp it there?What do you think shall I do? Shall I exchange chips?My suggestion is to first solder a large, very large capacitor to pin 4 and 6 of J101 to smooth the supply for the RAM and to thereby test whether I shall swap the capacitors in the power supply. Do some of you have any ideas?Thank you in advance!Update:now I soldered a 6800µF capacitor to pin 4 and 10 of J101 to dampen the voltage and the situation remains the same. Again 890mV Pk-Pk on the supply voltage at the U115 SRAM chip. Again a peak in the measured signal at every 8th sample, but with a little offset between the channels. I conclude, the issue will not be the power supply. Will this be defective SRAM chips??? Multiple defective chips??? No, I do not expect this to be defective SRAM chips. Does someone have a clue what can be the reason of the signal some posts ago the signal of a TDS540 black-and-light-blue display?

author: bert-bert
author_rank: Contributor
timestamp: July 07, 2025, 08:29:25 pm
content: yes, the SRAM of the TDS540 is defective.CH1 white Pin 15 D3 DD32 of U115CH2 green Pin 27 /WE of U115CH3 yellow Pin 20 /CS1 of U115U115 works flawlesslyCH1 white Pin 15 D3 DD0 of U111CH2 green Pin 27 /WE of U111CH3 yellow Pin 20 /CS1 of U111DD0 always reads low, so U111 is defectiveCH1 white Pin 13 D2 DD23 of U113CH2 green Pin 27 /WE of U113CH3 yellow Pin 20 /CS1 of U113always when U113 is read (/WE high and /CS1 low), D2 is high, it is never low, so U113 is defective(not shown) here D2 DD23 is always written lowso we have at least two defective SRAM chips on that channel. There will also be defective SRAM chips on the other channels. They're IDT 7164S25 chips. Such chips are available at digikey, but at 3.44$ per piece at an minimum order quantity of 88 pieces, i.e. $302.72 plus shipping to Austria. Does someone have spare IDT 7164S chips lying around or a defective TDS540 TDS520 acquisition board with 1M option and is willing to sell that?

author: TERRA Operative
author_rank: Super Contributor
timestamp: July 07, 2025, 11:29:24 pm
content: This might do the trick?https://www.mouser.com/ProductDetail/Alliance-Memory/AS7C164A-15JCN?qs=LD2UibpCYJrwS8TM%252BVE%2F6Q%3D%3D

author: madao
author_rank: Frequent Contributor
timestamp: July 08, 2025, 03:01:12 am
content: Ask me ! I have bag 6264-20ns SRAMI can send 10 pieces to you.It is very common of failed SRAM in TDS540/520 with capacitor plague. (failure rate of SRAM in capacitor plague-TDS is high : over 50% case with 1-3 dead SRAM)

author: bert-bert
author_rank: Contributor
timestamp: July 18, 2025, 10:23:44 pm
content: TERRA Operative, thank you for the hint, and matt, thank you for selling some CY7C199-20VC that one can tweak by bending out pin 1 and pin 2 to make contact to the pads for the large chip even though the other pins 3-14 contact the pads for the small chip and shorting pin 1 and 2.In the meantime I exchanged U111 and U113 of the TDS540 and the measured signal improved. The spikes in the measured signal were less than before. But there is still some wrong signal about every 8th sample, but not constantly, it varies.But just at the moment I was sitting in the dark as the fuse in the power supply of the TDS540 blew. So now I'll have to repair the TDS540 power supply. Yeah, I don't like tinkering with power supplies that much.There is an 6A 250V 6.35x31.5mm fuse in the holder. Does someone of you know if that shall be a:FF Very Fast Acting Fuse(Flink Flink)F Fast Acting Fuse(Flink)M Medium Acting Fuse(Mitteltrage)T Slow Acting Fuse(Trage)TT Very Slow Acting Fuse(Trage Trage)I guess it will not be just the fuse, but I'll definitively have to replace the fuse. So I'll have to find out what type to use.Does someone of you have a clue what will be dead in the power supply? There is no visible damage in the power supply except in the fuse.the last bootlog before the fuse blew:Code:Bootrom Header Checksum passed.Bootrom Total Checksum passed.BootRom Check Sum passed.Bus Error Timeout test passed.Kernel Diagnostics Complete.Calling SDM (monitor) Routine.Enabling Bus Control register. Value = 0x67IMR 1 Register test passed.Misc. Register test passed.Timer Interrupt test (Auto-Vector) passed.NVRam DSACK test passed.NVRam Write protected.Flashrom DSACK and JumpCode test passed.Flashrom Checksums passed.Bootrom Diagnostics Complete.Transferring control to the Flashrom.-> Console Loopback O.K. <-.^^^^ ^^^^^^ ^^^^ ^^ VxWorks Development System^^ ^^^^ ~~~~~~~~ ~~^^ ^^ ~~~ ~^^ ^^ ~~~^^^^ ~ ~~~^^ ~~ ~~~VxWorks version 4.0.2.Stripped Stand Alone Rom Version.Columbia Proc. Brd. Rev GG065801System Ram Size = 1048576, Proc ID = 0x18Clock Interval = 13108 usecs,Bootline Storage Size = 296 stored @0x4000068Flash ID = 0x0, Flash Wait states = 2 (Misc. reg = 0x14),KERNEL: WIND version 1.0. GCC COMPILEDCopyright 1991-2001, Tektronix, Inc.made on: Wed Feb 12 15:28:50 PST 1992.copyright Wind River Systems, Inc., 1986, 1987, 1988, 1989Executing DiagnosticsStart Power-On Diag SequencehwAccountant probe routinesProbe for unexpected pending intsDsp Instr mem sizeDsp D2 mem sizeDsp D1 mem sizeDsy Vect0 mem sizeDsy Vect1 mem sizeDsy Wfm0 mem sizeDsy Wfm1 mem sizeDsy Text0 mem sizeDsy Text1 mem sizeAcq number of digitizersAcq mem sizeCpu timer interval uSecCpu Dram sizeNvRam mem sizeOpt RS232/ Cent presencedspForcedBus ................... passcpuDiagD2MiscReg ............... passcpuDiagDSPIntMaskReg ........... passcpuDiagDsyAccess ............... passdsp68kMemTest .................. passcpuDiagFIFOMem ................. passdspRunVerify ................... passdspBusRequestTest .............. passdspImplicitBusAccess ........... passdspTristarMemTest .............. passdsyDiagResetReg ................ passdsyDiagVscReg .................. passdsyDiagPPRegMem ................ passdsyDiagRasRegMem ............... passdsyDiagRegSelect ............... passdsyDiagRamdacRegMem ............ passdsyDiagAllMem .................. passdsySeqYTModeV0Intens ........... passdsyDiagSeqXYModeV1 ............. passdsyRastModeV0Walk .............. passdsyRastModeV1Attrib ............ passdsyWaitClock ................... passcpuDiagAllInts ................. passoptRS232DuartIO ................ UNTESTEDnvLibrariansDiag ............... ***FAIL***..error details:ERRORID: 149 diagnostic test failure nvLibrariansDiagLibs with crcc failures:ExtConstcalLibrarianDefaultCk .......... ***FAIL***..error details:ERRORID: 149 diagnostic test failure calLibrarianDefaultCkLibs set to factory defaults:IntConstdspForcedBus ................... passacqProcThermistor .............. passdigDiagD1Conf .................. ***FAIL***..error details:ERRORID: 149 diagnostic test failure acqdataconf** addr = 0x7300000 exp data = 0x7fff actual = 0xffff*** WAS TESTING DIG A ***digDiagConf .................... ***FAIL***..error details:ERRORID: 149 diagnostic test failure acqdataconf** addr = 0x7300000 exp data = 0x7fff actual = 0xffff*** WAS TESTING DIG A ***vertAttenStrobeDiag ............ passvertAttenShiftReg .............. passdacRangeDiag ................... ***FAIL***..error details:ERRORID: 149 diagnostic test failure Dac Range Test** DAC system failurefpDiagConf ..................... passExecuting SmalltalkhwAccountant probe routinesProbe for unexpected pending intsDsp Instr mem sizeDsp D2 mem sizeDsp D1 mem sizeDsy Vect0 mem sizeDsy Vect1 mem sizeDsy Wfm0 mem sizeDsy Wfm1 mem sizeDsy Text0 mem sizeDsy Text1 mem sizeAcq number of digitizersAcq mem sizeCpu timer interval uSecCpu Dram sizeNvRam mem sizeOpt RS232/ Cent presence[Stripped vxWorks]:Smalltalk/V Sun Version 1.12Copyright (C) 1990 Object Technology International Inc.ERRORID: 149 diagnostic test failure extended cal librarian resetI do not like that I get the following all the time, and a similar message for the TDS520:Code:ERRORID: 149 diagnostic test failure acqdataconf** addr = 0x7300000 exp data = 0x7fff actual = 0xffff*** WAS TESTING DIG A ***0x7300000 is the SRAM Acquisition memory, and as far as I can tell, this will be U111, but I just replaced U111. Did I not replace it well enough? Will there be a partially broken trace???Thank you in advance!

author: bert-bert
author_rank: Contributor
timestamp: July 20, 2025, 05:43:40 pm
content: Well there is a marking 312 on the fuse that I did not pay attention to up to now. But when I google for the fuse rating and 312 I see fast blow F fuses, so I guess it will be a fast fuse.I still don't understand why there are these errors in the selftest even after repairing some SRAM.^^ TDS540 ^^ vv TDS520 vvso, back to the TDS520I just replaced U908, U912 (both DG444), U903 (TL072), U1705 (TL074) and nothing changed. Not even a tiny bit. I conclude, these parts were fine, even though they looked really bad. I don't think that the capacitors increase in value by corrosion, so I guess I am hunting something that is fine here. I just do not understand why the output signal of the DAC measures so different in the TDS540. But currently I cannot compare with the TDS540...I guess I should have followed matts hint:Quote from: madao on June 17, 2025, 06:27:55 pmupdate:there is no switching happening at RAMPSW1, ~RAMPSW1, RAMPST1, ~RAMPST1. I do not like this. What does this mean? We have about 7V at TP502, so the VCO works. Does this mean that U1001 is defective???

author: bert-bert
author_rank: Contributor
timestamp: July 23, 2025, 08:16:36 pm
content: Hello everyone,I did some further investigations, but I'm somewhat out of luck.For the TDS540 I'm waiting for the parcel with replacement fuses to arrive.In the TDS520 the jitter/interpolation ramp leaves me puzzled.Now and then it works. I already had a (distored) signal in the display, but this was only once. There must be a loose contact somewhere.U1602B has 0V between the differential inputs pin 5 and 6, so everything around this is working flawlessly.Q1601 has about 0.7V between base and emitter, so this will be active.The same for Q1617.So, we have a current path across Q1603, Q1601, Q1617.But we have about -1.5V at pin 3 of the LM311 U1603.There are 0V across R1628, so the jitter ramp does not cause the voltage to be so low, there were a voltage drop at R1628 if the jitter ramp drew much current, and the R1631 is so large, the jitter ramp can only make a very tiny difference.The voltage at Pin 3 of U1603, i.e. the voltage of the ramp, is controlled by CR1603 and CR1604 as far as I see. These two diodes limit the negative voltage.U1602A outputs about 11V, this is what I expect when the input pin 2 is below 0V.The LM311 U1603 outputs about 5V. This is what I expect for a schmitt trigger with this input.The emitter of Q1601 and Q1602 measure about 4V.The emitter of Q1616 and Q1617 measure about 2V.Does anyone have an idea what to test next??? I measured hundred times for open traces, connected two maybe broken traces, but that did not change anything.I have no idea any more...Well, I just have an idea. I'll keep you updated.update:there was an open trace between Q1603 and R1635, so the current across Q1603 and Q1601 was too little. Yeah, found!But it does not work either. I see a working jitter ramp, and the voltage at Pin 3 of U1603 is about 0V, but I still get filling pretrigger. Strange. Before I repaired this trace, once I had a trigger. Really strange.

author: vaualbus
author_rank: Frequent Contributor
timestamp: July 23, 2025, 09:41:12 pm
content: I imagine you replaced all caps?Have you paid attention because not all electrolyte cap have the same values.

author: bert-bert
author_rank: Contributor
timestamp: July 23, 2025, 10:00:00 pm
content: Thank you vaualbus for that hint!97paul recapped this scope. I guess he will have used the right caps. Even though, one shall pay attention of this, this is not an error, that sounds like wrong capacitor values to me. It was 'working' for a moment on Monday.

author: bert-bert
author_rank: Contributor
timestamp: July 25, 2025, 06:08:52 pm
content: I did repair the jitter ramps of the TDS520 in the meantime, but the scope still does not work ...In addition to soldering a connection to R1635 for the 22mA current source, I had to solder a connection to R1631 and R1681 for the 11µA ramp control.Now, as you see on the photos, the jitter ramp works, but somehow the scope does not succeed to fill the pretrigger either.TDS520CH1 yellow Pin 3 of U1603CH2 turqouise Pin 7 of U1603just filling pretrigger on TDS520TDS540CH1 white Pin 3 of U1603CH2 green Pin 7 of U1603jitter ramp RAMP1 in TDS540 works flawlesslythe jitter ramp works just the same, but the control signals are different. I have no clue why.Does someone have a clue?And the fuse in the scopes are 6A 1/4" x 1 1/4" type 312 fast blow fuses as written on the back of the scope. Dumb me that I did not look there. And the power supply in the TDS540 just works again after exchanging the fuse. Strange. Nothing defective. Just a blown fuse.Does someone have an idea what can be the reason for "Filling Pretrigger" when the jitter ramps work flawlessly but are controlled strangely?Thank you in advance!update:TDS520CH1 yellow Pin 28 CLKB of U501 clock bufferCH2 pink Pin 2 CLKA of U501 clock bufferTDS520CH1 yellow TP126 DCLKBno signal at all at TP226 DCLKADoes this mean the ADC converter U750 will be dead?

author: bert-bert
author_rank: Contributor
timestamp: July 26, 2025, 12:14:15 pm
content: vaualbus, Paul confirmed that he took care to replace the capacitors with ones with the same rating.Both clock signals at U501 will be fine. I compared them to the TDS540 and they aren't so large there either and they vary in the TDS520.The ADC in the TDS540 also does not output a clock signal all the time as far as I can tell, so this need not be an error. update: No, sorry, this must have been an measurement error. It always outputs a 125MHz signal at all of the ADCs.Now the Filling Pretrigger message is only very rare in the TDS520. Mostly it is Autoing, but showing no trace. Does someone have a clue what that can mean? Will the trace be above or below the visible screen? Or will there be none? I cannot run a SPC as I get a feature not available message once I enter the CAL menu.matt (madao) gave me the hint that there can be shorted address lines at the SRAM and there are ones in the TDS540. I'll investigate further.

author: bert-bert
author_rank: Contributor
timestamp: August 08, 2025, 03:06:52 pm
content: regarding the TDS520:well, at first the good news, the clock signal is fixed. There were two pull-down resistors for the clock signal between ADC and demuxer corroded and unconnected. Connecting them yields a signal. :-)But the bad news, I cannot get the SRAM fixed up to now, as it seems not to be the SRAM itself.I get an error at the first possible SRAM address, but the error varies a little, sometimes 0xc0ff, sometimes 0xd0ff, once 0x80ff instead of 0x7fff. So I replaced U211 before analyzing that far, but that did not change anything. I cannot find an open trace on the acquisition board, I cannot find a shorted trace around the SRAM. I somewhat don't have a clue what to expect further. The error is different on CH1 and on CH2, but both channels are affacted.Connecting a signal to the input changes the displayed signal, but there is always this terrible noise.I show you a picture of the scope screen to see what the errors look like. Sometimes the spikes repeat every 16th sample, but they move around, so it's a somewhat non-deterministic error.Does someone have an idea what to do further here???Thank you in advance!

author: bert-bert
author_rank: Contributor
timestamp: August 09, 2025, 04:58:01 pm
content: here I deal with the TDS540:I always haveCode:ERRORID: 149 diagnostic test failure acqdataconf** addr = 0x7300000 exp data = 0x7fff actual = 0xffff*** WAS TESTING DIG A ***in the console logSo I suspected a defective U411. But I changed U411 and nothing changed. I connected a 6800µF capacitor to J101 so that a defective power supply can be ruled out. Not really a change. Maybe a tiny bit better, as the noise varies a little more now, but this might be wrong.So I connected a 470µF capacitor directly to U411 on Pin 14 and Pin 28. Now I have much change. The error message is just the same, but there is much, much more noise on the respective channel 1. And it's not just one SRAM chip that misbehaves now, but more than one.So the capacitors change something, but not to the good. Maybe I'll have to just replace C26, C27, C29, C30 in the power supply.CH1 black and CH2 green Pin 28 of U411 connected to a 470µF capacitorGND of both channels is connected to Pin 14 of U411 connected to GND of the 470µF capacitor6800µF capacitor connected to J101this seems to be just the start of the self-test routinge of the SRAM at power upCH1 black Pin 28 of U414GND of CH1 is connected to Pin 14 of U414CH2 green Pin 28 of U411 connected to a 470µF capacitorGND of CH2 is connected to Pin 14 of U411 connected to GND of the 470µF capacitor6800µF capacitor connected to J101I changed all the 16 capacitors around the SRAM some days ago, so these will not be the reason for the noise. Maybe I shall change more capacitors then the 16, but I think these 16 are the most important ones.I measured the contact of every pin of U411 to U400 and I saw a connection for every pin. So I guess this cannot be corrosion of the trace. I did not check what pin of U400 it connects to, as I guess there shall always just be a connection to one pin, and I cannot identify the right pin without much effort on this large U400.Does someone want to recommend something else than suspecting the power supply or does someone want to confirm that this will be the power supply? Thank you in advance!Yeah, I have a USB floppy drive emulator now for creating these screenshots :-)update:CH1 black Pin 28 of U414GND of CH1 is connected to Pin 14 of U414CH2 green Pin 28 of U411 connected to a 470µF capacitorGND of CH2 is connected to Pin 14 of U411 connected to GND of the 470µF capacitorno extra capacitor connected to J101

author: bert-bert
author_rank: Contributor
timestamp: August 10, 2025, 03:00:11 pm
content: removing the capacitor does not change anything. The spikes in the signal on CH1 stay as they were at the last, even though I reproduced what had much less spikes before. Maybe some RAM died in the meantime.Now I disassembled the power supply enclosure and measured the four capacitors C26, C27, C29, C30 that are connected together in soldered-in state.Hardly any measurement device measures any sensible value, most say that the value is over the range, but one shows 4100µF 270mOhm ESR. And that looks reasonable, but I believe, the ESR is large. What do you think? The 6800µF capacitor that I connected to test shows 6900µF 140mOhm ESR. Also a large ESR, but shorting the measurement leads gives a resistance of 260mOhm. So I will not be able to measure this precisely with this cheap Chinese LRC measurement device.I am tempted to replace these four capacitors in these two power supplies and look whether this changes something.