TDS 420 trigger - Tek gurus to the rescue please - Page 1
Forum section: electronics / repair

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 09, 2020, 01:54:09 am
content: Admittedly I've already spent more time on this than it's worth...It started with the usual wash and SMD recap I found a couple of cut traces (photo).I've also been lifting IC's in the heavily contaminated areas to check traces under them.Since the scope isn't behaving better than when I received it, all I've gained is a "Fp - PASS".All four acquisition channels work with reasonable noise levels, react to horizontal and vertical adjustments and changes in acquisition memory size.The scope will display and update un-synced waveforms on screen but as soon as trigger kicks-in the waveforms stop updating.A press on "FORCE TRIGGER" will cause a refresh although not every time.The problem here is that there's no schematic available, and although I've been in a few DSO's before including Tek's here I'm lacking a little detail on how things are controlled so a few clues from those who know better would be appreciated.The error log is returning a "Wrong hardware configuration. Acq mem size probe, expect: 7fff, actual: 0"I'm guessing that a control line is stuck somewhere (something to do with an acquisition memory fill complete, ready to re-trigger) and CPU is locked out of checking the RAM that's forever busy.I've been through looking for information on some of the ASIC's on the Acq. PCB to try and understand a little better, the ones I've found in other Tek scopes if this may be of use are:The "DACULATORS" I10412The trigger selectors M496 (U81, U82 in the TDS420)Does anyone know the part number of U140 the one with the heatsink after the trigger selectors?Here's the error log:Code:Skipping All Bootrom Tests.Transferring control to the Flashrom.sysDramControllerInitsysDramByteStrobeTestsysDramTestbcopy(<Idata>)bzero(<bss>)intVecBaseSet(getVbr())sysSymTbl=standAloneSymTblsysDevDramTest0x0 bytes of development dram foundvalidateDataSpaceOuter Kernel DSACK TestPending Interrupt TestWalk IPL to Zero TestTimer Int TestStart 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 sizeAcq 8051 presenceAcq ADG209C presenceAcq record length sizeRRORId: 64 srongyhardware confWgaratioi Acq tem siCe prlbo,cexke t. 7fff, ac.ua.: 0................ passclockCalVerify ................. passcpuDiagBatTest ................. passcpuDiagAllInts ................. passcpuEEromLibDiag ................ passcalLibDefaultCk ................ passdspForcedBus ................... passdsp68kD2MemTest ................ passdsp68kMemTest .................. passdspRunVerify ................... passdspBusRequestTest .............. passdspImplicitBusAccess ........... passdspTristarMemTest .............. passdspDsyToDspInts ................ passdspAcqToDspInts ................ ***FAIL***..error details:dspAcqToDspIntsacqToDspIntPollTest: Acq not accessabledsyDiagResetReg ................ passatBusTest ...................... passdsyDiagResetReg ................ passdsyDiagVscReg .................. passdsyDiagPPRegMem ................ passdsyDiagRasRegMem ............... passdsyDiagRegSelect ............... passdsyDiagRamdacRegMem ............ passdsyDiagAllMem .................. passdsySeqYTModeV0Intens ........... passdsyDiagSeqXYModeV1 ............. passdsyRastModeV0Walk .............. passdsyRastModeV1Attrib ............ passdsyWaitClock ................... passattn8051testResult ............. passattnDACReadback ................ passacq8051testResult .............. passadgRegDiag ..................... passdsyWaitClock ................... passadgMemTestDiag ................. ***FAIL***..error details:adgMemTestDiag: ADG #1, ACQ Mem #1** Test can't be run - no Acq memory foundacqRampDiagAll ................. ***FAIL***..error details:runAcqDiagCh1** ramp amplitude: exp>=0xe0 act=0x0** CH1 path FAILEDdsyWaitClock ................... passfpDiagConf ..................... passfpAllLedOn ..................... passfpAllLedOff .................... passfpProbeDacTest ................. passRRORID: 135 diagnostic test failure pu_diag sequencenet not started$Header: scopeST.version,v 1.36 92/06/25 17:46:18 aland Exp $->Smalltalk/V Sun Version 1.12Copyright (C) 1990 Object Technology International Inc.

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 10, 2020, 02:25:10 am
content: I received a notification telling me Madao had left a reply, nothing to be seen... strange!A little more information on the ASICS, 2232 uses ADG209B, TDS420 uses ADG209C should be close enough.

author: Smoky
author_rank: Frequent Contributor
timestamp: November 10, 2020, 02:44:44 am
content: Shakalnokturn, I have two extra parts boards for a TDS420. I'll be happy to remove any parts that you need and mail them to you

author: lucatz
author_rank: Contributor
timestamp: November 10, 2020, 08:22:52 pm
content: http://www.ko4bb.com/getsimple/index.php?id=manuals&dir=TektronixLots of info here for TekI have a TDS 540, once I cleaned it all up and changed all caps. I had to run a acquisition calibration from menu to get to pass and then all was good. Maybe you have to do same on 420?Luca

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 10, 2020, 10:19:23 pm
content: Smoky:Thanks for the offer, the odds are that there's nothing serious behind the problem I will let you know if it comes to a bad ASIC.Luca:I have the schematics for the TDS544 and 2232 that I've been viewing for reference. (The TDS400 are somewhere between the two.)I have tried running SPC, without effect.I think SPC is only any help in bringing vertical misalignments back to normal. It will compensate for frontend drift in time and temperature, I'm not even sure it has any effect on timing offsets.All the other fails in the log are probably linked to this one:Code:acqRampDiagAll ................. ***FAIL***..error details:runAcqDiagCh1** ramp amplitude: exp>=0xe0 act=0x0Anyone know how the ramp amplitude is measured for the self diagnostics?Are the ramps based on the LM311's in this scope?

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 14, 2020, 01:43:21 am
content: Although the ADG209B is likely identical in function and signalling to the ADG208C the pinouts are different one being PGA the other TQFP...A shame, as following the control lines in and out of the trigger/TB logic would have been a big help.I've been poking around a lot and come across some waveforms on TTL that don't seem quite right.I have doubts for the first capture that looks glitchy it could just be fast pulses, the others however really seem wrong.Bus conflicts because something isn't being disabled at the right time?I'm getting this sort of mess on:U44, 45, 54, 55, 56 (74F573) on most inputs.U36, 37 (74F245) on both sides.U107 (74F244) on all outputs.U29, 30, 31 (74LS377) on all "D" inputs.

author: madao
author_rank: Frequent Contributor
timestamp: November 21, 2020, 09:02:42 am
content: I have removed reply,because i have seen later: you have already post schematic of TDS540/520 above trigger ICs.It means: my answes is totally useless.acqRamp-blahblah -> often ciruit with LM311 near couple of eletrolytics. I have fixing few TDS420/460 with Ramp-fail. Most case: resistor divider is open. (this resistor divider is on left corner of picture)If you need good trigger-IC, i can spend a good IC to you. Shipping to france is with 5€ possible. I have salvaged him from TDS430A corpse.

author: shakalnokturn
author_rank: Super Contributor
timestamp: November 23, 2020, 12:15:57 am
content: Thanks for reply and offer on trigger IC madao, if I do need one it makes more sense asking you than Smoky.As far as I can tell for now the three trigger IC's with heatsinks should be OK.Even though I don't know what the third and undocumented one does exactly I suppose it's OK as I'm getting the trigger output on the differential lines (2 pairs) that feed sot-23 transistors around it.Are there2 ramps in the TDS400 series? I saw a working ramp on the other LM311 (U101), i'm not sure about the U154 in your picture though.I've put the TDS420 aside for some time, I have other repairs to get on with. Will keep the topic updated when I get back to it.

author: horiachirculescu@gmail.co
author_rank: Newbie
timestamp: June 20, 2022, 06:13:16 am
content: Hello,I have a problem related totrigComparatorTest TRIGAandrunAcqDiagCh1 ramp amplitudeI have access to the serial portTest failing with Acquisition and AttenuationOn the attenuation board I had capacitor problems - the ones between the 2 voltage reg. (maybe a design problem?) One track bad near a small via.Which LM311 IC is the comparator involved (seems that there are 3 on the board U101. U141 and 154)Any thoughts ?(...later edit...) found that U101 is the comparator, the ramp generator is implemented using 3 SOT-32 transistors, some resistors and 2 capacitors in parallel - the ones above U101 white labell.Thank you and have a nice day from Romania!

author: horiachirculescu@gmail.co
author_rank: Newbie
timestamp: June 23, 2022, 06:18:55 am
content: Yesterday I have solved my TDS420 issue.On the Acquisition board there is one xtal oscillator. Seems that in the factory the xtal terminals were left a little bit too long and the case of the xtal shorted a small capacitor located under the xtal. I believe somewhere in the process of the previous interventions (repair of the power source - blown transistor) the metal case somehow touched the xtal (despite the fact that there is plenty of room....) - or maybe it is like this from the factory...In order to short the terminals I should pull out the board from the chassis (to access the other solder side) but instead I have wrapped the xtal case in heat shrink foil and put also a drop of solder mask over the terminal of the capacitor.All is working as expected once again - passed all the tests, including SPC

author: horiachirculescu@gmail.co
author_rank: Newbie
timestamp: July 07, 2022, 07:55:53 am
content: Hello, does anyone knows what it is with this jumper (J14 on the CPU board - from the right)