Need Help Repair Tektronix TDS520B  - Page 1
Forum section: electronics / repair

author: chihaxinh
author_rank: Regular Contributor
timestamp: August 04, 2016, 09:58:58 am
content: Hi EveryoneI have one Tek TDS520B , so when power on , all led flash , fan run click click and loop again and again.So when search information about repair tds 5xx 6xx 7xx on internet i starting open case and check All.1st Step : Check PSU- A lot electrolytic capacitor fillter low vol and 24V have leaky . So i desoder all cap and note value / vol rate.So i need to go store buy capacitor in last week . I checked Mainboard and Acq board dont have any capacitor leak ( Mother board have repair and change cap by some one ) so i decied replace all electrolytic again. ( For sure all in good conditional ).I Have one questionCan i replace all electrolytics 33uF /10V by tantanum capacitor ? I dont want using electrolytics in acq board ( prevent cap leak in future ).Many thank your support !Nam Nguyen Hai

author: bdivi
author_rank: Regular Contributor
timestamp: August 04, 2016, 12:21:23 pm
content: I replaced all electrolitics on the digital and acquisition boards by tantalum capacitors and it's all been good for more than 3 years.Just make sure you wash the hell out of the boards after removing the old leaky capacitors - brush and lots of IPA are your friends here.Cheers

author: chihaxinh
author_rank: Regular Contributor
timestamp: August 04, 2016, 12:32:10 pm
content: Quote from: bdivi on August 04, 2016, 12:21:23 pmMany thank bdiviEarly you repair tds 520 , do you have any problem in PSU ? If you repair PSU, can you share your experience ?

author: bdivi
author_rank: Regular Contributor
timestamp: August 04, 2016, 02:08:56 pm
content: I only repaired the boards not the PSU - it was ok and still is.btw my scope is 540A but the electrolytic issue is identical.

author: David Hess
author_rank: Super Contributor
timestamp: August 04, 2016, 02:39:29 pm
content: Quote from: chihaxinh on August 04, 2016, 09:58:58 amYes, you can replace the bulk decoupling capacitors with solid tantalums and with solid tantalums, you can use 2 to 4 times less capacitance and still get the same ESR.

author: nctnico
author_rank: Super Contributor
timestamp: August 04, 2016, 07:04:19 pm
content: No, you can't use tantalums in TDS500/600/700 series scopes to replace electrolytics! In some places the circuits depend on the ESR of the capacitors (IIRC in the main oscillator circuit) so tantalum and MLCC capacitors may mess things up. Another problem with tantalums is that the rush-in current needs to be controlled. Also Tektronix made a mistake in some spots which puts a higher voltage on the capacitor than it is rated for. All in all tantalums are not a good replacement. Just go for electrolytics and don't try to improve what doesn't need improving.

author: David Hess
author_rank: Super Contributor
timestamp: August 04, 2016, 11:19:11 pm
content: I am only referring to places where the small aluminum electrolytic capacitors were used for local bulk decoupling. Other spots would have to be evaluated based on application.

author: chihaxinh
author_rank: Regular Contributor
timestamp: August 05, 2016, 02:14:37 am
content: Thank for all comment !So tantanum good choice for decoupling ( aka bypass capacitor ) for filtering power and cancer high freq noise !New update: I checking PSU have 4 cap 1nF Y class crack . So what type capacitor i can replace , in my country Y class capacitor hard to find .Another question : How to check PSU after repair ? ( dont connect to main board and acq board )Many thank your support !Nam Nguyen Hai

author: David Hess
author_rank: Super Contributor
timestamp: August 05, 2016, 03:59:58 am
content: Quote from: chihaxinh on August 05, 2016, 02:14:37 amThat is a common problem. Y class capacitors can be used as replacements for X class capacitors but not the reverse which does not help you. Paper, film, or ceramic capacitors with significant voltage derating can be used as replacements. Peak voltage for a 240 volt AC line is about 370 volts so I would want a 800 volt DC or higher capacitor. The higher the better.The power supply will operate without these if necessary but EMI will be increased.QuoteUse a dummy load on the various low voltage outputs for testing before connecting the other boards.

author: chihaxinh
author_rank: Regular Contributor
timestamp: August 05, 2016, 04:24:32 am
content: Quote from: David Hess on August 05, 2016, 03:59:58 amThank for your help , Let me repair in weekend and report for you . Let go to find dummy load !

author: chihaxinh
author_rank: Regular Contributor
timestamp: August 18, 2016, 04:35:11 pm
content: I desolder all tin in hole so very hard and take 4hour for complateTektronix layout very complex , one pin have big track on top and other in bottom ! So next time it's solder all new cap !

author: chihaxinh
author_rank: Regular Contributor
timestamp: September 19, 2016, 02:17:34 am
content: Hi AllAfter replace all capacitor, i turn on PSU with Bulk Lamp 500W series limit current . Lamp flash at a rate of about once per second , likely protect overload current it's active .I extract 2 page PSU and attach in post . Next time i checking all diode in secondary size SMPS

author: singapol
author_rank: Frequent Contributor
timestamp: September 19, 2016, 07:02:47 am
content: Quote from: chihaxinh on September 19, 2016, 02:17:34 amQuoteThis is because power supply is inHiccup mode. Please read pg.1-29 low voltage supply for better understanding.QuoteYour problem is similar to this TDS684 although the circuit is different.https://www.eevblog.com/forum/testgear/fixing-tek-tds684-psu/Refering to TDS520b A17 circuit U12 outputs +15V Bias voltage for PWM ic U5 (SG3525A) See circuit A18 pg.1 & 2. If +15 Bias is missing then U5 will not work. So check A17 U12 other components like VR24 (p6ke150),CR46 ( BYM26C). C117 ( 47uf 35V). Good luck.

author: chihaxinh
author_rank: Regular Contributor
timestamp: September 27, 2016, 02:08:12 am
content: Quote from: singapolHi SingapolWhen i checked my PSU have primary like TDS544A PSU , but secondary side like TDS520BPrimary Side schematics in attachmentIn primary side i checked Q8 - BU508A it's OKSecondary Side in attackmentIn secondary side i checked all Diode after T6 , It's OK , and i checked CR29 CR33 CR27 in output size it's ok .Everything look like ok , no crack cap and no burn active componant.What should i do ?

author: singapol
author_rank: Frequent Contributor
timestamp: September 30, 2016, 09:56:39 pm
content: Quote from: chihaxinh on September 27, 2016, 02:08:12 amBy this you mean output voltages at CR29 = +15V, CR33 = +5V and CR27 = -5.1V . There is also CR34.In fact there are 5 voltages namely -15V and +24V. If any one is missing it will trigger hiccup mode untillit is fixed. There is also stand by circuit.Below is the discription of how the power supply works. Good luck.Quote

author: nctnico
author_rank: Super Contributor
timestamp: September 30, 2016, 10:02:03 pm
content: Quote from: chihaxinh on September 19, 2016, 02:17:34 amYou need to load the 24V rail of the PSU with at least the fan otherwise you'll get this behaviour.

author: chihaxinh
author_rank: Regular Contributor
timestamp: October 25, 2016, 02:09:07 am
content: Hi allMany thank for support !I Have free time and go back to repair TDS520BI checked follow your guide but dont help ... in second side of T6 - A17 (2) page 359 i dont have any AC out.Next step i checked pinout of second side , i have missing oscillator in +-5V Rail-2-RailMissing osicllator in:- Pin 7-8 T6 for +5V- Pin E12-E13 T6 for -5V- Pin E10 - E11 T6 - for 5V and 5.1V feedbackOther pin in second side have oscillator but don't have any AC output .I active componant in second side i checked ok . No Mosfet burn, short, no diode fail or open , all cap and opamp replace.I thing T6 have short winding in second side or burn in case . So if Transformer short , everything go to hiccup mode.Many thank your support !Nam.

author: singapol
author_rank: Frequent Contributor
timestamp: October 25, 2016, 08:08:28 am
content: chihaxinh,if you look at A17 schematic the low voltage supply mainly go to A10 Acquisition board.Like +5V - 12A, -5 -12A, -15V - 1.5A. :oSo the only way to know whether secondary coil is short or not is to unload or disconnect supply to A10. Unplug the respective connectors to A10 and test AC voltage on T6 again.If there is AC voltage and correct Dc voltage at A17 then suspect A10 board.

author: chihaxinh
author_rank: Regular Contributor
timestamp: November 17, 2016, 03:51:37 am
content: Quote from: singapol on October 25, 2016, 08:08:28 amMany thank singapolNow i have free time and go back to repair TDS520 . After checking schematics , i find out my version PSU it's mixing with TDS540 PSU and TDS520B PSU.My PSU like version in link below.http://jvgavila.com/tds524a.htmMy PSU not using MC34262 Power Factor Controllers . By using MC14093 ( ~ CD4093 logic) create pulse for Boost Converter ( TDS540 PSU Schematics).it's point measurement voltage .In Bulk Cap in have only 280V ( Have 408V if boost converter working ). I thing i have problem in PFC Board.I thing Q5 and Q6 not switching and we dont have much 408V DC in bulk caps.I Don't know why not running, T1 it's current sensor and return CUR SENS+ and CUR SENS- to PFC Board. I Checking it's ok, all specs like datasheet.Standby supply worked .I have some attach picture in thread. Pls advice me solution to check and fix.Many tks so much !Nam Nguyen Hai

author: nctnico
author_rank: Super Contributor
timestamp: November 17, 2016, 05:51:22 am
content: What is the voltage across the mains rectifier and what is your mains voltage?Also don't forget to load the 24V rail with the fan because the power supply will go into hickup-mode without it. I also spend a couple of hours trying to troubleshoot one of these power supplies only to find out it was perfectly fine but it just needed the fan to be connected!

author: chihaxinh
author_rank: Regular Contributor
timestamp: November 17, 2016, 07:04:20 am
content: Quote from: nctnico on November 17, 2016, 05:51:22 amI Try load 24V rail with Fan but not help ! In Bulk Cap allway below 408V ( 280V )My Main voltage ( 220V ) .And when attach fan to 24v rail ! Fan sound click click and vibaration ! Not runingUsing dummy load not help

author: nctnico
author_rank: Super Contributor
timestamp: November 17, 2016, 05:57:49 pm
content: If the bulk capacitor is below 400V then the problem is between the mains plug and that point.

author: chihaxinh
author_rank: Regular Contributor
timestamp: November 21, 2016, 03:51:42 am
content: Hi AllNow i have 440V in Bulk capacitor . and 5.1V for microprocessor board and 5.1V feedbackBut all voltage not like schematics . I place PSU Stand alone with connect FAN to 24V rail24V i connect to Fan have only 5V+15V LM317 i have only 2.7VOther i have Only 1.7VI using VOM Analog to check pin 4-8 of MC34802 . Have peak 15V , and pin 2 of Voltage reference LT1009 have 1.6 and go down to 0V.All diode i desolder, and check it's OK ( Red Highlight)All trans and regulator ic check it's OK ( Red Highlight )All Opamp i replace exclude MC34082 ( Yellow Highlight) .I have on question . Can i check PSU stand alone ( not go back to case and connecto to microprocessor board and acq board ). Because i checked on internet said PSU like ATX Power , have Standby switch . and 5V Standby Signal ?Many thank so much !Best regardsNam Nguyen Hai

author: chihaxinh
author_rank: Regular Contributor
timestamp: November 21, 2016, 08:36:13 am
content: Hi AllI connect PSU to ACQ , Main board and CRT Board , now CRT Board fail and go to hiccup mode. I detach connection to CRT and running.In Led DS1 display like 1 - A11 DRAM Processor/Display - Troubleshooting ProcedureBus Control RegisterVideohttps://goo.gl/photos/RTkaLwcu4L1vkukt9And i read can setting bypass check CRT , i want signal go to VGA display . Searching on Internet i see can setting S1001 . But see on table i don't understand how to bypass CRT test.Quotehttps://forum.tek.com/viewtopic.php?f=568&t=136381&hilit=TDS520+not+bootMany tks so much !Best RegardsNam Nguyen Hai

author: chihaxinh
author_rank: Regular Contributor
timestamp: November 21, 2016, 11:16:09 am
content: Hi AllI turn switch S1001 pin 6 - 7 on - Connect cable VGA to LCD . Running display in LCD but DS1 display .E ( FlashROM Checksum ) .

author: nctnico
author_rank: Super Contributor
timestamp: November 21, 2016, 02:53:15 pm
content: It seems the test only is failed if the dot or the 7 segment display is blinking.

author: chihaxinh
author_rank: Regular Contributor
timestamp: November 22, 2016, 01:46:55 am
content: Hi AllSory my mistake . LED DS1 display .E not .e ( it's uppercase letter ) , so i thing have problem like broken trace or something like that.It's TDS520B , not have much electrolytics capacitor. All cap i replace by new cap, esr have around 2.2R .It's have 11 cap 33uF/10V and 10uF /35V .So next time i desolder NVRAM and firmware IC to backup ! If anyone have Firmware or NVRAM data can share to me ?Many tks you!Best RegardsNam Nguyen Hai

author: singapol
author_rank: Frequent Contributor
timestamp: November 22, 2016, 06:53:15 am
content: See if you can do diagnostic tests here:http://old.timmestein.nl/index.php?page=tek-tds520-repairYou can copy nvram data using programmer and download to new nvram with fresh lithium battery.Or if not put in new nvram and calibrate manually:2430 2430A, 2432, 2440: calibration and faults due to NVRAM ...https://forum.tek.com/viewtopic.php?t=137131or extreme recovery of old nvram by cutting and removing epoxy to get at battery terminal :https://hohlerde.org/rauch/elektronik/geraete/tek2440/index.en.html

author: chihaxinh
author_rank: Regular Contributor
timestamp: November 22, 2016, 07:09:03 am
content: Quote from: singapol on November 22, 2016, 06:53:15 amHi SingapolNVRAM keep calibration value . in Tektronix 24xx calibration process very easy with signal gen and power source . But with TDS 5xx it's not easy , we need high speed signal gen and some special equipment.Repair it's not easy , in next time i decided to replace CRT by LCD display, but we need equipment finish booting.

author: David Hess
author_rank: Super Contributor
timestamp: November 22, 2016, 07:27:25 am
content: Quote from: chihaxinh on November 22, 2016, 07:09:03 amOn the 24xx DSOs, the external calibration process is easy. On the 24xx analog oscilloscopes, it is more difficult but still possible with just the proper signal sources. I think all of the TDS oscilloscopes also require special software which was not generally available.

author: chihaxinh
author_rank: Regular Contributor
timestamp: November 22, 2016, 07:43:40 am
content: Quote from: David Hess on November 22, 2016, 07:27:25 amYes. TDS5xx have software but running on GPIB card very old version ( ISA ) , and windows 3.1 .My friend have Xeltek 501S programer , first step need backup NVRAM and Firmware , on internet some body post repair guide have only TDS520 or TDS520A not "B" version.Hope NVRam not dead ...

author: chihaxinh
author_rank: Regular Contributor
timestamp: November 22, 2016, 03:52:59 pm
content: New updateAfter replace all electrolytic caps in Acq board ! Ds1 display on top segment only , likely boot hang !And i connect osc to lcd display, lcd display many horizone line - Like bad video ram !Next time i disasembly front panel and replace all electrolytic caps

author: PrecisionAnalytic
author_rank: Regular Contributor
timestamp: January 08, 2018, 07:09:22 pm
content: Quote from: bdivi on August 04, 2016, 12:21:23 pmWhat brand, type and specification of tantalum capacitors did you use?All the best