Tektronix TDS2024 Oscilloscope - Repair Log - Page 1
Forum section: electronics / repair

author: sean0118
author_rank: Frequent Contributor
timestamp: July 31, 2021, 03:45:06 am
content: Sydney is still in Covid lockdown so the scope repair marathon is continuing. I'm not sure if this one will be fixable though, might be parts only.Someone has already had a go at repairing this, symptoms were the LCD backlight and a few buttons were lighting up. I checked the 1kHz cal with another scope an measured it as being close to 3kHz which is probably a bad sign.It gets worse though, I had it turned on while measuring power supply voltages, everything seemed okay but after a few minutes the +35V rail suddenly jumped to +70V. I turned it off quickly, so didn't measure the other voltage rails again, but I assume they doubled in voltage as well. But I did see a few wisps of smoke rise from around the backlight transformer circuit. The main board was attached at the time, and because someone else has already had a go at repairing this I wonder if it's seen sustained over voltage for a long time.I'll worry about the mainboard more later, for the moment I'll focus on the power supply. The first thing I noticed is they are usingLelon electrolytic capacitors, in my opinion these are trash C or D grade capacitors, very surprised to see them used by Tektronix. Also, if you are trouble shooting one of these take note that the MOSFET heatsink is floating at -160V.It looks like the feedback to the controller (KA7552) is from the 3.3V rail. There's a little Lelon 2.2uF capacitor that's on the 3.3V side of the optocoupler, it's hard to see from the photo but it looks like the bottom bung might be bulging out slightly, I wonder if this might be overheating and going close to short, making the controller bump the voltages up.I've had a bit of a look around, can't see if this is a common issue, but with the Lelon caps I assume it might be. I also need to work out how to power up the supply without the main board attached, there's an LT pin, might need pulling up or down?Capacitor in feedback path:edit: nvm LT is Line Trigger of course

author: tautech
author_rank: Super Contributor
timestamp: August 01, 2021, 09:29:15 pm
content: No issue with Lelon here over some 8 years but your TDS is probably some years older.3KHz on the probe compensation output was the first sign there was something wrong with my TDS2102B which turned out to be a corroded pin on a 100 pin IC. These non fan cooled top vented scopes can allow dust to settle that can be corrosive when atmospheric moisture is added and the only sign you might see is a black spot on a IC pin that when carefully poked the corrosion falls off to show there is no connection.Good luck with the repair.BTW do you have the SM ?Can email the 2ch version if you need it.

author: sean0118
author_rank: Frequent Contributor
timestamp: August 03, 2021, 12:59:24 am
content: Quote from: tautech on August 01, 2021, 09:29:15 pmOkay I may have been a bit too harsh on the Lelons, the main output capacitors are RXK, which maybe aren't too bad. I've pulled them all though, their capacitance and ESR look okay, but I'll replace them anyway.I'm starting to think maybe the mainboard has a fault, maybe it's overheating and pulling the 3.3V rail low? I had a look over it but couldn't see anything obvious, I'm yet to look at the board for display / user interface. It's interesting your cal was also 3kHz, maybe that's just the default when the board is dead. Was your faulty IC on the main board?I don't have a schematic, only a service manual with block diagrams. The 2ch schematic would be very useful.

author: tautech
author_rank: Super Contributor
timestamp: August 03, 2021, 01:14:41 am
content: No schematics are available for these AFAIK. Only the SM that I got after registering on the Tek website back before TekWiki was launched.Here's the page for yours:https://w140.com/tekwiki/wiki/TDS2024My TDS2102B boot faulted with a USB fail from the IC with the corroded through pin which then triggers the 3 KHz probe comp output which IIRC is a replace mainboard flag in the fault finding flowchart.For yours indeed the PSU instability is worrying as it may have done some irreversible damage to the mainboard.

author: sean0118
author_rank: Frequent Contributor
timestamp: August 03, 2021, 11:30:18 am
content: Quote from: tautech on August 03, 2021, 01:14:41 amOh, that makes more sense that SM stands for service manual. Wishful thinking on my part that a schematic was available.Still it's interesting to know how yours failed, I'll need to take a closer look at mine, will update once the new capacitors arrive.

author: sean0118
author_rank: Frequent Contributor
timestamp: August 13, 2021, 10:46:30 am
content: Okay, I have some good news and some bad news.I replaced the capacitors on the power supply board and the voltages seem stable now. I've attached a spreadsheet which might be useful to others, it lists all the cap sizes and possible replacements (I ordered from LCSC).The bad news is the earlier spike in voltage seems to have taken out the backlight inverter. The transistors and film capacitor seem okay, so I think it might be the HV transformer that's fried. The backlight doesn't turn on and the transformer gets pretty warm, so I've pulled out a series filter inductor to disable it for the moment.I've had a good look over the mainboard and it looks okay, except for some cold solder joints on the BNC GND pins.However, with the mainboard powered up (while monitoring the voltage rails) I foundU400is getting too hot to touch. It's from National Semiconductor and is markedEE48AC 7853-01, but I can't find anything about it online. There's two of these on the board, it looks like this one if part of the acquisition circuit for CH1 and CH2.I'm hoping this isn't a custom part but I suspect it might be. I still need to investigate the components around it, but so far all the ceramic caps etc seem okay.U400 National Semiconductor EE48AC 7853-01https://imgur.com/a/ilZOF1k

author: sean0118
author_rank: Frequent Contributor
timestamp: August 15, 2021, 01:40:44 am
content: I'm pretty sure EE48AC 7853-01 is a completely custom ASIC. Can't find anything about it online.I might pull it and see if it allows the scope to boot. Might be able to get the other two channels working, but I suspect it might just be good for parts.Let me know if anyone has any suggestions.

author: tautech
author_rank: Super Contributor
timestamp: August 15, 2021, 02:10:56 am
content: FWIW TDS2012B U400 is EE63RC 9858-00 but just one of course...same thing Google comes up with zilch !

author: sean0118
author_rank: Frequent Contributor
timestamp: August 15, 2021, 04:39:50 am
content: Thanks.Good news though, I went through and measured the resistance of every pin to GND and compared it to the other EE48AC (Excel spreadsheet attached to save others the time lol).There were a few pins, the corner tabs and the bottom pad which were only 13 Ohms to GND compared to 188 Ohms.I found a capacitor array (C403) on the bottom of the board which connects to the bottom pad. I pulled this of and the resistance for both EE48AC went to 500 Ohms! I booted it up and the cal output now goes to 1KHz, so I guess the EE48AC might be undamaged.But, I can't see anything on the display, the backlight is off but even when I shine a light into it I can't see anything...

author: sean0118
author_rank: Frequent Contributor
timestamp: August 15, 2021, 05:15:56 am
content: Okay the display is actually working, it's just really, really hard to see without the backlight.I saw other people have upgraded their TDS scopes with LED strips, I might need to do something similar, unless I can fix the backlight power supply.

author: tautech
author_rank: Super Contributor
timestamp: August 15, 2021, 05:26:17 am
content: Quote from: sean0118 on August 15, 2021, 05:15:56 amGood progress !Do you have another scope to help diagnose the backlight supply ?Looking at my PSU it just looks like a push/pull oscillator and you should be able to sense the EMI with another scope probe held near to see if it's oscillating.Some years back I was given a TDS1002 with a dead backlight and it just turned out to be the C in the RC for the oscillator had drifted into the pF and it wouldn't oscillate anymore. Replacing the C fixed it.

author: sean0118
author_rank: Frequent Contributor
timestamp: August 15, 2021, 05:39:46 am
content: Quote from: tautech on August 15, 2021, 05:26:17 amThanks, that's a good idea.A bit of smoke did escape from that area of the board when the power rails doubled in voltage (backlight was lighting up before that). I did pull and test the cap and two transistors earlier, but I should double check.If all else fails I might do some transformer surgery.

author: tautech
author_rank: Super Contributor
timestamp: August 15, 2021, 05:46:41 am
content: Yeah well I'd certainly be checking the primary, secondary and local resistors.Sing out if you need the xformer winding resistances.....secondary easy to measure = 430 ohms.

author: sean0118
author_rank: Frequent Contributor
timestamp: August 15, 2021, 06:03:24 am
content: Transistors and capacitors seem okay (just testing with a multimeter). Resistors are a good point, I still need to test them.On the transformer I'm getting 177 Ohms for the colour display winding and 2M for the black and white. If you're getting 430 I assume I have a problem.edit: Looks like there's two winding on the primary with a center tap? I'm getting ~1k for each.

author: sean0118
author_rank: Frequent Contributor
timestamp: August 15, 2021, 06:32:37 am
content: Okay I pulled the transformer.The primary windings are not 1k, I was measuring a resistor.I'm a bit confused about the circuit of the primary winding/s, but I'm getting ~0 Ohms between the three center pins, and ~0 Ohms between the two outer pins. I'm measuring open between the outer and inner pins. I hope that's not too confusing...Secondary windings are unchanged out of circuit.

author: tautech
author_rank: Super Contributor
timestamp: August 15, 2021, 06:42:50 am
content: Backlight transformer primary pin measurements in circuit. (last used working)From edge of PCBMeasured with Smart Tweezers 1khz test frequency.Pin 1-2 = 1.61kPin 5-6 = 1.61kPin 3&4 = commonPins 2&5 - 3/4 = ~140 milliohm 28 uHSecondary @ 1khz test frequency403 ohms 366 mH

author: sean0118
author_rank: Frequent Contributor
timestamp: August 17, 2021, 09:01:48 am
content: Thanks, I think your transformer might be similar, but just for the black and white display? I've only got 5 pins on the primary. Mine has two outputs, for either black and white or colour.Anyway, I was pretty sure my transformer was cooked so I opened it in the hopes of being able to rewind it, but looks like the enamel has melted off the wire and fused together so cant unwind it to see how many turns there are.Seems like an upgrade to an LED backlight might be a good idea. There's some very cheap kits on ebay, but the problem is they need an input between 9V and 28V. I've only got -4V, +3.3V, +6V and +35V. Could I put it across -4V and +6V? The -4V was used for the CCFL inverter so with that disabled it should have some headroom.

author: tautech
author_rank: Super Contributor
timestamp: August 17, 2021, 10:09:54 am
content: No my TDS2012B is color display just like yours.Backlight transformer on the PSU has 6 pins primary side and 3 pins secondary side.If necessary I can remove it and get DMM measurements of the windings and inductance of each with my Smart Tweezers. As you have the wire gauge diameter calculating the wire length should be straightforward once the resistance is known.

author: sean0118
author_rank: Frequent Contributor
timestamp: August 17, 2021, 10:59:55 am
content: Quote from: tautech on August 17, 2021, 10:09:54 amThat's a good point, I am sort of tempted to try that to see if I can get it working. But I think this one's probably seen a lot of use, so the CCFL tube might be aged anyway. I think an LED strip might be the way to go, even if I have to design a custom driver.

author: tautech
author_rank: Super Contributor
timestamp: August 17, 2021, 11:50:11 am
content: Quote from: sean0118 on August 17, 2021, 10:59:55 amIf you can see the service menu it should list the total runtime IIRC.

author: sean0118
author_rank: Frequent Contributor
timestamp: September 12, 2021, 05:12:29 am
content: Okay, good news the LED backlight kit arrived (PCB model number GYD-09).I was hoping to modify it to only need +6V. The board uses a DF6113 LED driver IC and I managed to find aschematiconline. The datasheet reference design is a fairly simple boost converter, however this board has repurposed the IC to make an inverter circuit. I don't think they are even using the feedback pin (FB) as it's being pulled down to GND. The current sense pin (CS) is used instead to regulate the current through the LEDs.From testing it drops out and stops switching the MOSFET at about 8V. I thought I could lower this my changing the inductor value, but that just changed the switching frequency, it still drops out around 8V. I'm not sure what determines the voltage it drops out at?Anyway, I decided to give up on that and power it from 10V (using the +6V and -4V rails) which worked. I modified the board a little bit, changing the 220uF input capacitor to a low ESR type, I also added a 10uF electrolytic across the LED strip. I'm not sure if this is really a good idea, but older board revisions do have a footprint for one there.I also changed the current sense resistance (R4 & R7) to 2.5 Ohms (four 10 Ohm 1/4W in parallel, looks dodgy but does the job). This limits the maximum output current as by default it can draw well over 1A, which is too much for the power supply in the TDS. I also added a trimpot across the ENA (3.3V), DIM and GND pins, which allows the brightness to be reduced, but I didn't end up using this and left DIM at 0V (max brightness). With this setup the display is bright and I'm measuring only 90mA across the sense resistors which seems pretty reasonable.I cut the LED strip down to the correct size then just used double sided tape to attach it. I then stuck some sticky tape and foil over it to reflect any escaping light back to the screen. A little bit of a hack but works well.I still need to go back and replace the capacitor aray which failed, I suspect it isn't critical though, I'll put four 0402 capacitors in its place. I'm also going to mount the LED driver board properly (it's only attached with double sided tape atm).Also interesting, checking the error log there's heaps or errors there:7 DI ADG421 Diag Failed, 1 SL SL_stopAcq: Proc B, 2 SL SL_stopAcq: A!=B. Only error "7 DI" is listed in the manaual, with the cause listed as ADG421 diagnostics failed / main board or power supply failure.I'm glad I can call this one a success because I had my doubts there for awhile.edit: I forgot to mention, I'll probably use plastic hardware to mount the PCB and put some kapton tape under it as the board GND is now at -4V. I'll go back and replace the sticky tape covering both sides of the foil with kapton as well as it should last a lot longer. I also measured the power supply rails to make sure they weren't being loaded down (-4.3V, +3.4V, +6.4V, +31V).edit 2: I also forgot to mention that it successfully passed the self cal without error.edit 3: Just occurred to me the input voltage required for startup is probably set by the forward voltage drop of the LEDs, maybe some large resistor in parallel would allow it to start switching at a lower input voltage?

author: pasta2018
author_rank: Regular Contributor
timestamp: April 07, 2024, 01:38:33 pm
content: Quote from: sean0118 on August 15, 2021, 04:39:50 amI have a tds2024，and it reports ch3 and ch4 failure，I measured U700，the 180ohm is only 3 ohm which connected to C703，maybe the same problem. Do I have to install a new one or just swap it ？ if replace it with a new one ,what is the value of ccapacitor array

author: pasta2018
author_rank: Regular Contributor
timestamp: April 08, 2024, 03:04:50 am
content: Quote from: pasta2018 on April 07, 2024, 01:38:33 pmIt's about 100nf 0603*4

author: factory
author_rank: Super Contributor
timestamp: December 11, 2024, 09:26:39 pm
content: The info from this thread was very helpful, in the repair of a TDS2014 with a 12 DI fault (channel 3 diagnostic failed), other symptoms were power up fail for channels 3 & 4, probe cal signal measured at approx 3kHz and a strange offset for both channels 3 & 4 when the position control was used.C633 was to blame, one section now identified as a 2.7 ohm resistor.I've replaced it with a Yageo 100nF 50V array, CA0612KRX7R9BB104 from Mouser (two intact sections of the old part still measured at 100nF), while it was apart I took the opportunity to replace the Lelon caps with Nichicons.Full repair documented here;https://www.vintage-radio.net/forum/showthread.php?p=1675757#post1675757David

author: Sergio Romas
author_rank: Newbie
timestamp: May 22, 2025, 11:39:38 pm
content: Hello friendsMy name is Sergio, I am 67 years old and I just joined the forum.My nephew gave me a Tektronix TDS2014 oscilloscope, but it is not working. It only lights up the backlight, not any LED on the front panel. I tested the power supply voltages and they are all present.As I am a technician and engineer graduated over 40 years ago, but always worked in the administrative area of ​​Telecommunications companies, I do not have the skills to be able to repair this excellent equipment and that is why I am resorting to this forum, in order to see if anyone could help me with tips and procedures that I can do, since I no longer know what I should do.I appreciate your help.