A Tektronix TDS3014B with two strange issues - Page 1
Forum section: electronics / repair

author: bsproj
author_rank: Newbie
timestamp: July 26, 2016, 10:58:17 pm
content: Hi,i've recently bought an used TDS3014B (service manual). It works perfectly, except for 2 apparently unrelated issues.The first issue is a strange overheating of the power supply board.This overheating occurs only when theoscilloscope is turned off. The heat is produced by two resistors of the RC snubber network located on the Artesyn NAN40-7615-01 customized power supply board (datasheet). TheThese resistors reach a temperature of approx 80-90 °C when the oscilloscope is turned off or when the board is totally disconnected from any load. This make the oscilloscope rear cover hot, about 40 °C. When the oscilloscope is turned on (or when a load is applied to the output of the PSU), the overheating disappears. Anyway, the output voltage of the output board is correct (15 V).The mains voltage is 230 V with a frequency of 50 Hz (Italy). The design of this switching PSU appears very simple, maybe similar to the following schematic.Is this overheat common in this kind of PSU? Are there any forumers with the same problem?The second issue is anoise at high sampling rates. The noise istotally absentwhen the sampling rate is less than 5 MS/s (> 400 µs/div). For any sampling rate equal or higher than 5 MS/s, the tracks appear a little bit more noisy. In particular, you can see a periodic noise, similar to a low level sine or sqare wave. This noise has the exactly same aspect on the screen (same amplitude and same number of cycles/div) for any sampling rate higher than 5 MS/s. This periodic noise is very clear if I use the "average" acquisition mode.(click for high resolution)Is this normal for the TDS3000B series?Thank you.Niki(Italy)

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 27, 2016, 12:22:39 am
content: Niki,Welcome to the forum !!You are lucky, I have just finished repairing a TDS3012. I am waiting for some case parts before I post details of my repair.I traced out the circuit for the Artesyn NAN40-7615-01 Power Supply to help me repair. After I traced the schematic I made an LTspice model to confirm that I have the circuit correct. The circuit is not 100% accurate, but it is very close.The LTspice model is missing the input filter, inrush thermistor (PTC), rectifier and the bulk capacitor.Here is a picture of the board installed in the scope:And here is a thermal image of the power supply, this was taken with the scope running.The hot parts are:RT1R3 and R5, snubber for the MOSFET.D3 Output rectifierR7 which is a load resistor on the output.Here is a thermal image with the scope off. The power supply is running all the time the scope is plugged in.The hot parts are:R3, R5 snubberR7 across the 15V output.These thermal images were taken with the scope running from 115V. The temperatures may be different if the scope is powered from 230V.The temperatures you are measuring are probably normal, but I would check the value of R7. If R7 is open, the temperature of R3 and R5 will increase.When the scope is on, the fan is running, so the resistors are cooled by the fan.Thank me, if this helps.Regards,Jay_Diddy_B

author: tautech
author_rank: Super Contributor
timestamp: July 27, 2016, 12:35:06 am
content: Frequency of the SMPS operation for both on and off modes might help diagnose the health of the PSU for the OP and others finding this thread. Easy enough to do with a scope probe held near the x former and no direct connection needed.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 27, 2016, 01:36:28 am
content: Quote from: tautech on July 27, 2016, 12:35:06 amTautech asked, so here they are:Note:The scope was powered using an Elgar 501 AC Power Supply, the output is floating. This allows me to connect the scope ground clip to the source of the MOSFET. The scope tip was connected to the Drain of the MOSFET. So the scope pictures are Vds.DO NOT TRY THIS AT HOME, DO NOT TRY THIS IF YOU ARE NOT FAMILIAR WITH SWITCHING POWER SUPPLIES.A Tektronix 100x, high voltage probe, P6009 was used for this measurement.These measurements were taken with a line voltage of 110V ac.With scope on, the switching frequency is around 84kHzWith scope off, the switching frequency is close to 300 kHz.I believe that this type of power supply will either work or be severely damaged, I have never seen one half-working.In order to fix this one I changed:The main MOSFET (blown up)The 0.56 flameproof resistor, R36, in the MOSFET source (fused open)The 100 Ohm resistor, R33, blown open.D1, gate drive Zener, blown shortQ2 and Q3 just in case, they are cheap.I checked the bridge rectifier, the fuse, and RT1, in my case these parts were o.k.These power supply are fairly readily available new. It is a 5 x 3 x 1.2 inch form factor, 40W and 15V output. The -01 in the part number may mean that the output was set, by changing a resistor to 14.6V for some reason. I would use LPS44 from Artesyn ($45.90 USD from Digikey).Regards,Jay_Diddy_B

author: tautech
author_rank: Super Contributor
timestamp: July 27, 2016, 02:11:38 am
content: Thanks Jay.The probe on the MOSFET gate would have been sufficient and at much lower voltage.That is alarming that this rather crude (not taking the piss) SMPS runs at 300 kHz with no load.That snubber is definitely working overtime in the original design based on your RE schematic.Time for some tweaks?EditI much prefer the method used in the image from AOE: zener and diode.

author: Hydrawerk
author_rank: Super Contributor
timestamp: July 27, 2016, 02:39:13 am
content: Well, your link was broken, i repaired it.http://www.pewa.de/DATENBLATT/DBL_TEK_TDS3000-SERVICE-MANUAL_ENGLISCH.PDF

author: bsproj
author_rank: Newbie
timestamp: July 27, 2016, 08:27:25 am
content: Hi,thank you a millionfor your detailed report. I'll check the value of the load resistor R7 just to be sure. Anyway the overheating of my PSU is probably normal using the oscilloscope with 230 V mains. Maybe is a really good idea to replace this PSU with a more reliable one, like the mentioned Artesyn LPS44.And what about the increased noise at high sampling rate? Does your TDS3012 present the same sudden increase of noise when you switch from 400 µs/div (2.5 MS/s) to 200 µs/div (5 MS/s)?(click for high resolution)Thanks for your help!

author: tautech
author_rank: Super Contributor
timestamp: July 27, 2016, 09:30:56 am
content: Quote from: bsproj on July 27, 2016, 08:27:25 amWe do that with the "Say Thanks" botton at the top right of the post.Jay asked for your thanks, it would be rude not to.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 27, 2016, 10:13:22 am
content: Quote from: bsproj on July 27, 2016, 08:27:25 amHi,Power SupplyThe NAN40-7615-01 is a well designed power supply and should be as reliable as any others. I am sure mine was killed by a surge on the line voltage input, probably lightning. The power supply is on if the scope is plugged in. I am sure that most of them are running 24 hours a day, 7 days a week.The LPS44 is also a good power supply. The LPS44 was made by a power supply company called 'Aztec'. Astec was acquired by Artesyn.If you do anything, you could change all the electrolytic capacitors in the power supply with good quality 105C capacitors from a component distributor. Do not buy them on eBay etc.Waveform noiseI set the TDS3012, two channel scope, to the same conditions as your scope:5V/div, 200us/div and 400us/divThere is a noticeable increase in noise. Here are the photographs:200us/div400us/divI do not have the floppy drive installed at the moment, so I used a camera.It looks very similar to what you are seeing.Ciao,Jay_Diddy_B

author: bsproj
author_rank: Newbie
timestamp: July 27, 2016, 10:52:13 am
content: Thanks Jay! So my Tek is in working order.Your help has been very useful.Grazie!Niki

author: HighVoltage
author_rank: Super Contributor
timestamp: July 27, 2016, 01:58:00 pm
content: A friend here in Germany has three TDS3000 series scopes and all of them suffered from a failing PSU.One would not expect this from a Tektronix scope.I still have one of these scope but don't use it much and so far it has not failed.There is some really good information in this thread, thanks for that.

author: MarkL
author_rank: Unknown
timestamp: July 27, 2016, 04:29:52 pm
content: The only reason these power supplies run all the time is to charge the battery pack. The scope doesn't need 24x7 power for anything else. I'm betting most scopes don't have the battery pack, given how outrageously expensive they are.With a turned-off TDS3054 and no battery pack, I'm measuring real power 3.7W @ 120VAC and 7.4W @ 240VAC. Perhaps the extra heat dissipation is the reason for more failures at 240V.Also fairly wasteful for no added benefit.A real AC on/off switch could be a mod opportunity to preserve the power supply and save energy, but it unfortunately involves messing with the line wiring.

author: Jwalling
author_rank: Unknown
timestamp: July 27, 2016, 06:02:53 pm
content: Quote from: bsproj on July 27, 2016, 08:27:25 amFWIW, I see the same slightly increased noise on a TDS3054B.Jay

author: bsproj
author_rank: Newbie
timestamp: July 28, 2016, 02:09:06 pm
content: Thank you for your answers.Quote from: MarkL on July 27, 2016, 04:29:52 pmDo you think a 120 VAC operation could increase the life expectancy of this PSU?I've a few unused 240 VAC center-tapped transformer. I could use one of them as an autotransformer in order to obtain a 120 VAC socket.Is this a good idea?Niki

author: MarkL
author_rank: Unknown
timestamp: July 28, 2016, 07:41:12 pm
content: Quote from: bsproj on July 28, 2016, 02:09:06 pmWho can say for sure if this will help, but a lower temperature is generally good for the longevity of any circuit. Make sure you preserve the ground continuity to the scope if you build a converter.You might not save any energy, though, since there's going to be loss in your autotransformer. It will draw a small amount of power even if nothing is connected to the output and become a phantom load itself. (If you're concerned about the energy, that is.)The back panel on my 3054 got noticeably hotter when running on 240V, although I didn't take it apart to confirm it was R3 + R5. Seems likely though, looking at the circuit from Jay_Diddy_B.

author: bsproj
author_rank: Newbie
timestamp: July 29, 2016, 10:20:50 pm
content: Quote from: MarkL on July 28, 2016, 07:41:12 pmI've just tested the temperature running my 3014 with 120 VAC. The overheating is now less alarming.Actually my Tek is connected to mains only some hours a day. This is enough to overheat it (expecially during the summer), but not enough to be worried about the energy loss. So, I'm going to keep the autotransformer plugged in. I really hope this will increase the life expectancy of the PSU.Thank you for your help.Niki

author: hugo
author_rank: Regular Contributor
timestamp: July 31, 2016, 01:47:12 am
content: Hi Niki you've forgot to mention what is the room temperature !

author: bsproj
author_rank: Newbie
timestamp: July 31, 2016, 10:10:54 am
content: Hi Hugo. The temperature is usually about 25±5 °C during the summer.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 31, 2016, 11:36:37 am
content: Hi Group,I can confirm the input power measurements. These were made using a DSO-X 3034A with the Power Analyzer option. A current probe and voltage probe were used. I am measuring a TDS 3012 with the Artesyn NAN40-7615-01 Power Supply.Input power was supplied using an Elgar 501 AC bench power supply.Here are the results:110VPower is 3.26W230VPower is 6.37WI will post a thermal image later.Regards,Jay_Diddy_B

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 31, 2016, 02:44:42 pm
content: Hi Group,Here is a thermal image of the Power Supply Board. The TDS3012 is powered from 220V (nominal) the scope is off. The hot parts are R3 and R5, the MOSFET is warm.I am not sure if this is a problem, resistors can run hot like this. I think line voltage transients are more of threat.Here is a picture of the output voltage ripple with the scope on. The power supply is running around 91 kHz. The switching frequency was independent of the line voltage.

author: bsproj
author_rank: Newbie
timestamp: July 31, 2016, 03:46:53 pm
content: Hi Jay, thank you for your report. Your thermal image is consistent with my previous temperature measurements.It's interesting that the different mains voltage causes a variation of 40 °C in the temperature of the two resistors. This make me more convinced to run my Tek at 120 VAC.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: July 31, 2016, 05:36:49 pm
content: Niki,You could always move to a 120V country...Regards,Jay_Diddy_B

author: tautech
author_rank: Super Contributor
timestamp: July 31, 2016, 08:12:27 pm
content: IMO it would seem wise to power this DSO from a switched power strip and by doing so have the option to easily remove the power when not in use.It might also be worthy of further modification of the snubber to reduce heat when the scope is not in use but powered.Thanks to Jay and bsproj for investigation of this and sharing on the forum.Edit spelling

author: bsproj
author_rank: Newbie
timestamp: July 31, 2016, 08:36:31 pm
content: Hi tautech,actually this is the perfect solution. My oscilloscope has already connected to a switched power strip, with a lot of other instruments. In my case is more convenient to use a DIY step-down transformer instead another switched socket.Quote from: Jay_Diddy_B on July 31, 2016, 05:36:49 pmIt would be a good idea to kill two birds with a stone: I'll get a cooler Tek, and I'll improve my broken english!

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: August 03, 2016, 09:15:27 pm
content: Hi,I got the parts to complete the repair of my TDS3012. When I got the scope, it was literally a 'basket case' The back was off, the floppy was out, the power supply was broken.I repaired the power supply. I described the repair earlier in this thread. I needed to get the missing case parts.Two missing feetTwo Hub assemblies to hold the handle onTwo hub covers, to hide the hub assembliesThe Power Switch ButtonThe total cost delivered around $160.00These parts will fit any of the following scopes:TDS3012 TDS3014 TDS3032 TDS3034 TDS3052 TDS3054Regards,Jay_Diddy_B

author: Maxis
author_rank: Contributor
timestamp: September 24, 2018, 09:42:57 pm
content: Dear forum members,This is my first post on this forum. I wanted to share my experience in fixing the TDS3014 power supply.The power supply schematics traced Jay_Diddy_B helped me a lot in fixing my 3014.The problem was in the mains flyback converter, which couldn't properly regulate its output voltage (was jumping from 19V to 23V up/down) causing the scope to do sporradic things, crashing SW, hanging, rebooting, etc.The root cause of the failure was in the voltage reference/shunt regulator TL431. It was heating up like crazy leaving black spot of the burned PCB under it.I've checked the other components, they seem to be in spec. After the replacement of TL431, the new regulator also heats up to 70 degrees. The output voltage with and w/o the load and the ripple figure are fine. I'm running the power supply from 240V AC mains. The scope runs like new again.But now I'm questioning whether the problem is really fixed.Is it normal that TL431 heats up so much?I haven't seen it being glowing red on the thermal scan images kindly provided in this forum. Actually TL431 almost dissipates 400mW! It had left the same kind of burns on the PCB like the snubber network resistors and the load resistance.If this is not a normal operation, IMHO, I can only assume that the optocoupler has degraded with the time and doesn't have the same Current Transfer Ratio (if the CTR would fall low). Hence TL431 is supposed to put more current through IR LED in order to keep the output voltage on target, which pushes the TL431 operating mode beyond the spec.For the moment I'm waiting for the CNY17-3 optocoupler to arrive, then I'll try replacing it.However, if such a heavy operating mode in standby is normal, IMHO, the TDS3000 power supply is prone to fail with the time.I'm just wondering, is it only my scope or are TDS3000 having a glowing red reference IC when running from 240V AC?Thank you!All the Best,Maxim

author: Maxis
author_rank: Contributor
timestamp: September 25, 2018, 10:45:55 pm
content: Hello All!A little update - coudn't get the original TCDT1103G, but quickly dropped in CNY17-3 (disconnecting the base of the phototransistor beforehand). Apart from a little pinout difference (and a package geometry too) these two parts have similar characteristics.And bingo!After the replacement of the optocoupler the current flowing through the IR LED is much lower. LM431 is barely warm. IMHO, since the scope was always connected to the mains for many years while sitting on the bench, the optocoupler has degraded (IMHO the IR LED did) and this was the root cause. So, in order to limit the output voltage, the LM431 had to pump lots of current though IR LED in order to compensate for the degraded Current Transfer Ratio. This caused TL431 dissipating around 500mW. Eventually this voltage reference got killed by the continuous overheating making the NAN power supply output unregulated (up to 30V instead of 14.7V). I wonder whether the output load resistance was tailored to limit the output voltage in such event (single fault protection) when the scope is OFF. Anyway apart from continuous rebooting and FW crashes the scope didn't burnWhat is amazing is that the Tektronix power converter (the one generating all the voltages from 14.7V and connected to the NAN AC/DC converter) supported the recurring overvoltage up to 30V protecting the rest of the scope (sometimes it's good to overdesign things)!Now, IMHO, the scope is finally fixed and its thermal profile is not any different from presented above on the IR scans.Maybe someone would find it helpful.Thank you and all the Best,MaximP.S. Now I'll try fixing/calibrating my 2245A with the old-new repaired TDS3014!

author: ElectronicsMeetingPlace
author_rank: Newbie
timestamp: June 24, 2022, 03:20:56 pm
content: Hello all, first post!Working on a NAN40-7615-01 out of a Tek scope. The main switching mosfet was found shorted along with the zener and other parts mentioned in earlier post. I want to verify the resistance of R7 on the board. This one overheated and I can't read the colors of the bands on the resistor. It reads 220ohm when I check resistance with Fluke (one lead unsoldered from board).

author: sicco
author_rank: Regular Contributor
timestamp: June 25, 2022, 08:22:32 pm
content: Red, Red, Brown.

author: lern01
author_rank: Regular Contributor
timestamp: December 09, 2023, 01:46:07 pm
content: TDS3014B has a power-on time of more than 20 million hours. What is the reason? There are still two problems: 1. The language selection and other settings cannot be saved, After restarting, the parameters are still the same as before. 2. The time is displayed like this. Is it related to DS1742W?Can anyone help me?

author: sicco
author_rank: Regular Contributor
timestamp: December 10, 2023, 03:35:43 pm
content: Yes your DS1742W has a battery that’s now exhausted. Where that battery sits inside the DS1742W, how to Dremel into it, how you could go DS1744W, or other alternatives is all listed at various places in this forum.Also how network MAC address can be restored in case you need that.