Siglent SDS1202x-E fried FAN driver transistor - SOLVED - - Page 1
Forum section: electronics / repair

author: tppc
author_rank: Regular Contributor
timestamp: January 27, 2024, 05:37:22 pm
content: Hi everyone,the fan on my SDS1202X-E oscilloscope started making erratic and really annoying noise.So I decided to replace it with a quieter one from Noctua.Before ordering the new one, I wanted to check the voltage on the fan connector (test probes under the PCB).This is when I accidently shorted one pin to the chassis and fried the SMD transistor that drives (or used to drive) the fan.The positive end of the fan is connected to GND.The negative is driven by the Collector or Drain of the fried transistor.The Emitter or Source of the transistor goes to -10V supply.Can anyone help identifying this mystery transistor?What was it before it became an ugly piece of coal?BTW, for those interested in reducing the fan noise of their SDS1202X-E oscilloscope, NOCTUA NF-A6X25 fits well.Best Regards.

author: tppc
author_rank: Regular Contributor
timestamp: January 28, 2024, 10:43:38 am
content: Hi everyone,long story short :- Does anyone have even a partial schematic showing the fan drive section?or- Is anyone willing to open his SDS1202x-E and read the marking on Q34?Best Regards

author: CharlotteSwiss
author_rank: Frequent Contributor
timestamp: January 28, 2024, 11:37:37 am
content: Noctua is a guarantee. I have the SM, but it only reports Q34, no information (only 12vdc to power the fan). The diagram I have is completely useless. If no one helps you, I will open my 1202. But in a few days, I'm away from home. HI

author: tautech
author_rank: Super Contributor
timestamp: January 29, 2024, 12:32:30 am
content: Q34 is marked A2RX however that is some distance from the fan connector.I have a dead warranty replacement SDS1202X-E PCB here if you need further help.

author: tppc
author_rank: Regular Contributor
timestamp: January 29, 2024, 06:15:08 pm
content: Quote from: CharlotteSwiss on January 28, 2024, 11:37:37 amHi,I am a big fan (pun intended) of Noctua. I replaced nearly all the fans in my instruments with quieter Noctua models.You won't need to open your scope, since Tautech found the marking on Q34.Thanks for your offer anyway.Kind Regards

author: tppc
author_rank: Regular Contributor
timestamp: January 29, 2024, 06:36:34 pm
content: Quote from: tautech on January 29, 2024, 12:32:30 amYes, the distance to the fan connector is normal.Q34 switches -10V VEE coming from the power supply.It is located right behind the PSU connector.A2RX: I could just guess the A on the fried one.I didn't find yet the reference corresponding to this marking, but I will search.Quote from: tautech on January 29, 2024, 12:32:30 amHopefully, I will not cause any further damage while replacing Q34.Thanks so much for your help.

author: tautech
author_rank: Super Contributor
timestamp: January 29, 2024, 07:44:59 pm
content: Quick look brings up this but unsure if it's the correct package:https://www.onepcba.com/XC6114A323MR

author: tautech
author_rank: Super Contributor
timestamp: January 29, 2024, 08:10:47 pm
content: Think it's just A2R.....https://www.aliexpress.com/item/32330365420.html

author: CharlotteSwiss
author_rank: Frequent Contributor
timestamp: January 30, 2024, 07:39:19 am
content: Quote from: tppc on January 29, 2024, 06:15:08 pmBetter if I don't have to open my 1202; it won't be difficult to change that Q34.Looking at your image of the board, I see that down at Siglent they spare no expense with hot glue on the componentsI also replaced all the fan with Noctua ones, my PCs are ultra silent. I also use Noctua coolers. HI

author: tautech
author_rank: Super Contributor
timestamp: January 30, 2024, 08:01:02 am
content: Quote from: CharlotteSwiss on January 30, 2024, 07:39:19 amOnly on the PSU and it's not hot snot, it's silicone.While the PSU is a Siglent design they outsource production.

author: SeanB
author_rank: Super Contributor
timestamp: January 30, 2024, 11:23:11 am
content: Would move those screws and nuts in the bag though, using 2 cable ties to attach them to the metal chassis, probably using the round punched holes to the side of the fan, keeping them from touching the components, even if the bag disintegrates. Would also run the nuts up to the top by the screw head as well.

author: tppc
author_rank: Regular Contributor
timestamp: June 22, 2024, 12:29:06 pm
content: Quote from: tautech on January 29, 2024, 08:10:47 pmHi everyone,I could not find any result for the codesA2RXorA2R.A2could be almost anything from diodes, mosfets to voltage regulators...Can anyone have access to theSDS1202X-Eparts list and check the reference forQ34?Best Regards.

author: fzabkar
author_rank: Super Contributor
timestamp: June 22, 2024, 03:58:17 pm
content: https://www.micro-bridge.com/data/syncpower/SPN3402.pdf(A2yw)https://www.aosmd.com/sites/default/files/res/datasheets/AO3402.pdfhttp://markingcodes.com/search/c/a2xx

author: tppc
author_rank: Regular Contributor
timestamp: June 22, 2024, 05:31:19 pm
content: thank you very much!SPN3402 seems to be the right one.I desoldered the broken transistor but now the scope does not power up anymoreAll PSU voltages OK except -VEE which reads -8.8V instead of -10V.I need to investigate more. :'(

author: tautech
author_rank: Super Contributor
timestamp: June 22, 2024, 08:24:58 pm
content: Quote from: tppc on June 22, 2024, 12:29:06 pmSchematics are not available.I've done the work for you and given you a link to the transistor.I have a SDS1202X-E warranty claim PCB should you need other parts identified.

author: CharlotteSwiss
author_rank: Frequent Contributor
timestamp: June 22, 2024, 10:15:45 pm
content: Q34 is used to have -10Vdc for the analogue circuits

author: fzabkar
author_rank: Super Contributor
timestamp: June 22, 2024, 10:59:31 pm
content: Is Q34 the pass transistor in a linear -10V AVEE supply?

author: CharlotteSwiss
author_rank: Frequent Contributor
timestamp: June 22, 2024, 11:16:26 pm
content: I think so, the image is from the Siglent service manual, but it doesn't say anything more.

author: fzabkar
author_rank: Super Contributor
timestamp: June 22, 2024, 11:27:35 pm
content: Quote from: CharlotteSwiss on June 22, 2024, 11:16:26 pmThen it could be a PNP transistor. You need to trace the circuit in this area.

author: tppc
author_rank: Regular Contributor
timestamp: June 22, 2024, 11:39:49 pm
content: Quote from: fzabkar on June 22, 2024, 11:27:35 pmI did trace the area :Quote from: tppc on January 27, 2024, 05:37:22 pm

author: tppc
author_rank: Regular Contributor
timestamp: June 22, 2024, 11:43:56 pm
content: Quote from: tautech on June 22, 2024, 08:24:58 pmThanks for your help. however, The aliexpress link does not give the transistor reference and the product is not available.

author: tppc
author_rank: Regular Contributor
timestamp: June 22, 2024, 11:49:41 pm
content: Quote from: fzabkar on June 22, 2024, 10:59:31 pmno, the -10V AVEE commes from the PSU board (SMPS, not linear)Q34 is used as a swich to power the fan from GND to -10V AVEE

author: tppc
author_rank: Regular Contributor
timestamp: June 22, 2024, 11:54:27 pm
content: Quote from: CharlotteSwiss on June 22, 2024, 10:15:45 pmYes, it is a test point on the main board.-10V AVEE can also be probed on pin 9 of the power cable plug

author: fzabkar
author_rank: Super Contributor
timestamp: June 23, 2024, 12:20:02 am
content: Quote from: tppc on June 22, 2024, 11:49:41 pmThen how can removing the transistor that switches the fan prevent the -10V supply from working properly???Quote from: tppcOr are you just saying that you have now encountered a different fault unrelated to the first? I'm confused ...

author: tppc
author_rank: Regular Contributor
timestamp: June 23, 2024, 12:38:09 am
content: Quote from: fzabkar on June 23, 2024, 12:20:02 amYes, I think it is unrelated. Maybe I broke somthing while disconnecting the PSU 12 pins connector.I need to take out the main board and inspect it carefully. (which I did not do yet)

author: tppc
author_rank: Regular Contributor
timestamp: June 23, 2024, 04:08:26 pm
content: Hi everyone,My SDS1202x-E is up and running again!While disconnecting the 12 pins power supply connector, I broke the SMD capacitor C176.There was no visible damage, but in fact, it was actually shorted.This did pull the stand-by power from 5V down to 1.25V (reference voltage of the 1117 LDO voltage regulator U17).Thus preventing the mainboard to start.I replaced C176 since there was no marking, I chose a 10 µF MLCC SMD 1206 I happend to have in stock.The scope starts nicely and the fan spins at its normal speed.Damned, I though I had a valid reason to upgrade to the new SDS824X HD oscilloscopeNot this time Marco, not this time!Thanks to all contributors who helped me in any way.

author: CharlotteSwiss
author_rank: Frequent Contributor
timestamp: June 23, 2024, 04:15:17 pm
content: Okay. But have you replaced Q34? With what?

author: tppc
author_rank: Regular Contributor
timestamp: June 23, 2024, 04:24:47 pm
content: Yes, I did replace Q34 with a 2N7002 (SOT23 SMD) MOSFET I had in stock.I know, 2N7002 caracteristics are not even close to those of SPN3402.However, it does the job (temporarily).I ordered a kit of 40 SPN340x MOSFETS.

author: CharlotteSwiss
author_rank: Frequent Contributor
timestamp: June 23, 2024, 07:17:58 pm
content: Ok, so long live the 1202X-E