Rigol DG4162 function Gen has defect USB port - Page 1
Forum section: electronics / repair

author: rooky
author_rank: Contributor
timestamp: October 18, 2017, 07:09:32 pm
content: Hi experts!I would like to ask for your help.Accidentally I damaged the USB port of myRigol DG4162 function generator by shorting the+ and - pins of the USB port.Since then the USB port does not detect/read/write any USB stick andthere is now power on the +5V pin.Does anyone of you have the circuit diagram of this device ordetails on what exactly I need to check/ repair in order toget the USB port fixed again?Thank you in advance for your help!Best regardsRooky

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 18, 2017, 10:52:31 pm
content: Check for a ferrite bead or 1 Ohm resistor near the USB-Port. Most likely it burned out due to excessive current. With any luck, the traces haven't been damaged.If the traces are damaged, you should be able to replace them with a simple cable.Did you smell magic smoke from inside the unit when you shorted the pins?

author: rooky
author_rank: Contributor
timestamp: October 19, 2017, 07:18:55 pm
content: Hi SaabFan,thanks for your reply. unfortunately there is no ferrit beat or 1Ohm resistor next to the USB port circuit.There is a npn transistor smd labled 1WW (equals a BF822 as far as I figured out) which is connected with its collector to the ground(!?) which also connects to the metal shield housing of the USB port and Base and emitter go into the lower side of the pcb witch I dod not disassemble yet.The npn seems to be defect since meassuring it with a multimeter did not show any connection between base and emitter/collector. changing it did not help at all. There must be something else defect... I have to totally disassamble the device to see the other side of the circuit connections.I was hoping that somebody in this forum has maybe already some experience with the circuit of the device.I will keep searching....but thanks again for your advice.Best regardsRooky

author: wraper
author_rank: Unknown
timestamp: October 19, 2017, 07:32:49 pm
content: Quote from: SaabFAN on October 18, 2017, 10:52:31 pmNobody uses 1 ohm resistors on USB port. It just would be out of USB spec right away. There can be either polyfuse or some switch (IC, mosfet).Quote from: rooky on October 19, 2017, 07:18:55 pmIt's very unlikely for ground to be disconnected from USB port by some sort of device. Likely you got something wrong. There may be a MOSFET switch on +5V. BJT is very unlikely to be used related to USB. Also BF822 is completely unsuited to be used in oscilloscope because it's high voltage low current transistor.

author: rooky
author_rank: Contributor
timestamp: October 20, 2017, 05:01:02 am
content: Hi wrapperThanks for your answer!Yes I was also wondering that there is a high voltage non connected with the collector to ground.The SOT-23 3-pin housing has the labor 1VW1n or 1WW1n. The first Letter is not clearly readable.. it could be a V, a U or a W. second letter is for sure a W ( could this mean manufactured in chine?)The 1n is smaler and printed vertically.The base and emitter of what I beleihe is a Transistor are connected to the two middle pins of the USB pins going further into the PCBNo other smd parts are connected around the outer PCB side. To se the other side I have to completely disassemble the DG4162.Do you have an idea what the 1V... smd part could be ?ThanksRooky

author: wraper
author_rank: Unknown
timestamp: October 20, 2017, 10:29:33 am
content: Quote from: rooky on October 20, 2017, 05:01:02 amThat is not a transistor. This is dual ESD protection TVS diode like on the picture. If there is no 5V on USB, this part has nothing to do with this. You should only look what's on the +5V line.

author: rooky
author_rank: Contributor
timestamp: October 20, 2017, 12:49:58 pm
content: Hi wraperThanks a lot! I believe this isbtoken to . Do you know the naming of this so I can order a new on.I will check on the 5v supply side to see why there is no power.

author: wraper
author_rank: Unknown
timestamp: October 20, 2017, 01:43:39 pm
content: Quote from: rooky on October 20, 2017, 12:49:58 pmWhy would it? If this part was faulty, most likely, it would measure short, not open. If this is bidirectional TVS as on top of the picture, it is completely normal to measure open both ways. Even if there was enough voltage and current to make it open, IC providing this USB interface would certainly blow up as well. And there is no reason for this part to blow up if you just shorted 5V to GND or even data line, this part has higher clamping voltage.

author: rooky
author_rank: Contributor
timestamp: October 20, 2017, 02:05:08 pm
content: Thanks! understoodWill check 5V supplyThanks again

author: rooky
author_rank: Contributor
timestamp: October 20, 2017, 07:13:12 pm
content: Hi wraperI found some time to disassemble and do some measurement.5V is available as long as no USB stick is attached.As soon as a stick is insert the voltage goes down to 0.69 VThe USB power pin is connected to the circuit left of the USB portvia two smd devices which look like a two resistors.Guess they are something else ( resistor plus PTC??) see pictureThere is nothing on the other PCB.I assume the circuit on the left is the USB power supply.I tried to lookup the IC but could not found anything in the internet.Do you have any hint to determine what components these are and how to test which one is broken?Best regardsRooky

author: KuchateK
author_rank: Regular Contributor
timestamp: October 20, 2017, 09:00:56 pm
content: http://lmgtfy.com/?q=4435aFirst result.http://datasheet.octopart.com/FDS4435A-Fairchild-datasheet-51846.pdfIt matches perfectly considering you have four pins connected together on the PCB.

author: rooky
author_rank: Contributor
timestamp: October 20, 2017, 09:45:27 pm
content: You think that's the bad guy?The first smd device towards the power pin is measuring 0.9 ohmDies that sound OK?If the MOSFET is broken would then no Voltage at all?Since I get 5 V which drops if a stick is attached I am not sure if it is the defective part...

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 20, 2017, 09:45:27 pm
content: Quote from: wraper on October 19, 2017, 07:32:49 pmI've seen resistors in the Supply-Rails of USB-Ports on PC Motherboards. They're used as current sense resistors. If too much current is drawn, the USB-Controller reports a fault and disables the USB-Port.At least that's what my ASUS Motherboard did once when I accidentally shorted 5V and GND of my Arduino.It was most likely not 1 Ohm though but something in the mOhm-Area.

author: SaabFAN
author_rank: Frequent Contributor
timestamp: October 20, 2017, 10:06:22 pm
content: Quote from: rooky on October 20, 2017, 09:45:27 pmIt might very well be the MOSFET. If it is damaged and presents a high resistance (maybe even if switched off), there will be +5V on the rails if no current is drawn and a large voltage drop once current is drawn by a stick.Check the voltage-drops across each component.Might very well be that near the USB-Port everything is ok and the problem resides somewhere in the Power Supply.

author: wraper
author_rank: Unknown
timestamp: October 20, 2017, 10:40:30 pm
content: Black part is ferrite bead, white is ceramic fuse. Both should have low resistance. Measure voltage directly at MOSFET pins when USB stick is inserted.

author: rooky
author_rank: Contributor
timestamp: October 20, 2017, 11:27:43 pm
content: Thanks wraperI did the meassurementsit seems that the MOSFET P-Channel is always turnd on sinde its gate is alwasy 0V. no matter if stick is in or not.Only volatge difference are the voltages between what you said is the fuse and the coilDoes that make sense?Thanks for helpingRooky

author: rooky
author_rank: Contributor
timestamp: October 20, 2017, 11:29:49 pm
content: Hi wraper,gues we both should actually be in bed by now.... but this topic does not let me loos.....

author: rooky
author_rank: Contributor
timestamp: October 20, 2017, 11:33:58 pm
content: Thanks SaabFanI did the meassurements. Please see the post before to wraperWhat I am surprised is that the gate is always at 0V meaning the P-channels is always on.and has 5V at the gate and Source. But as soon as the stick is in the volate behind the Fuse and between the coils is droping to 0.76V....so you still think this is the mosfat which is defect?Thanksrooky

author: rooky
author_rank: Contributor
timestamp: October 20, 2017, 11:36:01 pm
content: sorry guys meant ferrit beat not coilby the way. the ferrit beat meassures 0.9 ohm and the fuse around 26ohmDoes that soud correct?ThanksRooky

author: wraper
author_rank: Unknown
timestamp: October 20, 2017, 11:37:57 pm
content: Quote from: rooky on October 20, 2017, 11:27:43 pmI don't quiet understand what you mean. What are those 3 voltages in numbers?

author: wraper
author_rank: Unknown
timestamp: October 20, 2017, 11:40:11 pm
content: Quote from: rooky on October 20, 2017, 11:36:01 pmApparently this fuse failed. Resistance should be close to 0 ohms.

author: rooky
author_rank: Contributor
timestamp: October 20, 2017, 11:43:24 pm
content: Hi wraperthe blue values are1. the volatge between ferrit beat and fuse => 0.76V if stick is in, 5V if stick is not in2. the volateg between the ferrit beat and the power pin of the US port => 0.76V if stick is in, 5V if stick is not indoes that help to make the picture clear?if the fuse is broken. what value do these fuses usually have? Could you give me a suggestion of a part I should get?Thanks!Rooky

author: wraper
author_rank: Unknown
timestamp: October 20, 2017, 11:49:49 pm
content: Quote from: rooky on October 20, 2017, 11:43:24 pmI was talking about 3 voltages I asked on the picture, not something else, but whatever. I would suggest to use 1A ceramic SMT fuse. You could also use PTC fuse but there will be more voltage drop on it as they have higher resistance. For testing you could just put a solder blob instead of it.

author: rooky
author_rank: Contributor
timestamp: October 20, 2017, 11:52:06 pm
content: If I would bridge the fuse for a short test, the USB should work again. Right?

author: wraper
author_rank: Unknown
timestamp: October 21, 2017, 12:07:36 am
content: Quote from: rooky on October 20, 2017, 11:52:06 pmit should

author: rooky
author_rank: Contributor
timestamp: October 21, 2017, 12:09:31 am
content: And it does!Thanks for your great help!All the best!Rooky

author: rooky
author_rank: Contributor
timestamp: October 21, 2017, 12:11:05 am
content: And it does!Thanks a lot for your great help!All the bestRooky