Help fixing Siglent SDG805 (Fixed)

[KaiDT]

Hi all,

I have 2 problems with SDG805, which is out of warranty now I believe.

First one is a problem in booting up where it is stuck on Siglent logo just like in this thread (https://www.eevblog.com/forum/testgear/siglent-sdg-805-boot-problem/). I have a look in that thread and there is no information on the procedure in solving the issue and it is a reason why I started a new thread.

Second problem is that its output is not what it is set in the menu and it is much lower. Waveform is also distorted as shown in the picture.

I had contacted local supplier and they said they only provide 1 year warranty and also cannot fix the second issue. They are recommending to buy new units. However, we are in public school and I cannot give justification to my boss in purchasing new units as 4 out of 12 units purchased have been malfunctioned with 3 years.

I am really hoping that you guys might be able to help and guide me, who has small knowledge in electronics, in attempting to fix these problems. Thank you!!

Edited: added one more pic on the unit with the output problem, in which I have measured power rails and they are all ok (+15, -15, +5, -5 and 1.2 V). T__T

[tautech]

Welcome to the forum.

First, are all units up to date for their firmware ? (very important !)
Latest firmware is V1.08.01.13R6 and you can get it here:
http://www.siglent.com/ENs/prodcut-gjjrj.aspx?id=71&tid=16&T=2

Note; there may be a number of firmware install steps to get units to the latest firmware version....carefully study the firmware release notes in the firmware package and follow all steps needed very carefully and exactly as written........NO shortcuts.

Get all units up to date before going further.

Corrupt output.
I strongly suspect this has come about from damaged output amplifiers however they can be replaced.
This is a result of output protection turned OFF. Note, it is OFF by default and the users responsibility to engage it. The toggle to turn it ON is in the Output Setup menu within the Utility menu.
SDG800 models do not have output protection and must be used carefully with a live (powered) DUT.

Boot freeze.
This is recoverable but much easier if the latest firmware is installed.
How many units are frozen ?
I can provide guidance on this recovery later after all units have the latest firmware installed.

[KaiDT]

Thanks tautech,

Since I have across boot problem thread, I have updated all units to V1.08.01.13R5. I do not know that there is V1.08.01.13R6 firmware. I will be updating all units to this firmware asap. I will also make sure the rest of unit have the output protection on.

Can you also point me to damaged output amplifiers that you suspected? Is there any way that I can test them?

Only one unit has boot freeze and I think its firmware is at 1.08.01.08 since it is the firmware on the other units that I have updated today. If you can, I would like to have guidance on this problem please.

I am really appreciated for your reply. tautech thank you very much.

edited: after updating to V1.08.01.13R6, I cannot find output protection in the Output Setup menu within the Utility menu.

[tautech]

IIRC it's the last IC before the output.
Looking for other threads to help you............

Just this one for now, more later.
https://www.eevblog.com/forum/testgear/the-sdg1000-and-sdg800-thread/
AFAIK the output amps are the same as in SDG1000 models and there is info about what they are ....if I can find it.

Let me get a SDG805 out and check the UI....the info about output protection will be in the User manual. 

[tautech]

My error. 

Output protection does not apply for SDG800 models. 

[KaiDT]

Don't worry. I will tell students to be careful with it. I have been looking in that sdg1000 and sdg800 thread. If all faulty units I have can be fixed, it would make my boss very happy ^^.

[tautech]

10pm and I must sign off but I will look for the info on what the output amp is later....unless member rf-loop watches and comes to the rescue.
I need record that IC # somewhere................ 

[Siglent America]

Just as a quick point
The SDG800 used to have no output protection but later units (Rev C HW or later ... 2017?) it was added.

[tautech]

Info on the IC's used for outputs in SDG1000 series is here:
https://www.eevblog.com/forum/testgear/the-sdg1000-and-sdg800-thread/msg646787/#msg646787

Note, the 1000 series 2ch AWG's had no-equal amplitude outputs however ch1 was the same spec as SDG800 models.
SDG1000 teardown pics:
https://www.eevblog.com/forum/reviews/siglent-sdg1010-function-generator-teardown/

SDG800 teardown pics:
https://www.eevblog.com/forum/testgear/teardown-of-siglent_s-sdg805-arbitrary-waveform-generator/

[KaiDT]

Info on the IC's used for outputs in SDG1000 series is here:
https://www.eevblog.com/forum/testgear/the-sdg1000-and-sdg800-thread/msg646787/#msg646787

Note, the 1000 series 2ch AWG's had no-equal amplitude outputs however ch1 was the same spec as SDG800 models.
SDG1000 teardown pics:
https://www.eevblog.com/forum/reviews/siglent-sdg1010-function-generator-teardown/

SDG800 teardown pics:
https://www.eevblog.com/forum/testgear/teardown-of-siglent_s-sdg805-arbitrary-waveform-generator/

Thank you very much. I am about to post a pic asking which one should be the output amplifiers. As Dave in video teardown always point to chip closed to 49.9 resistor, I found two positions on the board having these resistors. From rf-loop's the information, it is Ti THS3095 so it should be in the one in the photo, right?.

Next question is how can I know if this is failed or not. Is it possible to test it on board or it is better to remove it and test outside? I am so sorry to ask lots of questions. Hope you guys don't mind.

P.S. tautech do you have information on how to recover from boost freeze yet? I have watched Dave video on https://www.youtube.com/watch?v=tM2j9zuBiRQ. I am wondering if the procedure is the same.

Many Thanks

[tautech]

Thank you very much. I am about to post a pic asking which one should be the output amplifiers. As Dave in video teardown always point to chip closed to 49.9 resistor, I found two positions on the board having these resistors. From rf-loop's the information, it is Ti THS3095 so it should be in the one in the photo, right?.

Yes, note SDG1000 has 2 outputs, ch1 has the same 20Vp-p capability (into HiZ) as SDG800 while ch2 is only 6Vp-p.
You need to check the IC markings match for SDG800 vs SDG1000 ch1.

Next question is how can I know if this is failed or not. Is it possible to test it on board or it is better to remove it and test outside? I am so sorry to ask lots of questions. Hope you guys don't mind.

Scope the IC input and output and check for linearity.
Find the datasheet for the correct pinouts.

tautech do you have information on how to recover from boost freeze yet?

I have all the required SDG800 recovery tools but can only share them privately and require them NOT to become public.

Personally I'm disappointed with the poor support you have received from your local distributor and will be bringing this matter to Siglent's attention.

[KaiDT]

Scope the IC input and output and check for linearity.
Find the datasheet for the correct pinouts.

I am trying to check them now thanks.

I have all the required SDG800 recovery tools but can only share them privately and require them NOT to become public.

I understand it completely. Is it ok to sign NDA with Siglent about this? If that means I have the solution ^^. Again, thanks so much for your support.

I do not think Siglent have official distributor in Thailand. That might be why they do not care so much. Anyway, I shall try contact supplier that I purchased about this boost freeze again.

[TurboTom]

The THS3095 output stage should be configured for a gain of 10 according to R126 (909R) and R127 (100R). So if you set the generator to output a signal of 10Vpp, you should expect a signal of 1Vpp on pin 3 (non-inverting input) of U17.

But I would recommend to take a close look at R106 and R107. They appear dodgy in your photo. It's well possible that U17 is only used as the output amp at rather high levels and at lower levels, it's bypassed by the relays, and U15 is driving the load instead. So this one may also be the culprit for your problems. Check also the resistors in its vicinity and the clamping diode D3 (double diode actually).

Good luck,
Thomas

[KaiDT]

The THS3095 output stage should be configured for a gain of 10 according to R126 (909R) and R127 (100R). So if you set the generator to output a signal of 10Vpp, you should expect a signal of 1Vpp on pin 3 (non-inverting input) of U17.

But I would recommend to take a close look at R106 and R107. They appear dodgy in your photo. It's well possible that U17 is only used as the output amp at rather high levels and at lower levels, it's bypassed by the relays, and U15 is driving the load instead. So this one may also be the culprit for your problems. Check also the resistors in its vicinity and the clamping diode D3 (double diode actually).

Good luck,
Thomas

Thank you so much Thomas. I have been measuring supply rails for U17 and U15 and they are all fine (+15 and -15 for U17 and +5 and -5 for U15). I have also found that the output voltage of U17 is the same as the one measured at BNC, which is lower than set in the menu. I will do next on the U15. I will also be trying to get the waveform using Oscilloscope later. One more thing Thomas you really save me on the clamping diode. I have been trying to figure it out what A7> device is for most of the day today and could not find the answer until you posted it. Can I ask how do you figure it out that it is diode rather than a transistor?

Again thank you very much.

[rf-loop]

...how do you figure it out that it is diode rather than a transistor?

I'm not @TT but...

PCB label D3 (diodes are typically marked as D)
Tip: Then also you can look how it is connected directly between power + rail to - rail.

Typical on chip marking "A7" is for BAW99 when component looks like this.
Vishay data sheet https://www.vishay.com/docs/85718/bav99.pdf

[tautech]

Can I ask how do you figure it out that it is diode rather than a transistor?

Simple, the D# on the PCB overlay next to it.

Then also knowing the package style we might Google for: SMD code A7 SOT23 data pdf
Then check the datasheet for Device Making to be sure A7 is specified to know for sure you have identified the device correctly.

and rf-loop beat me to it. 

[tautech]

PM sent to KaiDT at Siglents request.

[KaiDT]

Thank you guys.

I have been using oscilloscope to get waveform from the input and output of U15 (OPA695) and U17 (THS3095) amplifiers. Here is what I found. The sine wave is set to have 4 Vpp at 1 kHz. The output of U15 is not a perfect sine wave and have Vpp of around 60 mV.



I assume, based on Thomas suggestion, that the output of U15 is then sent the input of U17. When I measure on the both input of U17, it looks similar to that. The gain of U17 is 10 which is  the same as Thomas posted. Based on this evidence, can I assume that U17 is ok, but the U15 should be the problem?




I have check D3 outside the board and it looks to be ok. However, when I check the input of U15, signal waveform is strange.




I said strange because when I measure on the good unit I cannot see the waveform on both inputs of U15. Based on this, is it ok to assume that the problem should be somewhere before the input of U15?

[TurboTom]

@KaiDT,

Please check R106 and R107 as I recommended in my post before. These resistors appear to have burn marks. They are meant as output protection resistors for U15 and are part of its feedback loop. If these are faulty, all kinds of funny things may happen. You're lucky that U17 is apparently still good - replacing it is a real PITA because it has an exposed (thermal) pad on the bottom that's soldered to the substantial ground plane of the PCB -- difficult to heat up without causing collateral damage...



P.S. I didn't ignore your question but @tautech and @rf-loop perfectly answered it so I don't have to add anything 

[nctnico]

R106 and R107 don't look dodgy; they are definitely burned! Replace these first and then look further.

[KaiDT]

@Thomas and @nctnico. Thanks again for your input.

I have measured resistance of both R106 and R107 on board and it shows something close to 25 ohm. I also take one out to measure it and its resistance is similar to the one measured on board. I think it looks dodgy on the previous photo possibly due to bad angle?

Here is the photo I took before I remove diode. They also look like to have burn mark   



I have also measured R113, label 68A, and it shows 500 ohm on both good and bad units. It increasingly looks like a complicated problem now, isn't it? 

More suggestion for me to try. I am all ears. Thanks guys

[TurboTom]

If the resistors measure okay, of course you don't need to replace them. Your new photo still makes me believe that they got pretty hot at least once because especially R107 shows some discoloration. So there may have been some considerable "reverse" current flowing through them.

Since U15 appears to be operating in inverting mode (provided R105's other terminal is connected to ground which is not exactly visible), you shouldn't be able to measure any voltage at its input terminals (no.2 (-) and no.3 (+)). If there is any signal observable there, the fault is definitely located around U15. If all the resistors and the diode are okay, I'ld bet my bottom dollar (or Euro that is... ) that U15 itself is faulty.

Cheers,
Thomas

[nctnico]

Perhaps a good mod is to put a few big fat TVS diodes across the output. At least any excessive reverse voltage will be blocked.

[KaiDT]

Since U15 appears to be operating in inverting mode (provided R105's other terminal is connected to ground which is not exactly visible)

I will check on R105 again tomorrow whether or not it is connected to ground.

you shouldn't be able to measure any voltage at its input terminals (no.2 (-) and no.3 (+)). If there is any signal observable there, the fault is definitely located around U15

That is what happened when I was using oscilloscope to get waveform there on good unit.

If all the resistors and the diode are okay, I'ld bet my bottom dollar (or Euro that is... ) that U15 itself is faulty.

I will get into it tomorrow and  will order OPA695 ASAP. One question on this. Can I do it without taking them out of the board? since I am having a hard time put it back there T__T. Can I measure the values on good unit and compare them with that of on bad unit? in order to identify the faulty component. I know that diode have to be off board otherwise it shows voltages in every direction    As I am not really expert in electronics, I hope I am not asking too many questions 

Perhaps a good mod is to put a few big fat TVS diodes across the output. At least any excessive reverse voltage will be blocked.

If it can help improve durability of the equipment, I would like to try it. Can you provide more information of this please?

Thank you so much guys

[TurboTom]

KaiDT -

usually you can get quite useful information even when probing components in-circuit. Of course, you should know what to expect and which are the common failure modes of components.

- probing resistors usually isn't a big deal. The test voltage of modern digital multimeters in resistance mode often isn't high enough to turn on silicon junctions. When in doubt, manually select a measurement range higher than what you would expect, this keeps the voltage drop across the resistor you're probing even lower (provided your multimeter uses a constant current approach to measure resistance which most of them do). If you measure a resistance higher than what you expect, the resistor is most probably shot (high capacitances with residual votages present may also cause this, but then you should see the reading drop slowly). Lower values may be the result of other resistive / inductive components arranged around the one you probe. Resistors virtually always fail open / intermittent / too high. In many cases they show scorch marks but that's not always the case.

- Capacitors are difficult to test properly in-circuit except for a short. Proper RLC bridges may provide some useful information but usually leave a lot room for interpretation, so considerable experience may be necessary here.

- Diodes and the junctions of transistors more often fail shorted than open, especially in case of power semiconductors. If they fail open, and the semiconductor is housed in a plastic casing, you can often see cracks or craters in the resin from the violent disintegration of the bonding wires. There are cases, though, where simply a bond connection inside a semiconductor enclosure fails which can be very difficult to identify and (from my own experience) always happen with "unobtainium" components  . Surprisingly, I've already come across several zener diodes in glass packages that failed open without any external traces to be found.
So, for example, if you use your DMM's diode test function to check the dual clamping diode in your SDG805 in-circuit, start with both diodes in conduction direction. If you find the expected 600...700mV forward threshold, you can already be 99% certain that the diode is still good. Blocking direction should show a higher voltage drop, but other semiconductors may interfere with that. Schottky diodes, especially the bigger, low-voltage ones, may almost appear like a short in conduction direction.

In your particular case, I would just replace U15 and test the generator again. SO8 ICs are easily removed by "drowning" one side in solder and while heating all four terminals, carefully liftig this side off the PCB by half a millimeter or so. Then, still heating the solder on this side, quickly slide a piece of thick (drawing) paper between the PCB and the IC's terminals. Now "drown" the other side of the IC in solder and lift it off the board with a pair of tweezers. After that, you only need to clean the PCB pads with some solder wick or a suction device. SO packages can still be soldered easily enough back in pin-by-pin.

Cheers,
Thomas