Siglent SDG1062X goes to overvoltage protection mode - repair successful

[scsi]

Hello all, I have Siglent SDG1062X function generator and I accidentally touched supply rail with one of generators lead and it went immediately to overvoltage protection mode,
but after this accident when I try to turn on output it detects overvoltage and shuts off. Does that mean I shorted it's output? Sending it back to Siglent will be pain, not sure what to do.

Peace.

Update: There is only DC voltage 4.7V on output irrespective of applied waveform, amplitude etc. (possibly blown output capacitor?)

[DaJMasta]

Sounds like a blown front end amp or protection diode.  Hard to say without seeing a schematic, but there may be visible evidence of it on the board.

[tautech]

Yes blown output amp is likely.
Threads that should be of help:
https://www.eevblog.com/forum/repair/help-fixing-siglent-sdg805/
https://www.eevblog.com/forum/testgear/the-sdg1000-and-sdg800-thread/msg787268/#msg787268
https://www.eevblog.com/forum/repair/sdg1025-overvoltage-and-relay-malfunction-repair/

Further to help identify blown components:
https://www.eevblog.com/forum/blog/eevblog-805-siglent-sdg2122x-arb-generator-teardown/
https://www.eevblog.com/forum/testgear/siglent-sdg1032x-mini-teardown/

[scsi]

I did a quick check today and foud LMH6702MA in question - I get 4.7V DC on pin 6 (output) is there any components aroud
that must be check in order to confirm that only op-amp went bad?

[DaJMasta]

Check the inputs.  If you can find the signal that's supposed to be coming out of it at either input pin, then there's a good chance the opamp has gone bad.

That said, I think the actual output amps are the THS3095s over the large exposed pad areas.  Start from the front panel and test moving back.  Also worth testing resistance of the inputs and outputs while powered down, if there's a short on anything, it's immediately suspect.  If you can narrow it down, you can also try removing the IC with hot air and testing again without it in place - if the behavior changes/comes good (not at the output, but at the previous stage) then you probably pulled the bad one.  If you remove the THS3095 (if it's the output amp) and the LMH6702 still has a bad output, then the bad one is probably still in circuit.  There is a chance the THS3095 is gone bad and it's pulling up the output of the LMH6702, for example, so before you go buy a $10 opamp, it's worth checking.

[scsi]

Checked TSH3095 for both channels DC voltages are the same

pin4 : -15V
pin7 : +15V
pin8 : +5V

nothing on others

That doesn't tell much right? These are supply voltages and enable state voltage.

LMH6702 with DC voltage on output runs hot compared to the other.

Update: I see a signal (mV) for bad channel on resistor 30A near LMH6702 when I activate output, there is nothing on the same resistor for good channel.

Update 2: checking TSH3095 on bad channel pin3 - set output for 10Vpp measuring ~30mVpp on pin3
               checking TSH3095 on good channel pin3 - set output for 10Vpp measuring ~1Vpp on pin3
 

[TurboTom]

@scsi -

check if there is any signal (DC or AC) on pin no. 2 of the suspicious LMH6702. Since it's configured as an inverting amplifier, there shouldn't be any. If you should find something there, it's very likely that the OPAMP is faulty. Replace it and continue the tests. There can still be a defective TSH3095 but with a good LMH6702, at least at low output amplitudes, the SigGen should be working again.

Cheers & good luck,
Thomas

[scsi]

check if there is any signal (DC or AC) on pin no. 2 of the suspicious LMH6702

Yep there is 30mV DC on pin 2 at the suspicious LMH6702 none on the other.

[TurboTom]

Is the polarity of the DC on pin 2 the same as on the output (pin 6)? If it is, go ahead and replace the OPAMP. If not, check the other terminal of the resistor (30A = 200R). If the voltage there is higher than on pin 2 of the opamp but the same polarity, the opamp is possibly okay and the problem is located before it.

[scsi]

Repair successful - changing LMH6702 did the job!

Thank you all for the input, special thanks to TurboTom!

[K0LO]

I had the exact same problem. I had Overvoltage Protection enabled on my SG1032X Function Generator. When Output 1 was accidentally connected to a circuit that had DC voltage (+42V) present on its input, the generator went into Overvoltage Protection mode. This was permanent.

I found U21, an LHM6702MA op amp had failed, exactly as described by the previous posts. Replacing the op amp fixed the problem.

I know that an OVP circuit cannot protect against every conceivable fault mode, but shouldn't it be able to protect against low DC voltages that are within the IEC or US OSHA safety limits?

[tautech]

I had the exact same problem. I had Overvoltage Protection enabled on my SG1032X Function Generator. When Output 1 was accidentally connected to a circuit that had DC voltage (+42V) present on its input, the generator went into Overvoltage Protection mode. This was permanent.

I found U21, an LHM6702MA op amp had failed, exactly as described by the previous posts. Replacing the op amp fixed the problem.

I know that an OVP circuit cannot protect against every conceivable fault mode, but shouldn't it be able to protect against low DC voltages that are within the IEC or US OSHA safety limits?

Welcome to the forum.

OVP specs are clearly stated in the User manual on P121.
https://siglentna.com//wp-content/uploads/dlm_uploads/2022/06/SDG1000X_UserManual_UM0201X-E01E.pdf

You far exceeded: The absolute value of (reverse) input voltage is higher than 11V±0.5V......

Yes there are times when we wish these arbs were more than a max + 10V device.

[KE4CDR]

Does anyone know where you can find the schematic for the SDG 1032?

[tautech]

Does anyone know where you can find the schematic for the SDG 1032?

It's not available.

Instead follow the links in reply #2 to other repairs and helpful threads.