This is my longest post so far but I have some good news following the trouble I had with my SDG 1020.
Following on from this set of posts...
Just got a sdg1020 as a bit of a repair project, you mention old version and new version. What is the difference and what was the serial number break. Thanks for any responses :-)
Repair?
What are the fault symptoms?
Siglent products have a 3 year warranty, post all but the last 4 SN digits, from that we can tell the build date, it may still be under warranty.
Hi Tautech,
It has been several months since my last post on this case but life got in the way of me sorting out the poor old SDG 1020, unfortunately I got it non working and I see that someone made a bit of a dogs breakfast in soldering in U55 which I believe is the - 15V voltage regulator. I would doubt that Siglent would honor any warranty on this as I am not the original owner and it has had already had a go at by someone else. Anyway the serial number without the last 4 digits is: SDG0000113.
The symptom is from memory that the waveform had DC offset problems and can be all over the place and may even be clipped........ will post any progress I make and any voltage readings I make :-). I am sure that the wave generation seems to be working but I would think that this an issue with the output stage given that the -15V regulator was replaced. This is why I wanted a schematic but if this is not available then fault finding will be a little more time consuming but no less fun.
Any help would be greatly appreciated.
Build date of your SDG1020 is Jan 2013.
Many source these units from overseas and then it is often too dificult to seek warranty repair and try then to fix units themselves which of course voids warranty.
I'm not aware of any schematics available, however IIRC there are links to imagery in this thread.
Member Lightages blew the output stage in his and sourced a new PCB direct from Siglent at his cost.
If you bought it cheaply enough it may be well worth a new PCB and then be as good as new.
If you contact them introduce yourself as an EEVblog member and I'm confident Siglent will assist.
Jade's email is in the profile of member Siglent in this thread:
https://www.eevblog.com/forum/testgear/siglent-technical-support-join-in-eevblog/
I can say that I have now got it working
The voltage readings I got for the power supply was in spec with +5v being 4.95v, - 5V at -4.98, +15V at 15.01V and -15 at -14.99 (this is all from memory). I had noticed that the + and - 15 Volt regulators were replaced. All my signals on channel 1 had a massive 10V offset if the P-P voltage was over 900 mV I also had clipping on sine waves. The DC offset would jump to positive or negative depending on what p-p voltage was set and all of my wave forms were only 1v p-p. Channel 2 was the same but had 5v offset.
I also had no square wave output on either channels, so this is what I had to start with. To fix this my initial approach was to do the following.
1. Work how the wave forms are generated and handled in the output stage
2. Work out how the DC offset is generated
3. go through the fault finding part of the service manual
I decided to go with the service manual and found something interesting, when looking at TA15 and TA16 these were well bellow spec when measuring with something like 500mV p-p. However if I power cycled and pressed no buttons then the waveform amplitude would be in specification. As soon as the output enable for channel 1 or 2 was pressed TA15 and TA16 would drop down to 500mV p-p. I thought this may have something wrong with the output stage loading these signals down but this was not the case as I had removed next op-amp in the circuit and I would be surprised if both channels were loading their wave forms down in the same way.
Then disaster struck, when looking at U19 for the potential reason of the DC offset the scope probe accidentally shorted pins 7 and 8 which shorted +15V to the chip disable pin then the chip literally burnt up immediately
power off walk away... this was the low point.
I removed this OP-Amp then checked to see if the signal generator still had life. Got wave forms so at this stage I ordered some new op-amps and hoped that I had not done any permanent damage. When refitting this op-amp I could not reconnect pin8 (missing pad
), quick look of the datasheet suggests that this would mean that the Op-amp would always stay powered on. Really would love to know where pin 8 of U19 went to
I had managed to get the output stage working as well as I could replacing a number of parts (some of which may have been OK to begin with) got my square wave back with replacing U37 as I think this is switched in as part of the sine to square circuit using a comparator (half of U35). But still had DC offset issues.
The DC offset and the gain voltage going to U25 and U26 (TI variable gain op amps VCA822ID) had to come from somewhere. So I started looking for another DAC and found it when looking at U72 which was a TI DAC8580 which is a 16bit serial interface DAC. This device was then connected to U47 which is a 74HC4051 demux/mux chip. Looking at test point T1 will show you the signal coming out of the DAC and you need a 1ms or so delayed trigger. I was then able to see what signals were affected by the DC offset setting and found that the following signals come from U47 (some of which I recently found out).
Pin1 is CH1 DC offset
Pin2 is CH2 DC offset
Pin3 is the signal from the DAC U72
Pin 12 is the gain setting voltage for U25 (buffered by U103) for CH1
Pin 13 is the gain setting voltage for U26 (buffered by U103) for CH2
Pins 5 and 15, I could not find out about but I suspect they are for setting up the comparator circuit on the sine to square wave conversion.
Pins 4 and 14 I will discuss later.
I then discovered that the DC offset signals from U47 were buffered by U89 (an Intersil ISL28210 op amp) and were mixed with the input of U45 via R145 in the case of CH1. So all of my output circuitry was working the main DACs seemed to work but the origin of the DC offset was the output of DAC U72. In fact looking at the wave forms on T1 made no sense as these were way off. So I tried to do a self calibration in the generator and this took far longer than the 15 seconds mentioned in the service manual. In fact it took near enough 2 to 3 minutes with no improvement.
So this got me thinking that there was a problem with the calibration circuit/channel given that:
A. the calibration routine took ages and
B. The values at T1 seemed to be at some limit.
So after more searching I noticed that there was another 74HC4051 mux chip (U42) and this had signals from the other circuitry going to it. In particular when looking at CH1 I wondered where the signal from R42 went to as it diapered in to an inner layer of the board. After some investigation I found that it went to U42 pin 1. So working forwards I found that U42 pin 3 went to U91 which was another Intersil ISL28210 and this was powered not by the +/- 5V but the +/- 15V. Now we are getting somewhere as this device was poorly, the output of U91 was in turn connected to U61_1 which was an odd 6 pin sot 23 device. It had a marking of X01C and on further investigation this was a serial 12 Bit ADC. Another Farnell order of replacement parts later... I fitted the new mux chip (U42), Op amp (U91) and ADC (U61_1) , tried to do a calibration and it looked good as it only took seconds. Checked the output and the Waveform generator was now working
Interestingly pins 4 and 14 of U47 were buffered by U103 and these voltages applied to the Reference pins of the main DACs. Where Pin 4 affected the CH1 DAC reference and Pin 14 affected CH2. This I think is the reason for the sudden drop in waveform from the main DACs as observed on TA15 and TA16 when the output key was pressed. Not certain about this, but as this is now working I am not too keen on poking around with the scope just in case I make another bad mistake.
This was a long drawn out repair but I learned a lot! I must also thank Tautech for their help and I hope that my little essay may help in some way.
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