Siglent ssa3021x issue

[dpenev]

Hi All,

I have Siglent SSA3021X and it was in a good use for years, its a nice instrument.
I have not used it for a few mounts and now today I saw there is an issue with it.
After powering up the display looks normal but in a few minutes it starts flickering.
At the moment it start flickering I hear a buzzing sound starts as well.
This render the display not usable at all.

I have tried few power on/off sequences.
During one of the test the complete SSA3021X beeped and rebooted by itself

Seems like power supply issue to me. As it is outside warranty I have opened it to check the capacitors.
They seems to look OK. I have measured the power supply voltages +15V, 6.5V and 9.5V to be in range.

Anyone having similar issues with SSA3021X ?
Anyone having an idea how to fix this?
       
Thanks

[Mario87]

Have you tried pinpointing what exactly begins to buzz when the screen flickers? That would be my 1st step.

[dpenev]

It seems it appears a pretty stupid reason.
I seems have not plugged the power cable fully. 
Now after 1h working with the instruments all looks normal.   

[dpenev]

I was too quick. The problem actually still persists.

I have investigated further. SSA3021X is powered with a power unit (SDY8.007.087C POWER141200) separate from the main board.
This power unit produces:
+6.5V - (in my case slightly bigger 7.5V)
-9.5V
POW-SIG - 50Hz about 5Vpp. Probably used for AC sync.  Please see the measurement
+15V - this one in my case seems to be problematic. It is usually 15V but after some time it starts pulsing. See the measurement
The main switching transistors (in the big heatsink) are two Fairchild FQPF9N50C which after a while are getting very hot probably around 100degC
The capacitors on this power module looks in order.

Anyone observing something similar with his SSA3021X?
I plan to replace the switching transistors and to see if it going to help.
           

[dpenev]

A small update. I found in a local shop switching mosfets with slightly bigger Ron.
Unfortunately the behavior is the same.
After a wile the display starts flickering and +15V become as I have measured in the previous post.
The heatsink is getting pretty hot (~90degC)

I have tried with external +15V power supply for the test but I was afraid to increase the current limit of that power supply more than 1.2A
and all this 1.2A current was drawn. (The order of the different power rails may be important or the voltage regulation may depend of the consumption from the 15V rail.)
If +15V is provided by SSA3021x power module the current is in the 0.3A range.
I don't see current increase when my display start flickering.

I have ordered the original switching transistors FQPF9N50CF but I start thinking that it may be some other component in the power module
Or something happened at the display side.

Anyone having some knowledge in the SSA3021X power module?
Or can I purchase SDY8.007.087C POWER141200 from Siglent?
Or anyone having broken SSA3021X which I can take power module from for the test?

[tautech]

Yes of course you can source the PSU from Siglent.
Have you checked the PSU output values against service manual spec ?
https://int.siglent.com/u_file/document/SSA3000X_ServiceManual_E01B.pdf

[dpenev]

Thanks Tautech for the document.
I was not able to find the specification of the power supply module outputs however.

BTW I have spent some time on the power supply module.
It is based on TEA1610.
In my particular case however the main switching power unit was OK.

The display is powered with 15V which are regulated by a LM317 chip.
On my unit this chip was overheating probably.
I have replaced it and have put bigger heatsink.
Now my SSA is up and running.

In case someone has an issue with SSA3021X power supply unit I may give him a hint.
At least next few months before I forget everything

[tautech]

Thanks Tautech for the document.
I was not able to find the specification of the power supply module outputs however.

Yes, sorry it is not good Siglent provide a Service manual with out that very basic information. 
I will attempt to have this changed.

BTW I have spent some time on the power supply module.
It is based on TEA1610.
In my particular case however the main switching power unit was OK.

The display is powered with 15V which are regulated by a LM317 chip.
On my unit this chip was overheating probably.
I have replaced it and have put bigger heatsink.
Now my SSA is up and running.

 

In case someone has an issue with SSA3021X power supply unit I may give him a hint.
At least next few months before I forget everything

Please for the benefit of others document your repair here.

On which PCB was the display power LM317 ?
On the digital PCB ?

[tautech]

With a few minutes to have a look at currently available documentation this PSU PCB is behind the display.
Is this the one you repaired ?

[dpenev]

No I am talking about the main Power supply module. It is separate module ~10cmx10cm in a metal shield.
It is located at the rear side of the SSA3021X.
It provides voltages as I have documented in my previous messages.
6.5V Seems for the Analog circuitry. It is optimized for efficiency and I guess most of the power is drawn from it.
My problem was with the 15V, ~300ma. It was problematic as I have measured with the scope see previous messages.
During the disturbed 15V I saw my display flickering so I assume this 15V is for the display.
This 15V is regulated with LM317 on this main power supply unit.
I have fixed it by replacing the chip and put bigger heatsink.
Unfortunately I don't have pictures.         

[tautech]

Some info from Siglent.....SSA3000X shares the same PSU as some of their scopes.

[807]

The PSU board is the first board Dave looks at in his teardown video @2:35...

[dpenev]

My saga with the SSA3021X unfortunately continue.
It has been working for a while with the replaced LM317 chip but the issues starts again.
Now the analyzer is working about 10 min and then the display goes off (black).
I have not opened the analyzer but I am pretty sure it is again this LM317 chip for the 15V.
After replacing the previous one I have also glued two times bigger heatsink still it seems the chip overheat.
I remember the consumption from 15V was about 0.6A.
Anyone knowing how much consumption from 15V should be?

I don't remember clearly what was the input voltage of the LM317 but I do remember it was bigger than I would expect.
Probably that's why this chip overloads.
I will have to open the instrument again
   

[dpenev]

Before the LM317 there is an series resistor 2.2ohm.
The consumption from  15V rail on my instrument is 0.31A and the drop across the LM317 is 6.6V.
This makes 2W. As per the datasheet we have 60degC/W for the SOT-223, so we will be 120degC above the ambient.
We have heatsink which improves the situation but still I think 2W are a lot.
Probably the display has increased his consumption from 15V or the input voltage of the LM317 is increased

For now as it is simpler I am changing the input serial resistor from 2.2Ohm to 10Ohm and this way dissipate some energy off the LM317.
I have noticed also that the high voltage switching transistors are heating a lot as well. 

Strange I am having those issues.
Anyone share his thoughts ?
       

[seronday]

I measured the load current on the +15volt supply at 260mA on an operational SSA3021X.

The power supply in this SSA3021X uses an 7815 three terminal regulator for the +15V with an input of 17.5 Volts.
There is no heatsink on the 7815.

Attached is picture of power supply board.

Regards.

[807]

Looks like there's been a revision on the PSU board. The one in the teardown video doesn't have the upright, large component next to the connector (is that the 7815?).

Also, the mains input chokes have changed.

[807]

...This power unit produces:
+6.5V - (in my case slightly bigger 7.5V)
-9.5V
POW-SIG - 50Hz about 5Vpp. Probably used for AC sync.  Please see the measurement
+15V - this one in my case seems to be problematic. It is usually 15V but after some time it starts pulsing. See the measurement...

Just looking back at your earlier post, I notice that the +6.5v is out of specification according to the spec sheet posted by tautech. Your voltage is around 15% high instead of around 5%.

[Emo]

Hi, are you able to test this device in  110/120V The issue has been seen by another member on this board and might be related to the supply being wide input type, that switches ranges. The high line and the excessive heat points towards this supply not being able to switch and tries to regulate 230V in the 120V range.
Eric

[dpenev]

Just looking back at your earlier post, I notice that the +6.5v is out of specification according to the spec sheet posted by tautech. Your voltage is around 15% high instead of around 5%.

Indeed 807, my 6.5V is out of spec.

BTW my power module is same version as yours.
Please see the attached picture.
The original heatsink on the LM317 is white as on your device. I have replaced it with bigger blue one.
On my module I have also removed the 2.2 Ohm resistor beside the LM317 and soldered 10 Ohm for testing on the back   

Thanks seronday, I have 0.31A from +15V, probably they have optimized this a bit in newer versions. My analyzer is about 5 years old.   

Hi, are you able to test this device in  110/120V The issue has been seen by another member on this board and might be related to the supply being wide input type, that switches ranges. The high line and the excessive heat points towards this supply not being able to switch and tries to regulate 230V in the 120V range.
Eric

ssa3021x is specified to work with 230Vrms and it was working fine 5 years.   

Guys do you have the heatsink of the main transistors heating a lot?
In my case it gets to 80, 90 degC even with the fan working.
Please don't touch when connected to mains !!! as the heatsink is electrically connected to high voltage !!!

[seronday]

The power supply volts on the unit that I looked at were +6.5V, -9.5V, +14.8V.
Input volts to the 15V regulator is 17.5V
Input volts to the -9.5V regulator is 13.4V
Mains voltage is 240VAC.

The SSA is re-assembled again now.
If I have an opportunity to open it up again, I can try to measure some P/S temperatures for you.

This SSA3021X was obtained in Jan 2017.

Regards.

[dpenev]

Thanks seronday,

My power unit seems off the spec.

Someone preferably in Europe having such a power unit for sale?

[Emo]

ssa3021x is specified to work with 230Vrms and it was working fine 5 years.

Hi, the unit is indeed suppoost to work. Hoever it doesn’t, so something is not OK. As another member in the past also had a faulty automatic range switching, this was ment to drill down into the issue

Eric

[807]

...BTW my power module is same version as yours.
Please see the attached picture.
The original heatsink on the LM317 is white as on your device. I have replaced it with bigger blue one.
On my module I have also removed the 2.2 Ohm resistor beside the LM317 and soldered 10 Ohm for testing on the back...

The photos I posted were from the teardown video that Dave posted on youtube.

I have the Plus version of this analyzer. I suspect it uses the same PSU, but I've only had it a couple of months, so don't want to open it up.

The fact that your +6.5v is too high, as well as the trouble with the 15v supply, suggests a problem earlier on in the chain. What regulates the +6.5v rail?

[dpenev]

The fact that your +6.5v is too high, as well as the trouble with the 15v supply, suggests a problem earlier on in the chain. What regulates the +6.5v rail?

The whole power module is TEA1610 based. Schematics is very close to the schematics from the datasheet.
Siglent used ideal diodes after the switching transformer for the 6.5V to save some power.

I have checked further.
The regulation feedback is implemented with TL431C shunt regulator. See the attached picture.
The reference of the TL431C is 2.5V.
The resistive divider is calculated for 2.5V and 6.5V at the output.
Strangely enough I measure 2.5V at the reference but my 6.5V is more than 8V without load.
My only explanation is that TL431C draw lot of current from its reference pin.(much more than specified 4uA)
Or there is something on the PCB which I don't see now.

Tomorrow I will replace the  TL431C as this is the simplest  I can do.
     

[dpenev]

Ok some more to update, I got few hours to play with my power supply. 
Replace of TL431C didn't help.
Then I figured out that the TL431C reference pin can draw big current if the cathode is below the 2.5V
This pointed me to the optocoupler PC817. Its LED is driven by the TL431C with 18mA which I thought is a lot.
I have replaced the optocoupler with similar one.

Now I have my voltages as they are specified 6.5V, 15V etc however I have 150Hz- 350Hz switching noise superimposed to my voltage rails.
Bellow measurements of the 6.5V rail (AC mode on scope) with no load and with 10 Ohm load.

Things are getting difficult again