singxer Sa-1 Help, XLR input does not work anymore

[teruster]

A weird problem with my Singxer SA-1... XLR not working all of a sudden...

Hello, I hope this is the right section for seeking help.
I have been using my Singxer Sa-1 this with my SMSL D1SE DAC for over an year now without any issues until yesterday When I disconnected both in the morning as I needed to change the room setup a bit.Took about 45 minutes then I plugged both back on and found out there was no sound coming from the headphones! I hooked up RCA out with Singxer's RCA Inputs and it worked flawlessly. Weirdly though the front switch on the amp doesnt seem to work anymore, as in when iam playing via RCA it doesnt matter if i flick the switch to XLR it keeps playing. I switched to XLR OUT ONLY on my DAC and suddenly it stops playing - switch back to RCA OUT on dac and it starts playing again so its definitely the amp and its XLR input. Could it be the front switch got faulty somehow? it doesnt seem to go in "XLR" input mode somehow. Or did I somehow broke the XLR inputs? Cant do a warranty on this as I bought it when I was in another country, i need to fix this, Any advice on how to troubleshoot this please?

 

[Extreme_Boky]

If you can take to top cover off, take and post high res, in focus, well-lit photos of the ICs I circled in red, and in particular of those 2 ICs I double circled...

 

[teruster]

Hey Boky,
Thank you so much for responding! Attaching the pics as requested...

 

[Extreme_Boky]

The photos you sent are still not showing the part number of that single-in-line IC... is it a uPC1237HA by any chance?

Anyway, what I did see from your photo is a couple of quadruple CMOS AND gates ICs and a HEX inverter IC (6 HEX inverters encapsulated in a single IC). I think that these ICs (and the switch labelled as INPUT) are used to switch between RCA <-> XLR inputs. What I expect to be the root cause of your problem is a static discharge when you unplugged/plugged the cables into that amp... but I might be wrong.

What can you do to fix the problem...

First, just confirm that the above is indeed the case; that you indeed do have a problem Do the following:

Unplug everything from the amp and place it on a bench/desk. Power it up. Plug the headphones and set the volume pot to around 10 o'clock. Start with the right INPUT XLR socket first. Touch the INPUT XLR socket pins with your finger, one pin at a time. Pins 2 and 3 are input pins; pin 1 is ground. So, touch pin 2 (or 3) and see if you are getting the amplified 50 (60 in States) Hz buzz through your headphones WHILE THE INPUT switch is selected to RCA input. If you are... there's a problem.

You should get the fault-finding gist from the above paragraph... Test both channels (both RCA inputs and both XLR inputs) while paying attention to what the input switch is set to.

If the input switch is set to RCA input, then you should hear the amplified 50Hz buzz only when you touch the RCA middle pin.
If the input switch is set to XLR, then you should get the amplified 50Hz buzz only when you touch pin 2 or 3 on the XLRs.

If the input switch is not working as intended... then those CMOS ICs are most likely faulty. They are SMD... I do not believe you have the equipment and know-how to replace them yourself... so, just send the whole amp back to the manufacturer for repair.

Good luck.

 

[teruster]

wow thank you so much for the detailed info which I would have never known on my own! Iam sorry which single-in-line-IC you are referring to? The one which you double-circled?



Ok so from what I understand, This is what i need to do:

1- I need to disconnect everything, all the cables from the amp, its already on a desk. Do you mean to take the entire pcb out or just the top lid?

2- I plug in my headphones first , Then connect the power cable and turn it on.

3- Dial the volume knob to 10'O Clock.

4- Now this is where I am confused, how am i supposed to touch the XLR input pins with my finger? They are female , should i just touch those holes or what? Kindly clarify this.

Oh I remember doing one thing though, before plugging the amp (when i changed my room setup), i unscrewed the 4 feet below and then put the screw back in without the feet- just wanted to see if it could fit in this new rack i bought, turns out it didnt- but I did power it on at that time briefly and then powered it off to take out the screws and put the feet back in. Do you think those screws somehow could have done something when they were put back in without the round feet?

 

[Extreme_Boky]

wow thank you so much for the detailed info which I would have never known on my own! Iam sorry which single-in-line-IC you are referring to? The one which you double-circled?



Ok so from what I understand, This is what i need to do:

1- I need to disconnect everything, all the cables from the amp, its already on a desk. Do you mean to take the entire pcb out or just the top lid?

If the amp is on the desk, then you are good to go. No need to do anything else

2- I plug in my headphones first , Then connect the power cable and turn it on.

Yes

3- Dial the volume knob to 10'O Clock.

Yes

4- Now this is where I am confused, how am i supposed to touch the XLR input pins with my finger? They are female , should i just touch those holes or what? Kindly clarify this.

Use a paper clip or something similar.

Oh I remember doing one thing though, before plugging the amp (when i changed my room setup), i unscrewed the 4 feet below and then put the screw back in without the feet- just wanted to see if it could fit in this new rack i bought, turns out it didnt- but I did power it on at that time briefly and then powered it off to take out the screws and put the feet back in. Do you think those screws somehow could have done something when they were put back in without the round feet?

You have most likely revealed the root cause right here..... With no feet, the crews are now touching the PCB and shorting the PCB tracks to the metal case (which sits at the ground potential). Put the rubber feet back and hope that everything will be good again....

Good luck.

 

[teruster]

If the amp is on the desk, then you are good to go. No need to do anything else

Yes

Yes

Use a paper clip or something similar.

You have most likely revealed the root cause right here..... With no feet, the crews are now touching the PCB and shorting the PCB tracks to the metal case (which sits at the ground potential). Put the rubber feet back and hope that everything will be good again....

Good luck.

Here I am attaching the files again, hope you see the correct part number now, if not then let me know which exact IC part you were referring to.

I just got done with the testing and it seems there is no static/buzz anything heard from XLR inputs no matter which INPUT SELECTOR I use, complete silence.

RCA input pins however give the buzz on both XLR/RCA INPUT SWITCH SELECTOR.

 

[raif71]

Just asking the OP, did you do any DC Offset Mod on the SA-1 ?

 

[Extreme_Boky]

Here I am attaching the files again, hope you see the correct part number now, if not then let me know which exact IC part you were referring to.

I just got done with the testing and it seems there is no static/buzz anything heard from XLR inputs no matter which INPUT SELECTOR I use, complete silence.

RCA input pins however give the buzz on both XLR/RCA INPUT SWITCH SELECTOR.

Ok, the photos confirm what I expected to see, the uPC1237HA which is a protection IC (short circuit as well as large output offset), and delay/thump ON/OFF protection. Nice IC... has been around for more than 3 decades and I personally used it a lot....

You have not confirmed that you re-installed the rubber feet.... did you see my previous post??

You have most likely revealed the root cause right here..... With no feet, the crews are now touching the PCB and shorting the PCB tracks to the metal case (which sits at the ground potential). Put the rubber feet back and hope that everything will be good again....

Good luck.

 

[teruster]

yes rubber feet were installed after I removed them previously, they always had been ON since then...

 

[teruster]

Just asking the OP, did you do any DC Offset Mod on the SA-1 ?

yes I did, I put in the jumpers from DAY 1.

 

[Extreme_Boky]

Ok, so the last thing to do is to make absolutely sure that you can not hear any buzz through XLR inputs.... If this is the case, then you have fried something inside because you removed the rubber feet... and the crew(s) touched and possibly damaged, or shorted two adjacent PCB tracks

The bypass of the sound-coupling caps (DC Offset Mod) is okay... I do not think that caused the problem you are facing now. However, this modification turns that amp into a DC-coupled amplifier...any DC present at the inputs will be amplified.... the uPC1237HA will handle it (well, it should...) but I really need to see the schematic diagram to comment with 100% certainty. Have you also played with different sources... have you possibly plugged something (source) that could have a DC offset at its output?

 

[teruster]

nope, I always used the same XLR cables with my D1SE DAC from DAY 1, this is the first time I am using RCA cables...

Oh well, guess i'll have to remove the PCB then and see from the bottom side if something is fried..

 

[Extreme_Boky]

Yes.. I was going to suggest that. Look for damaged tracks... good luck.

EDIT: If it is not too much to ask, once you have removed the PCB, please take well-lit in-focus photos of the PCB underside tracks.... I was going to buy one of these.... and then modify it to bypass all input selection circuitry - pretty much have the XLRs permanently connected to those 4 amplifier channels via the shortest possible path (that means bypassing the volume pot as well).... I reckon this little amp could sound like a million bucks with these mods.... not to mention if fed by 2 liner (external) power supplies.

 

[teruster]

yup, those 4 screw marks are there on the bottom :/ What should I do? I have a guy who does PCB stuff and soldering etc, but I need to tell him exactly what to fix...

I uploaded Hi-res images and a video of the PCB as you requested @Extreme_Boky , you can download the RAR file here... https://drive.google.com/file/d/1ic4cCystT7O9AGsulx33z9vCYdlExH96/view?usp=sharing

 

[Extreme_Boky]

That RAR archive is corrupt, I can not extract it... it extracts to 49% and then freezes.... try using 7zip...

I think you'll be okay... just fix the broken tracks here:

I need to see better photos because I can not tell if there are any VIAs that might be broken here... but I think you're good:

So... just fix the first photo tracks and see if it works..

 

[Extreme_Boky]

Actually, don't worry about posting another .rar file.... the below photo is very good and perfectly usable, thanks.

By the way... YES, I can tell that all you need to do is to restore those 3 tracks and you should be good to go. Good luck.

 

[raif71]

That RAR archive is corrupt, I can not extract it... it extracts to 49% and then freezes.... try using 7zip...

I think you'll be okay... just fix the broken tracks here:

View attachment 282952


I need to see better photos because I can not tell if there are any VIAs that might be broken here... but I think you're good:

View attachment 282953

View attachment 282955

So... just fix the first photo tracks and see if it works..

so what could be the reason the circle appeared on the 3 tracks? manufacturing defect? some sort of weird "crop" circles ?

 

[Graham849]

OP wrote: “Oh I remember doing one thing though, before plugging the amp (when i changed my room setup), i unscrewed the 4 feet below and then put the screw back in without the feet- just wanted to see if it could fit in this new rack i bought, turns out it didnt- but I did power it on at that time briefly and then powered it off to take out the screws and put the feet back in. Do you think those screws somehow could have done something when they were put back in without the round feet?“

 

[raif71]

OP wrote: “Oh I remember doing one thing though, before plugging the amp (when i changed my room setup), i unscrewed the 4 feet below and then put the screw back in without the feet- just wanted to see if it could fit in this new rack i bought, turns out it didnt- but I did power it on at that time briefly and then powered it off to take out the screws and put the feet back in. Do you think those screws somehow could have done something when they were put back in without the round feet?“

Meaning, the pcb board was screwed?