Author Topic: Line out distortion  (Read 301 times)

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Offline GregB

Line out distortion
« on: November 21, 2021, 04:31:16 PM »
Hi all,

Yesterday, I noticed my PSR-S950 was distorting the audio on the line outs.  Not at the headphone jack, not at the speakers, just at the line outs on the back of the keyboard.

Booting to the test program and using an RTA on my phone, I was able to verify the distortion, as well as to find that there's a little bit of left/right channel crosstalk too.  A glance at the service manual leads me to believe the NE5532 op amp for the line outs is blown; maybe I zapped it with static electricity (I'm in very dry air at the moment) when I was hooking the cables up?

Just curious if anyone else has encountered this.  From the service manual schematic, there appears to be some basic ESD protection on the line outs.

- Greg
PSR-S950
PSR-520
1920 Bush & Lane Upright Grand
 

Offline GregB

Re: Line out distortion
« Reply #1 on: November 28, 2021, 08:40:37 AM »
Hi all,

After a bit more diagnostic work, I determined that IC5, a NE5532D, on the AJACK board was the likely culprit, so I replaced that IC this evening, which involved some surface-mount soldering work.  That has mostly resolved my problem; at least the audio is clear now and I'm getting 3.6 dBu output instead of -1 dBu on the line outs during the L/R channel test.  Note that the regular NE5532D is hard to get, but the NE5532AD is very common.  The only difference appears to be that the latter has a guaranteed maximum noise level, whereas the former only has a typical level.

One note about the AJACK board...  The schematic shows series chokes on the line outs and AUX in, but none of those three connections actually have them.  They're just plain ol' jumpers on the actual AJACK board.  I'm guessing they were omitted because Yamaha determined they weren't needed for EMI compliance, but this may have limited the ESD resilience of the AJACK board.

I modified my keyboard's AJACK board to add ESD protection (TVS silicon avalanche diodes) to the mic in, aux in, and line outs, and I added MOV protection on the DC 16V in.  The DC in already has reverse polarity and overcurrent protection, which effectively protects the MOV from overcurrent, too.  (note - I make no guarantee of the suitability or reliability of the modifications I made - my mods are rather hackish)

I may still have an issue with the mute circuit as well causing some remaining channel crosstalk, but that's a project for another day. :)  The mute circuit consists of three bipolar transistors.

(attached images: AJACK board with missing chokes L15 through L20; and my modified AJACK board with MOV and TVS protection)

- Greg
PSR-S950
PSR-520
1920 Bush & Lane Upright Grand
 

Offline overover

Re: Line out distortion
« Reply #2 on: November 28, 2021, 08:49:45 AM »
Hi Greg,

Thank you for the detailed report regarding the repair and modification of your S950!


Best regard,
Chris
Everyone always said: "This is not possible!" - Then someone came and ... just did it!
 

Online Toril S

Re: Line out distortion
« Reply #3 on: November 28, 2021, 03:10:21 PM »
I can only say WOW!
Toril S

Genos, Tyros 5, PSR S975, PSR 2100
and PSR-47.
Former keyboards: PSR-S970.

https://www.youtube.com/channel/UCLVwWdb36Yd3LMBjAnm6pTQ?view_as=subscriber



Toril's PSR Performer Page
 

Offline GregB

Re: Line out distortion
« Reply #4 on: November 29, 2021, 01:13:51 AM »
Ok, I've just placed the order for the mute circuit transistors (and some other supplies).  There's still definitely an issue with the outputs, even though they're now operating cleaner and closer to spec (now in-spec for output level, still out of spec for channel crosstalk).  Apparently mute circuit transistors commonly succumb to ESD.

At this point it would have been almost as cheap for me to just order an entire new S950 AJACK board, if it were easily available.  Yamaha 24x7 Parts does not show it in stock, unfortunately, and I didn't find any other US sources that had it.  Sometimes I have to remind myself that my S950 is 7 years old now (I've been eyeing the SX900 as it has some features that'd be useful to me, but we're not ready to make that investment yet).

- Greg
PSR-S950
PSR-520
1920 Bush & Lane Upright Grand
 

Offline overover

Re: Line out distortion
« Reply #5 on: November 29, 2021, 07:54:40 AM »
Ok, I've just placed the order for the mute circuit transistors (and some other supplies).  There's still definitely an issue with the outputs, even though they're now operating cleaner and closer to spec (now in-spec for output level, still out of spec for channel crosstalk).  Apparently mute circuit transistors commonly succumb to ESD.

At this point it would have been almost as cheap for me to just order an entire new S950 AJACK board, if it were easily available.  Yamaha 24x7 Parts does not show it in stock, unfortunately, and I didn't find any other US sources that had it.  Sometimes I have to remind myself that my S950 is 7 years old now (I've been eyeing the SX900 as it has some features that'd be useful to me, but we're not ready to make that investment yet).

- Greg

Hi Greg,

Yes, the S950 AJACK board is relatively inexpensive. At the German company "Audio-Service Schierbecker, Hamburg" (www.audio-service.com) it costs around 27 euros. According to the information on the website, it is available, but they say "delivery time possible". (See also the attached picture.)


Best regards,
Chris
« Last Edit: November 29, 2021, 07:55:44 AM by overover »
Everyone always said: "This is not possible!" - Then someone came and ... just did it!
 

Offline GregB

Re: Line out distortion
« Reply #6 on: November 29, 2021, 04:38:35 PM »
Huh, that's really odd.  The AJACK board, as they picture it, would not fit in the S950, as the board extends well beyond the connectors.  That part of the board would have to be cut or snapped off.

- Greg
PSR-S950
PSR-520
1920 Bush & Lane Upright Grand
 

Offline overover

Re: Line out distortion
« Reply #7 on: November 29, 2021, 05:57:58 PM »
Huh, that's really odd.  The AJACK board, as they picture it, would not fit in the S950, as the board extends well beyond the connectors.  That part of the board would have to be cut or snapped off.

- Greg

Hi Greg,

maybe this is only a "symbolic" picture. As far as I know, this company sells only original Yamaha spare parts.That's why the board should actually fit if it's the right Part No.


Best regards,
Chris
Everyone always said: "This is not possible!" - Then someone came and ... just did it!