Sony SQD-2020 SQ function problem.

[RockaMarka88]

Hello, quaddies.

Recently I’ve been having an issue with my Sony SQD-2020 decoder.

When listening to SQ records, I have the decoder in SQ mode, but after about 10 mins the front left and right channels suddenly cut out, leaving only the rear left and right channels sounding. Strangely, all the other systems on the decoder - 2-4 and R-MTX - work fine; it’s just SQ mode that’s playing up.

I’ve tried unplugging and plugging the RCA connections back in again, but still no joy.

Anyone have any ideas what this could be?

Regards,

Mark

 

[Doug G.]

I don't have a 2020 but I do have a couple of 2050s and the main board has feed-thoughs which connect a part of a circuit on one side of the board to another part of the circuit on the other side of the board. These are notorious for getting intermittant with age and must be resoldered. Both of my 2050s needed the fix which I did myself.

Doug

 

[RockaMarka88]

I don't have a 2020 but I do have a couple of 2050s and the main board has feed-thoughs which connect a part of a circuit on one side of the board to another part of the circuit on the other side of the board. These are notorious for getting intermittant with age and must be resoldered. Both of my 2050s needed the fix which I did myself.

Doug

Hello again, Doug.

Thanks for your quick response.

When you say “feed through”, what exactly do you mean?

 

[elvi]

The 2020 uses "Vias" to connect a circuit trace from the top layer of the Pwb to the bottom Pwb.
These via or paths are set with solder on both sides, and heat causes the board to expand, and the solder joints crack over time.
This is a common failure mode of systems with cross pwb via. ( sansui qrx 8001 and 9001 most famously)

Any competent shop can rework these, but it is time consuming.

My SQD 2020 suffers from this, and it's on the list for a future rework.
I now use a Surround Master.

 

[Doug G.]

I apologize for missing your last post in December.

As elvi indicated, "feed throughs" are connections from one side of a board to the other side. There are fairly large size holes in the board with solder pads around the holes on both sides. A piece of wire or pin is run through each hole and soldered to each side, thus connecting the circuitry on one side to the circuitry on the other side.

Two-sided boards (and even three or four "layered" boards, these days), are used when the circuitry become's complex enough where a one-sided board cannot contain all the circuit paths necessary to connect all components and so, multiple "sides" are used and are connected with these "feed throughs" or, more recently, plated through holes.

Doug

 

[Soundfield]

Two-sided boards (and even three or four "layered" boards, these days,...

In the military electronics field I worked in, twenty layer boards were pretty common even decades ago. No great problem producing fifty+ layer boards today, in fact the only practical limit is the board thickness you are prepared to accept. Not cheap though, and the consequences of making just a single mistake on the design of any one layer are astronomically expensive when you discover them in a mass production run!

 

[Doug G.]

"Can't we just leave that trace go to R136x instead of to R135z?"

"Nope, scrap 'em all."



Doug

 

[elvi]

"Can't we just leave that trace go to R136x instead of to R135z?"

"Nope, scrap 'em all."



Doug

That's what the little spool of blue wire is for ...

 

[DuncanS]

That's what the little spool of blue wire is for ...

One of my designs needed a modification to make it work, so I wrote a 'simple' instruction something like "feed the insulated wire through the large via by X and solder either end to pin 1 of components Y & Z". The modified boards then went to the test department. I got a phone call can you come downstairs your modified boards keep blowing up! I wandered down, looked at the board and noticed the wire had been stripped, fed through the via, then the insulation fitted back (as PTFE really difficult to do!), so made conductive contact with the via which was a supply rail! I went to production and said why are you doing this? to be told why feed it through the via if you didn't want it to make contact, I said thats why the wire is insulated so it won't make contact (there was no other way to get the mod wire to the right point, 18-layer PCB), got blank looks! Made my instructions more 'complicated' from then on.

 

[par4ken]

One of my designs needed a modification to make it work, so I wrote a 'simple' instruction something like "feed the insulated wire through the large via by X and solder either end to pin 1 of components Y & Z". The modified boards then went to the test department. I got a phone call can you come downstairs your modified boards keep blowing up! I wandered down, looked at the board and noticed the via had been stripped, fed through the via, then the insulation fitted back (as PTFE really difficult to do!), so made conductive contact with the via which was a supply rail! I went to production and said why are you doing this? to be told why feed it through the via if you didn't want it to make contact, I said thats why the wire is insulated so it won't make contact (there was no other way to get the mod wire to the right point, 18-layer PCB), got blank looks! Made my instructions more 'complicated' from then on.

I'm amazed when people can't follow very simple instructions. You have to make the instructions complicated so people won't overthink (and screw up) your simple ones!

 

[elvi]

.. just try authoring behavioral specifications..

You have to define everything!!

So, lets get back on track.

I use the following process to correct failing via.
The SQD used a simple solder dot. No copper rivet or wire. The solder cracks when heated.
I suck out the old solder. I take very fine copper braid, and insert through the via. I do have to drill out the via.
Solder one side quickly, and try not to fill the braid with solder.
Flip the pwb, snip the braid and stuff/pack the via with a probe, and solder the 2nd side.
The braid will flex with pwb expansion.

Feel free to pass this rework technique on.