Sansui AU-6600 repair - F-2092a board mod?

[quadmatrix82]

Hi Sansui experts, I’m restoring a Sansui AU-6600 and noticed the power supply eq board F-2092a has this damage on the trace side - do you think this is a factory change to the board or someone has done this in an attempt to mod or repair previously?

 

[Sansuiman]

Looks to be an intentional factory mod. Not the cleanest one I've seen, but have worked on Sansui gear where a trace was cut and grooved out to break continuity at some point in a circuit. This could be due to a mis-manufactured circuit board, or a running change that altered part of the circuit creating a need to break that trace.

 

[quadmatrix82]

Looks to be an intentional factory mod. Not the cleanest one I've seen, but have worked on Sansui gear where a trace was cut and grooved out to break continuity at some point in a circuit. This could be due to an mis-manufactured circuit board, or a running change that altered part of the circuit creating a need to break that trace.

Think you’re right I’ll assume factory for now and carry on!! Cheers

 

[bolero]

I have one to restore: will compare once I get it open

 

[quadmatrix82]

Confirming works well so must be a factory change

 

[bolero]

Mine is labelled F2092-1 as well

Is that up by the phono inputs? I see it actually has phono 1 & 2 inputs, even though the AU-6600 only has a phono 1 switch option.

It's ( almost? ) the same board used in the AU-7700, which does have phono 1 & 2 options.

So maybe they cut one of the phono input traces to kill noise or something.

Ps did you keep the main filter caps at 6800 uF? Or go bigger?

 

[bolero]

Weird: it looks like the trace running from the R tuner input?

Which in the SM shows a gap there & also by the RCA jack. I thought it was a misprint. Do you get L&R sound from your tuner inputs?

 

[quadmatrix82]

Mine is labelled F2092-1 as well

Is that up by the phono inputs? I see it actually has phono 1 & 2 inputs, even though the AU-6600 only has a phono 1 switch option.

It's ( almost? ) the same board used in the AU-7700, which does have phono 1 & 2 options.

So maybe they cut one of the phono input traces to kill noise or something.

Ps did you keep the main filter caps at 6800 uF? Or go bigger?

Hi there yea it’s close to the phono inputs, you are right this model only has one phono input.

I kept the power supply capacitors stock with new 6800uf Nichicon gold tune capacitors, nice solder lug connection makes it easy to remount and dimensions were perfect without having to change clamps bit higher than original but enough room none the less

 

[quadmatrix82]

I

Weird: it looks like the trace running from the R tuner input?

Which in the SM shows a gap there & also by the RCA jack. I thought it was a misprint. Do you get L&R sound from your tuner inputs?

I’ll try later but works perfect on aux

 

[quadmatrix82]

Tuner works great

 

[bolero]

Ah, thanks!

I'm still working out how to get the boards apart

But I think I see a shielded blue cable soldered in there, on the other side. And my trace is cut too. Maybe the circuitboard trace was acting like an antenna?

It looks like the board with the outputs slides right out, attached to the heatsink? Otherwise it looks complicated to get in there

 

[quadmatrix82]

Which board do you want to remove? The output main board? There’s two gold screws component side and then remove the screws on the rear heatsink side and back and then remove the wiring plugs and it will come out

 

[bolero]

Perfect, thanks!

Yes just need access to front & back of those boards, to recap

 

[quadmatrix82]

cool goodluck with it, make sure to replace all the 2sa726 and 2sc1313 in this amp - very unreliable, you can use KSA992 and KSC1845 respectively.

 

[bolero]

Thanks! Yep got a bunch of those too

 

[bolero]

man, I'm tempted to use a pair of 12,000 uF caps instead. The Nichicon 6,800 uF 63v caps I bought are tiny in comparison to the stock 6,800 uF 50v caps in there.

The 12,000 uF will fit right in those brackets. Otherwise I'll have to shim with something.

Confirmed there is a blue shielded wire installed instead of the PCB trace ( which is cut at both ends ) for the Tuner RCA Right channel input.

 

[bolero]

Just a note about board F-2092 again:

C01, C02 are .47uF orange electrolytics labelled "BRN" on the schematic, with a .01uF mylar bypass cap across them. There's no translation of "BRN" on the schematic, but I found this:

https://audiokarma.org/forums/index.php?threads/real-meaning-of-brn-in-caps.475010/

Below Rated Noise?

The orange caps have a weird symbol on them and "LR" whatever that means.

 

[quadmatrix82]

Just a note about board F-2092 again:

C01, C02 are .47uF orange electrolytics labelled "BRN" on the schematic, with a .01uF mylar bypass cap across them. There's no translation of "BRN" on the schematic, but I found this:

https://audiokarma.org/forums/index.php?threads/real-meaning-of-brn-in-caps.475010/

Below Rated Noise?

The orange caps have a weird symbol on them and "LR" whatever that means.

These are a low leakage capacitor you should use a low leakage capacitor such as Nichicon kl series to replace it I used a wima film for the 0.01uf

I personally wouldn’t upgrade the power supply that much too much strain on the power switch and transformer you can get a perfect fit 6800uf from parts connection

 

[bolero]

Thanks!

Mystery resolved: I'll get some in my next parts order

I did end up using the small 6800 uF caps: I'll wrap some weatherstripping around them or something, to hold them in the brackets. There's only 1 firm solder connection underneath, so otherwise they'll flop a bit if the amp is flipped sideways/upside down.

 

[bolero]

cool goodluck with it, make sure to replace all the 2sa726 and 2sc1313 in this amp - very unreliable, you can use KSA992 and KSC1845 respectively.

Question: is it a good idea to measure the new KSA992 & KSC1845 replacements, to gain match them between L/R channels?

There are a lot of them in there!