My first QS-500 project

[matjo]

This week I started on a really beaten-up Sansui QS-500. I bought it without the wood case, and covered in dust. Since I had no idea in what "electrical" state it was, I hooked it up on my Variac and Dim Bulb Current Limiter. And YES, it was still working, sound came out the speakers I connected. So, I decided to do a full recap of capacitors and transistors.

It took me 2 nights of research which transistors are the right replacements; there are a few used that I've never seen before (for example: the 2SC959-2SA606 pair). Fortunately Mouser could deliver 99% of my needs. And they delivered quick! Within 4 days to The Netherlands.

The QS-500 has 3 prints that are easy removable (like the 555a I've been working on already many times).

I'm not finished yet; some capacitors need to be replaced on the backside of the unit, but I am so excited about this project, I wanted to share the results so far.

A big thank you for Audiokarma and the posts by Overundr1 and Leestereo (who else) for their contributions; I took a lot of info from these posts.

 

[matjo]

Already a few months ago I made e new wood case for this baby.

 

[matjo]

The unit was covered in dust due to the lack of a proper cover.

 

[matjo]

After receiving the needed parts; I started working on the easy prints; the F-1388 (Synthesizer); the F-1357 (oscillator) and the F1180 (driver)

The F-1388 before:

and after:

I've replaced the 1uF's with film types; the XA495BL transistors with ZTX694B's and 2SC1000's with KSC1845's.

 

[matjo]

the F-1357 (oscillator)

Here I only had to change 3 capacitors; and of course a little bit of cleaning on the backside.

 

[matjo]

The driver F-1180 was a bit more work; I've also placed the suggested Baxandall diode mod as recommended by LeeStereo.
I've decided to let the 2SC959-2SA606 pair in place; although the oxidation is severe; the 2SC281 that is connected to the 2SC959 with a copper plate has a metal cover; I was not sure what the effect would be if I would replace this transistor with a SC1815 for example; perhaps someone can give me a good suggestion?

The 2SC458LG has been replaced by KSC1845's; the 2SC627's were replaced by MJE1532G

I also had difficulties finding the right multi-turns. Either the pins did not align with the holes on the board, or the size was incorrect or the adjustment-screw was located at the wrong position. Anybody with a good suggestion is welcome!

 

[KeithD]

I have a QR-6500, which uses the F-1180C driver board, so not sure if it is equivalent. The trimmers I used for replacements on the two driver boards are:

 

[matjo]

I have a QR-6500, which uses the F-1180C driver board, so not sure if it is equivalent. The trimmers I used for replacements on the two driver boards are:

View attachment 2896031

Thank you KeithD for your input! Much appreciated! I was also looking at the same trimmers; I thought by looking at the way they are shaped that it would not fit on the board. But if you managed to do it; I will not hesitate to order some.

 

[KeithD]

I detailed my refurb of the QR-6500 in this thread. Description of what I did on the driver board with pictures are in posts 19 and 20 of that thread. Enjoy!

 

[Sansuiman]

Well done. The new case looks especially nice, properly designed and built. I am curious though at the lack of venting in the top. these have a rear channel power amp, and the factory cases had slots routed in them to allow heat to escape.

 

[matjo]

Well done. The new case looks especially nice, properly designed and built. I am curious though at the lack of venting in the top. these have a rear channel power amp, and the factory cases had slots routed in them to allow heat to escape.

Thank you for the compliment! I must say, with building the case I had help of colleagues on board of the ship I work; the veneer I did myself. Still work in progress; I still have to make the ventilation; looking into the best way to do it without ruining the case (lack of woodworking equipment is a major problem in my case).

 

[sKiZo]

Now all ya gotta do is figure out how to set the balance on the thing ... luck wit dat, eh! I actually had to RTFM to figure that out.

Nice unit tho ... pre- vario matrix, but I always liked the synth on that better than the newer versions for non-encoded stuff.

** BONUS - My version of "where's Waldo" ... find the QS500! <G>

You want "different" ... currently driving the front channels in holographic matrix using the Carver C4000. Ain't blowed up yet!

PS - just noticed your location. Please to send me a wheel of Leyden ... BEST ... cheese ... ever!!!

 

[matjo]

Now all ya gotta do is figure out how to set the balance on the thing ... luck wit dat, eh! I actually had to RTFM to figure that out.

Nice unit tho ... pre- vario matrix, but I always liked the synth on that better than the newer versions for non-encoded stuff.

** BONUS - My version of "where's Waldo" ... find the QS500! <G>

You want "different" ... currently driving the front channels in holographic matrix using the Carver C4000. Ain't blowed up yet!

PS - just noticed your location. Please to send me a wheel of Leyden ... BEST ... cheese ... ever!!!

You are so right about the Leiden Cheese! It is delicious! I've also read your posts regarding the QS-100 and learned a lot.
I have the NTE129MCP matched PNP-NPN replacement on stock but still confused what exactly to replace; the schematics mention that the SC959 and SA606 is considered a pair; but the locations on the board are NOT the ones connected with a piece of copper (that would be the TR803/TR804 and the TR808/TR809). So I am confused.......

 

[matjo]

and this is the result so far. Audiokarma member ARGOU showed in his QS-100 post that he also managed to replace the MODULES 905/907. Sounds interesting! I will give this a try too....
When I will be back from my next term on board (mid July), I will start cleaning the amp and creating a proper ventilation in the wood case.