My beautiful SX-1980

Tuesday, September 19, 2017

Pioneer SA-9500 power amp board repair with a twist!

The SX-1250 gold tier restoration is going to be posted here very soon, I have to finish processing the photos. In the meantime, I thought I would showcase this "straight forward" repair that turned out to have a few surprises. 

This SA-9500 came in to my shop needed the right channel rebuilt, it suffered a nasty failure that left 3 of the 4 outputs and both driver transistors shorted out as well as a few burnt resistors and a bad emitter resistor. 

Board before, note the burnt covers on the 150 ohm resistors.

New parts! I managed to find NOS drivers and outputs, for the resistors I used Vishay/Dale resistors and Bourns trim pots, 25 turn for the offset for easier offset adjustment and single turn for the bias.

All done! Replaced all the emitter resistors as well as the base resistors. I also replaced the 2SA726 differential input transistors with a 1% beta matched set of Fairchild KSA992 transistors.

All the old parts. The 150 ohm resistors got toasty!

The bias trimpot actually melted a little from the current overload and is burnt internally.

Got everything replaced, I also replaced the trimpots and the 2SA726 differential input pair in the left channel as they were flaky. Hooked it up to the DBT and fired her up, success!.....orrrr so I thought.

A loud hum greeted me through both channels when I hooked up speakers. Drat. A hum through both channels generally indicates a ground problem or a bad power supply, so I first looked at the input/phono amp board and checked the ground traces. Aha! A ground trace had completely lifted and appears to have had a current overload, as it was falling apart and appeared slightly burnt. I scrape away the old trace so it doesn't cause problems and solder a wire in place of it. Check the rest of the ground traces and ground points, they all look good. Fire it back up, hum is lower in volume but still there. Okay, that means it must be the power supply then. I first check the 470uF smoothing caps for the +60V and -60V regulated supplies. First one I check:

Yeahhhhhh, I think we may have found the problem. That's measuring 8.39nF, it should measure around 470uF, and the ESR is off the charts.

I replace both 470uF caps and just to make sure, I check the other caps.

Supposed to be a 47uF cap, it measures 966pF. 😲

Supposed to be a 100uF cap, measures 18.579uF. ESR for both is off the charts as well.

That is just a sample of what I found, in all only 2 caps still measured even remotely close to their original specs. Time for a power supply rebuild!

Power supply before, note I have replaced the 470uF caps already.

And after! I went ahead and replaced all the diodes and transistors as well, upgrading three of them to TO-126 case transistors and two (the positive and negative feedback transistors) to a TO-92L case transistors for better heat dissipation and longer life. The two current source diodes were replaced along with the bridge rectifier diodes.

All the old parts from the power supply.

Fired it up again and success! Dead quiet in both channels. Adjusted the +48V and -48V rails to exactly 48V via the PS trimpots and reset the bias and offset again to spec and we have a fixed SA-9500 and a very happy owner!

If you liked what you see, be sure to hit that +1 button down below. Comments and critiques are always welcome!

Friday, August 11, 2017

Lots of exciting things upcoming!

I have some cool and exciting stuff I will be posting soon, first will be a SX-1250 super restore, where I go above and beyond the normal restore and replace a lot more caps and go into more detail on what is done. I also have a Pioneer SPEC-2 restoration coming up. I'm also going to begin posting some of the stuff that comes in for repair only, gear like a Fisher RS-1080, McIntosh MC7270, Sansui 9090DB and more! For those who want to inquire about my services, both repair and restoration, I have added a business phone number to my profile.

Friday, March 3, 2017

Man, it's been awhile!

Hey everyone! Man, it's been awhile, I almost had forgotten about this blog. I'm still alive and kicking, I got a new shop location this past year and have been very busy with it. I plan on updating this blog again here soon, I've had a bunch of stuff I've gotten over the past 2 years, some of it very nice high end vintage. Stay tuned!

Friday, February 28, 2014

Pioneer SX-5590 recap and restore (beauty shots added!)

I recently got in a Pioneer SX-5590 to recap and restore, the thing is in excellent condition overall, case, top grill and faceplate are almost immaculate. I'm using the Panasonic FM and FC series for the audio path caps, Nichicon KL series for the orange low leakage caps, Nichicon PW series for the power supply, stabilizer and protection boards, Nichicon VX series for the axial caps and Panasonic ECQ poly films for caps under 1uF. The owner asked me to go through it and give it the works, so here are the results!

Before photos:

Receiver on the bench:

EQ amp:

Flat amp:

Tone amp. This one had a broken pot for the 10KHz adjustment, so I'll be replacing that.

New pot installed, old pot out:

Filter amp:

Power supply:

Left power amp:

I did not get a pic of the right power amp. I thought I had it, but when I reviewed the photos, I found that it was nowhere to be found! Oops. It is however very similar to the left power amp.

Protection board:

There was a tech in here before me and replaced several things on the stabilizer board along with one on this board. It is C6, a 100uF 50v cap and they replaced it with a 68uF 100v cap. Huh? The stabilizer board is even more interesting.

Stabilizer board. This board is by far the worst off, a lot of heat stress and the previous tech did a mash-up of weird cap brands when they replaced the original caps, which, judging from the rest of the components and the board, likely had bad heat stress and dried out. They also replaced a few transistors and one diode with questionable replacements.

Weird cap brands, I've never heard of these except for the green Samsung caps.

The back of the board shows a lot of heat stress to the solder joints as well, several cracked joints along with the previous tech's work being a little sloppy, they didn't clean the flux off and the joints look cold.

And now for the after photos!

EQ amp, 12 caps and 14 transistors were replaced. Four transistors near the big red poly caps, the two on each side in a horizontal configuration are differential pairs and were gain matched. This isn't a critical step and won't mess up the amp if you don't do it, but it does help with the balance and overall sound in my experience.

Flat amp, 12 caps and 6 transistors were replaced.

Tone amp, 26 caps and 4 transistors were replaced along with the 10KHz adjustment pot.

Filter amp, 4 caps and 2 transistors were replaced.

Power supply, 4 caps were replaced and all the fuses were checked for proper rating and condition.

Left power amp, 5 caps and 3 transistors were replaced on this board, the differential pair and the overcurrent sensor, Q11. Also replaced were the 2 trim pots, the solder joints were touched up and the pins for the outputs at the top of the board and the pins at the bottom were cleaned. The differential pair were gain matched, but again, not a critical step and it won't blow up the amp if you don't do this. Gain matching simply helps the offset adjustment balance better

Right power amp, same thing as the left amp.

Protection board, 6 caps and 3 transistors were replaced along with the relay, the 3 transistors were all upgraded with bigger case styles to help with heat dissipation and longevity. Also touched up the solder joints and cleaned the pins.

Stabilizer board, it looks sooo much better now. 16 caps, 13 transistors, 6 diodes and 2 trim pots were replaced. Several of the transistors also were upgraded with bigger cases for better heat dissipation. New micas and thermal paste was applied for the regulator transistors on the heatsinks, the pins were cleaned and pretty much all the solder joints were cleaned of the old solder and re-soldered.

With the de-soldering and soldering comes a lot of flux, a lot of boards I've come across that were previously worked on do not have this removed. It leads to a cruddy looking board and in the case of a preamp board, can vastly increase the noise floor and crosstalk depending on the type of flux. I always try to clean up all the boards, the results are something like this: (note: this board is a worst case scenario, most don't have quite this much flux on them)

After the cleaning and re-soldering:

I also replaced the filter caps, originals are Nichicon 22000uF 80v, the new ones are NCC 24000uF 100v

Left channel:

Right channel:

Old filter caps:

New vs old:

New filter caps in the clamp:

And after!

Cleaned up the chassis a little as well, here's a few samples:

Before of the left side:

Before of the right side:

And after!

Left side:

Right side

Everything is almost back together!

Top shot:

I replaced all the lamps with LED's. Take a look!

New LED dial lamp vs old incandescent:

New indicator lamps, LED is on the left, incandescent is on the right. The LED looks almost identical to the incandescent as far as color, but is a lot brighter without being too bright. In person it looks perfect.

Before and after of the dial lamps, the difference is quite startling with the camera, in person the difference is not as big, though the color difference is very real. Note: I had already replaced the indicator lamps with LED's, so that's why they look the same in both shots.


And after with the new LED's:

A total of 156 components along with 13 lamps were replaced. Powered up on the DBT (Dim-Bulb Tester) and checked the bias and offset, bias set perfectly and the offset was within 2mV of zero without adjustment (that's what gain matching does). Turned the bias back down, took it off the DBT and went to full line power. Checked and set the stabilizer voltages, then set the bias and checked the offset, it was still within 2mV of zero. Hooked it up to my Polk SDA-1C's and gave it a trial run. Here is the result:


This thing sounds fabulous! Very clean and balanced sound, amazing soundstage, tight, very well focused and transparency that just makes you sit down and listen with utter pleasure to your music. I could listen to this amp all day through these speakers. It's the same as a 1250, so what you hear with this receiver is pretty much what all 1250's and 5590's sound like once restored. I could never recommend this amp enough, with the right speakers, it is magical.

I'll have some beauty shots coming soon, so stay tuned!

03/02/14: Beauty shots!

And that wraps up this restore! Feel free to leave me comments, questions or criticisms, and if you like this restore post be sure to click that +1 button!