My beautiful SX-1980

Friday, January 12, 2018

Pioneer SX-1280 Gold Tier Restoration


Up today is a customer's SX-1280, AK member suitekids. This receiver is one of his babies and he asked me to give it the best, so here are the results!

This 1280 has been serviced before, the previous tech did a dubious mod to the protection circuit which I'll be showing here a little later. We'll start with the preamp boards.


First up, the flat amp board, a 2 stage DC circuit employing a FET input stage for higher input impedance. It also utilizes NFB for a lower output impedance.


And after. 10 caps and 2 transistors were replaced. Panasonic FM and ECW poly caps were used here. The 4.7uF input caps were replaced with a polypropylene as space allowed it. Transistor replacements are low noise Fairchild equivalents.


Here are some photos showing how much the original input caps have deteriorated.

At 120Hz:


At 1KHz:


Way out of tolerance and high loss as well. A near perfect cap's loss tangent should be around -90°.

Moving on, we have the tone amp board. This is also a 2 stage NFB circuit.


And after. This board has a lot of parts that are replaced, 36 caps and 4 transistors were replaced here. Replacements are Nichicon KL for the orange low noise caps and tantalums, Rifa and Wima polypropylenes for the caps under 1uF and Panasonic FM for everything else. Transistor replacements are low noise Fairchild equivalents.


Next, we have the function board.


And after. Just two caps to replace here, using Panasonic FM and FC here:


Now, we have the filter amp board. A couple caps have been replaced already on here, though they are not the ideal replacements.


And after! 8 caps and 2 transistors were replaced, Nichicon KL for the caps above 1uF and Wima polypropylene for the caps under 1uF. Transistor replacements are low noise Fairchild equivalents.
 

The meter amp board is sometimes overlooked, but it does have a few caps that need replaced.


And after! Nichicon PW caps were used here.

Next, the phono amp. This is the last board on the bottom of the receiver that needs to be done.


And after! 14 caps and 10 transistors were replaced, Panasonic FM used for the blue filters, Nichicon KL for the orange low noise caps and Nichicon ES were used for the 4.7uF output bipolar caps. The mylar films were replaced with Panasonic ECQ and Wima FKP caps.


Moving on to the power amp boards, here is the right power amp board:


An unpleasant surprise greeted me when I flipped the board over, the previous tech destroyed part of a trace leading to the DC-offset adjustment pot when they replaced it, and the jumper they put in is a little remiss. Not hard to repair thankfully.


I bypassed the broken trace completely and soldered some small gauge solid core wire to a solder joint further up the trace. Makes for a much cleaner look.


The 2SA979 dual transistor I replaced with a 1% beta matched pair of KSA992 transistors put face to face and heatshrinked together for better thermal tracking and stability. I've found that the 979 tends to become leaky, causing the offset to jump around a lot and make it hard to dial in, even with a multi-turn pot. The 1uF input cap was also upgraded with a Panasonic polypropylene.
  

And after! 9 caps, 3 transistors and both trim pots were replaced. The molex pins were also cleaned to a nice shiny surface.


The left amp board before:


And after! Same as the right amp board, except this one didn't need any traces repaired!


Big one here, the regulated power supply board. This was already recapped by the previous tech, however the cap replacements used were less than ideal and most of the them were not low impedance. Amazingly the soft start relay was replaced with the proper Omron replacement.


While I was replacing the relay (just so everything is new), I noticed this. That is pin 1, which is the 120V AC in to the soft start circuit. This thing did work when I got it, so it must have been just barely hanging on and me moving the board to get to the back broke it loose.





Much better!



And after! 16 caps, 7 transistors, 7 diodes and the relay were replaced. An extra heatsink was added to Q5 as well. Nichicon PW along with Nichicon TVX caps were used here. Diodes and transistors were all On-Semi/Fairchild, with several transistors getting upgraded to a TO-92L case style for better heat dissipation and longer life.


Up now is the protection board. One of the concerns brought up by suitekids when he sent this to me was the fact that there was no protection delay at all and would thump his speakers pretty hard. Anybody see what's wrong in this photo?


This is a good mod, right? I mean, it allows the relay to engage, so it's obviously a good thing! 😒


And after, looks a lot better! The protection relay was replaced with the proper replacement, but for the sake of everything being new I replaced it again. 6 caps, 2 transistors and the relay were replaced, Nichicon PW was used here and relay driver was upgraded to a TO-126 case style for better heat dissipation and longer life.


And finally, the tuner board.


And after! 26 caps were replaced, Nichicon KL were used for the low noise and tantalum caps above 1uF, Wima and Kemet stacked film polys used for caps under 1uF and Panasonic FM and FC for everything else. The tuning capacitor was also cleaned.


Filter caps were also replaced and upgraded. Before:



And after! Filter caps were upgraded from 15000uF to 22000uF, this is safe to do as the 1280 has a soft start circuit. I also cleaned and polished the chassis and transformer, came out pretty nice!

 


Fired her up, set the offset and bias to spec, let it play for an hour to settle everything in, then reset the offset and bias adjustments. Got a video of it playing, this thing sounds phenomenal!


And now some beauty shots! Protect anything damaged by drool, you have been warned! :-P




And that completes this restoration! Feel free to leave comments or questions. Up next will be a Pioneer SPEC-2, so stay tuned!
An unpleasant surprise greeted me when I flipped the board over, the previous tech destroyed part of a trace leading to the offset pot when they replaced it, and the jumper they put in is a little remiss. Not too difficult to solve, just annoying.
An unpleasant surprise greeted me when I flipped the board over, the previous tech destroyed part of a trace leading to the offset pot when they replaced it, and the jumper they put in is a little remiss. Not too difficult to solve, just annoying.

Tuesday, October 3, 2017

Pioneer SX-1250 Gold Tier Restoration!


I'm pleased to announce I now offer 3 tiers of recap/restoration work. This is a recent development in light of several tests and experimentation with various types of capacitors and their affect on the sound. The first tier, silver, is the standard restoration and is what you have seen in previous posts. Next, the gold tier restoration, goes quite a bit further, replacing more caps and changing the cap dielectric of several caps. This offers an even better sounding amp compared to the standard recap. Several other components (rectifiers, diodes etc) are also upgraded depending on the amp or receiver in question. 

Finally there is the platinum tier restoration, which is a fully custom, all out electrical restore of an amp or receiver, all resistors, diodes, rectifiers, transistors and capacitors are replaced or upgraded where needed and the circuit may be modded for better performance or sound quality. Some components like outputs may and may not be replaced, but that will depend on the amp or receiver in question. The owner will be able to select the parts that go into the amp if they wish, such as a certain brand of capacitor (Nichicon KA, Elna Silmic etc). I will also soon be offering a complete performance evaluation of any amp or receiver that comes in for restore.

With that being said, here is the first SX-1250 gold tier restoration!

This was sent in by an Audiokarma member from Illinois, the receiver cosmetically was in very nice shape, some dust and dirt from age and weird white speckles all over the faceplate.

Let's dive in! Starting on the bottom boards, underneath are the power supply, tone amp, flat amp, filter amp and function switch boards.


First up, the flat amp board. Before...


And after! 24 caps and 6 transistors were replaced along with four 1S2473 getting changed to 1N4148 diodes. Cap replacements are Panasonic FM and FC for the electrolytic caps and Panasonic ECW polypropylene for the 1uF mylar film caps. Also used were Wima polypropylene caps. Transistor and diode replacements are by Fairchild.


Next up, the tone amp board. Before:


And after! 36 caps were replaced along with 4 transistors. Cap replacements are Panasonic FM for the normal electrolytic caps, Nichicon KL for the bright orange low leakage caps and the tantalum caps (they make a difference in the noise floor of the amp) and the mylar film caps are replaced with Wima and Vishay polypropylene caps. Transistor replacements are by Fairchild.


Up next, the filter amp. Before:


And after! 10 caps and 2 transistors were replaced. Cap replacements are Nichicon KL for the tantalum caps and the mylar films are replaced with a combination of Wima and Vishay polypropylene caps. Transistors are Fairchild as before.


While here I also took apart the filter switches and deep cleaned them, as they are notorious for causing channel dropouts and other problems. Just spraying Deoxit into the switch doesn't always help either. Below are a few photos of the process, all the contacts were cleaned with a eraser, soaked in Deoxit, then the switch put back together and worked around 50 times each to ensure they are scrubbed clean.




With those done, let's move onto the function switch board. Before:


And after! Just one little 220uF cap on here, replacement is a Panasonic FM.


Moving on, we now arrive at the power supply board. Before:


And after! 4 caps were replaced, I used Nichicon TVX and PW here. All fuses were checked for proper rating and to make sure they didn't have any corrosion.


Now onto the top! Here we find the 4 removable boards, left and right power amp boards, protection board and stabilizer (regulated power supply) board. Also up here is the phono amp board under the silver cover to the far right..


Let's start with the left power amp board. Before:


And after! 12 caps, 3 transistors and both trimpots for the bias and offset were replaced. Replacements are Nichicon PW for the big 470uF caps, Panasonic FM for the 220uF and Nichicon KL for the low leakage 10uF. For the 1uF input cap a Panasonic ECW polypropylene was used. Also used were Wima polypropylene caps. Bourns trimpots replaced the offset and bias trimpots. The input pair were replaced with 1% beta matched KSA992 transistors, also replaced was the overcurrent sensor transistor which is known to go bad and cause the protection circuit to trip on and off constantly when at low volume. 


Here are some photos showing the difference between the old and new caps. There is a real, measurable difference between old and new caps, even if they seem fine in capacitance there are other things such as ESR and dielectric loss. Even the film caps are not as good as the new poly caps. Here is an example of the ESR difference between the old mylar film vs the new poly film (lower is better):



A fairly sizable difference.

Moving on, the molex connectors pins are always dirty and this was no exception, cleaning these is an important part of any restore. Before:



And after!



Now for the right amp board, this is the same as the left.


And after! Same parts and process as the left channel were used.


Pins all clean!


All 8 outputs for both channels were removed, the heatsinks and old thermal paste cleaned off and new thermal paste was applied.

Now for the stabilizer (regulated power supply) board. This board was previously recapped by another shop, however they did not replace or upgrade any of the transistors. They used a mix of good Nichicon caps and cheap Chinese generic brand caps, some of Nichicon caps used however were not of a low impedance style.


And after! This board runs very hot so all diodes and transistors are replaced along with the caps. Several transistors get upgraded to bigger case styles to better handle and dissipate the heat. In total 16 caps, 13 transistors, 6 diodes and both trimpots for the +65V and -65V supplies are replaced. Nichicon PW was used for all the radial caps with a Nichicon TVX being used for the 1000uF axial cap. Transistors and diodes are by Fairchild and ON-Semi. Trimpots are made by Bourns.


And last but not least, the EQ amp (phono amp) board. 


And after! 18 caps, 14 transistors and 6 diodes were replaced. The differential pairs (the 4 with the orange dots) were replaced by 1% beta matched KSA992 transistors. Panasonic FC and FM were used for the electrolytic caps, Nichicon KL was used for the orange low leakage and tantalum caps and the 1uF input caps were replaced with Panasonic ECW polypropylenes. Transistors and diodes are by Fairchild.


Here are some photos showing a cap on this board and how much is has deteriorated. There were many caps I tested across all the boards with similar levels of dielectric degradation and loss.

Old:



New:



Almost done! I replaced the soft start relay as well, the old relay contacts tend to build up carbon and other impurities and or become pitted, causing the resistance between the contacts to rise and forcing power draw through the soft start resistor when the relay contacts can't keep enough current flowing. In severe cases it can blow out the soft start resistor or cause the thermal fuse to open because the receiver cannot draw enough current through the relay, overheating the resistor.

The soft start relay in the 1250 has a flanged case, meaning the new relay case will not work. Thankfully, the new Omron relay is a direct fit into the old case. All I have to do is pop the new case off and fit the old case on.

New relay on the left, old on the right


And voila! Old case on new relay!


 Mounted and wired in!


All four filter caps were also replaced with UCC 22000uF 100v replacements, they are a perfect drop in replacement for the old caps. All that has to be done is enlarge the ring terminal and ground bar holes slightly.



And all done! Fired her up on a DBT (Dim Bulb Tester) to make sure there were no problems, check the bias and made sure it set correctly, then turned it back to zero, took it off the DBT and fired it up line power. Set the offset to 0.5mV each side. The bias was set to 75mV each side, lower than the 100mV the manual calls for, but it runs cooler this way and I recommend doing it for this reason. There are no determinants to the sound or operation in doing this


All the lamps, both dial and indicator were changed to LED lamps, I kept the color as close to the originals as possible. The dial lamps were slightly different color and brighter, but the indicators are almost identical.



And we're all done! Hook up my Polk SDA-1C speakers, hook up my source and hit play. HOLY. CRAP. I know there's always an improvement in sound when I recap a receiver, but this difference is FAR beyond just a standard recap. The highs and mids are out of this world. I compared my own 1250 which just has a standard recap at the moment and yep, I am hearing the difference. I am now a firm believer in replacing mylar films with polypropylene films, the difference has to be heard to be believed. And if you're going from an un-restored, no caps replaced receiver to this, the difference will make your jaw drop.

The final thing to do was to clean the faceplate and knobs, they had some weird speckles of something all over it. I also oiled and polished the wood case and wooden blocks on the sides of the faceplate. The chassis and transformer was also cleaned. Came out looking like this. 

(Drool alert ahead, protect your keyboard. You have been warned!)










Ran and burned it in for almost 2 weeks, flawless performance. Readjusted bias and offset at the end of the burn in period, gave her the final check over and this one is on its way back!

If you like what you see, be sure to hit that +1 button. Please feel free to leave comments or questions!