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Another SX-828 re-cap

CosmoK

CosmoK

Active Member
After a year of sitting on my bench, I finally rebuilt my first pioneer receiver, an SX-828. Here are some notes and resources that may be useful to others, followed by some questions.

First off, the receiver is good-looking and sturdy. The owners manual and service manual are available at https://www.hifiengine.com/manual_library/pioneer/sx-828.shtml

My unit has the AWM-025-A protection circuit board, which was used on the SX-838. You can get the schematic from the SX-838 service manual. I didn't check this before ordering parts and bought the wrong capacitors for this board. There was also one (polarized) axial capacitor soldered directly to the chassis near the fuses. I bought a radial capacitor out of ignorance, but it still fit.

I re-capped the power supply, protection board, head amp (pre amp), FM board (tone control), and main amp. I did not fiddle with the AM/FM boards, because I don't have time to re-align them right now.

This was my fourth reciever (but first Pioneer), the re-capping procedure was pretty standard:
(1) Order Elna Silmic II capacitors from digikey for all the electrolytics listed in the service manual. Go up a voltage rating if possible, I used some caps that were up a couple voltage ratings (6 V --> 50 V) and these were a tight fit... something to think about avoiding.
(2) I stuffed the main filter caps. I removed the originals, cut them in half about where the clamp sits, removed the internal goo, put the new (smaller caps) inside the cans, drilled some holes in the top of the can and ran wires from the new caps to the original contacts, added some stuffing to keep the new caps from rattling around (I used scotchfil, because I had it on hand, but something less thermally insulating would be smarter!), taped the cans closed with electrical tape, and re-installed them with the original clamps.
(3) In general the boards were pretty brittle and I tried to go as gentle as possible to avoid lifting traces, etc. I broke almost all of the plastic board spacers.
(4) It is my custom to draw a sketch of each board and note the polarization, capacitance, and voltage of each capacitor before I start desoldering. I then triple check the sketch of the original values, the polarity printed on the circuit board, and the information in the service manual before installing the new capacitors (sometimes these things disagree, and then I use the original values/orientation)

I replaced all the transistors that could be switched to KSC1845, KSC2383, or KSA992. I roughly matched the hfe of the 1845s before installing them on the head amp board. I always double check the pinout on the new and old transistor to prevent a mix-up.

I also replaced the two TO-60s on the power supply board with KSC2073TU and bought new heat sink mounts from mouser. The board had scorch marks under these guys, so they had to go. The original plastic heat sink screws were toast.

I did not touch the two 2SK30 transistors on AF board. These transistors apparently have a high voltage rating and are hard to replace (see https://audiokarma.org/forums/index.php?threads/sx-626-recap-troubleshooting.455318/).

I bought an LED kit for the lamps so I wouldn't have to fuss with matching specs. The installation was something of a PITA. They key is pushing out the black plastic rivets on the black faceplate instead of taking off the entire front section (see https://audiokarma.org/forums/index.php?threads/pioneer-sx-828-lamp-replacement.350777/). I managed to do all the fuse style lamps and all the function indicators across the top without removing the tuner string. The fuse lamps over the signal meters were very difficult to finagle out from under all the wires, but I did it with patience. For the function indicators, I pushed the existing lights out the front, by pushing from the back with the blunt end of a bic ben (lots of brittle old glue and plastic that made a little mess). The new LEDs bulbs were a hair to too small and kept slipping out of place. So after I had soldered the wires, I taped the bulb wires in place with some electrical tape on the housing for the dial fuse lamps.

The dial pointer was pretty easy, I just gingerly bent the metal clips to open the housing and slipped the new bulb in. I still haven't installed the speaker indicator lights because they seem to require disassembling the tuner string apparatus and I haven't found time to do that yet.

Lastly, there is a secret idle current adjustment procedure for the SX-828 (not in service manual). I followed the advice here: https://audiokarma.org/forums/index.php?threads/sx-828-idle-current-dc-offest-adjustments.566246/
 
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Here's the cliff note version of my surprises:

(1) Check which protection board is in your unit before buying capacitors
(2) There's one axial capacitor soldered to the chassis near the fuses
(3) Buy new heat sink mounts from mouser for the TO-60 transistors on the power supply board. The original plastic screws are probably toast.
(4) Buy new plastic/nylon board spacers (stand-offs), as you will likely obliterate the originals. I will try to post the part number/size when I order them.
(5) The idle current adjustment is not in the manual!
markthefixer said:
15 mA per channel, and read across 1 ohm (11 to 17) and (12 to 18) that would be 0.015 volts or 15 millivolts
Click to expand...
 
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I have a 828 and I'm thinking about trying to do some of this work. A tec fixed my relay problem so now it powers up but it now has a nasty crack and pop from the left channel. He says he can't find the problem and it will cost too much time and money to be worth fixing. I have no tools or knowledge but it's worthless now so what the heck.
 
Now for some questions:

(A) Anyone have an efficient method of replacing the speaker indicator lights (just below the signal meters) without a ton of disassembly?
(B) I planned to re-grease the output transistors, but the original grease was more like a glue. As I was reaching for a tiny screwdriver to try pry the transistors off, I decided to back off because I didn't want to break something that was working. Does anyone have any advice on this? Should I leave the transistors alone, or is there an easy way to take them out?
(C) Anyone know the part number for the plastic board spacers in the SX-828 or a similar model?
(D) There are several SR3AM-8 diodes on the power supply board. I am considering replacing these with 1n5406, but there is some disagreement at Audiokarma. On one-hand several people have used them successfully, on the other hand people have pointed out that they might not be sufficient to handle the required power (see https://www.audiokarma.org/forums/index.php?threads/sr3am-8-replacements.218849/). I am hesitant to try to installing something too beefy as the diodes are really packed on the board, so there's not a ton of space for more material. Any recommendations?
(E) I bought a new relay, but decided not to install it because the original works fine. Should I install the new part anyway?
 
My unit had one weak channel before the recap as well. In terms of sonic improvements, replacing the main filter caps and working on the power-supply and protection board restored the power and bass. But, I still had some left/right channel problems, and a popping sound with the low switch (de-oxit did not fix this). Ultimately, working on the AF (tone) board fixed these issues, but the board is sort of complicated and a pain to get at.

Now that I'm done, the SX-828 sounds really good. I'm running it with KLH 5 speakers and it sounds very smooth (maybe a little warm?) and has plenty of bass. Previously, I was using a restored Sansui Eight with these speakers, and that combination had a bit more clarity, because it was very strong in the mids and lighter on bass, which I sometimes loved and sometimes did not. The Sansui Eight sometimes sounded harsh with bad quality recordings, but so far, the SX-828 is smoother and more forgiving. I've also spent a lot of time listening to a Marantz 2245 (45 wpc), and while the SX-828 is only listed at 54 wpc, the pioneer sounds/feels substantially more powerful, possibly because it has a little more low end. Both are very easy to listen to. These are just my amateur opinions. In summary, I really like the sound of the SX-828 with the KLH 5s. And it looks awesome.
 
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A. A tec I talked to said it's almost a total disassembly of the front panel to get to those 3 little lights
 
been a while and it is a pain but not impossible. push to the back and out cut the wires strip and splice to existing.its a solder heat shrink op,but better than attacking the gang switch i used hemostats and wooden bbq skewer to poke them back in.
 
You can do the speaker lights from the receiver underside. Just use needle nose pliers to get them in there. It’s not that hard. You may have to clip some wire ties and move wires around.

The relay is worth doing. Just take the old one out of its case and put the guts of the new one in the old case.

I replace the big diodes with 1N5404s, which work fine.
 
Thanks for the tips, they are helpful. To summarize:

(A) No tuner disassembly required to install the speaker lights, just attack it from the underside with a BBQ skewer!

(B) ? (verdict still out on whether it is worth breaking the output transistors loose from the thermal paste... now more like glue). I will poke around in there when I open the receiver back up and see if I can get the transistors out without brutalizing them.

(C) The mfr # CBLS50-C seems to be the correct standoff for the SX-x50 units, but this part is obsolete as of 6 months ago. Matching the two hole diameters and board/mount thicknesses, I *think* digikey part 36-8810-ND ($0.26) should work, or digikey part DLCBS3-8-19-ND ($0.88), which accommodates a wider range of board and mount plate thicknesses (I haven't actually measured the board and mount plate thicknesses with a caliper).

(D) I will install 1N5404 diodes on the power supply.

(E) I will replace the relay. The replacement has mounts and pins on opposite sides, the solution I found was to add standoff supports (see https://audiokarma.org/forums/index.php?threads/pioneer-sx-828-relay-question.484738/), but I like your solution of just switching the guts from the new to old case.
 
I have one that was having volume pot problems or so I thought. Finally found a great tech who told me that it was so hacked up by people who thought they were techs that he basically had to do a total refurb including the power supply board. Now that it's done it sounds incredible. I have it paired with a set of Advent 5002's and I'm finding it to be a great match but then I think it would make any speakers sound great.IMG_20191102_155836.jpg
 
CosmoK, thanks a lot for taking the time to give all of this information. I am currently rebuildin an sx 525 that I have tried to get some advise on, but I have a nice sx 828 and am more inclined to take a Crack at it now that I've read this.
Did you end up changing the power transistors? It is actually in good working condition but I want it to good for a long time.
Thanks again, Ken
 
I ordered the parts, but I've been too busy enjoying listening to this receiver to put it back on the bench for the final fixes. Actually, I've just been busy with work and family. When I finally get a free day, I'll replace the PCB mounts, speaker indicator lights, the relay, the power supply diodes and transistors, 4 electrolytic capacitors on the surprise version of the protection board, and the output transistors.

When this happens I will report back. I'm not going to lie, it sounds so damn good now, I'm not sure why I'm messing with it...

One thing I would complain about with the pioneer (after rebuilding a 2285b and 2245 marantz and a Sansui Eight) is that it had a lot of capcitor/transitor leads that were bent flush against the bottom of the PCBs (the PCB holes were also quite narrow). This made it hard to desolder components without overheating the board (i.e., lifting pads, etc.). In the end, I learned to reheat the old solder then push the component farther IN, so that I could create a little space between the lead and board where I could suck the old solder out.
 
Four months later and I finally finished the project. Here are my notes:

(1) I replaced all the diodes and transistors on the power supply and protection board (mine was the SX-838 version), including the flyback diode between pins 9 and 10 on the protection circuit (with cathode on pin 10). I also finished up replacing all the capacitors and the 1 or 2 W resistors on the power supply. On the power supply, at D5 I put replaced the FR2-02 with a 1N5404. The leads of the 1N5404 were very slightly too big, so I had to work a tweezer tip in the hole a bit to open it up for the new part.

(2) I replaced the speaker indicator lights by removing the front black plate and then pushing the lights out through the front. I first pushed on them from the top on the inside with an L shaped Allen key to break the glue, then I pulled them out the front (gingerly) with tweezers and/or needle nose pliers. It was simple to fish the lights back in through the front, and all the soldering was easy through the bottom. I did not glue the lights in place, but I wiggled them into the right position by gently pulling on the wires, I'm pretty sure the lights will stay put, unless someone opens the case and starts pushing and pulling the wires.

(3) I got the output transistors out by pulling straight up on their tops using a pair of pliers. The mica underneath was in rough shape, so I removed it. There was basically no thermal grease left. I ended up greasing both sides of a new mica insulator and putting in new on-semi output transistors. There are more knowledgeable people than me who like to leave in the original output transistors when possible, but without a "real" transistor tester, I was worried the old ones could have been stressed at some point in the last 48 years and might have issues that I couldn't see without the proper equipment. I re-adjusted the idle current and DC bias, and when I hooked up my speakers, I couldn't tell the difference between the new and old output transistors.

(4) I replaced the original variable resistors on the amp board with Bourns multi turn trimmers. The adjustments are much smoother and more exact now.

(5) The board stand offs worked, but I had to pre-squeeze/flatten them with a pliers so that they would fit in the board holes. They are very tight, but they work with patience.

(6) The relay was a bit of fiasco. I tried to use the stand offs, but either they are cheap, or I am ham-handed because I sheared off the screw part of the second standoff as I was installing it. I.e., the thread was getting pretty tight so I was applying some pretty good torque (with my fingers) and it just broke. I had to drill out the sheared off bit. Then I went to remove the first standoff and sheared it as I was backing it out. Then I swapped the guts between the new and old cases, which worked okay, but I had to chisel off a little plastic with a tiny screw driver. But, the relay didn't work, it appeared to be always closed for the right channel and always open for the left. This could have been caused by the following problems:
(a) The new relay has a different pin-out, and I wired wrong. I did some google searching, but was having problems finding a wiring diagram for both the old and new relays. Maybe relay terminals are obvious, but I don't have enough experience at this point to be 100% certain.
(b) The old case may have been too tight for the new relay and prevented the relay from mechanically opening/closing
(c) The protection circuit was behaving strangely because I later discovered that C6 was installed backward on the protection board (again the SX-838 version)!
At any rate, I re-installed the original relay and (eventually) fixed C6, and the receiver sounds fantastic. I really have a soft spot for this unit.

The saga of reversed polarity at C6: The unit clicked out of protection and I had no problem adjusting the idle current or DC offset. I closed the unit up and hooked it up in the living room... no relay click. Took it back to the bench, relay clicked. Then the relay wouldn't click, take the case of the unit, relay clicked. At this point, I thought there must be a bad solder joint, loose wire, bit of metal laying on a board, component shorting to the chassis, a flaky transistor, or something of this nature. Then I got the unit to play for about 20 minutes, before the relay shut off the speakers. At this point I pulled up the schematic and started checking the voltage on each pin on the protection board and power supply. All voltages checked out, except pin 9 on the protection board, it was reading about 29V, when it was supposed to be 8 V. Up-stream from there the voltages looked bad on Q7, but good coming into Q6 (D5, D6, and D7 also looked good). So, I double checked to the pinout on Q7, and tried replacing it. This didn't work, so then I turned my attention to the stuff around Q7: R26, R27, R28, and C6. Well, C6 was backward, duh. An easy fix, but it took some detective work, and contrary to my expectation, this backward capacitor did not explode like a firecracker.

After flipping C6, I thought about re-trying the relay replacement, but I ran out of time. I suspect the new relay would work fine now that the protection board is up to spec.
 
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The SX-828 is now connected to a PL-55X turntable and a pair of Large Advents in my brother's living room. I'm really proud of putting this rig together. I'm mostly past claiming one system is better than another, but I will say that every time I walk into the room with this setup, I want to listen to music... which is the point.

P.s. I got the pair of beat-up Large Advents and had modest expectations for how they would sound, based on how dated and ugly they looked with their grills off. After I re-capped and re-foamed them, I finally hooked them up and was astonished by how good they sounded. Very solid rock speakers.
 
I have a new to me SX-828 and I'm trying to figure out what i want to do with it. This thread was a good read, thanks for posting and it's nice to hear someone having a positive experience with their SX-828.
 
I have 2 sx828’s. Both of mine were found in excellent cosmetic condition but suffered from electrical issues. I followed threads here on AK and was able to get them restored. If yours suffers from any of the normal issues of noise or clicking in and out of protection I would recommend going through the unit completely. When restored the 828 is a very good receiver.
 
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