Pioneer SX-550 Refurbish

Happy New Year Everyone!
I have a SX-550 that I am refurbishing for a friend. Right now, the usual on these is happening with the switch, flickering lights. I have pulled the switch and have resurfaced the points using 1200 grit sandpaper sprayed down with DeOxit. I put the sandpaper between the contacts and lightly pressed down on them as I dragged the sandpaper between. I just have to re-install the switch. I have made up a Cap list as well as a Transistor replacement list. I have most of the transistors here and only lack a few, which I am going to order as soon as I get verification on the replacements. I have all the capacitors in the list.

Thank you for your help!

Power/Speaker switch is re-installed. Hooked up to DBT to check for arching of switch and all is good, DBT went dim. Lights stay lit with no flickering. Turned unit off and just went thru and sprayed DeOxit on all the rotaries and push button switches. Will give another shot after a while and check output voltages after all dried.

Took unit off DBT and plugged directly into wall current. Powered it on, no smoke. Tried to adjust Idle current to 25mV as per SM, Right side was able to adjust, was previously set at 15mV. Left side, no such luck. Could only get it adjusted to 1.15mV and that is it.

oh gawd, everybody's got their OWN format...

no time for now. DaWoofer is owed his SX-1980 and I got BIG political trubbles in ILLaNOID.

Checked fuses. Only 2 out of 5 are the correct value. FU1 correct 4A, FU2 was 5A (Should Be 4A), FU3 was Correct @ 1.5A, FU4 was 2A (Should be 0.8A) and FU5 was 3A and should also be 0.8A. Have to take a run to get correct fuses in the morning.

markthefixer said:

oh gawd, everybody's got their OWN format...

no time for now. DaWoofer is owed his SX-1980 and I got BIG political trubbles in ILLaNOID.

Click to expand...

Hi Mark,
Sorry bout the format. I believe I am good with the replacements. Did a searched and verified most of these transistors. I am not changing all transistors on this. Just what needs to be changed. I just built the format like this for my future reference with attached hyperlinks for faster reference to Mouser and datasheets.

Take care!

I have not been able to adjust Idle current on the left side. The max I could get was 1.04VDC. Went through today and checked voltages as per SM.

LEFT CHANNEL
Q9 B= +0.89Vdc (+0.6Vdc)......................Q11 B= -0.54Vdc (-0.6Vdc)
C= +29.9Vdc (+30Vdc).............................C= -29.9Vdc (-30Vdc)
E= +0.01Vdc (?)......................................E= Unstable

RIGHT CHANNEL
Q10 B= +0.77Vdc (0.6Vdc)........................Q12 B= -0.52Vdc (-0.6Vdc)
C= +29.9Vdc (+30Vdc).............................C= -29.9Vdc (-30Vdc)
E= 0Vdc.................................................E= 0Vdc

Unsoldered the Outputs and Q9 Base to Emitter is open, no voltage drop. Also, R25 looked a bit chalky. Original is 4.3kOhm and replaced with 4.7kOhm.

Ordered new outputs along with others I did not have, will be here in a few days.

UPDATE on what I have done so far.

I have installed new output transistors and changed out the 100 ohm trim pots as they were reading in the upper 70 ohm range. Connected to DBT, all good. Plugged into wall, adjusted the Idle current to 25mV and re-adjusted after 20 minutes. Ran a reel to reel to it and some small speakers, sounded pretty good, still some noise in the switches so more DeOxit to do.

I've also started the Re-cap. I've have done the AF Assembly Board complete. I Stuffed the 2 Large Caps. Re-capped the AF muting board and installed new transistors on it. On the AF Ass'y Board, there were 2 Tantalum caps that were not listed or shown in the schematic. They are 10uf/25V and are both next to each other in between the bass and treble controls. I replaced them with 647-UKL1H100KDDANA
Also, Cap 46 was listed as 220/50v but was actually a 220/63v and looks to be original. All that I have are the 50v so I am going to have to order that one.

Although the transistors were all good (except for 1 output), I went ahead and changed out all transistors on the AF assembly board (except the 2 2SA798's). I wasn't going to, but, I did. Don't know if it will actually benefit from doing this.

Now, a couple of questions regarding the (2)2SA725 transistors and 2 capacitors. These are the Low Pass Filter Amp. Should I change them?
Q7, Q8 2SA725 PNP TO-92 bce 35v 5v 100mA 100mW 100mHz 150min(hfe)
Change to:
512-KSA992 PNP TO-92 ecb 120v 5v 50mA 500mW 50MHz 200min(hfe)
And Caps:
C42, C43 CSZA R47M 35 (0.47/35v)
Change to:
667-ECQ-V1H474JL3 (0.47/50v) or 647-UKL1HR47KDDANA (0.47/50v)

Also, the Auto Switch Transistor: Q6
2SC945 NPN TO-92 bce 50v 5v 100mA 250mW 125MHz 75hfe
Change to:
512-KSD1616AYTA NPN TO-92 ecb 120v 8v 1A 750mW 100MHz 135(min)hfe

I did not know if I would have to do a complete tuner alignment and MPX adjustment. I am staying away from the tuner section until I learn alignment but just did not know about these.

Thank you

If it were mine, I would change them out. The parts are inexpensive! As to the .47uf caps, I'm pretty sure the film caps are supposed to be quieter than the electrolytics, or at least more reliable. Same for the old vs new transistors.

It's not recommended to change the Tuner caps, unless you are going to have it re-aligned, but on my SX-780 and SX-1050, I didn't see any real change in operation after recapping the tuner boards. While I was recapping the tuners, I changed one cap at a time, marking them with the cap number as I removed them and testing the receiver between each one, so I could reinstall them if there was an issue. I feel that the SX-780 is a bit quieter on AM than it was before, but it could be due to recaping everything else.

I listen to Coast to Coast AM on the SX-780 at night when I go to bed :alien: :screwy: :lmao:

It's not just learning alignment, but rather the equipment needed to do it. One way or another you will end up spending 400 to 600 bucks minimum for a rf generator with controllable mux inputs as well as a distortion analyzer for the output.

The sections you propose working on is the stereo decoder, and it has one adjustment that can be relatively well set in a diy environment. So do them. The caps connected to the ha1156 chip, use stacked film caps - it will have a positive and permanent effect. C30, c31, c32.

the adjustment of vr1 on the stereo decoder splits the difference of the two points where the stereo lamp goes from off to on, when going low to high and from high to low, always starting out with the stereo lamp off. There are no separation or pilot rejection adjustments on this lower end model to be affected.

The 1137 chip's caps and adjustments need the generator and distortion analyzer. Part of it can be set on dead air, but the rest is critical.

Some folks are evangelizing a course of action that on the higher end models is a poor choice without an alignment. And I am forced to counter them continually to avoid the "silence give assent" syndrome. Sooner or later I will not be around to disagree, and people will have to learn the hard way. This saddens me. It is NOT about "generating alignment income" - I have far more work than I can ever hope to cover - and with all the other stuff I have freely shared, IF there was a way to do it, you can damn well bet I would have shared it long ago. It still bugs me that I can't... Every time I think of a potential way to DIY it, when I add up the costs of what's needed, it still comes out to the same baseline cost for the equipment to generate the necessary signal, and to evaluate the output signal.

Marty, Socal, thank you!

Thank you so much for your time Mark. I do, in fact have all the test equipment to do alignments, but lack one very important part, the knowledge. I am still reading a book I have and intend on starting to practice on cheap FM radios, not that the 550 is an expensive piece of gear, it's just not mine. I will change those out. Thank you again

The Equipment I have posted here: http://www.audiokarma.org/forums/showthread.php?t=495126

Another Update!

Sorry for the long delay on this, I've been having problems with my wrist and I will be having surgery on it soon.
Anyways, this is what is finished: Caps have been changed out, including the 3 Mark said to do. Transistors have been changed. All push button switches have been thoroughly cleaned and lubed. I removed all the rotaries and flushed the heck out of them, couldn't get them clean enough mounted.

Connected to DBT 57w bulb, damn thing stayed lit. I had soldered D3 Varistor in reversed, Duh. Luckily, I had on DBT. After that was re-installed correctly, I turned DBT on again, the light went semi dim but, not all the way. Connected some headphones, No Right Channel, only a low volume buzz and when I would touch the bass or treble rotary, I would get a low frequency hum.

I started looking at pinouts of the right channel tone control/balance area on board and Q15 was installed wrong...Duh #2! Turned DBT back on and there it is, music to my ears, FM. Both channels sounding good. No static on any switches or VR's.

Still need to re-flow rest of solder joints, clean tuner section and see if she drifts. I want so badly to hook up the equipment I have for alignment and make adjustments if she needs it but, I'm just not ready to tackle that task.

Will post more pics after all adjusted and put back together.



Pulled Heatsink (Outputs) back out for easier access to things. No, it wasn't me that cut the am bar antenna wires, that was done before.

Thank you all!

Hi--Nice thread! I have 3 sx 550s. I got one on eBay and loved it. Then the left channel started going staticky and cutting out intermittently. kicking the volume switch would bring back sometimes. When I saw another for cheap I got it and put the first in a closet. a few months later-same routine-repeat all of the above. now all 3 sit with same problem. Inside there is no obvious corrosion or leaky cap that I can see. CAN YOU ADVISE?? How to fix these?

dlthomas said:

Hi--Nice thread! I have 3 sx 550s. I got one on eBay and loved it. Then the left channel started going staticky and cutting out intermittently. kicking the volume switch would bring back sometimes. When I saw another for cheap I got it and put the first in a closet. a few months later-same routine-repeat all of the above. now all 3 sit with same problem. Inside there is no obvious corrosion or leaky cap that I can see. CAN YOU ADVISE?? How to fix these?

Click to expand...

Hi there. Better to start your own thread as it would make it easier for others to see it and be able to Taylor assistance for only yourself.
Coming into the end of other's thread only serves to bury it and not get the attention it deserves.
In the meantime have a good read of this thread.
http://audiokarma.org/forums/index.php?threads/the-idiots-guide-to-using-deoxit-revisited.207005/

Looking at replacing transistors on a 550, but I see mouser no longer have SA1220AYS and it's discontinued. Any other recommendations to replace the 2SA697?

rowifi said:

Looking at replacing transistors on a 550, but I see mouser no longer have SA1220AYS and it's discontinued. Any other recommendations to replace the 2SA697?

Click to expand...

One option would be KSA916Y (and KSC2316Y for its complement). Another, closer to the KSA122AY in specs, would be a BD140-16 (and complementary BD139-16). This will work for the 2SA697 in the SX-550, but not for all installations of the 2SA697A.

Hmmmm.... There are different approaches to the task at hand, making an SX-550 useable. When I got my last year I first of all looked whether it worked at all. Then I mended the faults first. Of course the mains switch, I mounted a new one at the back side. The original was very different from those I saw in the according threads (remember I am in Germany). It also crackled at one channel, this was caused by bad solderings at the balance pot (the front must be detached to get access to the solder points). Only when it worked flawlessly I recapped it. I did not replace transistors or diodes! Why should I? Smaller caps I replaced with foil caps. The receiver sounds beautiful!

Next thing I will do is tuning the bias to get the least crossover distorsions, of course not exceeding the specified range (15 to 40 mV after at least 15 minutes). I did that at my SA-8500 II and it sounded really nice then.

AF Amplifier Board AWK-056
AWK-056 c1 4.7uf 25v ceanl 4.7uf 50v 647-UKL1H4R7KDDANA
AWK-056 c2 4.7uf 25v ceanl 4.7uf 50v 647-UKL1H4R7KDDANA
AWK-056 c11 1uf 25v csza 1uf 50v 647-UKL1H010MDDANA
AWK-056 c12 1uf 25v csza 1uf 50v 647-UKL1H010MDDANA
AWK-056 c17 220uf 6v cea 220uf 16v 647-UPW1C221MPD
AWK-056 c18 220uf 6v cea 220uf 16v 647-UPW1C221MPD
AWK-056 c19 47uf 25v cea 47uf 35v 647-UPW1V470MED
AWK-056 c20 47uf 25v cea 47uf 35v 647-UPW1V470MED
AWK-056 c23 100uf 6v cea 100uf 16v 647-UPW1C101MED
AWK-056 c24 100uf 6v cea 100uf 16v 647-UPW1C101MED
AWK-056 c39 220uf 50v cea 220uf 63v 647-UPW1J221MPD
AWK-056 c46 220uf 50v cea 220uf 63v 647-UPW1J221MPD
AWK-056 c47 220uf 50v cea 220uf 63v 647-UPW1J221MPD
AWK-056 c40 100uf 50v cea 100uf 63v 647-UPW1J101MPD
AWK-056 c42 100uf 16v cea 100uf 35v 647-UPW1V101MPD
AWK-056 c43 100uf 25v cea 100uf 35v 647-UPW1V101MPD
AWK-056 c50 100uf 25v cea 100uf 35v 647-UPW1V101MPD
AWK-056 c45 470uf 50v cea 470uf 63v 647-UPW1J471MHD
AWK-056 c48 100uf 35v cea 100uf 35v 647-UPW1H101MPD
AWK-056 c51 100uf 35v cea 100uf 35v 647-UPW1H101MPD

AWK-056 q1 2sa798 pnp bcebce 512-KSA992FBU ecb x2 hfe matched
AWK-056 q2 2sa798 pnp bcebce 512-KSA992FBU ecb x2 hfe matched


AF Muting Board AWM-101
AWM-101 c3 10uf 35v cea 10uf 50v 647-UPW1H100MDD
AWM-101 c4 4.7uf 35v cea 4.7uf 35v 647-UPW1H4R7MDD
AWM-101 c5 0.1uf 50v cea 0.1uf 50v 647-UKL1H0R1MDDANA


RF Board AWE-072
AWE-072 c63 47uf 25v cea 47uf 50v 647-UPW1V470MED
AWE-072 c64 47uf 25v cea 47uf 50v 647-UPW1V470MED
AWE-072 c65 1uf 25v cssa 1uf 50v 647-UKL1H010MDDANA
AWE-072 c66 1uf 25v cssa 1uf 50v 647-UKL1H010MDDANA
AWE-072 c69 47uf 6v cea 47uf 16v 647-UPW1C470MDD
AWE-072 c70 47uf 6v cea 47uf 16v 647-UPW1C470MDD
AWE-072 c77 4.7 25v ceanl 4.7uf 50v 647-UKL1H4R7KDDANA
AWE-072 c78 4.7 25v ceanl 4.7uf 50v 647-UKL1H4R7KDDANA
AWE-072 c93 0.47uf 35v csza 0.47uf 50v 647-UKL1HR47KDDANA
AWE-072 c94 0.47uf 35v csza 0.47uf 50v 647-UKL1HR47KDDANA
AWE-072 c97 47uf 10v cea 47uf 35v 647-UPW1V470MED
AWE-072 c98 47uf 10v cea 47uf 35v 647-UPW1V470MED
AWE-072 c99 470uf 6v cea 470uf 16v 647-UPW1C471MPD
AWE-072 c100 470uf 6v cea 470uf 16v 647-UPW1C471MPD
AWE-072 c109 10uf 25v cea 10uf 35v 647-UPW1V100MDD
AWE-072 c111 0.1uf 35v csza 0.1uf 50v

AWE-072 q7 2sa725 pnp bce 512-KSA992FBU ecb
AWE-072 q8 2sa725 pnp bce 512-KSA992FBU ecb
AWE-072 q14 2sa725 pnp bce 512-KSA992FBU ecb
AWE-072 q15 2sa725 pnp bce 512-KSA992FBU ecb
AWE-072 q13 2sc1312 npn bce 512-KSC1845FTA ecb
AWE-072 q16 2sc1312 npn bce 512-KSC1845FTA ecb
AWE-072 q17 2sc1312 npn bce 512-KSC1845FTA ecb


Main Filter Capacitors
c6 6800uf 35v ach 6800uf 63v ECE-C1JA682EA