Sony STR-DA555ES - guide based on my recent repair


Novice Member
Feb 28, 2022
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Winnipeg, Canada
Hi all,

I try to post a guide or sorts whenever I repair something without one, and repair information on my 20+ year-old Sony amp appears to be scarce. This forum looks great, so here goes my 1st post...hope my guide can help others with a different Sony amp, but similar issues.

This for a Sony STR-DA555ES, but could easily apply to the 333 model as the 555 just has a 'fancy' remote (which is a bit of a pain). It has a bright sound, but with lots of low-end 'oomph'; the digital effects are a bit outdated, but my Oppo has individual channel outs, so I use the 5.1 direct with SACDs or streaming from my computer more than anything.

Background: a few months ago, I noticed loud "clicks" from my amp and a "pops" through the speaker about 5 minutes after I turned it on. Thought maybe caps were starting to go, but that wasn't the case. Eventually, my front left channel, then rear speakers cut out intermittently - no relays clicking at all - even with speaker select or when turning the input select knob. I lifted the amp a bit and dropped it, and it came back to life, but a few days later, the speakers started cutting out again. I even switched to the "B" speakers, which worked for some time, but ultimately failed as well. Then, the amp started to display a combination of "Protection" and "Protection (Fan)" randomly after the amp had been on for a while. I've seen this before with oxidized relays, but (after downloading the service manual), I saw there were at least 4 relays that control speaker outputs, and it was unlikely that all 4 oxidized at the same time.

Before we start - as a safety note, if you're opening up your amp, please use caution and read up on how to safely drain the caps - I didn't see a bleed/drain circuit in the schematics (service manual can be found easily online), so they will remain charged - and you definitely don't want them to discharge on you. The voltage from the two large power supply caps can be lethal - there are many videos on how to discharge caps in amplifiers - please consult them. Also, there's a chance you'll damage your amp beyond repair - please don't open the amp if you don't have experience with soldering and electronic repair.

I opened up the case (two PH2 screws on each side, two on top and three on the back), and used a plastic rod to tap on the speaker relays - sometimes I could bring back the sound, but it was always temporary, and sometimes the amp went instantly into "Protection" mode. A closer look was warranted.

The first board I wanted to have a look at was the rear speaker amplifier, but I didn't want to pull on a bunch of old connectors and risk breaking one, so (as per picture 1), I removed 7 screws and simply 'flipped' the board over. I instantly saw the issue - almost all the solder joints on the relay posts were cracked (see picture 2 to see what the cracks looked like under my scope). There were also cracks on some of the output wire solder joints, and although there weren't any cracks on the power amplifier connectors, it appeared as if they were definitely under thermal stress. I focused on the red circled areas in picture 1 (also on picture 3 - the board schematic), but inspected and reflowed any suspect solder joints. Reflowing means adding a dab of solder paste, then using a lead/tin alloy solder, heating up the joint and adding more solder until a solid solder joint is created. For some reason, there isn't much solder on most of the joints on this amp - the exception being the power transistors attached to the large heatsink - I didn't find any issues with those joints at all. I reassembled the rear board, making sure the power transistors were sitting on lots of thermal paste (there is plenty to spare on the heatsink).

There's a convenient panel on the bottom of the amp that's easy to remove (8 PH2 screws), and provides all the access that's required to address the rest of the cracked solder joints. Picture 4 outlines where I found all solder joint issues - it's a good idea to examine the entire board, but these areas are obviously exposed to heat and vibration and should be the focus of your investigation. Again, speaker relays, amplifiers ICs and power ICs. I've also outlined these areas in the schematic on picture 5. I've also circled a small transistor in blue on the schematic - if your amp constantly goes into "Protection" or "Protection (Fan)" mode, you may want to pay close attention to this transistor as it controls the fan that cools the heatsink. Picture 6 is a top view of the powerIC heatsinks - they become incredibly hot with just turning the amplifier on - picture 7 shows cracks on one of the powerICs. Interestingly, these cracks may "disappear" when the amp heats up, which may explain some odd behaviour when the amp is cold vs. hot.

I screwed the bottom cover back on, powered-up the amp and tested all functions - it worked perfectly - much better than it had been recently. I was definitely concerned that cracks would appear yet again, so thinking that fan technology has moved along in 20 years, I picked up a 120mm Corsair PC case fan and installed it in the amp case. I pulled power from the +15V power regulator and used a wire-wound aluminum-shrouded 200 ohm resistor (attached to the massive amp heatsink) to slow down the fan. It's a PWM-controlled fan, so I could have used thermistor and Arduino board to make it variable speed, but I chose the resistor to slow the fan down to barely a whisper and it's fine. As an added bonus, the fan came with an RGB element, so (at my kids' insistence), I connected the +5V RGB supply to the digital board power supply and added an optional LED element - caught it on a red colour in picture 8 (it's not as bright as the picture makes it out to be). I used my scope to ensure the fan and LEDs weren't adding any additional noise and the output was silent. All components that were normally impossible to touch were now just warm. If someone wants to add a fan, I took pictures of where the connections go - will post on request.

I have a newer Sony amp in the basement, and although it has HDMI switching, 7.1 support, better DTS, etc. - it doesn't sound as nice as my old 555, which is why I wanted to repair it and add a fan to hopefully make it last another 20 years.

Hope this helps - thanks for reading!
- Andrew


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