Yamaha AX-500 Repair Attempt - [picture heavy]

[LEECH666]

Good day citizens of the Audio Karma forums!

Yesterday I embarked on a journey to finally give it a shot to repair the Yamaha AX-500 that has been sitting on my pile of amps to be repaired. I am by no means a pro at amp repair but I do have some education in electronics and a good selection of tools available. Anyway this thread is meant to document my progress. I may fail in the end, who knows.

The story of this amp is that I bought it for 20 Euros (iirc) on a my local versions of Craigs List because I though it might be a fun project. It's been sitting on my pile for a couple of years now and since I recently had an intermittent crackling channel on my Pioneer A-77X that needed servicing (resoldering all the cold joints) I finally got the motivation to work on this amp.

//EDIT: I completely forgot the error description. When powered on the power led is lit but the relay doesn't click. I haven't done much more testing yet. My guess is that there is something wrong with the protection circuit and probably cold / dry joints.

So I started off with inspecting the amp a little.

I've already read about the corrosive / conductive glue that what used at the time and that it is in many cases the reason why amps who had this glue used fail.

There seems to be some blooming corrosion thingy going on on that resistor leg.

More of the dreaded gunk. But corrosion isn't as bad here. I wonder why it blooms in some places and doesn't so much in others.

Turning the amp on it's back I noticed that the soldering didn't look like factory. Looks like someone already tried to reflow some of the joints on this amp previously. The soldering looked rather poor on a first glance.

This is one of my favorite bad solder joint right there on the top. The one next to the one with the heavy flux deposit. (second most left one on the top). It looks somewhat intact here but after brushing over it ...

... it crumbled away leaving a big crater in the joint. I've never seen anything like this. Maybe it's a side effect of the corrosion by the glue. I was so fascinated by this that I also made a GIF of me poking around the cavity with my multimeter probe.

More bad or dirty looking solder joints.

 

[LEECH666]

This must be an older revision of this amp as I found pictures of the same board where the two black wires weren't bodged on as an afterthought and proper holes and pads were existent.

More glue and corrosion(?). Not sure why the contacts on that switch are shiny but green.

I lake the "waving" capacitor leg. "Hi my name is capacitor, pleased to meet you. Let's shake hands.".

I took of the front plate which I shouldn't have done in hindsight. More on that later.

This is where I started with some cleaning. One of the boards before and after dust cleaning.

I came up with a novel flux removal methode where I used an old brush head of my electric toothbrush. In conjunction with 99% IPA it worked quite well.

After brushing down the amp board with the electric toothbrush, another normal toothbrush and some other brushes this is how the board looked. The soldering isn't as bad as it seemed at first but still bad and too many joints are still cold or have the halo showing so I will most likely reflow the entire board soon.

This is how the top side looked after the bottom side was cleaned. Brushed it down with glas cleaner and a soft long bristle brush and then did another pass with IPA.

 

[LEECH666]

The capacitors needed to come out. Still measure okay. My Pace (de)soldering station can be be seen in the background. Finally had a chance to use this cheap component tester that I bought on ebay some years ago. Measurements for those caps are still good as far as I can tell.

It was time to start the glue cleanup. Man this stuff can be hard to get off! I will replace the not so rotted but ugly wire links later on but for the moment they do not concern me.

I probably could have avoided some of those scratch marks if I was more careful. A bamboo stick which I saved from one of the asian takeaway restrourants meals, a sheet of sandpaper to sharpen the bamboo stick and some metal tweezer provided an okay means to remove the glue. The bamboo didn't scratch the PCB but the metal tweezers did.

Some more glue cleaning.

Looks like the blooming resistor leg was already rotted through and came apart during the glue cleanup.

And now DISASTER!! Oh well ... at least somewhat. While trying to turn the amp on my desk I slipped and had to save it from falling over. My hand knocked loose one of the LEDs on the front. If only I had left that front panel mounted. Oh well looks like the copper laminate got ripped. But nothing I can't fix. Annoying tho that this happened due to me being clumsy. I used a fibre glass pen to scrape of the solder mask and both sides and put some solder on the exposed copper.

I quickly forfitted the idea of using 0.1mm copper wire and used 0.5mm silver wire instead. I hope I put in the LED the right way around. The plastic spacer is also damaged but should still work well enough.

...

 

[LEECH666]

Since the leg was already kicking high into the air on that one resistor I though I'd measure the resistor. Seems to be fine, I will shorten the legs and reuse that one most likely. Maybe I will put in new "silver wire leads" to keep the stand off space the same.

And that's where I am today. Let's see what I can get done next.

//UPDATE:

Removed the resistor from the PCB.

Cut off the part of the leg that was rotten and shined the rest with some scotch bright.

Legs retinned.

Leg extension (unsoldered) and soldered.

Resistor soldered back onto the PCB. Maybe I should have cleaned up that hole before doing so.

While attempting to resolder some of the joints I noticed that some of them seem to contain grey dust or goop or debris underneath the solder. Not sure what this is , maybe dust or completely decayed solder? It seems to interfere with the new joints which is annoying.

//UPDATE 2:

Replaced some links and resoldered circa 1/3rd of the amp board. I used no clean flux paste and put it on with a small soft brush. Will deffo clean this up later on though. Blue line marks my progress.

 

[Nashou66]

Use Acetone to loosen the glue. I use a small oil painting paint brush to apply the acetone. Adding more till your chop stick can move it away. it will get gummy and should come right off.

So far you're doing well. Keep at it !

Nashou

 

[LEECH666]

Thanks for the hint Nashou66. I might try that on the phono stage once I get there. It's not a priority though since I do not really use phono. In any case I have acetone at hand but I was afraid it might strip the solder mask on these boards. I will try it anyway and will try to apply it only locally (on the glue). I've also put some chipped of glue into a vinegar bath to see if concentrated vinegar will soften it and yeah looks like it does. I am not sure I am comfortable with putting and leaving vinegar on the board though. The darkened glue was quite and much easier to chip away. The still rather yellowish glue was more though and still somewhat elastic and harder to get off. I still haven't figured out how to fully clean the capacitors. Maybe I will give acetone a try here as well. But for now it's bedtime.

 

[Nashou66]

Acetone may take the lettering off the capacitor. SO if using it for only the glue area it be ok, but be careful of the lettering on the caps.

Athanasios

 

[avionic]

completely decayed solder?

Completely oxidized solder that does not melt like solder.. The lead (Pb) has completely leached out of the connection. Leaving tin (Sn) behind.Oxidation is usually so bad that it creeps up the component lead as well.

 

[LEECH666]

Thanks for the hints Nashou66 and avionic. It's the first time I encounter lead free solder joints like that. ... aren't there a lot of lead free solder connections in modern electronics nowadays? Makes you think, eh. ;-). Anyway I am just kidding. I am soldering with Kester Sn63Pb37 and I will keep doing that until I run out of solder and can't get new leaded anymore.

 

[LEECH666]

I didn't get much done today regarding the amp. My eyes were still a bit strained and blurry today from looking through the monocular magnifier for a prolonged time when reflowing the amp board yesterday. Instead today I reorganized and improved my work bench a little. I added some more outlets to the bench and did some generic cleanup. Completely OT to this restoration attempt but that's ADHD for ya.

[I also found out how to manage the thumbnail size of the pictures. This should make my posts more readable. I would edit the old post but I can't anymore. Click the thumbnails for a link to Imgur and then click the three dots in the top right corner of the picture then click download image to get to the full sized image [[in case you care].]

I threw out some more links and scrubbed then retinned one more of theses 2.7k resistors.


I used some acetone and ethyl acetate to clean up the rest of the glue. The latter seems to be a tad bit more aggressive than acetone. I lost the bottom row of silk screen but overall I am happy with the results. Sadly I also damaged the wrapping a little bit and now I have to watch out to not short circuit the caps case to some wire links that may run beneath the caps. If that's I will have to find some other means to insulate the caps bottom. If necessary I will probably use some silicone foil and cut it to shape.


For whatever reason I thought I'd check the relay for oxidation on the contacts. I couldn't take the cap off so I unsoldered the relay. I then proceeded to use some paper with a thin spread of polishing compound (creme) to take off some of the oxidation. I continued to polish with some leather sticks (woodstick with leather glued to the end) which Armin from Good Old Hifi mentioned once and which I've bought many years ago.








Too many images ... have to split the post.

 

[LEECH666]

After that I proceeded to reflow the rest of the amp board. I feel like I am doing this restoration the wrong way around, haha. Here is the still greasy board.


And here it is after cleanup with IPA, brushes and tissues.



That's all I got for now ...

 

[avionic]

or whatever reason I thought I'd check the relay for oxidation on the contacts. I couldn't take the cap off so I unsoldered the relay. I then proceeded to use some paper with a thin spread of polishing compound (creme) to take off some of the oxidation. I continued to polish with some leather sticks (woodstick with leather glued to the end) which Armin from Good Old Hifi mentioned once and which I've bought many years ago.

My SOP ...
I just replace them...
https://www.mouser.com/ProductDetail/653-G4W2212PUSTV5

 

[LEECH666]

On Thursday I decided to rest my eyes a little bit because for some reason looking through the monocular screws with my visiong where my other eye retains blurry vision for some time after prolonged use. So I got distracted again and started building a dim light bulb tester but yeah that's just semi related. On Friday I didn't have time to do anything as I wen to a live concert and was busy all day. Yesterday though I found some time to work on the amp again.

Dim bulb tester. It's not finished as I am waiting for an IEC socket and some faston connectors to arrive via mail. I am going with the design found here; https://retrorepairsandrefurbs.com/2022/06/13/building-a-dim-bulb-tester-for-vintage-radios-tvs/

I finished replacing all the links that I took out and put the capactiors and resistors back. Then I went on to tackle the remaining joints that I couldn't reach without taking out the amp board. I disconnected the headphone socket fromt he front plate assembly and then it was only 7 screws and the board became loose.

Since I am still waiting to complete my bulb tester I proceeded to take out the phono board and gave it a good clean with IPA, soapy water and more IPA.

More glue to remove so it was bamboo and tweezer time again.

After the cleanup I noticed that the glue had attacked the solder joints here and left some corrosion.

I took out the caps and removed the glue. This time IPA and my fingernails were enough to take of the glue of the caps.

I also took apart the switch and oh boy was that hard to get back together again. Especially getting the latchiung mechanism (the blue plastic part, metal pin and spring) back togehter took me some time and was a bit stressfull. The metal pin kept falling out again and again. Not sure why I didn't take a look at my pictures, guess I thought I didn't take a photo or something. That would have made putting it back together much easier. The contacts "tabs" (for the lack of a better word, sorry English isn't my first language, Hello from Germany!) were pretty clean so no need to clean those but in hindsight I probably should have cleaned the golden contacts inside the switch before putting it back together. Especivally the first one on the left seems to have some tarnishing going on.

Next I went on to reflow the entire board.

And that's all so far.

Oh two more things. Does anyone know of a good table with ESR values that shouldn't be exceeded or has some other experiences to share on when to replace a capacitor based on ESR measurements? Any good rules of thumb?

In one of the phono board pictures you can see two links being soldered across two resistors, effectively shorting out those components. Does anyone know if this is factory for this unit? It just seems odd to put the components there and then short them out. Maybe it's some amendment that was put in by a service tech? Sorry I forgot the specific word that describes basically when a manufacturer fixes an issue and informs their service techs to put that in on the next service visit of that device.

 

[elnaldo]

* usually Ethyl Acetate is softer than Acetone, even nicer with plastic surfaces. I mainly use Ethyl Acetate to soften glues, and only use Acetone when I need something stronger.

There are many tables and charts on the Internet about ESR vs Capacitante and Voltage.

 

[LEECH666]

Oh that's good to know. Maybe it was just my impression that the acetate worked better but I could've been wrong. They both were kind of the same when I used them on the caps.

 

[LEECH666]

Let's continue the thread.

There are some trace cuts to patch in some the inductors on the phono board that I didn't notice before. This makes me assume that the bridged resistors are also factory but I am still not entirely certain on that. Will have to see if I can find pictures of the phono board somewhere on the net.

I put the inductors and capacitors back on the board but in hindsight this was a somewhat wasted endeavour.

I continued to reflow the entire speaker board. This wasn't totally necessary since almost all of the solder joints still looked to be in pretty good factory like condition.

I took out the transformer to clean some more of the case.

Well crap! I broke some more stuff. One of the leads broke away partly from all the fiddling around with the transformer. I didn't feel that it was still making good connection with some of the strands broken in the wire so I rewound the wire and then soldered it onto the metal prong.

This RCA jack of the phono stage broke. I tried to fill it with hot glue and that worked okay but then I got picky and tried to clean the glue a little and then it came apart again and I tried again and long story short I melted the plastic part enough for it to get deformed. That didn't all turn out so well. Damn. Anyway I will try JB Weld next.

Looks like this RCA jack here (eBay link) might work as a replacement but looks like pretty cheap quality too.

I've also completed my dim bulb tester since all the remaining parts and a faston crimp tool that I totally forgot about at first all arrived today.

Here it is in action with a Dremel being the DUT (device under test).

And that's all I got done in the last couple of days since the 23rd.

Over the next couple of days I will need to do my taxes so I probably won't have much time to work on the amp. I hope that after I'm done with that that I'll can get on with the testing.

Cheers!

 

[LEECH666]

Didn't get too much done over the last days, as mentioned in my previous post but today I had the time and drive to try to glue back together that broken RCA socket. Usually when I try to glue stuff it ends in disaster.

This is the first time I ever used a JB Weld product and I decided to use the Kwik variant which supposedly sets in 6 minutes.

Used some Tesa film tape to mask of the sockets somewhat. The advertised 6 minutes setting time were a little too short for my liking but overall it turned out okay before the epoxy became too hard to shape any further.

After curing I filed down the compound a little to get it into shape.

Soldered everything back in place and put it in the case and then used a sharpie equivalent pen to find out where I had to drill a new hole.

I took the measurement of the inner screw diameter (2.5mm not accounting for the threads) and drilled a hole using 1mm, 1.5mm, 2mm and finally 2.5mm drill bits.

SUCCESS!! Not perfect but works well enough.

And that's all I have for today. Again I will be pretty busy on this weekend so I don't know when I will finally start testing the electronics of the amp.

Cheers!

 

[LEECH666]

Good day citizens of the Audio Karma forums!

Yesterday I embarked on a journey to finally give it a shot to repair the Yamaha AX-500 that has been sitting on my pile of amps to be repaired.
...
More bad or dirty looking solder joints.

Looks like some pictures and lines of text got lost in my initial post when I hit the "no more than 20 image link per post"-limit the first time. Just for completeness here is what I've omitted.

This is my second favorite solder joint in this amp. It's so bad you can shine a light through it. This time there is no corrosion to blame.

Taxes are done so I hope I can get onto testing next week but I am also waiting on some part to build an 8/4 Ohm audio dummy load so maybe I will wait for those parts to arrive before continuing. Time will tell.

Cheers.

 

[raycarr00]

nice going! hopefully, you'll get your parts before becoming disinterested(I did. took mouser 11/2 months to get me parts.)
thanks for the thread. Amazing pictures!

 

[LEECH666]

Hi raycarr00,

yeah I hope I don't lose interest too but for the moment it's on my todo list to finish this amp. But you know other stuff gets in the way constantly and I am a bit of a chaotic person and have sleep issues sometimes but I digress.

I cheaped out and ordered high power 100W resistors (2x 4R and 2x 8R) and an aluminium heatsink to build the dummy load and will probably mount the connector just on a metal bracket. The first iteration might be a bit more barebone though. The parts are already in Belgium according to tracking so it shouldn't take them that much longer to arrive here in Germany.

The pictures are taken on my smartphone. (Xiaomi) Poco X3 NFC (Chinese "El cheapo" - haha) but actually it's pretty good considering the price. I just don't really like being part of the Xiaomi Botnet it comes with but I digress again. I actually wanted to take the photos on my compact Sony RX100 MK3 which does better pictures iirc but the handling is a bit more clunky and I had lend it out to a friend who went to Kenya for vacation and wanted to take pictures of the wild life.

Cheers!