Need advice - Optonica SA - 5605 left channel distortion

[Krosya]

Ok,
Turkey day and shopping days are done with, so I can start focusing on this. I got my de-soldering pump and braid, and even looked at all the circled by you spots, fixed some up, now they look cleaner. No change as far as distortion goes. So, what should I tackle next? I did look at the link about testing transistors.
Did not try to take out the output transistors yet - they are kinda hard to get to - looks like I will have to lift the whole board out to get to the screws that hold them. Funny enough, those resistors I thought tested bad, - I re-tested and now they seem to work. I think I will go over all of them again, just to make sure. Let me know what else I can do/test. I will most likely have some time tomorrow and/or day after to play with this. Thanks!

 

[jheu02]

Ok,
So, what should I tackle next? I did look at the link about testing transistors.
Did not try to take out the output transistors yet - they are kinda hard to get to - looks like I will have to lift the whole board out to get to the screws that hold them. Funny enough, those resistors I thought tested bad, - I re-tested and now they seem to work. I think I will go over all of them again, just to make sure. Let me know what else I can do/test. I will most likely have some time tomorrow and/or day after to play with this. Thanks!

Now that you can check some of the components out of circuit, we may find out where the failure has occurred.

The resistors...did you desolder 1 leg to get them out of the circuit?

r.e. output transistors - sorry it's an inconvenience, but sometimes you have to do a bunch of work to eliminate sources of problems. If I sound a little flippant, sorry, I just see too many young people (not that you are) whine about having to actually do some work to get a desired result. Hopefully this is not the case.

Is the distortion issue still ONLY occuring when you turn up the volume????

If so, you're going to need to desolder the legs of the varistor I've asked about several times to electrically check it. This may involve desoldering the good right channel one for comparison. You will also probably need to desolder some of the transistors you circled earlier and test them to determine whether they are the issue.

IF it's not functioning properly, it's not adjusting the voltage to the output transistors as they heat up. This COULD be the case as you turn up the volume, thus, they are being overdriven at higher volume level leading to the distortion.

Just trying to direct you from afar how I would be trying to tackle the problem if it was in front of me, but alas, it's not. So, having to make you my eyes and ears, and I'm certainly not a pro at this...sorry.

 

[Krosya]

Ok, did some more careful checking today - distortion seems to be always there, but is more obvious when I turn up the volume. Thats why I thought it was only at louder levels. But with right music it can be heard even at lower levels too.
I re-checked resistors and one - R530, which is next to the transistor that heats up and attached to heat sink, is bad. Took it out of circuit and all. Also, was able to check that transistor - its B649A - one that heats up and is attached to heat sink - it checks out fine.
I will pull the output transistors later - when I have more time. I'm not afraid of doing more work - I'm worried that since I'm new at this , I may break something else in a process, so was wondering if there was a trick to getting to them, short of pulling the whole board out. But if thats the only way - I will do that, just need to have more time to do it right - dont want to hurry things.
Always appreciate your advice and guidance - I'm just trying to go very slowly and carefully, so I dont mess anything else up while trying to fix this.
Thanks again!

 

[jheu02]

Ok. Gotcha about not wanting to mess things up and being extra careful. Sorry, it's been awhile since I took projects on and must have forgotten MY hesitancy at times.

So, definitely one resistor bad and the possibility of other damage. That's good info about distortion present at all volumes. Though it could still be output related, I would focus more on that area of the board and the components that are most likely to be affected. Was R530 that one that had been replaced by the physically larger blue one? If so, we really need to find the root problem causing that resistor to fail and it's probably a device that's drawing too much current. Will look at the other SM and see what else I think needs pulled/tested.

EDIT: I just took a quick look at the SM. Can you follow the trace and see if R530 is connected to the emitter of that transistor that gets warm? If so, you probably will need to pull and check the output that corresponds to it. It could be shorted...drawing high current and causing that resistor to heat up. Pull both on that side but it will most likely be the 2SB655 that's having issues.

 

[Krosya]

No, R530 looks original - its counterpart for the other channel is the same. I will keep checking things as time allows. If you have any specific ideas as to what I should look into next - let know. For now I will re-check other resistors and maybe transistors on the board. I will not touch the output transistors at this time, but will leave that for when I have some more time to get to them.Thanks

 

[Krosya]

here is a pic of that R530 next to the transistor (attached to the heat sink) that gets hot (its a B649A, btw):

 

[jheu02]

Here's where I think you should focus your efforts for now. Looking back through your pics I see the issue with trying to remove the output, but if you have a stubby Philips Head (or whatever screw head is used to hold the output in) you may have enough room to get it out for testing. Otherwise you may be able to still test it by desoldering the extension pins from where they enter the board.

1. R528, the one that looks like it's been replaced before. It looks pretty tired and almost heatstressed. It is also electrically connected to the emitter of the warm Q.

2. IF that tests bad or way out of spec, check Q516 (circled in blue)

3. Desolder at least one leg of D510. Those are the leads of the varistor mounted to the heat sink. CAREFULLY pull it out of circuit and check with the diode function. You should get a 0L reading in one direction and roughly 1.6V with the leads reversed if the varistor is good.

4. If you don’t have a stubby screwdriver, desolder the pins to Q520 (individually circled in red). These are from the metal extension pieces of the output's mounting bracket. Then you should be able to test the output by probing those pins or the extensions themselves.

5. D508 could be damaged (or part of the reason for) in the process with the overheat of Q512. Just desolder one leg to get an accurate test.

 

[Krosya]

I had some time to mess with this today. I decided to test the output transistor - one closest to the one that gets warm. Took me a long time and a lot of creativity, but i got it unscrewed. And tested, ans it tests fine. Took even longer to put it back. Unfortunatelly since it took so much time, i didnt get to test other things you told me to check, so thats on my list to do next. Not sure if i will be able to do much till the weekend, but i will try and update here with the progress.
Thank you, again!

 

[jheu02]

That's kind of surprising since that resistor is tied to the output, but good to know.

Looking again at the trace side for Q512, the warm one, the Base has a pretty big blob of solder on it and could be touching the collector. You may want to hit the connections briefly with the solder wick to remove a little and make sure there's no bridge between them

 

[Krosya]

Well, I have a development and not a good one. I found a replacement resistor for that bad one - 4.7 ohm, 1/4 watts 5% and put it in. At first it sounded good - I couldnt hear any distortion , but when I went to turn up the volume - receiver went into protection mode. It comes on and tuner looks like working, lights are on, but no sound from either channel now and power light that starts as red and then turns green, just stays red - protection mode. I'm pretty sure I re-installer that output transistor right, because I tested it and with the old (bad) resistor in place it was still having same distortion. Changing resistor seems to have caused this once volume was turned up. Did I blow output transistors? What do you think I need to check now?

 

[jheu02]

I would say that before you do any more testing, look up and build a Dim Bulb Tester! It will limit a high current situation and help save parts while doing the testing, whilst giving a visual indication that something is still wrong. Check those solder blobs I mentioned and clean them up, making sure you don’t have bridges between any of the legs.

There is a reason why that 4.7ohm resistor tested bad (what actually did it test...high ohms, open.... I don't think you ever mentioned). Usually resistors don't just go bad with time, but some other issue like high current causes it to fail. So, we need to determine which part is causing the situation. But yes, by replacing that resistor and running it you could have blown an output, which now registers as a short and is causing the protection circuit to trip.

 

[jheu02]

You mentioned difficulty removing the output to test. Did you either break the mica insulator or forget to reinstall it when you put the output back into the socket?

 

[Krosya]

I think you are right, I forgot to put that insulator when I put it back! Great, now I have more parts to replace.... since I only took one off and therefore it's just only that one that doesn't have insulator, do you think it's just that one that blew or all/more of the outputs?
You know, I dont even remember seeing one there. Maybe it just fell out and I didnt notice? Or is it so thin I didnt notice it? I looked around where I did the work and cant find this insulator laying around, but if its so thin, I might have just simply didnt pay attention and lost it. I guess I will need to buy those too.

 

[Krosya]

Ok, took another look at things - it looks like insulator pad is still in place - looks like it was stuck to the heat sink and thats why I didnt see it. Its possible that it got damaged some place when I was re-installing the transistor and shorted things out? I will have to do it the right way - take out the whole board and remover outputs that way, so I can see whats going on there. I ordered some replacements for the outputs, so I will wait till they arrive and take things apart then. Meanwhile I will try and put together that dim bulb tester.
BTW. resistor that I replaced tested open. (the original one that is). Thanks again for your help and patience .

Where can I get those insulator pads, do you know?

 

[jheu02]

If the insulator did get damaged or is misaligned then yes, the collector (case of the transistor) would have shorted against the metal of the heat sink which would cause the protection circuit to trip.

We still don't know if that actually happened or if there's some other issue. That's where a lot of testing of components will need to happen. You’ll need to be VERY methodical with the testing, and I wouldn't do any more power on tests before you confirm some things. THIS WILL TAKE TIME. You said in your initial post to treat you as a 3 yr old from an instructions standpoint.

Where did you order your output transistor from, what did you order, etc? When replacing these (if they are bad) there are some rules you need to follow or you could make things worse. I won't get into details just yet, but you will need to replace both outputs on that side if the one is blown to make sure they match in some critical specs. There are a lot of fake or substandard copies out there, so it's important to order from a reputable supplier. Ebay and amazon are not on most people's radar as good sources for components.

I have already given you some things to test and look at, some desoldering and or cleanup work to do. So you should start there.

 

[Krosya]

I did order output transistors from ebay. They say they are original - same ones as I have in this Optonica. It will take a little while to receive them. What are the good places to order them from, in case ones I ordered are not good?
I need to order those insulators though, so if you know a good place - let me know , please.
I try to focus on making that dim bulb this weekend. Need to get parts for it. If I have some time left (its a busy weekend), I will test those other things you said to look into.
Thanks

 

[Krosya]

Ok, small update - I built dim bulb tester. Touched up on some solder joints. Will try to do more soon.

 

[jheu02]

I haven't given vendors yet because (I feel) you're better off first figuring out what you need to order, and then place the order for those parts, plus perhaps some other parts that may also be good to replace. Since the original parts are no longer manufactured, it's risky to order off of sites like ebay that claim to have original parts. Many of these are Chinese fakes. Not saying that you'll never find a proper part, but in most cases it's better to just replace the original with a modern part that has equal or better specs than the original...(better power handling/voltage/lower noise, etc).

That said, many on this forum who work on their own gear or others order from the following vendors:
Mouser
Digikey

The above two are by far the most used for modern components, many of which are superior to trying to find original parts.

These others are trusted and used by several, especially if the needed part isn't found at one of the above. Bdent is also a source of some of the original transistors if an adequate modern replacement can't be sourced.

Newark
Bdent
Allied

As you do your testing, we'll come up with a list of the parts you need to get it up and running.

 

[jheu02]

Don't take this the wrong way, but please, when testing the transistors, don't just report that "they test fine". Record the numbers of the different combinations and post them using the format I listed in post #20 on page 1 of the thread. It's important!

If no parts blew in your power up, just the protection circuit engaged, here's one thing you could try before removing the board to get at the outputs...

Plug the receiver into the DBT and using a 100W - 150W bulb attempt to power up. Be ready to kill the power quickly, but I suspect you'll see a brightly glowing bulb, indicating a short. Write down what you observe.
Then...

Desolder the leads I circled that extend from the output transistors...both of them on the bad side to effectively take them electrically out of the circuit without physically removing them since it's a pain.. You can attempt to test the outputs by using those legs, or the case, whichever's easier, and report what readings you get. Make sure there's no metal of the pin touching the traces the three legs (6 total) get soldered to. You can even use a little electrical tape on the solder pads if needed. Then plug the receiver into the DBT, attempt to power up and see if the relay engages.

If it does engage, and the bulb dims, at least one of the outputs on that side is blown. So, we'll need to at least plan on replacing them (both of them most likely).

Here's where it's important to know what you're ordering regarding transistors...Though I don't see it stated anywhere in the other SM, most have a statment like "when replacing output transistors, it's necessary to make sure that the new transistor is from the same class (or hFE group) as the original." The SM of the other unit indicates 2SD675A (B) and 2SB655A (B). So, if your case shows an A, and the replacement you ordered is a B or C, they are NOT compatible replacements, even if it's the same basic number (2SD675). If the case states A or B and the replacement is also an A or B respectively, you can try to use it.

Make sense???

 

[Krosya]

Well,
Here is a pickle - I tested it with the DBT and light goes bright for a second and then dims a good deal, as if its fine. I thought I didnt make my DBT right - checked wiring against info online (thread on this forum) - all looks the same. I checked a couple of other receivers that are working for sure - same result - light dims. So, now I'm really confused - Optonica's red protection light is still on. It lights up. I can tell that tuner works, just no sound. Yet DBT shows no short. What can this be?