Yamaha a-520 Repair Help

[enticer340]

Hello all, was wondering if I could get some opinions on a old integrated amp I am trying to get going again. Now I am a mechanic by trade but play with electronics on the side sort of. My dad bought this Yamaha A-520 new when he was 17 so I really want to make it work again, about 8 years ago he put a new transformer in it because the old one failed and it worked fine for a few days after that and then a puff of smoke and nothing. it sat since then and now I have been digging into it and found 2 bad power transistors on one channel (2SA1265 and 2SC3182) and 2 bad driver transistors if that's the term (SA1306A and 2SC3298A) on the same channel and about 7 blown resistors. everything else looks good and I have new parts on order just was curious if there is anything else to look for when these components fail on a older amp. Any input would be appreciated thanks!

[FlexibleMammoth]

Just my two cents here:
Get matched power transistors. They are more expensive, but if you cheap out here, it will go up in smoke again once you turn up the volume.
And replace all electrolytic caps if the amp is really old. Check the PCB for heavy burn marks (burnt fiberglass is a conductor) and scrape if necessary.

Also get yourself a variable isolation transformer (Note: a Variac is NOT an isolation transformer) to bring up the repaired amp slowly and watch for more smoke or strange smell. Also, an isolation transformer really helps you to not die a slow and painful death if you touch something that has high voltage on it.

[Armadillo]

Well here is my opinion;

Before you spend even ten cents on it, do your maths on all the total costs of "ALL" the components you going to buy [including a new transformer] and weigh the worth of time and money on an "integrated amplifier".  Also accept the risks that you may end up not getting it fixed.
Alternatively also check the after market resale value of it.

https://www.ebay.com/p/Vintage-Yamaha-A-520-Stereo-Integrated-Amplifier-75watts-Channel-Tested-Works/1501569515

Or consider putting it up on ebay as broken for parts and collect some returns instead.

[Bashstreet]

Hello all, was wondering if I could get some opinions on a old integrated amp I am trying to get going again. Now I am a mechanic by trade but play with electronics on the side sort of. My dad bought this Yamaha A-520 new when he was 17 so I really want to make it work again, about 8 years ago he put a new transformer in it because the old one failed and it worked fine for a few days after that and then a puff of smoke and nothing. it sat since then and now I have been digging into it and found 2 bad power transistors on one channel (2SA1265 and 2SC3182) and 2 bad driver transistors if that's the term (SA1306A and 2SC3298A) on the same channel and about 7 blown resistors. everything else looks good and I have new parts on order just was curious if there is anything else to look for when these components fail on a older amp. Any input would be appreciated thanks!

I think you have identified the most damaged areas and components.
You can replace the damaged components (do any trace repair etc) and then further diagnose the unit if needed.

That said it would be sensible to find the reason why the damage happened.
I am a bit concerned of the transformer your father swapped.

It is possible it has incorrect voltages it was not wired correctly or is defective.

Find service manual and make sure the transformer is suitable and is correctly wired BEFORE you retest it after repairs.

[Armadillo]

Weeeeeeell first he said nothing about a burnt transformer (that was back in the day when his dad fixed it) and secondly he really wants to fix it since it was his dad's, so let him.
However it would really be a good idea to check the transformer for shorts or open windings, that could be a showstopper.

Please read Bashstreet comment about it above.   

[enticer340]

Thanks for the replies, the transformer is a replacement right from Yamaha and from what I can tell is wired right, I realize I can purchase another a-520 for around 100 Canadian or less I wanted to fix this just because it was my fathers that's all, I did buy matched sanken transistors for replacements and my plan was to replace what I know is bad and see if it works or not, i have the service manual and have been figuring out the wiring diagram, it probably is due for a recap. Now I have seen people wire a light bulb in series with the amp as a poor mans current limiter I guess for when you power up a new build?. I enjoy diving into this sort of stuff on the side so the money factor isn't a big deal to me because its fun. I appreciate the input from everyone, all my parts show up this week.

[Chriss]

Hi!
Nice to hear about peoples who care about the memories of the past of his/her parents.
I'm on your side.
Do it, fix it but don't give up.

- your safety should be on the first plase.
If you can buy an isolation transformer. You can use it in any future projects and you will be safe as you're units too.
- the bulb in series is a must have if you won't gambling with the new parts. Put a 100w light bulb in series with the main input of your amp.
When you changed the broken parts and checked for any other damage power up the amp.
The bulb will lite up for a sec or two and then dimm out.  If it stay shining that means your amp has a short somewhere.

- try to figure out the schematic diagram of the are where the parts was burned. So you can maybe get the reason why it burned out.
- before you put back into the place the new parts check if some short is appear on the place where the parts will be fitted.
I mean if you have to put back a transistor,  before you do that, check for some sort of short between the pin hole on the pcb. If let's say the pin hole basis and emiter are in short don't put the new transistor. First find whay is it in short.
- change all electrolyte caps. Don't think about is it good or not.
Just change them all.
Old caps a very bad caps in every meaning.  :-)
- check for defective diodes. You can have diodes in short even if they are not burnt and can't be recognized by visual inspection.
Don't forget to check the bridge rectifier if some there. That is also full filled with diodes.
- I would send the main transformer to pros and let them check in what condition is it.

I hope I helped a bit to organize the repairing process steps and you will fix the unit.

Good luck!

Sent from my GT-I8260 using Tapatalk

[Bashstreet]

Thanks for the replies, the transformer is a replacement right from Yamaha

That means nothing.
Check yourself if the transformer is correct gives correct voltages etc do not trust (it is from Yamaha) always check i am almost certain it is the transformer or something connected to its functionality.

[orbanp]

Hi Enticer,

Yes, you should fix that amp!
Having that 100W lamp in series to power up the amp without load is a good advice, follow it!

I would not do whole-scale electrolytic cap replacement, would only change the bad ones. Chances are the caps are just fine.
If the top of an electrolytic cap is bulging then it is bad, that needs to be replaced. Other than that you could check them in the circuit with an ESR-meter. You can build your own cheap ESR-meter, just google it!

This site has extensive info on audio circuits, check them out:
http://sound.whsites.net/articles.htm
Check the article section on "Beginners' Luck - The beginners' Guide to ...", and especially the articles on "Amplifier Troubleshooting and Repair Guide".

Good luck, Peter

[Armadillo]

it was my fathers that's all,

I am sorry. You know English is not my mother tongue but I suppose if you add the word "late", it would have been clearer to me.
Nevertheless. I am sorry for not getting it correct.
Yeah... all the best to get it fixed.
 

[Bashstreet]

Hi Enticer,

Yes, you should fix that amp!
Having that 100W lamp in series to power up the amp without load is a good advice, follow it!

I would not do whole-scale electrolytic cap replacement, would only change the bad ones. Chances are the caps are just fine.
If the top of an electrolytic cap is bulging then it is bad, that needs to be replaced. Other than that you could check them in the circuit with an ESR-meter. You can build your own cheap ESR-meter, just google it!

This site has extensive info on audio circuits, check them out:
http://sound.whsites.net/articles.htm
Check the article section on "Beginners' Luck - The beginners' Guide to ...", and especially the articles on "Amplifier Troubleshooting and Repair Guide".

Good luck, Peter

30+ year old electrolytic caps have reached end of their operating life and should be replaced.
If the capacitors are high quality they can still be functional although i think that particular amplifier used rather poor caps...

It all depends if he wants to use the amplifier and restore it to factory speck.

ESR meter is great tool but it do not tell if the capacitors are leaking electrically what indeed is maybe the most common failure mode in old capacitors of the age...
I am rather certain if not all most of the electrolytics have turned leaky.

Better replace them maybe with exception of the 2 large caps what can be quite expensive and last generally longest.

[Chriss]

Change all caps.
Don't mess with esr meter etc. Keep in mind you are not a qualified person who can and know how to check caps.
So, just changed them all.

Don't build any esr meter by your self.
Esr meters must be calibrated. A bad esr meter circuit would you turn in the wrong way. And you as a beginner need the feeling of success.
A better option is to buy an esr meter from ebay from china. They are several $ .
Even a high end lab esr meter can't tell you if a cap is leaking. So.
Change all the caps.

Good luck and keep posting your situation.

Sent from my GT-I8260 using Tapatalk