Hello, I'm fairly new to this level of electronic repairs. I've rebuilt several antique radios with no troubles, and have done tuneups on several guitar amplifiers with no troubles. But this one, is a little daunting, but I'd love to be able to fix it on my own. The amp is an Onkyo Integra model A-8087. I've inspected the amp visually and find no obvious or glaring issues. The amp has a 7amp main fuse, and it blows almost immediately when powering on the amp. I powered the amp up with a variac and a dim-bulb tester, and the bulb lights very brightly. I don't really even know where to start looking. Any help would be appreciated.
Onkyo Integra A-8087, keeps blowing fuse
- Thread starter Kreek123
- Start date
Binkman
Lunatic Member
Greetings and welcome to AK.!
service manual here free to join no nags or hacks.
https://www.hifiengine.com/manual_library/onkyo/a-8087.shtml
Not bad schema. I have a-8057 model.
For certain you have a short. could be the output transistors or in the power supply region. dim bulb tester is enough for this testing variac not needed. All testing is done with no speakers connected or any input loads. I'd put the unit in Aux. and vol. off etal.
I would unsolder the leads of the output transistors from the main board no need to pull. then run another dbt test. if fuse still blows then most likely in the power supply or down stream short possible.
here's a link from member 'avionic' for testing the transistors with your dmm with pics. (ty avionic.
)
any help needed we're here. considering your previous experience pretty sure you'll adapt to SS easy. if you have an o'scope you could really shine but dmm can get you by.
bink
service manual here free to join no nags or hacks.
https://www.hifiengine.com/manual_library/onkyo/a-8087.shtml
Not bad schema. I have a-8057 model.
For certain you have a short. could be the output transistors or in the power supply region. dim bulb tester is enough for this testing variac not needed. All testing is done with no speakers connected or any input loads. I'd put the unit in Aux. and vol. off etal.
I would unsolder the leads of the output transistors from the main board no need to pull. then run another dbt test. if fuse still blows then most likely in the power supply or down stream short possible.
here's a link from member 'avionic' for testing the transistors with your dmm with pics. (ty avionic.
)any help needed we're here. considering your previous experience pretty sure you'll adapt to SS easy. if you have an o'scope you could really shine but dmm can get you by.
bink
Well that's a very encouraging response, thank you! I was worried I'd be told to go back to my radios until I learned more! I do have an oscilloscope available for testing. I'll do what you suggest, unsolder the output transistor leads and test again.
Also, I don't see any link for the transistor testing. Am I missing it?
Thanks again.
I do have an oscilloscope available for testing. I'll do what you suggest, unsolder the output transistor leads and test again.Also, I don't see any link for the transistor testing. Am I missing it?
Thanks again.
Ok, so I de-soldered the leads on all the output transistors, powered up the amp with the dim-bulb tester, the power light lights up, and a few seconds after I press the power button, I hear a click sound, kinda like a relay, and that's it. No light on the dim-bulb tester at all. It looks like the amp is operating normally, save for no output transistors connected. I tested each output transistor with my DMM, four 2SA1186 PNP's, and four 2SC2837 NPN's, all tested good with the DMM. Any suggestion as to what to do next? I'm feeling out of my depth.
Concentrate on one channel first, solder just one pair of transistors on that channel.....that is one NPN and one PNP first, then do the dim bulb test. If it is ok, than solder on the other pair. If it is ok, this channel is fine. Then do the same thing on the other channel until you see it fails. Then report back.
The circuit looks to be a well design one, just the heatsink is too small and they have to reduce the bias current to keep it cool.
The circuit looks to be a well design one, just the heatsink is too small and they have to reduce the bias current to keep it cool.
Last edited:
That's such a simple and logical idea. I don't know why I didn't think of it. LOL!
Ok, so just to be clear, the transistors are laid out in what looks to be two C2837's and two A1186's on each side. I'm assuming that I solder two C2837's and two A1186's, and that's one channel, correct?
Edit: Never mind, I just re-read your post and see that you told me exactly how to solder them and in what order. Sorry about that.
Ok, so just to be clear, the transistors are laid out in what looks to be two C2837's and two A1186's on each side. I'm assuming that I solder two C2837's and two A1186's, and that's one channel, correct?
Edit: Never mind, I just re-read your post and see that you told me exactly how to solder them and in what order. Sorry about that.
So, that was an adventure.
First: I soldered one C2837, and one A1186. Powered up, Dim-bulb tester light bulb lit bright.
Second: I unsoldered the A1186, but left the one C2837 soldered, powered up, dim-bulb tester lit a little very briefly, then went off.
Third: I unsoldered the previously soldered C2837, and soldered the other C2837 and A1186. Powered up, and the dim-bulb tester lit bright. Unsoldered the A1186 leaving the one C2837 soldered, powered up, dim-bulb tester lit a little very briefly, then went off. Here's where things got exciting.
Fourth: I soldered the other C2837 so that I had the two C2837's, and no A1186. Powered up, the light lit briefly, then went off, and then the amp made the click sound like it does when it powers up, and sparks flew and the light lit bright. Couldn't shut down fast enough! Then I looked around until I found where the sparks came from. One C2837 looked like it shorted to the heat sink.
This is likely my fault. Quite a while back, I removed the transistors and cleaned the old dried up heat sink compound and remounted the transistors. I'm guessing they are supposed to be insulated from the heat sink? A quick google search revealed insulation pads for just this situation. I'm guessing that should be my next step, before anything else is done.
Interestingly enough, the transistor still tests good with my DMM.
First: I soldered one C2837, and one A1186. Powered up, Dim-bulb tester light bulb lit bright.
Second: I unsoldered the A1186, but left the one C2837 soldered, powered up, dim-bulb tester lit a little very briefly, then went off.
Third: I unsoldered the previously soldered C2837, and soldered the other C2837 and A1186. Powered up, and the dim-bulb tester lit bright. Unsoldered the A1186 leaving the one C2837 soldered, powered up, dim-bulb tester lit a little very briefly, then went off. Here's where things got exciting.
Fourth: I soldered the other C2837 so that I had the two C2837's, and no A1186. Powered up, the light lit briefly, then went off, and then the amp made the click sound like it does when it powers up, and sparks flew and the light lit bright. Couldn't shut down fast enough! Then I looked around until I found where the sparks came from. One C2837 looked like it shorted to the heat sink.
This is likely my fault. Quite a while back, I removed the transistors and cleaned the old dried up heat sink compound and remounted the transistors. I'm guessing they are supposed to be insulated from the heat sink? A quick google search revealed insulation pads for just this situation. I'm guessing that should be my next step, before anything else is done.
Interestingly enough, the transistor still tests good with my DMM.
You mean you don't have insulating pads between the transistors and heatsink? That's not good!!!!
I use this pads, no grease needed.https://www.digikey.com/product-detail/en/bergquist/SP600-114/BER107-ND/201902
If you short the metal tap to heatsink( grounded), that should not hurt the transistor. If it is good, don't change the transistor just yet. If you change transistor, you have to worry about matching the transistors. If the burned mark is sticking out, use a small file to file down only the point where it stick out ONLY), don't file the smooth area down. You need flast surface to have good heat conduction.
I use this pads, no grease needed.https://www.digikey.com/product-detail/en/bergquist/SP600-114/BER107-ND/201902
If you short the metal tap to heatsink( grounded), that should not hurt the transistor. If it is good, don't change the transistor just yet. If you change transistor, you have to worry about matching the transistors. If the burned mark is sticking out, use a small file to file down only the point where it stick out ONLY), don't file the smooth area down. You need flast surface to have good heat conduction.
Last edited:
Binkman
Lunatic Member
Avionics transistor test link
http://audiokarma.org/forums/index.php?threads/testing-transistors.201303/#post-2362176
sorry got ahead of my posts.
seems like making good progress.
IMO with no main transistor spacers somebody been in there before you. odds are you blew a driver transistor(s) so may have to pull those and still go back the power supply. Oscope ideal for checking rails for shorts. bad rectifier always possible.
http://audiokarma.org/forums/index.php?threads/testing-transistors.201303/#post-2362176
sorry got ahead of my posts.
seems like making good progress.
IMO with no main transistor spacers somebody been in there before you. odds are you blew a driver transistor(s) so may have to pull those and still go back the power supply. Oscope ideal for checking rails for shorts. bad rectifier always possible.
