Onkyo Amp help

[docstu]

Okay all. I have another oldie but goodie from my closet. I have an Onkyo 7055 amplifier that I took out of service maybe 25 years ago because one channel had become intermittent when it got good and warm. I'm by my own admission a Neanderthal with a soldering iron and a VOM. I'm guessing after reading lots of posts that I have capacitor issues and maybe an iffy transistor. I'm looking at this as a learning project. I know I'll have more in it than it's worth these days but that isn't an issue with me. How do I jump into this? Any guidance would really be appreciated. If this works I'll probably use it in one of my offices to drive some old acoustic suspension speakers. I have a pair of AR 2's that used to be part of it's system that I've redone.

Thanks

 

[z-adamson]

Well, the first thing to do would be to give it a visual….any burned resistors, exploded caps, cracked solder joints?

Also, separate the amp from the preamp. Test the amp with another known good preamp. If the problem goes away, the problem is in the pre. If the problem remains, the problem is in the amp.

 

[cademan]

I would say to check for any solder joints that get intermittent when things heat up.

 

[50nstillhifi]

A visual inspection is usually the first "tell-all". Then simply following the supply to the regulator to the power amplification stage will narrow your area of concern. Measurements are good but in readily accessed boards, simply touching the transistors (near sinks) that should be hot.. and are not can lead you to test the suspect signal path. I used this method in finding the faulty regulator transistor for a Sherwood amp. After replacement (a more involved procedure), the amp performed flawlessly.

 

[Blue Shadow]

Did you get the service manual from hifiengine?

When I had a unit that changed as it warmed up, Thain grabbed a poker, plastic stick or something none conductive and pushed a bit on all sorts of components and that changed the problem...was a bad solder joint on one leg.

Have you cleaned the controls and such...not expecting this is the issue though, think more a solder joint or a transistor that doesn't want to be warm...use cooling spray to diagnose this one.

Maybe with the unit unplugged and the caps discharged, you could move things around a bit in case a connector or other non-soldered connection is not good in a warm climate.

Lots of things to try but get the SM and give it a look and follow along with what those that talk specific steps to do and report progress.

 

[whoaru99]

Yeah, need to fix it before shotgunning in new caps. Unless it's a specific known issue with that model, I doubt capacitors in general are source of that problem.

 

[docstu]

Thanks for the info guys. I've gotten inside and cleaned everything. Cleaned the switches while I was at it. Got out the magnifying headset and I don't see any bad joints. Wiggled everything and nothing seems loose. I just worry that turning it on will let out all of the smoke. Should I go ahead and try to power it up? I guess there's not much to lose. Not like it's a Macintosh!

 

[cademan]

Shouldn't do anything bad. If anything, it will continue to be intermittent in one channel.

 

[z-adamson]

Thanks for the info guys. I've gotten inside and cleaned everything. Cleaned the switches while I was at it. Got out the magnifying headset and I don't see any bad joints. Wiggled everything and nothing seems loose. I just worry that turning it on will let out all of the smoke. Should I go ahead and try to power it up? I guess there's not much to lose. Not like it's a Macintosh!

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