Yet another Adcom GFA-565 problem

[spind]

Steve,

I'd recommend Columbus Radio if you want to stay local. This is a specific problem though, and I'm not sure if they have seen it before. They're really getting up there in age, but still seem to be in business. Do you have any experience yourself? I could probably help out, though not being a pro I hesitate to work on other people's equipment. I do have test equipment and access to an ultrasonic cleaner.

Steve.

[Lockport]

Originally posted by anatech
Hi Steve,...

"One is 21.3 Ohms, the other is 11.3"


That isn't right either. There are resistors from RCA shield to ground, so these may need to be replaced. The only other thing I can think of is that your meter and / or probes are not reliable and may give varying readings on the resistance function.

-Chris

...

Chris, after a few hours warm up which perhaps they needed: If I place the digital multimeter's red probe on the RCA Ground, and the black on the speaker ground terminal, I get 8.4, if I reverse the probes I get 2.6. The other amp yields 21.2 and 0.00?

What's up with that?

Steve

[Lockport]

Originally posted by spind
Steve,

I'd recommend Columbus Radio if you want to stay local. This is a specific problem though, and I'm not sure if they have seen it before. They're really getting up there in age, but still seem to be in business. Do you have any experience yourself? I could probably help out, though not being a pro I hesitate to work on other people's equipment. I do have test equipment and access to an ultrasonic cleaner.

Steve.

Steve,

Columbus Radio sounds like a plan. I have met them before, too. I called and spoke on the phone, described the problem, the degree of DC offset and that the boards probably were never cleaned properly. He is busy to Christmas and a trade show after but I told him I would bring them round in mid-January.

Steve

[Zen Mod]

Originally posted by Lockport


Chris, after a few hours warm up which perhaps they needed: If I place the digital multimeter's red probe on the RCA Ground, and the black on the speaker ground terminal, I get 8.4, if I reverse the probes I get 2.6. The other amp yields 21.2 and 0.00?

What's up with that?

Steve

there is no any connection with warm up .

anatech told you to measure that with amps powered off ....... at least some time , to let all caps to discharge .

just find capable tech .
otherwise you'll obviously stack with them , or even make some greater damage - either to amps or speakers .

welding machines aren't for fun .

[Lockport]

Originally posted by Zen Mod



there is no any connection with warm up .

anatech told you to measure that with amps powered off ....... at least some time , to let all caps to discharge .

Right. I thought he meant without speakers or line in.
That being said one is 5.5 the other 10.3

Originally posted by Zen Mod
just find capable tech .
otherwise you'll obviously stack with them , or even make some greater damage - either to amps or speakers .

welding machines aren't for fun .

I hear that. Lucky once, I guess.

[anatech]

Hey Choky,
Hi, and thank you. You do get around! One of these days I am going to try your ...... SHUNTY! Looks pretty good to me to examine, poke and prod.

Hi Steve,
You must measure with the amps powered off and discharged. Any voltage across your speaker terminals will interfere with your resistance measurements. In other words, you will make silly readings that don't make any sense at all.

He is busy to Christmas and a trade show after but I told him I would bring them round in mid-January.

Most good technicians are very busy. This is expected.

In the mean time, do not use your amplifiers! Never use any equipment that is not operating properly. To do otherwise may simply end up costing you a great deal more money. Beg, borrow or steal (not really) another amp until these are properly repaired.

-Chris

[Lockport]

Thanks all for tolerating my incompetence.

I feel comfortable with the service center I will be going to. I have the amps unplugged and set aside for now. Will see in mid January what the results of their service will yield and will let you all know. As for now, I am out of town for a week.

Happy holidays!
Steve

[anatech]

Hi Steve,
Good luck with your amps and let us know how it all turned out.

Enjoy your holidays and Merry Christmas!

-Chris

[Lockport]

Hi all! Its been a while...recession and all.

I finally got my amps back and here is how it went.

They said the boards were originally sprayed with an adhesive coating that, after a while, became conductive. It wasn't electrolyte on the boards. They said an ultrasound would not clean this stuff, anyway. They needed to scrap it off. They also said the boards had some caps replaced at one time. As the amps were supposed to have had this done before I bought them, I am guessing the elctrolyte was cleaned off the glue, at the same time some of the caps were replaced.

Getting them home I see they will pass the Mic/Dolby set up sequence on the Sony (they failed before), but I still see they are a lot quieter than they originally were. Is it possible these issues have damaged the preamp abilities of my Sony receiver?

Unfortunatly I put them back in the cabinet without measuruing the offset. That's next.
Thanks

[spind]

Good news that you got them back. Hopefully they are far enough away from the river

Steve.