New Construction. Some issues solved. Some not. Need advice.

[Paul Birkeland]

The single lit LED is generally a poor ground connection from the bias string, or a funky solder joint on a transistor in that C4S.  (The 0V at the output supports a bad transistor solder joint)

[harv-e]

OK.  That's fixed.  I cleaned off the board with some alcohol and found a tiny solder bridge shorting that transistor.  So the regulator board and been completely "resoldered."  All lights work.  Audio from both speakers. 

And so now I am back to the original problem - motorboating sound coming out of both speakers even with the inputs shorted.  I am OK with hiss.  But not this constant putt putt puttering.  To my mind, this is  a power supply problem since it is coming from both speakers.....and I do not believe it is a solder connection as I have gone over these on the regulator board  (I have not redone the joints on the power supply board).  I have to believe that it is a bad component.....but I do not have a clue as to which one it is. 

The voltages before the "resolder all the joints" issue seem to be within specs......and that's why I was advised to resolder the joints.

This is very annoying.  I have been patient trying to fix this, but I don't know what else to do.

Thanks.

Harvey

[corndog71]

Could it be interference from something nearby?

[harv-e]

Nope.  I replaced the EF86 tubes and the problem is GONE.  Actually, I replaced all the tubes, one at a time.  No change until I got to the EF86s

FINALLY

[harv-e]

Wellllll, so much for that.  An hour of use.....and the motor boating is back.

Sad.  Really thought this was going to be it.  I'm going to have to go elsewhere for product.  No reliable answers here.  Disappointing.

[Paul Birkeland]

We do offer repair services if you would like us to get it up and running for you.

-PB

[mcandmar]

I've experienced the motor boating phenomenon before with an old pair of Boston Acoustic computer speakers, traced the problem to a dodgy power supply cap right after the diode bridge.

[Doc B.]

I understand that you are frustrated. The suggestions may not have solved your original problem, but that does not mean our answers to questions are unreliable as you seemed to have had other issues come up that you were coached on fixing. I can't think of any other Eros that we have heard of having this motorboating problem and thus we don't have any previous experience dealing with it. You could just send it to us and let us fix it for you. If the issue is a bad part there will be no charge. If the issue is a construction error you will get a very nice preamp for a reasonable repair fee.

[Paul Birkeland]

Hello Harv-e,

I got into your repair yesterday afternoon and this morning, and I found that a couple of resistors may have been damaged on the 12BH7 socket, so I replaced them with more robust parts.

I also found some other parts that may have been a bit loose, and I tightened them all down to prevent any further contact issues.

Also, the ground wire from one of the input RCA jacks to the terminal strip was loose in the terminal strip and not soldered down.  This presented us with significant hum while running the amp in until I was able to find it by poking around with a pencil.  This is most likely to be the primary issue you were facing, and when you ended up replacing the tubes, the physical jarring of the Eros would have temporarily re-established this connection for you for a while.

I did end up replacing one of the C4S boards in the process of debugging, but in retrospect it wasn't at all necessary. 

We'll keep running the amp for a few days with the inputs shorted and the outputs driving speakers so we can be sure that you won't have any additional noise issues.

Sincerely,
PB