Any knows how a screw can cause protect mode (on Onkyo TX-SR605)?

T

tank209209

New Member
A friend gave me an Onkyo TX-SR605 which got into protection mode right after being powered on. I was able to isolate it to a screw which secures the vertical PCB board to the horizontal amp board -- if I loosen the screw or take it out, the receiver works normally; if I tighten it all the way, it gets into protection mode when powered on. See the marked screw in the attached pic.

For now, the issue seems fixed after I added a nylon washer on the screw. But what is the root cause? Is it a known grounding / isolation issue on this model at a PCB mounting point?

Any insights from TX-SR605 owners or Onkyo techs would be appreciated what may be the root cause.


onkyo-tx-sr604-screw.jpeg
 
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tank209209 said:
Yes that's what I did to bring it to normal. But how could it become a problem only after a few years' use?
Click to expand...
My friend had a large Sansui receiver that worked fine then one day went into protection. I took it home to look it over. Had the top and bottom off, receiver on it's side and eventually began checking functions when I couldn't find a problem.

Put it back together and tested it only to find it in protection again. Took the covers off, protection good.

As I was putting the bottom on I noticed one of the feet had a slightly longer screw than the others. This screw was under one of the circuit boards and when the weight of the unit flexed enough it would make contact and short circuit.

I'll guess that yours too is settling in after all of this time and finally flexed enough to short circuit.
 
kwayde said:
My friend had a large Sansui receiver that worked fine then one day went into protection. I took it home to look it over. Had the top and bottom off, receiver on it's side and eventually began checking functions when I couldn't find a problem.

Put it back together and tested it only to find it in protection again. Took the covers off, protection good.

As I was putting the bottom on I noticed one of the feet had a slightly longer screw than the others. This screw was under one of the circuit boards and when the weight of the unit flexed enough it would make contact and short circuit.

I'll guess that yours too is settling in after all of this time and finally flexed enough to short circuit.
Click to expand...
This is interesting, might well be what happened to my Onkyo as well. Thanks for sharing it!
 
tank209209 said:
Yes that's what I did to bring it to normal. But how could it become a problem only after a few years' use?
Click to expand...
There prolly is a small gap between the end of the screw and some hot point on a circuit board, underneath it. Boards can warp slightly with age. Voila! Contact and a short.

A shorter screw may work, too!
 
tank209209 said:
This is interesting, might well be what happened to my Onkyo as well. Thanks for sharing it!
Click to expand...
Just a follow-up, it turns out that it is more than a screw touching the chassis underneath the PCB. Now I got some humming noise from the speakers even without any input. It's probably a grounding issue -- I may have bypassed some grounding path and some current is leaking to the speakers? I'm yet to spend more time on it. Looks like I need to identify a short somewhere.
 
tank209209 said:
Just a follow-up, it turns out that it is more than a screw touching the chassis underneath the PCB. Now I got some humming noise from the speakers even without any input. It's probably a grounding issue -- I may have bypassed some grounding path and some current is leaking to the speakers? I'm yet to spend more time on it. Looks like I need to identify a short somewhere.
Click to expand...
Before doing any circuit surgery, I really go over the boards, wiring, and board traces with a lit magnifying glass. You want to find the short before you start removing parts, or sometimes things get a lot worse.

If you don't mind working with live voltage, this is what I do. The WOODEN chopsticks test. Connect the unit to speakers or headphones, then turn it on. Now, systematically go from one end of the unit to the other, tapping wires. boards, components, etc., and listen for changes in the hum. Once you find a sensitive area, isolate the source of the noise.

That can save a ton of work. Good luck! :thumbsup:

BTW... do NOT grab the chassis with your free hand. You do not want to test the "path of least resistance" with your body.
 
My Parasound HCA 1000a's overload LED"s were lighting up, so I did some research and found out that while there are many reasons why this can happen, a possible quick fix that had worked for many and been recommended by at least one person from Parasound was simply to tighten the screw found in between the 4 large capacitors under the hood. So I gave it a try and it worked! Nobody seems exactly why it works, but I was sure happy that it did.
 
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