I have a Technics SA-GX505 amp/receiver that runs fine for a while, shuts
off for a few minutes, and then will come back on, etc. It tends to run
longer at lower volumes before shutting off; however, no components appear
to be getting hot, not even the main power amp. And the cooling fan works
fine, which is driven from the speaker output level.

I have the service manual which is a little help, but nothing looks obvious.
It's not the output relays that are kicking in, but the main power supply
relay. It's RL 751 and its driver Q751 are driven by RLY (pin 27) on IC 901
the main microcomputer. So it appears the protection circuitry is working, I
just don't know what's triggering it. Any ideas what to check? Speaker
impedance is OK, and again, no obvious heat issues. In my experience, most
of these problems tend to be with the main power amp (IC 601- SVI3206C).
Should I just start there; any other ideas?

Many Thanks, -Bob

are you sure about that heat issue?

if you're 100% absolutely positive it's not heat..then it's possible
you got a bad sensor, OR, you could have a componet that's failing
under minimal heat, it could be a failed componet in the protection
curcutiry. if whatever pin on whatever chip that triggers the
protection cut off, if something in the circuit fails..it could cause
it to go high or low (talking logic-probe stuff here) and trigger it.

if you sent me a schametic, i may be able to give you some places to
look.

"butlercellars" wrote in message
...
. And the cooling fan works fine, which is driven from the speaker output
level.



Replace fan.

I don't know anything about that receiver, but if you just bought it
recently, you might want to check the voltage input selector. If
your in the US, set it to 120V. I've seen receivers come from out
the county that have a different input voltage selected. If it's
temperature related, try cooling the components using ciruit cooler
spray.

Good luck!

Replacing the fan was the first thing I did and I even tried the .1uf cap
across the fan trick, but results are the same. The amp even has the same
symptoms with or without the fan installed. I'm on my second can of
freeze-it, but that has no effect either. Any other ideas?


"Damir Friscic" wrote in message
...

"butlercellars" wrote in message
...
. And the cooling fan works fine, which is driven from the speaker output
level.



Replace fan.

butlercellars wrote:
Replacing the fan was the first thing I did and I even tried the .1uf cap
across the fan trick, but results are the same. The amp even has the same
symptoms with or without the fan installed. I'm on my second can of
freeze-it, but that has no effect either. Any other ideas?


"Damir Friscic" wrote in message
...

"butlercellars" wrote in message
...

. And the cooling fan works fine, which is driven from the speaker output
level.



Replace fan.




I had a technics a while back in the shop that was giving be problems.
It would go into shutdown. The shutdown was caused by the fan
intermittently not turning. The fan tested fine out of the unit.
As i recall, it was either oxidized connector where the fan connected to
the unit, or bad solder joints on the connector.

Bob

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Bob,
I have the SA-GX550 and it is doing the same thing. If you figure out
anything on your own, please post the solution. I'll do the same. My
power IC is the SVI3206D. Contacts for the fan look fine.


--
fish*man

Hi there

I have an SA-GX505 with similar problem. But my receiver turns off
completely, like the ac power cord had been pulled out of the outlet,
like there was no AC power at all. What i find to be the cause of this
was the little transformer responseble for the standby power. If you
have any problem in finding it, look around the big transformer and
you´ll find the little one. This little motherf.. has become
intermitent with its 15 years of intense use and turns the receiver
off every time it warms up. Replece this S.O.B. and you will get your
equipment working fine...

Best regards.

Bob Urz Wrote:

I had a technics a while back in the shop that was giving be problems.
It would go into shutdown. The shutdown was caused by the fan
intermittently not turning. The fan tested fine out of the unit.
As i recall, it was either oxidized connector where the fan connected
to
the unit, or bad solder joints on the connector.

Bob



I saw an older entry on another forum. Basically said the amp would go
into protect shutdown if it didn't sense the fan running at higher
output levels. I have never seen my fan spin. The contacts look good
but I cleaned them anyway. Held a voltmeter across the contacts for a
long time but never saw anything. Good resistance across the fan. I'll
look below the contacts to the solder joints on the card next.


--
fish*man

fish*man Wrote:
I saw an older entry on another forum. Basically said the amp would go
into protect shutdown if it didn't sense the fan running at higher
output levels. I have never seen my fan spin. The contacts look good
but I cleaned them anyway. Held a voltmeter across the contacts for a
long time but never saw anything. Good resistance across the fan. I'll
look below the contacts to the solder joints on the card next.

Update: solder joints show good continuity. Fan circuit works as
advertised with volume above 10. Removing the fan and turning up the
volume activates the overload circuit, all as advertised.
Per troubleshooting guidance in manual, looking into possible speaker
issues as cause for activation of protection circuitry.
Anyone else having any luck? Butlercellars?


--
fish*man

fish*man Wrote:
Update: solder joints show good continuity. Fan circuit works as
advertised with volume above 10. Removing the fan and turning up the
volume activates the overload circuit, all as advertised.
Per troubleshooting guidance in manual, looking into possible speaker
issues as cause for activation of protection circuitry.
Anyone else having any luck? Butlercellars?

Swapped out speakers and checked both A side and B side. Same results.
Back to a problem with a component on one of the boards. Anybody out
there?


--
fish*man