Technics SU-G90 with some problems

[EugenioG]

hi!

first of all, I'm from Bahía Blanca, Argentina, and we don't have good and capable technical services here, with expertise with this amps, so I'm doing some research to solve this...or at least to find the cause, and them try to find somebody to solve it.

I own a SU-G90 amp (in my family since brand new), and after running some time, and more quickier as higher is the volume level, you hear some "electrical" sound, and then the amplifier goes to a "freeze status", turning off the following, for example: the surround (lowering the rear level), the superbass, the dat/vcr input...

After that happens, you can manually turn on everything again, and works properly for a few more minutes, and then "fails" again...

What do yo think it could be?
is that an overload issue?
is that a high temp issue?
is that a bad solder issue?

when the amp does that, i feel it hot.

I have checked it, and the fan works, and fan's speed is related which amp "charge"...higher volume, higher speed.

I will check the board for bad/cold solder joint.
Maybe I will clean and renew thermal paste.
Maybe I will add a new fan.

Any advice or suggestions are welcomed.

Thanks in advance.

Regards!

 

[quaddriver]

yep, do what I said in the other post. and resolder all the voltage regulators and the amp chip(s). and make sure you are not using too low of impedance speakers.

 

[EugenioG]

yep, do what I said in the other post. and resolder all the voltage regulators and the amp chip(s). and make sure you are not using too low of impedance speakers.

I need to get some flux to resolder

I'm using a pair of 8ohm SB-A52 speakers

 

[elnaldo]

I'd add, you need to inspect and resolder the whole unit, completely disassemble and check all the soldering. Specially areas looking brown or burnt, and connectors between boards, even connections to the transformer. I'm 100% sure you'll find many broken solder connections.

Also, check the fan connection to the PCB. In some models the fan has 2 metal tabs that are just pressing 2 contacts. That connection is not reliable anymore. I usually solder 2 wires jumping that connection, from the fan to the PCB contacts, long enough to allow to install the fan.

 

[EugenioG]

I'd add, you need to inspect and resolder the whole unit, completely disassemble and check all the soldering. Specially areas looking brown or burnt, and connectors between boards, even connections to the transformer. I'm 100% sure you'll find many broken solder connections.

Also, check the fan connection to the PCB. In some models the fan has 2 metal tabs that are just pressing 2 contacts. That connection is not reliable anymore. I usually solder 2 wires jumping that connection, from the fan to the PCB contacts, long enough to allow to install the fan.

Great!

Thanks for your advice!

In a few days I will put hands on the amp...I will keep you informed

Regards,

 

[mtranier]

Eugenio, pudiste reparar el problema. Yo tengo el mismo amplificador y tengo el inconveniente en los surround. Tienen un sonido muy bajo, casi inaudible, no se si es que hay que poner bafles especiales o va cualquiera que sea de la potencia admitida y la misma impedancia (no tengo ni consigo el manual). Si ves este mensaje me dices como va y si reparaste el amplificador me dices como para tenerlo en cuenta el dia que algo similar pase... Muchas gracias