Technics SA-DX1050 Fan stop working after awhile and won’t turn on again

[Jayde]

Hi I just bought this amplifier and it works fine, fan starts spinning after a while when inside gets warm than it stops and don’t switch on again causing amplifier to switch off due to heat up. I have cheched inside and only one board looks suspicious. I suspect one chip that can be seen burnt on top. I would appreciate any insights, for example how to check if it is this part and some tip where can I look for service manual books. Cheers

 

[mbz]

sm
TECHNICS SA-DX1050 SM 1 Service Manual download, schematics, eeprom, repair info for electronics experts
need to wait 30seconds for download link

 

[Jayde]

Thanks, so you think this chip is burnt? Happy new year!

 

[jaycee]

Doesnt look burnt.. just looks like flux residue. Give it a wipe with some isopropyl alcohol and i bet it comes clean

Measure the voltage on the fan when it stops.. is it that the fan is being switched off, or the fan is stalling?

 

[Jayde]

Ok there was lots of flux residue on the board so it might be it, I need to get a multimeter I will check it than, fan simply stops working after some time and although amplifier is hot inside fan doesn’t turn on anymore.

 

[mbz]

Suspect chip appears to be on the digital pcb, unlikely location for
fan motor control. SM shows the fan motor drive as discrete.
Need to work out if it's a problem with the control/drive or the
fan itself.

 

[wiseoldtech]

I wouldn't worry about "flux residue" - it's actually a moisture sealer coating.
The fans become intermittent due to dirty commutators, worn brushes, dry bearings.
And all heatsinked components need to be re-soldered to the board, along with the interlocking connectors between boards, and the rear jacks as well.

The whole thing needs to be apart to access these things.
Been there, done that, many times, for customers.

 

[nigelwright7557]

Fans have a shelf life and tend to go well before the amp does.
I had a similar problem with a Marshall guitar amp.
The fan was very noisy and stopped after a while.
A simple replacement fixed it.

 

[adason]

I used to have Technics receiver, almost top of line, actually my brother still has it, nothing never wrong with it, just the fan was turning on an off only in short music peaks. That did not make sense to me. The sensor for turning the fan based on signal, not temperature, resulting in brief movement of blades. Never very effective.
I bypased the fan swithing sensor, and put a switch on the back.
When my brother runs it low volume, its fine without fan. Once he wants to crank it up, he switches fan on constantly.
I always loved that receiver, do not remember exact model now, it had great phono section, good sounding amp, parametric equalizer, fun to look at spectrum analyzer and lots of other goddies...

 

[Jayde]

That’s some valuable informations, thanks, I will try resoldering all joints and replacing the fan, later I will get back to you with what have resolved that issue, cheers once again I’m still impressed that there is such forum where people from around the world can share their experiences with repairs, I’m self learner and this is very helpful.

 

[adason]

Perhaps first try to find out if the fan is ok. Unplug it from the board and use external power supply to run it. See how reliable it is. If it works, culprit is in the control board. If the fan has issue, replace it. Good luck.

 

[wiseoldtech]

I used to have Technics receiver, almost top of line, actually my brother still has it, nothing never wrong with it, just the fan was turning on an off only in short music peaks. That did not make sense to me. The sensor for turning the fan based on signal, not temperature, resulting in brief movement of blades. Never very effective.
I bypased the fan swithing sensor, and put a switch on the back.
When my brother runs it low volume, its fine without fan. Once he wants to crank it up, he switches fan on constantly.
I always loved that receiver, do not remember exact model now, it had great phono section, good sounding amp, parametric equalizer, fun to look at spectrum analyzer and lots of other goddies...

Technics designed the fan to respond to loud peaks and loud volume levels.
Thus the intermittent fan operation.
As much as I adore the Technics amps, I don't care for that fan operation.
I've modified the trigger circuitry to run constant, with a gradual-variable fan speed as the heatsink warms up, along with using a quieter computer type fan and additional shrouding for efficiency.